Pervaiz R. Khan's research while affiliated with King Saud University and other places

Key message Oxidative stress and the antioxidant enzymes’ activity are higher in damaged than in healthy Juniperus procera trees, in summer than in winter, and in dry than in wet condition. Abstract Many of the small stands of Juniperus procera in Saudi Arabia, confined mainly to Aseer Mountains in the southern part of the country, are suffering from branch dieback. As a part of the project on the structural and functional responses of healthy and dieback-affected trees to local environmental conditions of Al-Ghalab, Al-Yazeed, and Saodah locations, this study quantifies the oxidative stress generated and the consequent modulation of proline accumulation and antioxidant enzymes’ activity, as determined by chemical analysis of needle tissues from samples collected in summer and winter seasons. The level of TBARS, which indicated the extent of oxidative stress, was minimum (10.1 nM g−1 f w) at Al-Ghalab and maximum (28.1 nM g−1 f w) at Al-Yazeed, being relatively higher in summer than in winter. Healthy trees had a lower level of TBARS than those suffering from dieback. Proline content showed 147–54 µg g−1 in healthy trees and 460–99 µg g−1 f w in affected ones. Variation in the activity of superoxide dismutase, ascorbate peroxidase, glutathione reductase, and catalase was around 0.7–3.6, 0.01–0.09, 0.02–0.08, and 0.6–3.0 U mg−1 min−1, respectively, in healthy trees, whereas 2.3–6.1, 0.04–0.3, 0.04–0.3, and 2–5.8 U mg−1 min−1, respectively, in the dieback-affected trees of the different locations. Thus, the oxidative stress and the enzymatic stimulation were higher in damaged than in healthy trees and in summer than in winter season. Water-harvesting efforts at the collection sites showed ameliorative effects. Our observations suggest that J. procera tree can be made more tolerant toward stressful condition, and even the risk of dieback can be avoided or minimized by improving soil–water availability through adequate water-harvesting strategies in the drought-affected areas.

Dry scarified seeds of Datura innoxia Linn. were gamma-irradiated with 5, 10, 20, 40, 60 and 80 Gy radiation, using a cobalt-60 source at the rate of 0.623 Gy min-1 at room temperature, and germinated on MS-medium in a growth chamber under controlled conditions. Exposure to low dose(s) of radiation (5 Gy) caused stimulatory effect on seed germination. Analysis of 90-day-old seedlings revealed that growth rate of root and shoot, net photosynthetic rate (PN), stomatal conductance (gs) and the chlorophyll and carotenoids contents increased with 5 Gy radiations. Higher doses proved inhibitory for all the above parameters; the decline observed was positively correlated with increase in intensity of gamma radiation. Intercellular CO2 (Ci), on the other hand, showed an opposite trend, being lower with 5 Gy than in the control, but significantly higher with increased radiation doses. Hyoscyamine, a tropane alkaloid, exhibited only irregular and non-significant variation in its content, with no perceptible change in structure, in the treated material, indicating that gamma-irradiation caused no significant alteration in the quantity or quality of the compound.

