Molecular and physiological performance in response to drought stress in Iranian rice cultivars

The drought is one of the major challenges in rice production in Iran where it is the second most important crop after wheat. Hence, there is an increasing need to develop rice genotypes with drought-tolerant background. Determining drought tolerance mechanisms would be the first priority in order to have a successful rice breeding program. In the present study, three popular rice (Oryza sativa L.) cultivars including Neda, Amol3, and Sang-tarom having contrasting features against drought stress were tested in two water-deficit treatments at both vegetative and reproductive stages. Some important morphological and physiological characteristics related to the drought tolerance mechanism such as ABA content in leaves, size of stomatal apertures, and root length in vegetative phase as well as root volume and weight of panicles in reproductive phase were evaluated. Further, the expression profiles of four important transcription factors involved in drought tolerance regulatory networks, MYB3R-2, ZFP252, AP37, and AP59, were examined by means of quantitative RT-PCR. The data showed that the responses of Neda to drought stress conditions are closer to Amol3 than to Sang-tarom. In Neda, no reduction was observed in stomatal aperture size while the maximum dry and fresh weights of panicles found in Neda under mild drought stress conditions was a remarkable property among the cultivars in long-term drought stress. The genes expression profiles of AP37, AP59, MYB3R-2, and ZFP252 also showed lower levels of increase in Neda compared to Sang-tarom and Amol3.