Chlorophyll Fluorescence, Oxygen Consumption Rates and Germination of Green Soybean Seeds Produced Under Heat-Drought Stress.

Heat-drought stress during the late development of soybean seeds (Glycine max [L.] Merr.) adversely affects chlorophyll degradation, resulting in green seeds with low physiological quality. This study aimed to relate chlorophyll fluorescence, oxygen consumption rates, and germination characteristics in green and yellow soybean seeds produced under heat-drought stress conditions. Seeds produced under favorable growth conditions were used as controls. Seed chlorophyll fluorescence was measured as well as individual seed respiratory activity by measuring oxygen levels during germination over 90 h at 25°C. Results indicated that green seeds, with the highest chlorophyll fluorescence, exhibited the lowest initial metabolic rates and germination percentages. Additionally, green seeds took longer to consume 50% of the available oxygen, requiring 45.90 h compared to 25.54 h for yellow seeds and 19.63 h for control seeds. Germination rates and embryonic axis lengths were significantly lower for green seeds (11.1% germination and 0.59 cm length) compared to yellow seeds (65.4% and 1.04 cm) and control seeds (83.3% and 1.44 cm). A negative correlation was found between chlorophyll fluorescence and both metabolic rates and embryonic axis length, indicating that heat-drought stress severely impacts chlorophyll degradation, oxygen consumption, metabolic rates, and germination in green soybean seeds.