Polyamine-producing actinobacteria enhance biomass production and seed yield in Salicornia bigelovii

Thirty-five actinobacterial isolates obtained from Salicornia bigelovii rhizosphere in the United Arab Emirates were evaluated for their potential to produce polyamines and for their abilities to be rhizosphere-competent. The highly polyamine-producing Actinoplanes deccanensis UAE1 and Streptomyces euryhalinus UAE1 were selected, and their inoculation impacts on S. bigelovii were assessed under greenhouse conditions. Application of any of the two isolates significantly increased the length and dry weight of shoot and root tissues, photosynthetic pigments, and seed yields compared to control plants, suggesting that A. deccanensis and S. euryhalinus can promote S. bigelovii growth. The application of these isolates resulted in significant increases in the levels of endogenous free polyamines and plant growth regulators (auxins, gibberellic acid, and cytokinins), but a concomitant reduction in abscisic acid in S. bigelovii-tested tissues. Specifically, we found that putrescine, spermidine, and spermine produced by S. euryhalinus were the major contributors to plant growth parameters, but to a lesser extent by A. deccanensis. Both A. deccanensis and S. euryhalinus were, however, not capable of producing significant levels of other plant growth regulators in vitro. Plant yield was higher in the presence of S. euryhalinus than with A. deccanensis, suggesting relative superiority of S. euryhalinus as a rhizosphere-competent isolate compared to the nonrhizosphere-competent isolate A. deccanensis. This is the first study reporting the production of polyamines by marine actinobacteria and demonstrating the potential of polyamine-producing actinobacteria to enhance growth of halophytic plants through the increase in the endogenous levels of free polyamines and other plant growth regulators.