Plants are able to extract metal(loid) contaminants from the soil or water through their roots and translocate them to harvestable aerial shoots. Of late, this plant potential has been used as a phytotechnology, termed as phytoextraction, for cleaning the contaminated sites, and has successfully removed elements like As, Cd, Cu, Ni and Pb, among others. Exploring plants with high metal-accumulation capacity as well as engineering new hyperaccumulators is a need of the hour. Hyperaccumulators are supposed to have a >1 shoot/root metal-accumulation ratio, which they achieve by way of (a) overexpression of transport systems for improved sequestration, (b) tissue-specific protein expression, and (c) high concentration of metal chelators. Unlike non-hyperaccumulators, the hyperaccumulating species normally bind metal ions to weak oxygen ligands, and use strong ligands only for transient binding during transport to storage site. Adequate understanding of genetics, biochemistry and molecular biology of metal accumulation is a prelude to developing the transgenics with improved phytoremediation capacity. Current research in plant breeding, genomics and proteomics suggest promising leads to the creation of ‘remediation cultivars’. Several transporter genes associated with metal uptake, transport and accumulation have been identified. Efforts are underway to enhance the phytoextraction capacity of relevant species, not only by using chelating agents but also by attempting hybridization, protoplast fusion as well as genetic engineering through novel gene transfer, overexpression of genes and/or reverse gene insertion in order to enhance (a) transpiration rate, (b) uptake, translocation and metabolism of metals, (c) activity of enzymes related to rate-limiting steps, (d) transformation of accumulated metal to volatile form, and/or silencing gene(s) that encode proteases. Genome evolution in hyperaccumulators needs to be understood through a systematic study of ecological and molecular genomics. Sequencing of a complete genome of hyperaccumulators can help in identifying the promising functional non-coding regions in the genome, thus making the experimental analysis more accurate. In addition to the constitutive overexpression of a single gene, simultaneous expression of several genes in specific cellular components has to be focused. Other areas that require expert attention include identification of metal-transporter proteins and introduction of genes encoding the metal transporters; overexpression of metallothioneins (MTs) and phytochelatin synthase (PS) and overproduction of nicotianamine and histidine in plants. A comprehensive study of transgenic gene frequency, coveing several plant generations growing on polluted as well as non-polluted soils, may assess the possibility of gene escape into the environment and its transfer to the microorganisms present in the surroundings. The present review attempts not only to collect and collate the information available on mechanisms of metal accumulation and detoxification in plants and on factors affecting the tolerance and phytoextraction capacity of plants, but also to examine strategies that have been or can be devised for raising novel plant genotypes with elevated capacity of metal accumulation and toxicity tolerance.

This study, undertaken in the Riyadh region of Saudi Arabia, was focused on high initial density plantation and the subsequent thinning of Acacia salicina trees, to ensure high individual tree growth suitable for saw timber production. It investigated the effect of high stand density on restricting early branch development. Trees were planted in 1998, at a density of 6400 trees ha-1 (with spacing of 1.25 m × 1.25 m). After two years, half of the experiment was subjected to annual mechanical thinning up to 2003. From 2004 to 2010, the densities of 400 and 3200 trees ha-1 were maintained for the thinned and unthinned stands; respectively. In 2010, five trees from each of the two stands were selected randomly, felled, and processed for estimating the biomass of stem, branches, and foliage. Tree height, tree diameter, log diameter along the stem, number of branches, branch diameter and distance of each branch from tree base were measured. Thinning significantly increased the diameter at breast height (dbh) and the total tree height at the age of 12 years, the mean values being 25.2 cm, and 16.9 m for diameter and height, respectively, in thinned population (400 trees ha-1), while these were 12.2 cm and 10.7 m, respectively, in unthinned population (3200 stem trees ha-1). Though the individual stem volume increased significantly in thinned population, the total stem stand volume per hectare was far greater in the unthinned population. The thinned trees had a lower form factor (or stronger taper) than the unthinned trees. Thinning significantly increased the dry biomass of different plant parts and had a significant effect on the diameter of the thickest branch.

This study aimed at elucidating the process of cambial activity and wood formation in Acacia ehrenbergiana Hayne growing in the Al-Baha region of Saudi Arabia, has revealed that the vascular cambium was active for almost the whole year, producing phloem in two flushes (February-March and August-October), and xylem for about 11 months, with varying pace of cell division and differentiation. A close relationship existed between emergence of new leaves and initiation/acceleration of cambial activity and tissue differentiation. Monthly average of the maximum and mean daily temperature showed negative correlation with cambial-zone width. Relative humidity showed positive relationship with xylem differentiation. Leaf water deficit had an adverse effect on the cambial activity (r = -0.94, p < 0.01), xylem production (r = -0.93, p < 0.01) and phloem production (r = -0.97, p < 0.01). On the whole, moderate temperature, low water deficit and high relative humidity and rainfall favored cambial activity and vascular tissue formation. Annual production of xylem was about five times that of phloem. A. ehrenbergiana appears to be a drought-tolerant species by having narrow, dense and thick-walled vessels, thick-walled fibers, high wood density (0.9273 g cm(-3)), low vulnerability factor (4.20) and the capacity of thriving well at 35 to 47% water-saturation deficit.

