Content uploaded by Jaime A. Teixeira da Silva
Author content
All content in this area was uploaded by Jaime A. Teixeira da Silva on Dec 13, 2016
Content may be subject to copyright.
JAIME A. TEIXEIRA DA SILVA & al.
15
J. Plant Develop.
23(2016): 15-25
MORPHOGENESIS AND DEVELOPMENTAL BIOLOGY OF
AFRICAN VIOLET (SAINTPAULIA IONANTHA H. WENDL.)
Jaime A. TEIXEIRA DA SILVA
1
*, Yaser Hassan DEWIR2, 3, Adhityo WICAKSONO4,
Mafatlal M. KHER5, Haenghoon KIM6, Munetaka HOSOKAWA7, Songjun ZENG8
Abstract: African violet (Saintpaulia ionantha H. Wendl.) has been domesticated, bred and commercialized. It
is the most famous and popular of the Saintpaulia species, its ornamental value arising from its
attractive leaves and flowers. African violet plants are easy to propagate by adventitious organ
regeneration and are very sensitive to environmental factors including light, temperature, humidity,
CO2 concentration and photoperiod. This review offers a short synthesis on advances made in
conventional vegetative propagation by adventitious organ regeneration, select early historical in vitro
developmental perspectives, and vegetative and reproductive development of African violet.
Keywords: development; Gesneriaceae; thin cell layers; vegetative propagation
Introduction
African violet (Saintpaulia ionantha H. Wendl.; Gesneriaceae) has attractive leaves
and flowers (Fig. 1) that are typical of many members of the Gesneriaceae. African violet is
mainly used for ornamental purposes, thus aspects related to flower color, leaf patterning, or
yield are of interest to horticulturalists, plant breeders, molecular biologists, physiologists,
biotechnologists, and for the floriculture industry. Thus, the improvement of flower- and leaf-
related traits via vegetative propagation, the creation of somaclonal variation, and mutation
breeding are fundamental aspects of African violet research.
Plant morphogenesis is regulated by complex genetic networks in a synchronized
manner, and these serve as determining factors for numerous crop traits. Many constituents
of these networks have been extensively studied in the model plant, Arabidopsis thaliana L.
[VANHAEREN & al. 2016]. Multicellular plants have a unique group of cells that form new
organs and replenish the daily loss of cells, or regenerate organs after injury, the pluripotent
stem cells [AICHINGER & al. 2012]. Stem cells are located in stem cell niches that provide
1
P. O. Box 7, Miki-cho post office, Ikenobe 3011-2, Kagawa-ken, 761-0799 – Japan
2 Plant Production Department, P.O. Box 2460, College of Food & Agriculture Sciences, King Saud University,
Riyadh 11451 – Saudi Arabia
3 Department of Horticulture, Faculty of Agriculture, Kafrelsheikh University, Kafr El-Sheikh 33516 – Egypt
4 Laboratory of Paper Coating and Converting, Centre for Functional Material, Åbo Akademi University,
Porthaninkatu 3, 20500 Turku – Finland
5 B. R. Doshi School of Biosciences, Sardar Patel University, Sardar Patel Maidan, Vadtal Rd., P.O. Box 39, Vallabh
Vidyanagar, Gujarat, 388120 – India
6 Department of Well-being Resources, Sunchon National University, Suncheon, 540-742 – Korea
7 Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502 – Japan
8 Key Laboratory of South China Agricultural Plant Molecular Analysis and Gene Improvement, South China
Botanical Garden, the Chinese Academy of Sciences, Guangzhou, 510650 – China
* Corresponding author. E-mail: jaimetex@yahoo.com
MORPHOGENESIS AND DEVELOPMENTAL BIOLOGY OF AFRICAN VIOLET…
16
intercellular signals for differentiation such as hormonal control [ZHAO & al. 2010], or
transcription factors [STAHL & SIMON, 2010; SABLOWSKI, 2011]. This review provides
several details about traits related to development that could make this ornamental plant a
possible model plant for the study of morphogenesis, differentiation and organ formation. It
also addresses the environmental factors regulating vegetative growth and flowering,
inflorescence development, specific conditions for propagation of African violet and
biotechnological methods to improve flowering.
Conventional vegetative propagation: possible model plant for adventitious
organ regeneration (historical perspective)
FIGDOR (1907) may have been the first official report on adventitious regeneration
in the Gesneriaceae, including African violet adventitious regeneration. FAIRBURN (1936)
studied the propagation of African violet and other vegetatively propagated plants using leaf
cuttings, noting how the inclusion of petioles was essential to induce roots. NAYLOR &
JOHNSON (1937) described how portions of the leaf blade or petiole of African violet could
regenerate one or more plants within 6-15 weeks if placed on wet sand or in water in Petri
dishes when placed in a moist chamber. Even ex vitro, NAYLOR & JOHNSON (1937) noted
the development of callus from the cut surface, with root initials forming within as little as
10 days, emerging from, but not derived from, the callus, i.e., originating from cells within
the orginal explant. Their histological evidence showed that roots formed from thin-walled
cells found underneath the leaf epidermis, while shoots formed from exogenous cells of the
epidermal layer, i.e., shoots originated from epidermal cells.
