Proteomic and Molecular Biological Analyses of Response Mechanism in Rice (Oryza sativa L. cv. Koshihikari) Under Drought Stress.

Drought stress severely limits rice growth, while roots play a key role in sensing water deficits and triggering adaptive responses. To investigate time-dependent molecular responses in rice (Oryza sativa L. cv. Koshihikari) under drought stress induced by polyethylene glycol (PEG), seedlings were exposed to 10 and 20% PEG for 4 and 8 days, followed by morphological, proteomic, immunoblot, polymerase chain reaction, and ATP content analyses. Primary root length and total root fresh weight were significantly decreased with 20% PEG for 8 days compared with untreated. Proteomic analysis revealed changes in the abundance of rice root proteins under 20% PEG treatment between 4 and 8 days, with differentially abundant proteins enriched in Gene Ontology categories related to nuclear components, protein phosphorylation, and ATP binding. Selected proteins related to protein protection, redox-associated processes, and cytoskeletal responses were examined using immunoblot and polymerase chain reaction analyses. Glutathione S-transferase decreased and heat shock protein 70 increased with PEG for 8 days. The expression of NADPH-dependent codeinone reductase was upregulated and heat shock protein 17.9 was downregulated by PEG for 8 days. ATP content per unit fresh weight decreased in roots after PEG treatment. These results suggest that prolonged PEG-induced osmotic stress inhibits rice root growth through alterations in cellular energy status, the abundance of proteins involved in protein protection and glutathione S-transferase-mediated detoxification, and the expression of genes associated with reactive carbonyl species metabolism.