外源钙对干旱胁迫下桔梗幼苗生理特性和桔梗品质的影响

【目的】干旱胁迫抑制药用植物光合色素合成，降低植株光合活性、光合碳同化效率，阻碍养分运输，严重影响药材的产量和品质。钙是植物生理活动中多种酶的活化剂，同时Ca2+作为细胞内第二信使与植物非生物胁迫密切相关。揭示外源钙缓解桔梗干旱胁迫伤害的潜在生理机制，对利用外源钙提高干旱、半干旱地区桔梗耐旱性和药用品质具有重要意义。【方法】以桔梗幼苗为材料，采用盆栽试验在干旱条件下叶面喷施10 mmol/L CaCl2，研究外源钙对桔梗幼苗生长、光合气体交换参数、抗氧化酶活性及药用部位品质等的影响。【结果】（1）外源钙处理能促进干旱胁迫下桔梗根长和干鲜生物量显著增加。（2）外源钙使干旱胁迫下桔梗叶片气孔开度、叶绿素a含量、总叶绿素含量、类胡萝卜素含量、净光合速率（Pn）、气孔导度（Gs）和蒸腾速率（Tr）分别显著增加30.28%、57.67%、44.44%、100.33%、89.53%、60.00%和83.11%。（3）外源钙使干旱胁迫下桔梗叶片丙二醛（MDA）、过氧化氢（H2O2）含量分别显著降低13.82%和18.66%，同时使干旱胁迫下桔梗叶片中过氧化物酶（POD）、超氧化物歧化酶（SOD）和过氧化氢酶（CAT）活性分别增加了25.43%、7.90%和33.92%。（4）外源钙不仅促进桔梗根中药用成分皂苷D、多糖、总黄酮、游离氨基酸在正常条件下分别显著增加35.34%，34.87%，4.19%和6.52%，还使它们在干旱胁迫处理下分别显著增加10.94%、7.53%、6.07%和5.78%。（5）外源钙提高了干旱胁迫下桔梗根中可溶性蛋白含量，以及地上部和地下部矿质元素含量。【结论】喷施10 mmol/L CaCl2能进一步激发干旱环境中桔梗叶片抗氧化系统的保护作用，通过渗透调节提高光合色素含量和光合性能，协同促进次生代谢产物和矿质元素累积，改善药用部位品质，从而缓解干旱对桔梗幼苗的伤害。

Effects of Exogenous Calcium on Physiological Characteristics and Medicinal Quality of Seedlings under Drought Stress of Platycodon grandiflorus

[Objective] Drought stress inhibits the synthesis of photosynthetic pigments in medicinal plants, reduces plant photosynthetic activity and photosynthetic carbon assimilation efficiency, hinders nutrient transport, and seriously affects the quality and quality of medicinal materials; Calcium is an activator of various enzymes in plant physiological activities, and Ca2+, as the second intracellular messenger, is closely related to abiotic stress in plants; Present study investigated that the potential physiological mechanism of exogenous calcium enhances drought resistance and medicinal quality of Platycodon grandiflorus in arid and semi-arid areas tolerance drought stress. [Methods] A pot experiment was set up to explore the effects of exogenous application CaCl2（10 mmol/L） on plant growth, photosynthetic gas-exchange parameters, and quality of medicinal parts in P. grandiflorus seedings under drought stress. [Results](1) Exogenous calcium treatment could significantly increase the root length and dry and fresh biomass of Platycodon grandiflorus under drought stress. (2) Exogenous calcium significantly increased the stomatal aperture, chlorophyll a content, total chlorophyll content, carotenoid content, net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) by 30.28%, 57.67%, 44.44%, 100.33%, 89.53%, 60.00%, and 83.11%, respectively, in P. grandiflorus leaves under drought stress. (3) Exogenous calcium effectively reduced the content malondialdehyde (MDA) and hydrogen peroxide (H2O2) in P. grandiflorus leaves under drought stress, which is significantly reduced by 13.82% and 18.66% compared to drought stress treatment, respectively. Exogenous calcium increased the peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities in P. grandiflorus leaves by 25.43%, 7.90%, and 33.92%, respectively, compared to drought stress treatment, (4) Exogenous calcium alone significant increased medicinal components latycodin-D, polysaccharides, total flavonoids, and free amino acid content in P. grandiflorus roots by 35.34%, 34.87%, 4.19% and 6.52%, respectively. Compared with drought stress treatment, the content of latycodin-D, polysaccharides, total flavonoids and free amino acid were significantly increased by 10.94%, 7.53%, 6.07%, and 5.78% under exogenous calcium treatment, respectively. (5) Exogenous calcium increased the soluble protein content in the roots, and the mineral element content in shoot and root of P. grandifloras under drought stress. [Conclusion] Spraying 10 mmol/L CaCl2 enhanced the protective effect of antioxidant systems in P. grandifloras leaves under drought conditions, which increased the photosynthetic pigment content and photosynthetic performance through osmotic regulation and synergistically enhanced the accumulation of secondary metabolites. At the same time，exogenous CaCl2 enhanced the accumulation of secondary metabolites and mineral element and improved the quality of medicinal parts, resulting in alleviation of drought damage to P. grandifloras seedlings.