Concept of thin cell layer and morphogenesis
Basic findings within earlier attempts made by FIGDOR (1907), FAIRBURN (1936)
and NAYLOR & JOHNSON (1937) would later turn out to be an important reason for the
success of thin cell layers (TCLs) [TEIXEIRA DA SILVA & al. 2007; TEIXEIRA DA SILVA
& DOBRÁNSZKI, 2013, 2014; TEIXEIRA DA SILVA & al. 2015], especially longitudinal
TCLs, in African violet tissue culture, making African violet an important ornamental plant
model for developmental studies, like tobacco, and making it a possible viable form of in vitro
regeneration for other Saintpaulia species [TEIXEIRA DA SILVA & al. 2015]. To date, only
Fig. 1. A flowering African violet (Saintpaulia ionantha H. Wendl) (Gesneriaceae)
plant. Initially redrawn from EASTWOOD & al. 1998 (p. 50), then modified.
JAIME A. TEIXEIRA DA SILVA & al.
17
Fig. 2. Shoot development from epidermal tissue, as suggested by histological analyses by GEIER
(1983), LO & al. (1997), and NAYLOR & JOHNSON (1937).
Arrow indicates a meristematic center.
two studies employed TCLs, but even so, the term TCL was not used for the earlier study.
MURCH & al. (2003) used 0.25 mm thick petiole sections (i.e., transverse TCLs or tTCLs) to
regenerate somatic embryos while KHOSARI-NASAB & al. (2014) induced callus and shoots
from petiole and pedicel tTCLs. The ability to regenerate a large number of plantlets from a
limited amount of tissue (in terms of surface area and volume) underlies the basic success of
the TCL [TEIXEIRA DA SILVA & DOBRÁNSZKI, 2014], and thus the success of the tissue
culture of African violet. The origin of knowledge about this development came from early
studies on vegetative propagation in the 1930’s. Later, BROERTJES (1968), ENGELS & al.
(1980), GEIER (1983), BROERTJES & VAN HARTEN (1985), Ohki (1994) and
HOSOKAWA & al. (1998) confirmed similar histological evidence showing the involvement
of epidermal cells (Fig. 2) in the formation of adventitious shoots from the petioles of African
violet, noting, using chimeric tissue to base their assumption, the single cell origin of shoots,
and thus annulling the claim by NORRIS & al. (1983) that shoots are derived from multiple
cells. FINER & SMITH (1983) noticed that plastids that were in an arrested state of
development in the epidermis underwent changes after placing leaf cuttings on kinetin-
supplemented medium. REDWAY (1991) showed the epidermal origin of shoot primordia,
after callus formed, but also showed the formation of shoot primordia from palisade tissue,
which lies about 10 cell layers below the epidermal surface. This single cell origin of shoots
would allow solid (i.e., non-chimeric) mutants to be produced, forming an important basis for
mutation breeding studies. In Saintpaulia, some pinweel flower color cultivars are considered
to be periclinal chimeras, with the petal margin arising from the L1 layer but the center of the
petal from the L1+L2 layers. If shoot regeneration occurs from epidermal layers, then the flower
color phenotype is identical to that of the flower margin of the mother plant. LINEBERGER &
DRUCKENBROD (1985), ANDO & al. (1986) and PEARY & al. (1988) discuss shoot
regeneration from the epidermal layer using pinweel-flowered periclinal cultivars in more detail.
LINEBERGER & DRUCKENBROD (1985) found that whereas leaves, petioles, peduncles,
sepals and inflorescences formed plantlets within 3-5 months, it took 8-10 months from
subepidermal tissues, suggesting that the organogenic outcome reported in that study, and
possibly in all other African violet studies, depends on the timing of sampling, which is also a
function of the type of explant used [TEIXEIRA DA SILVA & DOBRÁNSZKI, 2013]. In
essence, regeneration from TCLs may be faster than from regular explants since a greater area
and volume of cells is exposed to the exogenously applied plant growth regulators in the in vitro
medium.
MORPHOGENESIS AND DEVELOPMENTAL BIOLOGY OF AFRICAN VIOLET…
18
In vitro morphogenesis and variability, sports and variegation
ANDO & al. (1986) cultured 19 edged-type cultivars with a white corolla and a
pigmented outer edge, and 9 Geneva edged-type cultivars with a pigmented corolla and a
white outer edge, either as leaf cuttings, or in tissue culture. They found that single-colour
cultivars did not form sports whereas single-colour sports, except for two cultivars, were
produced in the remaing (edged-type and Geneva edged-type) cultivars at an average of 22%,
but with a wide range of frequencies (0.9% to 68.8%), as a result of mutations. In contrast,
the sports from edged-type cultivars had single-coloured corollas, and those from Geneva
edged-type cultivars had white or extremely pale corollas, except for a single cultivar.
Whereas the edged form (‘Ms. Pretty’) could produce single colour sports through tissue
culture (i.e., reversion was possible), single colour sports of the same cultivar could never
produce an edged form. PEARY & al. (1988) found that the variegated pattern of a foliar
variegated cultivar (‘Tommie Lou’) was not caused by periclinal chimeras because the
pattern of leaf variegation did not change in potted plants derived from the tissue culture of
leaf and petal sections, or from subepidermal tissue. In contrast, tissue cultured plants of a
variegated flower cultivar (‘Candy Lou’) segregated into the chimeral components, i.e., the
chimera could not be stably propagated by tissue culture. Curiously, DÜMMER (1912)
observed the phenomenon of peloria (i.e., reversion of asymmetric flowers into symmetric
flowers) in S. ionantha.
