EVALUATING GENOTYPIC VARIATIONS AMONG DROUGHT-INDUCED SORGHUM CULTIVARS FOR ASCORBATE PEROXIDASES (APXS)

Drought is a major limiting factor for plant growth and productivity. The APX enzyme family plays crucial roles in mitigation of drought-induced adversities in plants. The present work investigated the effect of genotypic variations in three sorghum cultivars, Aldari, Beydari and Ogretmenoglu-77 for foliar expression and protein activities of APX1-9 genes under 5d and 10d drought stresses. The expression of sorghum APXs in leaves were between 1.13 (APX4; Aldari) and 0.54 (APX3; Ogretmenoglu) under 5d drought stress, while it ranged from 1.81 (APX6; Beydari) to 1.51 (APX5; Ogretmenoglu) fold changes (FC) under 10d drought. 5d stress resulted in mostly downregulation in APX expression, while 10d drought mostly upregulated them. Interestingly, APX6 gene showed similar regulation pattern -with downregulation- in all test cultivars under both treatments. Based on an arbitrary but significant cutoff (-1 < log2FC > + 1), genes with the meaningful levels of expression were found as APX1 (Ogretmenoglu-77; 10d stress), APX4 (Aldari; 5d stress), APX5 (Aldari/ Ogretmenoglu; 10d stress) and APX6 (Aldari/Beydari; 10d stress). As a response to 5d drought, a significant increase (similar to 2.25 fold) in total APX protein concentrations in Aldari was noted comparing to non-stressed (control) group. Foliar APX amounts demonstrated slight decrease and increase in Beydari and Ogretmenoglu77, respectively. On the other hand, under 10d stress, foliar APX concentrations slightly increased in Aldari and Ogretmenoglu-77 decreased slightly in Beydari. More notably, APX amounts in Beydari control groups were considerably higher than even in the other stressed groups. Naturally higher APX levels may imply the tolerance of this cultivar to drought. Moreover, in the assays of drought-induced lipid peroxidation, it was found that drought considerably increased the MDA concentrations in all sorghum cultivars. Furthermore, studies targeting sorghum cultivars under drought conditions were extremely scarce, and results presented here could be invaluable for guiding breeding effort to improve sorghum drought tolerance.