Prohexadione calcium (Pro-Ca), as a growth retardant, can effectively alleviate the damage of salt stress to plants. In order to explore the effects of NaCl stress on the physiological characteristics and panicle traits of rice plants as well as the alleviating effect of Pro-Ca at the booting stage, we performed pot experiments on two rice cultivars: conventional rice ‘Huanghuazhan’ and hybrid rice ‘Xiangliangyou900’. Rice plants were treated with 0.3% NaCl 48 hours after Pro-Ca (100 mg L−1) treatment to study the effects of Pro-Ca on the physiological characteristics of the leaves and panicles, as well as the panicle and yield traits of rice under salt stress. Our analysis indicated that NaCl treatment inhibited the morphological growth parameters and photosynthetic efficiency, destroyed the antioxidant defense systems of leaves and panicles, increased soluble protein and proline in both rice cultivars. Foliar application of Pro-Ca significantly increased the leaf area, uppermost internode length, panicle length, panicle weight, number of primary branches, number of grains per panicle, seed setting rate and yield under salt stress. Pro-Ca application significantly affected chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and apparent mesophyll conductance (AMC) in NaCl-treated rice cultivars compared with NaCl treatment alone. Moreover, Pro-Ca also increased ascorbic acid (AsA) content, enhanced superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) activity, and further increased the accumulation of soluble protein and proline in leaves and panicles. These results illustrated that foliar application of Pro-Ca at the booting stage could alleviate the damage caused by NaCl stress by regulating the physiological and metabolic processes of rice plants, thereby enhancing the stress resistance of the plants, increasing total rice yield in salt stress conditions.
Prohexadione-calcium (Pro-Ca) has been proved to play an important role in releasing abiotic stress in plants. However, there is still a lack of research on the mechanism of Pro-Ca alleviating salt stress in rice. To explore the protective effects of Pro-Ca on rice seedlings under salt stress, we investigated the effect of exogenous Pro-Ca on rice seedling under salt stress by conducting the following three treatment experiments: CK (control), S (50 mmol·L−1 NaCl saline solution) and S + Pro-Ca (50 mmol·L−1 NaCl saline solution + 100 mg·L−1 Pro-Ca). The results indicated that Pro-Ca modulated the expression of antioxidant enzyme-related genes (such as SOD2, PXMP2, MPV17, E1.11.1.7). Spraying Pro-Ca under salt stress significantly increased in ascorbate peroxidase, superoxide dismutase, and peroxidase activity by 84.2%, 75.2%, and 3.5% as compared to the salt treatment, as demonstrated by an example of a 24-hour treatment. Malondialdehyde level in Pro-Ca was also dramatically decreased by 5.8%. Moreover, spraying Pro-Ca under salt stress regulated the expression of photosynthesis genes (such as PsbS, PsbD) and chlorophyll metabolism genes (heml, PPD). Compared to salt stress treatment, spraying Pro-Ca under salt stress significantly increased in net photosynthetic rate by 167.2%. In addition, when rice shoots were sprayed with Pro-Ca under salt stress, the Na+ concentration was considerably reduced by 17.1% compared to salt treatment. In conclusion, Pro-Ca regulates antioxidant mechanisms and photosynthesis to aid in the growth of rice seedlings under salt stress.
Salt stress inhibits crop quality and yields, and growth regulators are used to enhance salt tolerance of crops. Here, we report the effect of prohexadione-calcium (Pro-Ca) on rice tillering under salt stress. The results showed the malondialdehyde (MDA) levels and electrolyte leakage in leaves were increased as well as the expression of the antioxidant enzymes was induced under salt stress. Foliar application of Pro-Ca reduced seedling height, increased the stem base width, improved the lodging resistance of rice, decreased MDA content and electrolyte leakage, and alleviated the membrane damage of rice under salt stress. Exogenous Pro-Ca also increased the net photosynthetic rate (Pn) and the stomatal conductance (Gs) of rice, decreased the intercellular CO2 concentration (Ci), and increased the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) of rice at the tillering stage under salt stress. In conclusion, Pro-Ca improved the salt tolerance of rice at the tillering stage by enhancing the lodging resistance of rice, alleviating cell membrane damage of leaves caused by NaCl stress, and enhancing photosynthesis and antioxidant capacity. Effect of Pro-Ca on rice at the tillering stage under 0.3% NaCl stress was discussed, which provided a theoretical basis for revealing physiological changes at the rice tillering stage.
