RESUMEN
The aim of this study was to contrast the effects of drought stress on polyamine oxidases gene expression and activity as well as photosynthetic efficiency in relatively tolerant (Karoon) and sensitive (260) maize genotype. d Reduction in leaf relative water content as a result of drought led to increase in root growth, but diminished shoot growth indices. Under drought stress, activity of antioxidant enzyme, catalase, significantly increased in both genotypes, whereas significant higher activity of superoxide dismutase and peroxidase was only observed in Karoon genotype. Expression of polyamine oxidase (PAO) genes (zmPAO1, zmPAO2, zmPAO3, zmPAO4, zmPAO5, zmPAO6) and activity of enzymatic polyamine oxidation was increased in both genotypes under drought stress. The enhancement in PAO gene expression and enzyme activity was more prominent in Karoon cultivar compared to 260. Chlorophyll a fluorescence and fast induction kinetics were negatively influenced by drought stress. These parameters were more affected in 260 cultivar compared with Karoon. Our results suggest that under drought stress, higher activity of polyamine oxidase pathway in backconversion of Spermine and spermidine to putrescine (protectant of photosynthetic apparatus) as well as higher antioxidant enzymes activity in Karoon cultivar, may play a role in higher efficiency of photosynthetic process in this cultivar.