Enhanced tolerance of transgenic sorghum expressing mtlD gene to water-deficit stress

Transgenic sorghum (T-4) lines with mannitol-1-phosphate dehydrogenase (mtlD) gene derived from Escherichia coli were evaluated for water-deficit stress tolerance in pot culture under greenhouse conditions. Leaf water relations, accumulation of total soluble sugars, membrane stability, antioxidative enzyme activity, yield and yield related parameters were analyzed in the plants subjected to well-watered and water-deficit stress conditions. Water-deficit stress caused a reduction in the soil moisture content resulting in visual symptoms of leaf rolling. Transgenics maintained relatively higher relative water content (RWC) than the untransformed control 15 d after withholding water. The transgenics accumulated more total soluble sugars when compared to untransformed control. Also the transgenics showed lower malondialdehyde (MDA) content and increased superoxide dismutase (SOD) activity. All these traits together contributed to the better performance of mtlD transgenics compared to untransformed control. Further, the percent decrease in total biomass and grain yield under water-deficit stress was lower in transgenics compared to control. Most importantly the root biomass was found to be significantlyhigher in the transgenics when compared to untransformed control. Among the transgenics, L2, L5 and L75 were found to be superior in terms of various physiological traits, such as, RWC, accumulation of total soluble sugars and SOD activity related to drought tolerance compared to control and other mtlD transgenic lines, L3, L4 and L72.