Production and scavenging of reactive oxygen species confer to differential sensitivity of rice and wheat to drought stress

Abstract

Drought poses a serious threat to crop production worldwide, and is expected particularly to affect rice production and hence food security. Given that wheat is known to tolerate drought better than rice, we compare rice and wheat (cv. Weebill) to understand the species level differences in drought adaptive mechanisms. We also compare two contrasting rice genotypes (IR64, drought susceptible, and Apo, drought tolerant) for such mechanisms under well-watered (100% field capacity, 100%FC) and water-limited (60%FC) conditions. The reduction in biomass of wheat under water limitation was smaller due to a higher rate of photosynthesis associated with maintenance of tissue turgor compared to rice genotypes. Drought caused greater inhibition of Photosystem II quantum efficiency, carboxylation efficiency, and photosynthetic capacity parameters in IR64 than in Apo. Transcript levels of photosynthesis-related genes were also significantly more repressed by water limitation in IR64, whilst the wheat genotype showed smaller reduction than Apo. Despite higher non-photochemical quenching (NPQ), a smaller increase in scavenging enzymes in IR64 resulted in more accumulation of reactive oxygen species (ROS) in 60%FC than in 100%FC compared to Apo. As a photoprotection mechanism, increased levels of NPQ resulted in lower ROS accumulation in wheat despite the similar increase in scavenging enzyme transcript levels as in Apo, signifying the importance of preventing oxidative burst for enhanced drought tolerance. In Apo, upregulation of the 9-cis-epoxycarotenoid dioxygenase 2 gene implies the use of xanthophyll pool for the ABA biosynthesis. Our data suggest that regulating photosynthesis and oxidative protection in the wheat genotype enhanced drought tolerance. Improving these traits for rice is crucial to develop drought-tolerant rice genotypes.