The NAC family being the largest plant-specific transcription factors functions in diverse and vital physiological processes during development. NAC proteins are known to be crucial in imparting tolerance to plants against abiotic stresses, such as drought and salinity, but the functions of most of them are still elusive. In this study, we report for the first time expression of the MuNAC4, a member of NAC transcription factor from horsegram (Macrotyloma uniflorum) conferring drought tolerance. The groundnut (Arachis hypogaea) transgenics were generated using recombinant MuNAC4 binary vector transformation approach. Molecular analysis of these transgenic lines confirmed the stable gene integration and expression of the MuNAC4 gene. Twelve lines of T5 generation exhibited significantly enhanced tolerance to drought stress with proliferated lateral root growth as compared to wild types. Transgenics exposed to long-term desiccation stress assays showed increased lateral roots and greenish growth. The physiological parameters analysis also suggests that overexpression of MuNAC4 plays a significant role in improving the water stress tolerance of transgenic groundnut, reducing the damage to membrane structures and enhancing osmotic adjustment and antioxidative enzyme regulation under stress. This study validates MuNAC4 as an important candidate gene for future phytoengineering approaches for drought tolerance in crop plants.

Polyamines can regulate the expression of antioxidant enzymes and impart plants tolerance to abiotic stresses. A comparative analysis of polyamines, their biosynthetic enzymes at kinetic and at transcriptional level, and their role in regulating the induction of antioxidant defense enzymes under salt stress condition in two foxtail millet (Setaria italica L.) cultivars, namely Prasad, a salt-tolerant, and Lepakshi, a salt-sensitive cultivar was conducted. Salt stress resulted in elevation of free polyamines due to increase in the activity of spermidine synthase and S-adenosyl methionine decarboxylase enzymes in cultivar Prasad compared to cultivar Lepakshi under different levels of NaCl stress. These enzyme activities were further confirmed at the transcript level via qRT-PCR analysis. The cultivar Prasad showed a greater decrease in diamine oxidase and polyamine oxidase activity, which results in the accumulation of polyamine pools over cultivar Lepakshi. Generation of free radicals, such as O 2 (·-) and H2O2, was also analyzed quantitatively. A significant increase in O 2 (·-) and H2O2 in the cultivar Lepakshi compared with cultivar Prasad was recorded in overall pool sizes. Further, histochemical staining showed lesser accumulation of O 2 (·-) and of H2O2 in the leaves of cultivar Prasad than cultivar Lepakshi. Our results also suggest the ability of polyamine oxidation in regulating the induction of antioxidative defense enzymes, which involve in the elimination of toxic levels of O 2 (·-) and H2O2, such as Mn-superoxide dismutase, catalase and ascorbate peroxidase. The contribution of polyamines in modulating antioxidative defense mechanism in NaCl stress tolerance is discussed.

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Abstract:Heavy metal pollution of air and agricultural soils is one of the most important ecological problems on world scale.Among the heavy metals, lead (Pb) is one of the common environmental pollutants. To investigate Pb effects on nutrient uptake, two groundnut (Arachis hypogaea L.) cultivars (cultivar K6 and cultivar K9) were grown in pot cultures and stressed with lead nitrate (Pb(NO 3 ) 2 ) at four concentrations (100, 200, 400 and 800 ppm). Pb is accumulated in roots and leaf tissues in dose dependent manner in both groundnut cultivars, which resulted in reduced root and shoot growth and lower uptake of all mineral ions tested. The content of mineral ions such as Ca, Na, Mg, Co, Cu, Ni, Zn and Mn reduced in root and leaf tissues of both cultivars due to Pb stress. But the reduction in mineral ion content was less in cultivar K6 than in cultivar K9. The deficiency of mineral nutrients correlates in a strong decrease in the contents of total chlorophyll, and anthocyanin in both cultivars, but these effects are less pronounced in cultivar K6 than in cultivar K9.