Culture supernatant fluids of 50 phosphate‐dissolving bacteria isolated from rhizospheres of crop plants were examined for IAA, gibberellins and cytokinins. These bacteria possessed phytase activity and 27 could dissolve rock phosphate. Twenty bacteria synthesized all 3 types of plant hormones, 43 produced IAA, 29 formed gibberellins and 45 cultures produced cytokinin‐like substances. Of the 50 bacteria tested 28 decomposed IAA. Plant growth inhibitors were detected in cultures of some isolates. The ecological significance of these rhizosphere bacteria and their mode of action when used as inoculants is considered.
In vitro methods of plant micro-propagation are being considered as a possible solution for the decline in seagrass communities registered worldwide. To achieve successful plant micro-propagation, culture conditions are commonly adjusted empirically within almost species-specific conditions, to comply to the following three conditions: (i) culture establishment (ii) shoot production and (iii) rooting and hardening for planting in soil. Cultures of Cymodocea nodosa were established from axenic explants of the apical meristem (approx. 0.5 cm) which regenerated new leaf or produced leaf regenerating calli (5% of cultivated explants) in media containing 10 À6 M of the cytokinin analogue TDZ. Longer ramet explants, not fully axenic, containing internode with leaf and roots were also affected by 10 À6 M cytokinins and auxin type of regulators, as they promoted leaf extension (in cm), particularly GA. None of the explants progressed further to massive shoot propagation and new plantlet production. Instead, experiments made with ramet explants which simulated potential produced plantlet revealed that there seems to be a strong interaction within leaf, rhizome and root, since the carbon fixed in the leaf was rapidly translocated to the rest of the tissue (50% in the roots in a FW basis). The explants preferred ammonium and dihydrogen inorganic phosphate as a nutrient source, efficiently assimilating the former regardless of whether such were added to the underground or surface tissue. However, underground tissue was required to maintain P status in the cultivated explants. #
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