Abstract:

【Objective】This research aims to investigate the effects of exogenous growth regulator 6-BA on the growth and physiology of Pseudostellaria heterophylla at the late growth stage and to provide a theoretical basis for efficient cultivation of P. heterophylla.【Method】 Different concentrations of 6-BA (0, 20, 40, 60 mg/L) were applied to the leaves in mid-May to determine the effects of 6-BA on root tuber growth, the antioxidant enzyme system, and the photosynthetic characteristics of P. heterophylla. 【Result】 (1) Compared to the control (CK), the root length, root diameter, fresh root yield, biomass per plant, dry weight of the aboveground part, and dry weight of the underground part of P. heterophylla in each 6-BA treatment group were significantly increased, with the 60 mg/L treatment showing the most pronounced effect. The fresh root yield and biomass per plant increased by 35.41% and 41.60%, respectively, compared to the CK, and these differences were statistically significant (P < 0.05). (2) The 6-BA treatment with an appropriate mass concentration significantly increased the activities of SOD and POD, as well as the chlorophyll and carotenoid contents in P. heterophylla leaves during the experiment. It also effectively mitigated the rising trend of MDA content and the declining trend of photosynthetic pigments. (3) The P_n, G_s, and T_r of P. heterophylla increased to varying degrees while C_i decreased, effectively alleviating the "nap" phenomenon of photosynthesis caused by non-stomatal restriction. The 60 mg/L treatment had the most significant effect. The daily mean, peak, and trough values of P_n increased by 51.76%, 41.24%, and 64.47%, respectively. (4) Compared to the control, the chlorophyll fluorescence parameters F_v/F_m, F_v'/F_m', Φ_PSⅡ, and qP in each 6-BA treatment group increased to varying degrees during the experiment, while the NPQ value decreased. (5) The φ_Po, ψ_o, φ_Eo, E_ABS/CSm, E_TRo/CSm, E_ETo/CSm, and c_PIabs significantly increased, while φ_Do and E_DIo/CSm decreased with 6-BA treatment at an appropriate mass concentration (60 mg/L). These results indicated that the 6-BA treatment enhances the efficiency of PSⅡ light energy absorption, allocation, and utilization, as well as leaf-specific activity, alleviating the photoinhibition caused by excess excitation energy. 【Conclusion】 The 6-BA treatment at an appropriate mass concentration effectively enhances the antioxidant activity and photosynthetic performance of P. heterophylla leaves at the late growth stage, promoting growth and increasing root yield. The improvement in photosynthetic performance is related to enhancing antioxidant activity and PSⅡ photochemical activity in the leaves.

Key words: Pseudostellaria heterophylla, 6-BA, antioxidant system, photosynthesis, chlorophyll fluorescence