This report describes a protocol for the in vitro shoot induction and plant regeneration from epicotyl explants of Cassia angustifolia on Murashige and Skoog (MS) medium supplemented with 6-ben-zyladenine (BA), Kinetin and 2-iP (0.5–10.0 lM). MS medium supplemented with BA (5.0 lM) was the most effective in inducing adventitious shoots and growth. The highest rate of shoot multiplication was achieved on MS medium supplemented with BA (5.0 lM) and Indole-3-acetic acid (IAA, 1.0 lM). The nodal segments excised from the shoots regenerated from BA (5.0 lM) and IAA (1.0 lM) were used as explants for next three round of micropropagation. The number of shoots significantly increased at successive round of micropropagation. For rooting, MS medium supplemented with 2.0 lM indole-3-butyric acid proved to be better than that supplemented with IAA or a-naphthalene acetic acid. The in vitro raised plantlets with well developed shoot and roots were successfully established in earthen pots contain-ing garden soil and were grown in greenhouse. About 52 plants (85 %) survived out of 60 plants transferred in garden soil.

Abstract This study, undertaken in the Riyadh region of Saudi Arabia, was focused on high initial density plantation and the subsequent thinning of Acacia salicina trees, to ensure high individual tree growth suitable for saw timber production. It investigated the effect of high stand density on restrictingearly branch development. Trees were planted in 1998, at a density of 6400 trees ha-1 (with spacing of 1.25 m x 1.25 m). After two years, half of the experiment was subjected to annual mechanical thinning up to 2003. From 2004 to 2010, the densities of 400 and 3200 trees ha-1 were maintained for the thinned and unthinned stands; respectively. In 2010, five trees from each of the two stands were selected randomly, felled, and processed for estimating the biomass of stem, branches, and foliage. Tree height, tree diameter, log diameter along the stem, number of branches, branch diameter and distance of each branch from tree base were measured. Thinning significantly increased the diameter at breast height (dbh) and the total tree height at the age of 12 years, the mean values being 25.2 cm, and 16.9 m for diameter and height, respectively, in thinned population (400 trees ha-1), while these were 12.2 cm and 10.7 m, respectively, in unthinned population (3200 stem trees ha-1). Though the individual stem volume increased significantly in thinned population, the total stem stand volume per hectare was far greater in the unthinned population. The thinned trees had a lower form factor (or stronger taper) than the unthinned trees. Thinning significantly increased the dry biomass of different plant parts and had a significant effect on the diameter of the thickest branch.

High frequency plantlet regeneration was achieved in cotyledonary nodes of Acacia gerrardii from 15 days old in vitro grown seedlings, cultured on Murashige and Skoog (MS) medium supplemented with benzyladenine (BA), kinetin (Kn) and-naphthalene acetic acid (NAA) either alone or in combinations. The highest regenerative response was observed on a medium containing 5.0 M BA and 0.5 M NAA where 90% of the cultures responded with an average shoot number (9.40 ± 0.70) per explant in 8 wk time. In vitro shootlets were transferred to root induction medium consisting of MS medium supplemented with auxins NAA or indole-3-butyric acid (IBA). Rooting was best in a medium supplemented with 2.0 M IBA. Rooted plantlets were acclimatized and transferred to the field with 70% survival rate. Increase in chlorophyll (Chl) a, b, carotenoid levels, MDA and proline contents were observed in plantlets acclimatized for 28 days. As the acclimatization continues, an upregulation of the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) enzyme activities were also observed. The results indicate that micropropagated plantlets develop an antioxidant enzyme system after ex vitro transfer, which suggests that the species can cope with the predicted climate change.