Morphogenetic efficiency of explants: effects of age, season, and position
SCOTT & MARSTON (1967) noted that 24 °C and misting were suitable for the
development of S. ionantha plantlets from leaf cuttings. According to HENTIG (1976),
reflecting studies conducted in the early 1970’s by this author, and using ‘Rhapsodie in Blau’
Typ 32 as the experimental material, there is a relationship between the length of the petiole
of leaf cuttings and adventitious shoot formation. HENTIG (1976) formulated three
important claims: 1) tissue from the fifth to tenth month of growth are most receptive; 2)
leaves of the middle leaf zone and youngest leaves from the upper zone regenerate earlier (by
4-5 days) than older leaves (i.e., in the lower zone), forming within 56 days; 3) shorter
petioles (1-3 cm) formed more adventitious shoots (and faster) than longer petioles (4-6 cm).
In HENTIG’s study, there were significant differences in the regeneration potential of young,
middle-aged and old leaves before 56 days, but after 56 days, leaves from all three age
categories were able to form adventitious shoots in 100% of explants. Even when leaves of
all three age categories with petioles of different lengths were used, no less than 60% of all
leaves were responsive, fortifying the notion that this is an ornamental plant that can be easily
propagated vegetatively. Depending on the age of the leaf and on the length of the petiole,
anything from 1 to 4 shoots could be produced per leaf.
Vegetative and reproductive development: role of environmental factors
JOHANSSON (1978) described members of the Saintpaulia genus as typically
being shade plants while POST (1942) and STROMME (1985) described African violet as
being day-neutral with respect to flower initiation and development. Inflorescences arise
from leaf axils. During plug production, daily integrated photosynthetic photon flux (PPFDI)
reaching African violet plants in summer range from 10-15 mol/m2/day but are as low as < 2
mol/m2/day in winter. However, temperature and PPFDI can influence the vegetative growth
of African violet. For example, HANCHEY (1955) noted that by increasing PPFDI from 0.31
to 1.9 mol/m2/day, the number of leaves doubled from 22 to 44. HILDRUM &
JAIME A. TEIXEIRA DA SILVA & al.
19
KRISTOFFERSEN (1969) noted that the number of flowers, buds, and inflorescences per
plant and flowers and buds per inflorescence of ‘Biedermeier Rhapsodie’ and ‘Biedermeier
Rosa’ increased when PPFDI was augmented from 3.1 to 9.3 mol/m2/day. This treatment
induced a maximum of 6.8 flower stalks/plant at 18 °C, but a maximum number of flowers
and buds/flower stalk (9.1) at 24 °C. A maximum of 42 flowers/plant could be produced
when daylight (i.e., most likely fluence rate) was cut by 75%, and when plants were exposed
to 27 °C. In contrast, flower initiation and development was inhibited when plants grown in
a greenhouse were exposed to < 2 mol/m2/day [STINSON & LAURIE, 1954]. HILDRUM
& KRISTOFFERSEN (1969) showed that both day and night temperature must be high to
stimulate a greater number of flower stalks, and that flower production is linked to leaf
production, given the source of inflorescences from leaf axils. This indicates that African
violet is not only highly sensitive to environmental variables such as tempearture and PPFDI,
but that these variables can be used to manipulate plant growth and development, both of
leaves and floral organs.
KWACK & KIM (1969) noted that sunlight reduced by half in the greenhouse was
the best condition in terms of the growth and ornamental quality of African violet plants. As
light intensity was decreased from full sunlight (5000-8000 foot-candles (f.c.)) to half
sunlight (1000-2000 f.c.) and shade (500 f.c.), leaf area increased, i.e. 9.26, 12.44 and 13.38
cm2, respectively. Full sunlight induced solarization, chlorosis in leaves or backward leaf
curling, even though it produced higher dry weight (1.29, 1.21 and 0.90 g for full sunlight,
half sunlight and shade, respectively). KIM & SANG (1982) argued that light intensity was
critical for four varieties (‘Monique’, ‘Robert O’, ‘Julianne’ and an undefined local variety)
of S. ionantha, since it is a semi-shaded plant. They confirmed that a light intensity of 5,000-
10,000 lux (6.25-12.50% of natural sunlight in a plastic house) was the best condition for
growth and ornamental value, i.e., photosynthesis, flowering percentage, number of
peduncles, number of florets/peduncle, petiole length and leaf area.
In an experiment assessing the effect of illumination and culture medium on S.
ionantha ‘Oriental Red’, LEE (1986) noted that 7000-8000 lux combined with a substrate
composed of 40% peatmoss, 25% sand, 20% perlite, 10% vermiculite, and 5% compost was
the best for producing wider leaves with greater leaf area (34-36 cm2), best petiole length
(5.8-6.2 cm), number of lateral shoots/explant (3.2), flowering rate (100%) and earliest
flowering (number of days to flowering = 70 days), and number of peduncles (8.2-12.0).
PARK (2008) examined the effect of nitrogen fertilizer and light intensity on three
varieties of S. ionantha and found that half-sunlight (4000 lux) and 200 mg/L NaNO3 was
the most effective combination for obtaining maximum fresh weight (FW) (e.g., for var.
‘Narita’ 1.9 g/cutting vs 0.9 g/cutting in full-sunlight and 0 mg/L NaNO3). The combination
of 4000 lux and 500 mg/L NaNO3 increased the number of roots, the number of shoots
(4.7/cutting vs 0/cutting), and chlorophyll content (52.4 mg/g FW vs 28.2 mg/g FW).
