Effects of temperature and light conditions during the late growth stage on delayed stem senescence and cytokinin levels in the xylem exudate of soybean

Abstract

Delayed stem senescence (DSS) in soybean plants is defined as retarded leaf and stem maturity, even if pods mature normally. This phenomenon is a serious problem for the combine harvesting of soybean in Japan. Our previous research showed that DSS occurred more frequently in June sowing than in July sowing, and the plants sown in June were exposed to higher temperature and higher solar radiation intensity during reproductive growth stage as compared to those sown in July. We additionally observed higher levels of cytokinins, plant hormones with senescence inhibition activity, in xylem exudate after pod‐setting stage (R4) under the DSS‐induced condition. Thus, this study investigated the effects of the respective environmental factors, temperature and light intensity, after R4 on cytokinin levels in the xylem exudate and the occurrence of DSS. Pot experiments were conducted in the experimental field of Nihon University (Fujisawa‐city, Kanagawa, Japan). In temperature treatments, soybean plants grown in the field environment were moved to an air‐conditioned room at R4 stage, whereas control of light intensity was achieved by shading using cheese clothes under the field condition. The temperature control experiments revealed that high temperature after R4 promoted the DSS symptom, while low temperature after R4 inhibited the occurrence of DSS. On the other hand, decreased light intensity after R4 did not affect the severity of DSS. The cytokinin levels in the xylem exudate at R5 correlated with the severity of DSS in the temperature treatments, but the change in light intensity did not influence the cytokinin levels. These results indicated that high temperature after pod‐setting stage have a profound effect on the occurrence of DSS, and this effect is mediated by the increased cytokinin levels in the xylem exudate.

Effects of post-silking low temperature on the starch and protein metabolism, endogenous hormone contents, and quality of grains in waxy maize

“…Sowing time experiments is an important means to explore the effects of temperature changes in natural environments (Isobe et al, 2022). Meanwhile, the pot trial can strictly control the growth environment of plants, which is beneficial to accurately determine the influence of experimental factors (Gheysari et al, 2021).…”