Spring low temperatures are a serious natural threat to wheat production in the Huang-Huai wheat region, and they are often accompanied by weak light environments during the day. To elucidate the response patterns and adaptation mechanisms of winter wheat leaves to low-temperature and weak-light environments, we simultaneously measured prompt chlorophyll a fluorescence, delayed chlorophyll a fluorescence, and modulated 820 nm light reflection; moreover, we analyzed the effects of low temperature and weak light treatment for different duration (2 h and 4 h) on the donor-side activity of photosystem II (PSII), the degree of PSII unit dissociation, the efficiency of light energy absorption and capture by PSII, electron transfer to Q_A⁻ and PSI terminal, PSI activity and cyclic electron transport activity in isolated wheat leaves under controlled conditions. The results, which were corroborated using the three methods, revealed that in low-temperature and weak-light environments, the degree of PSII unit dissociation, and the efficiency of light energy absorption, capture, and electron transfer to Q_A⁻ decreased, while the donor-side activity remained unaffected. In contrast, the efficiency of electron transfer to the PSI terminal and the overall performance of photosynthetic electron transport increased. Comprehensive analysis suggests that the increase in the electron receptor pool at the PSI terminal under low-temperature stress is a crucial factor contributing to the enhanced electron transfer efficiency to the PSI terminal and the improved overall performance of the photosynthetic electron transport chain, which is also a crucial factor in the high cold tolerance of winter wheat.

Henan Province, the foremost wheat-producing region in China, frequently experiences drought stress during the wheat seedling stage. Innovating the evaluation methods for drought resistance at this stage and identifying drought-resistant varieties are crucial for the effective utilization of germplasm. This study utilized 55 wheat varieties that have been bred and promoted in Henan Province in recent years as experimental materials. A 15% PEG-6000 solution was employed to simulate drought stress, and the primary morphological indicators of seedlings, relative chlorophyll content (SPAD), and various chlorophyll fluorescence parameters were assessed. The comprehensive drought resistance scores (D values) for each variety were determined by calculating the drought resistance coefficients for each index, employing principal component analysis, and conducting membership function analysis. Based on the cluster analysis of D values, 55 varieties were categorized into four groups: high drought resistance (10), medium drought resistance (28), low drought resistance (16), and drought-sensitive (1). Seven indicators—SPAD, fresh root weight, seedling height, fresh weight of the aboveground part, Fv/Fm, PItotal, and Mo—were selected as evaluation metrics for the drought resistance of wheat through stepwise regression analysis. The comprehensive evaluation system developed in this study, which is based on morphological and photosynthetic fluorescence characteristics, can swiftly and accurately assess the drought resistance of wheat seedlings. The key indicators identified for highly drought-resistant varieties may serve as valuable references for drought-resistant wheat breeding in Henan Province.