Using ‘Utah’ as the model cultivar combined with linear modeling to base their
assumptions, FAUST & HEINS (1993) determined maximum leaf unfolding rate (LUR) to
be 0.27 leaves/day when temperature was 25 °C while PPFDI was 10 mol/m2/day by using
shadecloth to cut natural PPFDI from a maximum of around 300 mol/m2/day. When they
decreased PPFDI from 10 to 1 mol/m2/day, optimal temperature was 23 °C, but this resulted
in a lower LUR (0.18 leaves/day). Only when the leaf blade extended from 38-46 mm could
an inflorescence begin to develop in the leaf axis [FAUST & HEINS, 1994]. Being able to
predict and balance temperature, PPFDI and thus LUR, would allow growers to plan their
greenhouse cultures for the market. For example, FAUST & HEINS (1993), by applying a
MORPHOGENESIS AND DEVELOPMENTAL BIOLOGY OF AFRICAN VIOLET…
20
PPFDI of 7 mol/m2/day at 22 °C, with a LUR of 0.244 leaves/day, formed 10.5 unfolded
leaves/plant within 45 days (R2=0.99). Also using non-linear models, FAUST & HEINS
(1994) showed that as daily temperature was increased from 18 to 26 °C, days from leaf
emergence to first open flower on the inflorescence of ‘Utah’ decreased from 86 to 55. They
concluded that PPF is the primary factor influencing flower initiation while average daily
temperature is the primary factor influencing the rate of inflorescence development. The three
cardinal temperatures (Tmin, Topt, and Tmax) for leaf appearance rate [FAUST & HEINS, 1993]
are 8 °C, variable (as this depends on PPFD) and 30.8 °C, respectively and for leaf elongation
rate [FAUST & HEINS, 1994], the values are 13.8 °C, 24 °C and 29 °C, respectively. In
contrast, STRECK (2004) found that Tmin was 10 °C and Tmax was 33 °C for both leaf
appearance rate and leaf elongation rate, and Topt was 24 °C, as also modeled by FAUST &
HEINS. CONOVER & POOLE (1981) were able to increase the percentage of inflorescences
that formed in African violet ‘Inge’ within 9 months from 6% to 62%, and then to 100%, by
exposing plants to 0.8, 1.6, and 3.2 mol/m2/day, respectively. However, as FAUST & HEINS
(1994) cautioned, even if LUR increases, a PPF of < 4 mol/m2/day will negatively affect the
number of developing inflorescences. Inflorescence development is acropetal [HASTON &
DE CRAENE, 2007] (Fig. 3). Consequently, for African violet, the production of potted
plants for season-dependent events such as Valentine’s Day, Mother’s Day, or Christmas,
can be perfectly timed with the desired number of leaves and flowers.
The leaves of African violet are very sensitive to light, temperature, humidity and
photoperiod [CHEN & HENNY, 2009], and minor changes in any of these factors can cause
yellow or brown leaf spots [ELLIOT, 1946; YUN & al. 1997a; YANG & al. 2001]. Leaf spot
is a cellular response confined to palisade cells in leaves, whose ultrastructure is destroyed
[YUN & al. 1996a, 1996b], caused by a rapid drop in temperature, as may occur in overhead
irrigation, especially at night, or by transferring plants from indoor to outdoor conditions, as
was shown for ‘Ritali’ plants [YUN & al. 1997a]. Unlike chilling injury, leaf spot is
irreversible. Outer leaves, which are more exposed to the surrounding environment, are more
susceptible to leaf spot, and even exposure to 20 °C water can induce this disorder
[MAEKAWA & al. 1987], which results from electrolyte leakage [MAEKAWA & al. 1990].
Leaf spot is a stress response caused by the rapid production of reactive oxygen species
(ROS) following sudden temperature shifts [YASUDA & al. 1997], and an increase in the
activity of antioxidant enzymes (superoxide dismutase and catalase). However, this response
may be cultivar-dependent since ‘Ritali’ and ‘Tamiko’ (with about 75% and 95% incidence
of leaf spot, respectively) were more susceptible to a drop from 30 °C to 15 °C than ‘Maui’
and ‘New Jersey’ (about <5% and 22% incidence, respectively) [YANG & al. 2001]. Sudden
drops in temperature causing leaf spot are also characteristic of ‘Ritali’ leaves that display
additional physiological disorders, namely a decrease in photosynthetic activity (especially a
negative effect on PSI and PSII activity and a decrease in chlorophyll fluorescence) [YUN &
al. 1997b, 1998], and plasmolysis [YUN & al. 1996a]. Recently, OHNISHI & al. (2015)
revealed evidence of the involvement of calcium ions (specifically Ca2+ channels) after the
degradation of the vacuolar membrane of palisade cells.
In a practical greenhouse trial to examine the response of stock plants and leaf
cuttings (with 15 mm long petioles, according to HENTIG, 1976) to different commercial
light sources (Grolux-low, Grolux-high, Verilux-low, Verilux-high, Fluora 77, Cool White
20, Cool White 30, Warm-White 30, Warm-White de Luxe 32, Interna 39 and Natura 36),
SCHNEIDER-MOLDRICKX & AMBERGER (1982) discovered significant differences in
the number of shoots that could be regenerated and in shoot FW. In their experiment, bulbs
emitted 36-72 µmol/m2/s, all test material was grown under a 16-h photoperiod, and data was
pooled for three cultivars (‘RH-26/74’, ‘Meta’, and ‘OP-50/75’). Cuttings cultivated under
JAIME A. TEIXEIRA DA SILVA & al.
