Abstract
The drought–stress response in plant involves the cross-talk between abscisic acid (ABA) and other phytohormones, such as jasmonates and ethylene. The auxin indole-3-acetic acid (IAA) plays an integral part in plant adaptation to drought stress. Investigation was made to see how the main auxin IAA interacted with other plant hormones under water stress, applied through two different growth conditions (solid and hydroponic). Medicago sativa plants nodulated by the Ensifer meliloti wild type 1021 (Ms-1021) and its IAA-overproducing RD64 derivative strains (Ms-RD64) were subjected to drought stress, comparing their response. When the expression of nifH gene and the activity of the nitrogenase enzyme were measured after stress treatments, Ms-RD64 plants recorded a significantly weaker damage. These results were correlated with a lower biomass reduction, and a higher Rubisco protein level measured for the Ms-RD64-stressed plants as compared to the Ms-1021-stressed ones. It has been verified that the stress response observed for Ms-RD64-stressed plants was related to the production of greater amount of low-molecular-weight osmolytes, such as proline and pinitol, measured in these plants. For the Ms-RD64 plants the immunoblotting analysis of thylakoid membrane proteins showed that some of the photosystem proteins increased after the stress. An increased non-photochemical quenching after the stress was also observed for these plants. The reduced wilting signs observed for these plants were also connected to the significant down-regulation of the MtAA03 gene involved in the ABA biosynthesis, and with the unchanged expression of the two genes (Mt-2g006330 and Mt-8g095330) of ABA signaling. When the expression level of the ethylene-signaling genes was evaluated by qPCR analysis no significant alteration of the key positive regulators was recorded for Ms-RD64-stressed plants. Coherently, these plants accumulated 40% less ethylene as compared to Ms-1021-stressed ones. The results presented herein indicate that the variations in endogenous IAA levels, triggered by the overproduction of rhizobial IAA inside root nodules, positively affected drought stress response in nodulated alfalfa plants.
Highlights
Environmental factors imposing stress on plants, including drought, salinity, heat, chilling, freezing, etc. cause widespread crop losses throughout the world
Integrating physiological, transcriptomic, and metabolomic measurements were carried out to analyze the effects of drought stress on Medicago plants nodulated by 1021 and RD64 strains, under perlite-sand soil and hydroponic conditions (PEG-treatment)
When the shoots fresh weights of nodulated Medicago plants were measured after six days of water deprivation a similar decline was recorded for both Ms-1021 and Ms-RD64 plants as compared to their controls (Figure 2)
Summary
Environmental factors imposing stress on plants, including drought, salinity, heat, chilling, freezing, etc. cause widespread crop losses throughout the world. Environmental factors imposing stress on plants, including drought, salinity, heat, chilling, freezing, etc. The constant increase in temperatures and the water scarcity are increasing the frequency of severe drought conditions. Drought stress reduces leaf size, stem extension and root proliferation, reducing water-use efficiency. Different strategies have been developed to improve water adsorption and stress tolerance in crop plants, including legumes. Environmental stresses require plants to perceive and react to these signals in a highly coordinated and interactive manner. Stress conditions greatly affect gene expression, leading to modifications in the composition of plant proteome and metabolome (Urano et al, 2010; Goldack et al, 2014; Zhang et al, 2014; Wang et al, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
