Abstract:

Syndiclis anlungensis is an critically endangered plant endemic to Guizhou, China. Its natural regeneration is difficult and the seed germination rate is extremely low. The physiological and biochemical mechanism of germination is still unclear. To investigate the germination mechanism of Syndiclis anlungensis seeds and provide a theoretical basis for its germplasm conservation and artificial propagation, this study used seeds of S. anlungensis as experimental materials. Eleven physiological and biochemical indicators, including soluble sugar (SS), starch (ST), soluble protein (SP), the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), α-amylase and β-amylase, as well as the contents of indole-3-acetic acid (IAA), abscisic acid (ABA) and gibberellic acid (GA₃), were determined at five germination stages using anthrone colorimetric method, Coomassie brilliant blue staining, ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and other methods. The results showed that during seed germination, the ST content continuously and significantly decreased (a reduction of 60.68%), the SS content increased rapidly at the early germination stage and then tended to stabilize, while the SP content increased rapidly at the early germination stage and then gradually declined. Enzyme activities exhibited regular changes, in which SOD and POD activities significantly increased at the early germination stage, CAT activity continuously decreased, and the activities of α-amylase and β-amylase fluctuated slightly. Changes in endogenous hormone contents revealed that ABA content significantly decreased during dormancy release (from 17.66 ng/g to 2.18 ng/g), IAA showed an overall upward trend, and GA₃ did not change significantly. Further analysis showed that the IAA/ABA and GA₃/ABA ratios significantly increased after the S3 stage (radicle and hypocotyl development stage), indicating that this stage is a critical turning point for hormone balance regulation. Correlation analysis indicated that the germination process was highly significantly negatively correlated with ST content, ABA content, GA₃ content and CAT activity (P<0.01), and significantly positively correlated with IAA content (P<0.05). In summary, the germination of S. anlungensis seeds relies on starch degradation as the main energy source; SOD and POD play positive regulatory roles in dormancy release; the decrease in ABA content is the key to breaking germination inhibition; and IAA plays an important role in the radicle and hypocotyl development stage. The S3 stage is a critical node for hormone balance regulation, and the synergistic interaction of nutrient metabolism, enzyme activities and hormone networks ensures the successful germination of the seeds. In this study, the physiological mechanism of its germination is clarified. In the future, artificial propagation research can be carried out in combination with exogenous hormone treatment and molecular regulation technology.

Key words: Syndiclis anlungensis, critically endangered plant, seed germination, storage substances, enzyme activities, endogenous hormones, physiological and biochemical mechanism