21
light bulbs emitting higher radiant energy formed more and heavier shoots than those exposed
to light bulbs emitting low levels of light energy. Grolux (emitting 63 µmol/m2/s) was the
most effective light source, forming 81 and 89 shoots/plot from stock plants and cuttings,
respectively, and 598 mg/shoot. The response was strongly cultivar-dependent, with ‘RH-
26/74’, ‘Meta’, and ‘OP-50/75’ forming 56, 94 and 80 shoots/plot and 589, 235 and 598
mg/shoot, respectively. A separate trial by the same authors showed that Warm-White 30
bulbs could induce the formation of as many as 122.1 shoots/plot in a cultivar-independent
manner. The use by BOSCHI & al. (2000) of red and blue spectral filters, with different red,
blue and far red ratios, on greenhouse African violet (cultivar unspecified) plants reduced
most growth parameters (shoot and root dry weight, chlorophyll content, chlorophyll/protein
ratio, net carbon dioxide (CO2) exchange), in some cases significantly, compared to control
polyethylene film, but did not alter the transpiration rate.
African violet plants (‘Rosa Roccoco’ and ‘Big Star’) exposed to continuous CO2
enrichment, in which CO2 concentration was increased from 330 to 1000-15,000 ppm,
showed 50-100% higher net photosynthetic rate and 23-30% higher relative growth rate, most
likely caused by the 39.6% increase in the number of formed leaves [MORTENSEN, 1984].
More refined experiments by MORTENSEN (1986) on ‘Nicole’, ‘Lena’ and ‘Rosa Roccoco’
showed that CO2 enrichment (900 µL/L) had a more profound and/or significant effect in all
three cultivars and in all parameters measured (greater dry weight, relative growth rate,
number of leaves, leaf diameter, and number of flowers and flower buds, but reduced number
of days to flowering) than ambient CO2 (335 µL/L), a 1-h daily pulse at 900 µL/L, or a
morning plus an evening pulse, each at 900 µL/L. For example, in ‘Nicole’, CO2 enrichment
resulted in 7.95 g/plant, a relative growth rate of 37.1 mg/g/day, 51.1 leaves/plant, 19.3 cm
wide leaves, 56.1 days to flowering, and 168.7 flowers and flower buds/plant. The equivalent
values for ambient (control) CO2 levels were 3.56, 28.4, 35.3, 17.6, 66.4 and 66.8,
respectively.
Vegetative growth can also be stimulated by the application of maleic hydrazide (MH).
LEMATTRE (1977) found that spraying three African violet cultivars (‘Rhapsodie’, ‘2000’,
and ‘2738’) with 0.1 to 0.2% MH resulted in a 47- to 176-fold increase in the number of
vegetative shoots that formed, depending on the concentration and the cultivar. For example,
in ‘2000’, while control plants formed only an average of 0.1 vegetaive buds per plant, the
application of 0.2% MH resulted in the formation of 17.6 vegetative buds, which could in
essence be used as clones, and to inhibit early flowering, although the genetic stability of
such clones was not tested. By applying 10 mg/L gibberellic acid (GA3) at two-week intervals
to four-month-old ‘Rhapsody blue’ plants, DVORSKÁ (1979) was able to increase the
number of flower stalks by about 25% (10-12 vs 6-9 in controls). Furthermore, in the same
study, a constant temperature of 22 °C resulted in the formation of 4-6 flower stalks in control
plants, whereas a 14 °C/22 °C (day/night) temperature gradient resulted in the formation of
7-11 flower stalks. HERKLOTZ (1964) found that a day and night temperature of 25 °C
favored regeneration from leaf cuttings than all other day/night temperature combinations
ranging from 15 °C to 30 °C. MARTÍN-MEX & al. (2005) found that the application of 0.001
µM salicylic acid significantly increased the number of leaves (19 vs 16 in the control) and
floral buds (14 vs 8 in the control), as well as rosette diameter (177 mm vs 139 mm in the
control), and shortened the days to flowering (74 vs 89 in the control). A similar finding by
JABBARZADEH & al. (2009) also confirmed the positive effects of a foliar application of
1 × 105 M salicylic acid on vegetative growth and flowering of African violet in terms of the
number of leaves, rosette diameter, the number of flower buds and the number of days from
planting to anthesis. These chemical methods provide means of delaying and/or enhancing
vegetative growth and/or flowering in African violet to meet market needs.
MORPHOGENESIS AND DEVELOPMENTAL BIOLOGY OF AFRICAN VIOLET…
22
Fig. 3. Inflorescence development typical for the Gesneriaceae. (A) A pair-flowered inflorescence
displays dichasial branching. (B) A plan view of the same inflorescence represented in (A). In A and
B, T = terminal flower, F = front flower, parentheses indicate directions of growth / flower expansion,
and numbers indicate the level of branching on the inflorescence axis. In B, CU represents a single
cyme unit with a hypopodium (peduncle supporting the cyme unit) with a terminal pair of lateral
bracteoles, subtending a terminal and an associated front flower. (C) The development of a
Saintpaulia ionantha inflorescence, divided into 8 stages (according to FAUST & HEINS 1994): 1)
visible reproductive bud (2 mm long) in the leaf axil; 2) visible peduncle subtending the primary bud;
3) peduncle starts to curve; 4) pedicel curves 90° relative to the peduncle; 5) pedicel curvature relative
to the peduncle <90° and secondary buds are at the top of the inflorescence; 6) angle between
peduncle and primary bud and pedicel increases, the pedicel is at the top of the inflorescence, and
the primary bud emerges from the leaf canopy; 7) upper half of pedicel and primary bud are
perpendicular to lower half of pedicel (i.e., at 90° angle); 8) the petals are perpendicular to the pedicel.
