Antioxidant response to drought, cold and nutrient stress in two ploidy levels of tobacco plants: low resource requirement confers polytolerance in polyploids?

Most polyploids can survive better under multiple stress conditions than their corresponding diploid; however, there is no established theory that can adequately explain this phenomenon at the molecular or physiological level. Here, we attempt to explain this interesting but puzzling problem from the perspectives of resource requirement and antioxidant response. In this experiment, we compared the antioxidative response and stomatal behavior of two ploidy levels of tobacco plants (tetraploid and its colchicine-induced octaploid) under drought, cold and nutrient deficit stress conditions. In comparison to tetraploid, less H2O2 accumulation and stronger reactive oxygen scavenging capacity (antioxidant enzyme activities and DPPH radical scavenging capacity) were observed in octaploid under stress free or stressful conditions. In accordant with these, less oxidative damage and higher redox values (ASC/DHA and GSH/GSSG) were also monitored in the octaploid than in the tetraploid under same conditions. In addition, a higher net rate of photosynthesis (Pn) and slower decline in the concentration of intercellular CO2(Ci) were measured in the octaploid compared to the tetraploid following high concentration ABA treatment (20 mg L-1), with more severe oxidative damage observed in the tetraploid than in the octaploid. On the basis of the resource acquisition theory, we consider that any environmental stress that can lower plant resource availability would favor survival in a slow-growing polyploid compared with that in a fast-growing diploid.