Morphological, physiological, and biochemical responses of rice ( Oryza sativa L.) varieties to drought stress via regulating respiration and ROS metabolism during germination

Germination marks a pivotal and sensitive phase in the life cycle of crops, with drought stress, precipitated by water scarcity, posing a significant impediment to the germination process in rice. Despite this, the regulation mechanism of respiratory and reactive oxygen species (ROS) metabolism during rice germination under drought stress remains to be fully elucidated. This manuscript presents an integrative analysis encompassing morphological, physiological, biochemical, and molecular attributes of germinated seeds from a cultivated droughtsensitive rice variety (JN10) and a drought-resistant rice variety (NG36). Our findings revealed that drought stress adversely affected the germination of both rice varieties, with NG36 exhibiting a more rapid germination rate compared to JN10 under such stress conditions. This differential response was attributed to the heightened activities of key enzymes, elevated levels of metabolic intermediates, and upregulated expression of genes encoding enzymes involved in ROS and respiratory metabolic pathways in NG36. To further dissect the interplay between these metabolic pathways, we selected specific enzyme activities for detailed examination. Notably, a robust positive linear correlation was established among phosphofructokinase (PFK), alpha-ketoglutarate dehydrogenase (KGDH), citrate synthase (CS), and isocitrate dehydrogenase (ICDH) in NG36. This correlation underscores the pivotal role of glycolytic pathways, particularly the tricarboxylic acid (TCA) cycle, in conferring drought resistance to NG36 during the germination phase under drought stress. To encapsulate our findings, the results of this investigation suggest that the rice cultivar NG36 manifests a heightened degree of drought tolerance relative to JN10. This is primarily achieved through the adept modulation of its respiratory metabolic pathways and the stringent preservation of ROS homeostasis during the germination phase under conditions of water deficit. These revelations provide unprecedented insights into the intricate regulatory mechanisms that subserve rice's drought resistance, potentially paving the way for the development of novel strategies in the breeding of rice cultivars with improved drought resilience.