(A and B) retraced, redrawn and modified from HASTON & DE CRAENE (2007) Fig. 1A and 1B
(p. 15); (C) redrawn and modified from FAUST & HEINS (1994) Fig. 1 (p. 728).
Conclusions and future perspectives
The easy regeneration potential of African violet, as evident from as far back as the
NAYLOR & JOHNSON (1937) study, alongside the debate about the single or multiple cell
orgin of shoot buds in earlier work, are some interesting aspects that require additional
attention from molecular cell biologists to address the factors that regulate morphogenesis in
African violet. African violet can be easily and rapidly cloned. This, together with its ability
to regenerate organs from different tissues, has facilitated several studies with the aim of
understanding organogenesis, organ development and its related in vitro physiology. Hence,
JAIME A. TEIXEIRA DA SILVA & al.
23
African violet is valued as a model plant at the research/laboratory level and this potential
can and should be further explored. Vegetative growth, flowering and floral organ
development of African violet can be manipulated in a greenhouse or growth chamber by
adjusting environmental variables including light source, intensity and quality, temperature,
CO2 enrichment, as well as chemical applications. Therefore, commercially, the production
of potted African violet plants can be planned for the market to meet consumer demands.
Acknowledgements
We are thankful to Ravi R. Sonani, Sardar Patel University and Sylvia DeMar,
Managing Editor, American Society for Horticultural Science for providing difficult-to-
access literature.
Author contribution statement and conflicts of interest statement
The authors contributed equally to all aspects of review development and writing.
The authors have no conflicts of interest to declare.
References
AICHINGER E., KORNET N., FRIEDRICH T. & LAUX T. 2012. Plant stem cell niches. Annu Rev. Plant Biol. 63:
615-636.
ANDO T., AKIYAMA Y. & YOKOI M. 1986. Flower colour sports in Saintpaulia cultivars. Sci. Hortic. 29: 191-197.
BOSCHI C., DI BENEDETTO A., PAPAYANI P., CREMONA C. & BENEDICTO D. 2000. Coverfilms and light
quality responses in Saintpaulia ionantha. Acta Hortic. 515: 135-140.
BROERTJES C. 1968. Mutation breeding of vegetatively propagated crops. In: Proceedings of 5th Eucarpia Congress.
Milan: 139-165.
BROERTJES C. & VAN HARTEN A. M. 1985. Single cell origin of adventitious buds. Euphytica. 34: 93-95.
CHEN J. & HENNY R. J. 2009. Cultural guidelines for commercial production of African violets (Saintpaulia ionantha)
ENH 1096. Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of
Food and Agricultural Sciences, University of Florida, USA, pp. 1-4.
CONOVER C. A. & POOLE R. T. 1981. Light acclimatization of African violet. HortScience. 16: 92-93.
DÜMMER R. A. 1912. Peloria in Saintpaulia ionantha, Wendland. Ann Bot. 26: 946-947.
DVORSKÁ L. 1979. The effect of growth regulators and temperature gradient on flowering of Saintpaulia ionantha
Wendl. Acta Hortic. 91: 507-510.
EASTWOOD A., BYTEBIER B., TYE H., TYE A., ROBERTSON A. & MAUNDER M. 1998. The conservation
status of Saintpaulia. Curtis’ Bot. Mag. 21: 462-471.
ELLIOT F.H. 1946. Saintpaulia leaf spot and temperature differential. Proc. Amer. Soc. Hortic. Sci. 47: 511-514.
ENGELS F. M., VAN DER LAAN F. M., LEENHOUTS H. P. & CHADWICK K. H. 1980. The regeneration of
epidermal cells of Saintpaulia leaves as a new plant-tissue system for cellular radiation biology. Int. J. Rad.
Biol. 38: 309-321.
FAIRBURN D. C. 1936. Plant propagation. Missouri Bot Garden Bull. 24: 45-92.
FAUST J. E. & HEINS R. D. 1993. Modeling leaf development of the African violet (Saintpaulia ionantha Wendl.). J.
Amer. Soc. Hortic. Sci. 118: 747-751.
FAUST J. E. & HEINS R. D. 1994. Modeling inflorescence development of the African violet (Saintpaulia ionantha
Wendl.). J. Amer. Soc. Hortic. Sci. 119: 727-734.
FIGDOR W. 1907. Ueber Resttutionserscheinugen an Blattern von Gesneriaceen. Jahrb. Wiss. Bot. 44: 41-46.
FINER J. J. & SMITH R. H. 1983. Structure and development of plastids in epidermal cells of African violet (Saintpaulia
ionantha Wendl.) in culture. Ann Bot. 51: 691-695.
GEIER T. 1983. Induction and selection of mutants in tissue cultures of Gesneriaceae. Acta Hortic. 131: 329-338.
HANCHEY R. H. 1955. Effects of fluorescent and natural light on vegetative and reproductive growth in Saintpaulia.
Proc. Amer. Soc. Hort. Sci. 66: 379-382.
HASTON E. & DE CRAENE L. P. R. 2007. Inflorescence and floral development in Streptocarpus and Saintpaulia
(Gesneriaceae) with particular reference to the impact of bracteole suppression. Plant Syst Evol. 265: 13-25.
MORPHOGENESIS AND DEVELOPMENTAL BIOLOGY OF AFRICAN VIOLET…
24
HENTIG W. U. V. 1976. Results of propagation with leaf cuttings of Saintpaulia ionantha. Acta Hortic. 64: 55-64.
