Photoperiod-induced changes in total nitrogen and soluble protein content in soybean leaves

Soybean (Glycine max (L.) Merr.) is a short-day plant highly sensitive to photoperiod, with this sensitivity largely regulated by maturity (E) genes. These genes influence a wide range of developmental processes, including flowering time, morphological traits, hormone levels, and carbon and nitrogen metabolism. Adaptation to photoperiod involves coordinated changes in morphology, physiology, and biochemistry, ensuring timely transition to reproductive development and optimal crop formation. Field experiments were conducted at the experimental plots of the Department of Physiology and Biochemistry of Plants and Microorganisms of V. N. Karazin Kharkiv National University. This study investigated the effects of photoperiod duration on total nitrogen and soluble protein content in the leaves of near-isogenic soybean lines of the Clark variety, differing in E1–E4 gene combinations. Short-day lines (Clark variety (e1E2E3E4e5E7), line L63-3016 (e1E2E3e4e5E7), line L 80-5879 (E1e2e3E4e5E7) and photoperiod-insensitive lines (L63-3117 (e1e2E3E4e5E7), L71-920 (e1e2e3E4e5E7) were grown under natural long-day conditions (16 h) until the V3 stage. Half of the plants were then exposed to short-day conditions (9 h) for 14 days using blackout treatments. Leaf samples were collected at four time points (before the start of the short day effect, during the short day effect - 7 and 14 days, a week after the short photoperiod effect) to assess total nitrogen and soluble protein levels. The results showed that dominant alleles of E1 and E2 delayed the transition to the reproductive phase and significantly affected nitrogen and protein accumulation. Specifically, E1 reduced total nitrogen under both photoperiods, while E2 increased it under long-day conditions. Both E1 and E2 lowered soluble protein content under short-day exposure. No significant effects of E3 and E4 were observed. These results demonstrate that the regulation of nitrogen metabolism and protein synthesis in soybean is closely modulated by the interaction between photoperiod and maturity gene expression.