Salt stress, as a principal abiotic stress, harms the growth and metabolism of rice, thus affecting its yield and quality. The tillering stage is the key growth period that controls rice yield. Prohexadione-calcium (Pro-Ca) can increase the lodging resistance of plants by reducing plant height, but its effects on rice leaves and roots at the tillering stage under salt stress are still unclear. This study aimed to evaluate the ability of foliar spraying of Pro-Ca to regulate growth quality at the rice tillering stage under salt stress. The results showed that salt stress reduced the tillering ability of the rice and the antioxidant enzyme activity in the roots. Salt stress also reduced the net photosynthetic rate (Pn), stomatal conductance (Gs) and intercellular CO2 concentration (Ci) of the rice leaves and increased the contents of osmotic regulatory substances in the leaves and roots. The application of exogenous Pro-Ca onto the leaves increased the tiller number of the rice under salt stress and significantly increased the photosynthetic capacity of the leaves. Additionally, it increased the activities of antioxidant enzymes and the AsA content. The contents of an osmotic regulation substance, malondialdehyde (MDA), and H2O2 in the leaves and roots also decreased. These results suggested that Pro-Ca can increase the tillering ability, photosynthetic capacity, osmotic adjustment substance content levels and antioxidant enzyme activity levels in rice and reduce membrane lipid peroxidation, thus improving the salt tolerance of rice at the tillering stage.
It is widely known that salt stress restricts rice growth and productivity severely. However, little information is available regarding the stage of rice seedlings subjected to the Heme oxygenase 1 (HO-1) inducer, Hemin. This study aimed to investigate the effects of salt stress on two rice varieties (Huanghuazhan and Xiangliangyou 900) and the effect of Hemin in promoting photosynthesis, carbohydrate metabolism, and key enzymes under salt-stress conditions. At the stage of three leaves and one heart, Huanghuazhan (HHZ) and Xiangliangyou 900 (XLY900) were sprayed with 5 μmol·L−1 Hemin and then subjected to 50 mM NaCl stress. The results showed that NaCl stress decreased the contents of chlorophyll a, chlorophyll b, and carotenoids. Furthermore, the net photosynthetic rate (Pn) decreased remarkably and the starch content was also lowered. However, NaCl treatment enhanced the concentration of sucrose and soluble sugar, simultaneously enhancing the sucrose metabolism. Nevertheless, the foliar spraying of exogenous Hemin mediated the increase in fructose and starch content, along with the activities of key enzymes’ soluble acid invertase (SAInv), basic/neutral invertase (A/N-Inv), and sucrose synthase (SS) in rice leaves under NaCl stress. The sucrose phosphate synthase (SPS) in leaves decreased significantly, and the fructose accumulation in leaves increased. Hemin also mediated the increase of starch content and the α-amylase, total amylase, and starch phosphorylase (SP) activities under NaCl stress. Under stress conditions, the application of the Heme oxygenase 1 (HO-1) inhibitor, ZnPP failed to alleviate the damage to rice seedlings by NaCl stress. The ZnPP treatment showed similar tendency to the NaCl treatment on pigment content, gas exchange parameters and carbon metabolism related products and enzymes. However, ZnPP decreased carotenoids, fructose, starch content and enzyme activities related to starch metabolism. The regulation effect of Hemin on HuangHuaZhan was better than XiangLiangYou 900. These results indicate that Hemin improved the effects of salt stress on the photosynthesis and physiological characteristics of rice leaves as a result of enhanced carbohydrate metabolism. Thus, Hemin could alleviate the damage caused by salt stress to a certain extent.
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