HERKLOTZ A. 1964. Influence of constant and daily alternating temperatures on growth and development of
Saintpaulia ionantha Wendl. Gartenbauwiss. 29: 425-438 (in German with English abstract).
HILDRUM H. & KRISTOFFERSEN T. 1969. The effect of temperature and light intensity on flowering in Saintpaulia
ionantha Wendl. Acta Hortic. 14: 249-259.
HOSOKAWA M., HOSSAIN M., TAKEMOTO T. & YAZAWA S. 1998. Particle-gun wounding of explants with
and without plant growth regulators effectively induces shoot formation in African violet. Plant Tissue
Cult. Biotechnol. 4: 35-41.
JABBARZADEH Z., KHOSH-KHUI M. & SALEHI H. 2009. The effect of foliar-applied salicylic acid on flowering
of African violet. Aust. J. Basic Appl. Sci. 3(4): 4693-4696.
JOHANSSON D. R. 1978. Saintpaulias in their natural environment with notes on their present status in Tanzania and
Kenya. Biol. Conserv. 14: 45-62.
KIM J. K. & SANG C. G. 1982. A study on the growth and flowering of Saintpaulia ionantha under controlled light
intensities. J. Kor. Soc. Hortic. Sci. 23: 323-331 (in Korean with English Abstract).
KHOSARI-NASAB M., ASGHARY E., MOVAFEGHI A. & POUREBAD N. 2014. Investigation of tTCLs technique
in regeneration of African violet (Saintpaulia ionantha). Adv. Env. Biol. 8(13): 985-988.
KWACK B. & KIM I. 1969. Growth and ornamental value of Saintpaulia and Hypoestes under the different light
conditions. J. Kor. Soc. Hortic. Sci. 6: 75-79 (in Korean with English abstract).
LEE Y. H. 1986. Effects of BAP pretreatments and media constituents on organogenesis in vitro from leaf segments of
Saintpaulia ionantha Wendl. MS thesis. Kyungsan National University, Jinju, Korea, pp. 1-39.
LEMATTRE P. 1977. Effect of maleic hydrazide on floral and vegetative development of Saintpaulia ionantha. Acta
Hortic. 68: 185-188.
LINEBERGER R. D. & DRUCKENBROD M. 1985. Chimeral nature of the pinwheel flowering African violets
(Saintpaulia, Gesneriaceae). Amer. J. Bot. 72: 1204-1212.
LO K. H., GILES K. L. & SAWHNEY V. K. 1997. Histological changes associated with acquisition of competence for
shoot regeneration in leaf discs of Saintpaufla ionantha x confusa hybrid (African violet) cultured in vitro.
Plant Cell Rep. 16: 421-425.
MAEKAWA S., TORISU Y., INAGAKI N. & TERABUN M. 1987. Leaf injury caused by drop in leaf temperature of
Saintpaulia ionantha. J. Jpn. Soc. Hortic. Sci. 55: 484-489. (in Japanese with English summary).
MAEKAWA S., TORISU Y., INAGAKI N. & TERABUN M. 1990. Relation between development of leaf spot and
electrolyte leakage. J. Jpn. Soc. Hortic. Sci. 58: 985-991. (in Japanese with English summary).
MARTÍN-MEX R., VILLANUEVA-COUOH E., HERRERA-CAMPOS T. & LARQUÉ-SAAVEDRA A. 2005.
Positive effect of salicylates on the flowering of African violet. Sci. Hortic. 103: 499-502.
MORTENSEN L. M. 1984. Photosynthetic adaptation in CO2 enriched air and the effect of intermittent CO2 application
on greenhouse plants. Acta Hortic. 162: 153-158.
MORTENSEN L. M. 1986. Effect of intermittent as compared to continuous CO2 enrichment on growth and flowering
of Chrysanthemum × morifolium Ramat. and Saintpaulia ionantha H. Wendl. Sci. Hortic. 29: 283-289.
MURCH S. J., VICTOR J. M. R. & SAXENA P. K. 2003. Auxin, calcium and sodium in somatic embryogenesis of
African violet (Saintpaulia ionantha Wendl. cv. Benjamin). Acta Hortic. 625: 201-209.
NAYLOR E. E. & JOHNSON B. 1937. A histological study of vegetative reproduction in Saintpaulia ionantha. Amer.
J. Bot. 24: 673-678.
NORRIS R. E., SMITH R. H. & VAUGHN K. C. 1983. Plant chimeras used to establish de novo origin of shoots.
Science. 220: 75-76.
OHKI S. 1994. Scanning electron microscopy of shoot differentiation in vitro from leaf explants of the African violet.
Plant Cell, Tiss. Org. Cult. 36: 157-162.
OHNISHI M., KADOHAMA N., SUZUKI Y., KAJIYAMA T., SHICHIJO C., ISHIZAKI K., FUKAKI H., IIDA H.,
KAMBARA H. & MIMURA T. 2015. Involvement of Ca2+ in vacuole degradation caused by a rapid
temperature decrease in Saintpaulia palisade cells: a case of gene expression analysis in a specialized small
tissue. Plant Cell Physiol. 56: 1297-1305.
PARK S. Y. 2008. Effect of nitrogen and light treatment on the rooting and growth of African violet (Saintpaulia
ionantha Wendl.) cutting. MSc thesis, Sangmyung University, Chunahn, Korea, pp. 1-46.
