Physio-biochemical assessment and expression analysis of genes associated with drought tolerance in sugarcane (Saccharum spp. hybrids) exposed to GA3 at grand growth stage

Drought is one of the most serious environmental factors limiting production of sugarcane worldwide. In order to assess the influence of gibberellins (GA(3)) on drought and plant growth, along with associated physio-biochemical attributes, expression of eight drought-responsive genes were quantified and analysed. At grand growth stage (120 DAP) two sugarcane varieties (CoLk94184, CoPK05191) were exposed to drought by withholding irrigation. GA(3) (35 ppm) was applied using battery-operated uniform controlled dispensing sprayer twice at 1-week intervals on 2-week drought-stressed plants. Physio-biochemical attributes including antioxidant enzyme activities were estimated following standard protocols. RT-PCR was performed to visualise the drought-associated gene expression patterns. Drought triggered a reduction in RWC and chlorophyll content but these recovered when droughted plants were exposed to GA(3). Proline content increased many fold in both varieties under stress, but decreased under the influence of GA(3). There was a mixed response of antioxidant enzyme activity, which distinctly declined after GA(3) exposure, together with a lesser reduction in dry matter content over that of control plants. With increasing stress, expression of pyrroline-5-carboxylase synthetase (P5CS) and betaine-aldehyde dehydrogenase genes was observed, selectively up-regulated in CoPK05191. Expression of proline oxidase/transporter was high in CoPK05191 but diminished along with proline content after exposure to GA(3.) CoLk94184 showed no significant difference in P5CS gene expression under stress condition, whereas expression of betaine-aldehyde dehydrogenase gene was unchanged in response to stress. Results demonstrated that exposure of droughted plants to GA(3) not only led to recovery of activity of drought-associated physio-biochemical attributes, but also minimised impact on cane dry weight and quality. Further, GA(3) application caused differential gene expression that possibly triggers increased responsiveness towards drought tolerance in sugarcane.