To investigate the seasonal dynamics of physiological and biochemical substances in leaves of male and female Idesia polycarpa and to provide a theoretical basis for rapid seedling sex identification, known-sex juvenile plants and unknown-sex seedlings were used as experimental materials. During the growing season (April-November), the temporal variations in leaf soluble sugars, soluble proteins, malondialdehyde (MDA), proline (Pro), peroxidase (POD), superoxide dismutase (SOD), polyphenol oxidase (PPO), total flavonoids, and volatile terpenes were determined. In juvenile plants, soluble sugar content was higher in females early in the season and followed a unimodal pattern (higher in June and lower in August), whereas it increased overall with month in males; soluble protein content decreased first and then increased, MDA content increased and then decreased with a peak in September, and Pro content increased overall through the season. In seedlings, soluble sugar content exhibited a bimodal pattern (relatively high in June and November); soluble protein content also decreased first and then increased; MDA increased first and then decreased, peaking in September; and Pro increased gradually with month. Enzyme activity analysis showed that POD activity in juvenile plants decreased first and then increased, and males generally exhibited higher POD activity than females during the middle and late growing season, with the greatest difference observed in August; POD activity in seedlings also showed a clear separation in August, indicating a stable and consistent sex-related divergence between the seedling and juvenile stages. Regarding secondary metabolites, total flavonoids and volatile terpenes in juvenile leaves showed an overall increasing trend, whereas total flavonoids in seedling leaves exhibited inconsistent trajectories among individuals and fluctuated over time, and volatile terpenes showed pronounced fluctuations. Based on the stable discriminatory power of POD activity, a threshold of 3100 U/(g·min) was proposed: seedlings measured in August using the guaiacol method were classified as male when POD activity exceeded the threshold and as female when it was below the threshold. This method is simple and low-cost and is suitable for rapid sex identification of I. polycarpa seedlings.
Li et al. (Wed,) studied this question.