Physio-biochemical characterizations in the drought induced rice (Oryza sativa L.): pathway to understand the drought tolerance mechanisms

Water stress management is one of the most significant issues in agricultural and crop research. Water stress affects more than 42 million hectares of rice cultivation lands in Asian countries. The current scenario constraints are the production of rice with higher quality to improve global food security and meet the food demands of the growing world's population. The present study investigates the effects of water stress on two rice varieties, (Aduthurai-ADT) ADT-45 and ADT-49, and characterizes the growth, physiological, biochemical and antioxidant activities of the rice cultivars. Histochemical staining with 3,3-diaminobenzidine (DAB) and Nitro Blue Tetrazolium (NBT) was used to detect drought-induced ROS species. FTIR (Fourier-transform infrared spectroscopy) and ESR (Electron Spin Resonance) spectra were performed on the control and drought samples. The results showed a decrease in shoot and root length, fresh and dry weight, RWC and decreasing photosynthetic pigments such as chlorophyll a and b. The content of carotenoids, reducing sugars, starch, proline and Malondialdehyde (MDA) were increased in drought-tolerant plants, while the protein and amino acid content dropped. A high level of free radical accumulation has been detected in drought-imposed samples in both rice varieties by histochemical staining. Enzymatic antioxidants such as Catalase (CAT), Peroxidase (POX), Ascorbate Peroxidase (APX) and Superoxide dismutase (SOD) activities were increased in drought-induced plants compared to the control of two rice varieties, scavenging Reactive Oxygen Species (ROS) species. Besides, (ESR was used to confirm that the remarkable signals indicating free radical accumulation were higher water-deficit plants than in control plants. ESR spectroscopy is a reliable approach for distinguishing between tolerant and sensitive rice types. FTIR spectroscopy was used to identify various functional groups in drought-imposed and control samples. FTIR was used in the study to get significant insights into a plant stress response and to find novel drought tolerance features. The present study reveals that the rice variety ADT-49 was more drought resistant than ADT-45. Our findings demonstrated that drought affects growth and physiological metabolism, giving a significant basis for drought escape or tolerance in developing new varieties. In order to increase the drought tolerance mechanism in rice crops, further investigation is needed on the application and function of plant hormones under drought stress circumstances.