PEARY J. S., LINEBERGER R. D., MALINICH T. J. & WERTZ M. K. 1988. Stability of leaf variegation in
Saintpaulia ionantha during in vitro propagation and during chimeral separation of a pinwheel flowering
form. Amer. J. Bot. 75: 603-608.
POST K. 1942. Effect of daylength and temperature on growth and flowering of some florist crops. Cornell Univ. Agric.
Exp. Sta. Bull. 787: 1-10.
REDWAY F. A. 1991. Histology and stereological analysis of shoot formation in leaf callus of Saintpaulia ionantha
Wendl. (African violet). Plant Sci. 73: 243-251.
JAIME A. TEIXEIRA DA SILVA & al.
25
SABLOWSKI R. 2011. Plant stem cell niches: from signalling to execution. Curr. Opin. Plant Biol. 14: 4-9.
SCHNEIDER-MOLDRICKX R. & AMBERGER S. 1982. Propagation of Saintpaulia ionantha under artificial lighting.
Acta Hortic. 128: 151-160.
SCOTT M. & MARSTON M. E. 1967. Effects of mist and basal temperature on the regeneration of Saintpaulia ionantha
Wendl. from leaf cuttings. Hortic Res. 7: 50-60.
STAHL Y. & SIMON R. 2010. Plant primary meristems: shared functions and regulatory mechanisms. Curr. Opin.
Plant Biol. 13: 53-58.
STINSON R. F. & LAURIE A. 1954. The effect of light intensity on the initiation and development of flower buds in
Saintpaulia ionantha. Proc. Amer. Soc. Hortic. Sci. 64: 459-467.
STRECK N. A. 2004. A temperature response function for modeling leaf growth and development of the African violet
(Saintpaulia ionantha Wendl.). Ciência Rural 34: 55-62.
STROMME E. 1985. Saintpaulia ionantha. In: A. Halevy (ed.). CRC Handbook of Flowering Vol. 3. CRC Press, Boca
Raton, FL, p. 48-49.
TEIXEIRA DA SILVA J. A., ALTAMURA M. M. & DOBRÁNSZKI J. 2015. The untapped potential of plant thin cell
layers. J. Hortic. Res. 23: 127-131.
TEIXEIRA DA SILVA J. A. & DOBRÁNSZKI J. 2013. How timing of sampling can affect the outcome of the
quantitative assessment of plant organogenesis. Sci. Hortic. 159: 59-66.
TEIXEIRA DA SILVA J. A. & DOBRÁNSZKI J. 2014. Dissecting the concept of the thin cell layer: theoretical basis
and practical application of the plant growth correction factor to apple, Cymbidium and chrysanthemum. J.
Plant Growth Reg. 33: 881-895.
TEIXEIRA DA SILVA J. A., TRAN THANH VAN K., BIONDI S., NHUT, D. T. & ALTAMURA M. M. 2007. Thin
cell layers: developmental building blocks in ornamental biotechnology. Floriculture Ornamental
Biotechnol. 1: 1-13.
VANHAEREN H., INZÉ D. & GONZALEZ N. 2016. Plant growth beyond limits. Trends Plant Sci. 21: 102-109.
YANG S. J., HOSOKAWA M., MIZUTA Y., YUN J. G., MANO J. & YAZAWA S. 2001. Antioxidant capacity is
correlated with susceptibility to leaf spot caused by a rapid temperature drop in Saintpaulia (African violet).
Sci. Hortic. 88: 59-69.
YASUDA Y., YUN J. G., MIYOSHI N., HAYASHI T., YAZAWA S. & FUJITA S. 1997. Production of radicals and
acute apoptotic changes of palisade cells in early steps of Saintpaulia leaf spot appearance. Acta Histochem.
Cytochem. 30: 303-307.
YUN J. G., HAYASHI T. & YAZAWA S. 1997a. Diurnal changes in leaf spot sensitivity of Saintpaulia (African violet).
Sci. Hortic. 70: 179-186.
YUN J. G., HAYASHI T., YAZAWA S., KATOH T. & YASUDA Y. 1996a. Acute morphological changes of palisade
cells of Saintpaulia leaves induced by a rapid temperature drop. J. Plant Res. 109: 339-342.
YUN J. G., HAYASHI T. & YAZAWA S. 1996b. Precise quantification of leaf spot in Saintpaulia by image analysis
with transmitted light. Env. Control Biol. 34: 329-334.
YUN J. G., HAYASHI, T., YAZAWA S., YASUDA Y. & KATOH T. 1997b. Degradation of photosynthetic activity
of Saintpaulia leaf by sudden temperature drop. Plant Sci. 127: 25-38.
YUN J. G., HAYASHI T., YAZAWA S., KATOH T. & YASUDA Y. 1998. Abrupt and irreversible reduction of
chlorophyll fluorescence associated with leaf spot in Saintpaulia (African violet). Sci. Hortic. 72: 157-169.
ZHAO Z., ANDERSEN S. U., LJUNG K., DOLEZAL K., MIOTK A., SCHULTHEISS S. J. & LOHMANN J. U.
2010. Hormonal control of the shoot stem-cell niche. Nature. 465: 1089-1092.
How to cite this article:
TEIXEIRA DA SILVA J. A., DEWIR Y. H., WICAKSONO A., KHER M. M., KIM H., HOSOKAWA M. & ZENG
S. 2016. Morphogenesis and developmental biology of African violet (Saintpaulia ionantha H. Wendl.).
J. Plant Develop. 23: 15-25.
Received: 13 October 2016 / Revised: 24 November 2016 / Accepted: 5 December 2016
