Flooding is a major environmental stress that damages agricultural production worldwide. Using the key regulator of submergence tolerance in rice, SUB1A, as a model, we have advanced our understanding of how plants coordinate transcriptional, hormonal, and metabolic responses to submergence. However, the contribution of SUB1A to recovery from sublethal submergence is still unknown. This study revealed SUB1A's additional role in the recovery phase: promotion of a rapid return to normal metabolic status upon desubmergence through quick recovery of photosystem II photochemistry and carbon fixation. We also investigated how SUB1A differentially regulates adaptive responses in two functionally distinct leaves, growing and mature leaves, under submergence. This study revealed that rice plants promote rapid carbohydrate and nitrogen remobilization and transport in mature leaves, supporting quick elongation growth of growing leaves. In the presence of SUB1A, these metabolic processes were suppressed in mature leaves, resulting in the avoidance of energy starvation in the source tissues. In growing leaves, SUB1A enhanced the accumulation of abscisic acid, but repressed the level of ACC, a precursor of ethylene, contributing to the restriction of elongation growth and leaf senescence in the sink tissues. Application of nitrogen fertilizers is a necessary step to maintain high grain yield in cereals, but plants absorb only 30-50% of supplied N. Wheat, one of the most widely grown crops in the world, requires a high level of nitrogen application to maintain grain yield and protein content. In this study, we investigated how nitrogen input affects the accumulation of major N and C compounds and expression of genes associated with N and C metabolism in flag leaves of wheat. We used two genotypes with distinct nitrogen use efficiencies (NUE), VA08MAS-369 and VA07W-415. VA08MAS-369 displayed higher grain yield, stover biomass, and stover N content at low N, which results from greater N-uptake efficiency in this genotype. Consistently, high N-uptake efficiency was reflected by increased mRNA accumulation of nitrate transporters and their transcriptional regulator, NAC2, in flag leaves at the post-anthesis stage. Overall, this study advanced our knowledge of the important mechanisms in plant response to flooding and N limitation in these key staple cereals. / PHD / Flooding is a serious natural disaster that damages agricultural production worldwide. Rice is a wetland plant that adapts to flooding conditions, but its tolerance to flooding varies in cultivars. Functional characterization of a submergence tolerance gene, SUB1A, has led to our understanding of various mechanisms that regulate flooding tolerance in rice and other plants. However, the role of SUB1A in plant recovery from mild submergence stress is still unknown. This study revealed that SUB1A contributes to the maintenance of photosynthetic performance and provides protection from sudden exposure to high light after floodwater subsides. These processes aid in a quick recovery from reduced metabolic activities. We also investigated the role of SUB1A in adaptive responses in growing and mature leaves of rice plants during submergence. Mature and growing leaves looked similar, but their functional importance was distinct. In general, mature leaves serve as energy production tissues through photosynthesis. The excess carbohydrate and nitrogen reserves produced in mature leaves are transferred to growing leaves that consume a large amount of energy for rapid growth. This study revealed that SUB1A restricted the consumption and transfer of energy reserves in mature leaves to avoid an energy crisis. In growing leaves, SUB1A suppressed elongation growth and leaf senescence through the proper regulation of key hormones controlling these processes. Nitrogen (N) fertilizer application is a necessary process to improve agricultural productivity in many crops. However, crops only take up 30-50% of applied N, resulting in water and air pollution and altered ecosystems. Improvement of plant N use efficiency (NUE) is one of the ways to address this issue. This study compared two soft red winter wheat lines with contrasting NUE under low and normal N supply. It was concluded that one line, VA08MAS-369, had higher grain yield and N uptake efficiency under low N supply. Our physiological and molecular study indicated that VA08MAS-369 significantly promoted N remobilization in leaves and N transport to grains after flowering under limited N. This study advanced our understanding of NUE mechanisms in winter wheat, which may aid the development of new cultivars with enhanced NUE through modern biotechnological approaches.