Humic acid improves the physiological and photosynthetic characteristics of millet seedlings under drought stress

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 (O � :2 and H 2 O 2 ) 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 CO 2 concentration and non-photochemical quenching. Furthermore, 200 mg L −1 HA significantly increased the maximum P 700 , 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.

Bread Wheat Productivity in Response to Humic Acid Supply and Supplementary Irrigation Mode in Three Northwestern Coastal Sites of Egypt

“…Furthermore, previous authors [59,[71][72][73] mentioned that HA increased the levels of 40 compounds that are associated with the stress response. HA molecules promote the osmotic adjustment ability, increase leaf water retention, as well the photosynthetic and antioxidant metabolism of plants under drought stress [74,75]. The integration of HA application and a water deficit makes it possible to assess the precision and efficiency of the system in researching the effect of HA on drought tolerance [45,76].…”

Biostimulants for the Regulation of Reactive Oxygen Species Metabolism in Plants under Abiotic Stress

“…•− and H 2 O 2 in the leaves of millet; however, HA application reduced the production rate of oxygen radicals along with the decreased activity of SOD and POD. Without the regulation of antioxidant enzymes, HA showed its effect on stomatal conductance, photosystem I and photosystem II activity which improved the photosynthetic performance while also helping to decrease ROS production and maintain membrane stability [94]. The effect of PGPB and HA was examined in drought-affected sugarcane.…”

Drought tolerance inBrassica napusis accompanied with enhanced antioxidative protection, photosynthetic and hormonal regulation at seedling stage

“…Similarly, in the present study, a significant decline in the synthesis of chlorophyll pigments was observed in all Brassica cultivars (Table 1). This might be due to the increased activity of chlorophyllase enzyme, oxidative-breakdown of pigments, thylakoidal membrane distortion, and nutrients deficiency (Shen et al, 2020). The activity of protochlorophyllid reductase was suppressed and chlorophyll synthesis could be reduced upon F I G U R E 4 (A) Net photosynthesis rate (Pn), (B) stomatal conductance to water (Gs), (C) intercellular CO 2 intake (Ci), and (D) transpiration rate (Tr) of B. napus cultivars under drought stress.…”