ABSTRACT We aimed to determine whether humic acid (HA) can alleviate the injury of millet caused by drought and its potential mechanism. Millet seeds (Jingu 21 and Zhangza 10) were soaked in different concentrations of HA (0, 50, 10, 200, and 300 mg L−1) for 12 h. The physiological and photosynthetic characteristics of millet seedlings, including growth parameters, osmotic regulators, antioxidase activity, photosynthesis, chlorophyll fluorescence, and P700 parameters, were determined before and after drought stress. HA significantly promoted the growth of millet seedlings under drought stress. Pretreatment with 100 mg L−1 or 200 mg L−1 HA significantly increased free proline, soluble protein, and activity of the antioxidant enzyme system (superoxide dismutase, peroxidase, and catalase) in both Zhangza 10 and Jingu 21. The accumulation of reactive oxygen species ( and H2O2) was reduced in HA treatments compared with that of the control (P < .05). Moreover, HA (100 mg L−1) significantly increased net photosynthetic rate, stomatal conductance, effective quantum yield of photosystem II, relative photosynthetic electron transfer rate of photosystem II, and photochemical quenching. HA also reduced intercellular CO2 concentration and non-photochemical quenching. Furthermore, 200 mg L−1 HA significantly increased the maximum P700, effective quantum yield of photosystem I, and relative photosynthetic electron transfer rate of photosystem I in Zhangza 10 and decreased non-photochemical energy dissipation in Jingu 21 and Zhangza 10 under drought stress. HA promoted the growth of millet seedlings under drought stress by promoting the osmotic adjustment ability and antioxidant capacity of seedlings and increased photosynthesis.

中文翻译：

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腐植酸改善干旱胁迫下小米幼苗的生理和光合特性

摘要 我们旨在确定腐植酸（HA）是否可以减轻干旱对小米的伤害及其潜在机制。将小米种子（金谷 21 号和章杂 10 号）在不同浓度的 HA（0、50、10、200 和 300 mg L-1）中浸泡 12 小时。在干旱胁迫前后测定了小米幼苗的生理和光合特性，包括生长参数、渗透调节剂、抗氧化酶活性、光合作用、叶绿素荧光和 P700 参数。HA显着促进干旱胁迫下小米幼苗的生长。用 100 mg L-1 或 200 mg L-1 HA 预处理显着增加了漳杂 10 号和金谷 21 号的游离脯氨酸、可溶性蛋白和抗氧化酶系统（超氧化物歧化酶、过氧化物酶和过氧化氢酶）的活性。与对照相比，HA 处理中活性氧（和 H2O2）的积累减少（P < .05）。此外，HA (100 mg L−1) 显着提高净光合速率、气孔导度、光系统 II 的有效量子产率、光系统 II 的相对光合电子转移速率和光化学猝灭。HA 还降低了细胞间 CO2 浓度和非光化学猝灭。此外，200 mg L-1 HA显着增加了干旱胁迫下漳杂10号光系统I的最大P700、有效量子产率和光合系统I的相对光合电子转移速率，降低了金谷21和漳杂10号的非光化学能量耗散。