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Linear regression curve showing the relationship between plants dry biomass (mg) 9 -1 and bacterial growth (10 CFU mL ), experiments are shown in the plot (r= 0.16).
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The interactions between plants with rhizosphere and root associated microorganisms have been considered because they are potentially useful in phytoremediation and are used as microbial inoculates (biofertilizers) that give bioprotection to plants against biotic and abiotic stresses. One of the methods safe and effective for introducing bioinocula...
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... The micro environments of the alginate beads were not only successful, but it is also important to mention that the size of the alginate beads produced (3 mm diameter) was adequate for the rhizobacteria. These alginate beads entrapped a significant number of 8 9 rhizobacteria (approximately 10 to 10 CFU), similar to the level obtained in alginate macro beds by Bashan et al. (2002). Bashan et al. (2002), Trejo et al. (2012) and Yabur et al. (2007) mention that alginate does not inhibit plant growth and that is why it is widely used in synthetic inoculants for PGPRs. Saxena (2011) inoculated wheat plants with immobilized bacterial strains; these significantly increased their shoot weight and length. The authors suggest that this increase may be due to the production of growth promoting substances by the inoculated bacteria. Their results were also corroborated by Chabot et al. (1993) who inoculated lettuce and corn plants with Pseudomonas sp. and observed an increase in plant height due to the siderophores and auxins produced by these bacteria. The presence of immobilized rhizobacteria led to the maintenance of the Axonopus affinis plantlets growth against cadmium. Even though this growth was small compared to the control plantlets, it suggests that the immobilized rhizobacteria protect. Figure 3 shows the correlation between the gains of the total dry biomass of A. affinis inoculated with the three immobilized rhizobacteria and the bacterial growth measured at the end of the experiments. The correlation showed the particular effect of the control and cadmium experiments inoculated with Serratia sp. strain 6 and Achromobacter sp. strain C1; there was an increase in the biomass and growth of both rhizobacteria compared to Pseudomonas sp. strain Sp7E. This rhizobacteria showed the lowest plant biomass and bacterial growth with two extreme responses; plants inoculated without the heavy metal are at the left side and middle of the figure; it shows their response in the experiment inoculated with the bacteria and Cd (1 and 1.5 mM). Plants at the top of the figure had higher total plant biomass in the experiments inoculated with the rhizobacteria and Cd (0.5 mM). Jézéquel and Lebeau (2008) showed that the beads made with alginate offer a lower mechanical resistance. These authors entrapped Bacillus sp. ZAN- 044 and Streptomyces sp. R25 in the beads and considered it as a transitional state to allow the adaptation of the bacterial cells to their new environment, before the cells are released from the beads. Van Elsaset al. (1992) noted that most of the immobilized rhizobacteria released endured in the root zone. Another work regarding the effect of immobilized rhizobacteria is the work of Aino et al. (1997) on the colonization of tomato roots with Pseudomonas fluorescens embedded in alginate beads. In this study, we suggest the colonization of roots of A. affinis plantlets by the rhizobacteria released from the alginate beds, as evident in the close interactions and adherence of alginate beads to the roots. This is shown in Achromobacter sp. strain C1 (Figure 4). It is important to mention that these evidences were a ...
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Rhizoremediation considers the phytoextraction and soil bioaugmenta-tion strategies and optimize the synergistic effect between plants and microorganisms with a physiological basis related only to plants. It is known that plant growth-promoting rhizobacteria (PGPR) affect the plants growth facilitating the uptake of nutrients and protecting them; this interaction has been attractive because the biotechnological potential of microorganisms for metal removal from soils and transport of them to the plants. In the following sections of this chapter, the authors give some analysis of the importance about the establishment of " plant-PGPR bio-assays " as tools to compare the relationships between in vitro physiological characteristics of rhizobacteria isolated from plant metal accumulators and the plant's physiology response, as follows: importance of siderophores as plant growth-promoting trait, evaluation of the in vitro production of siderophores by rhizobacte-ria, utility of the measurement of antioxidant activity in plants as indicator of heavy metal stress, and, finally, the description of cadmium effect by the antioxidant activity in two bioassays, with plant cell cultures and plantlets inoculated with a siderophore-producing bacteria (SPB).
