Exogenous brassinosteroids alleviate calcium deficiency-induced tip-burn by maintaining cell wall structural stability and higher photosynthesis in mini Chinese Cabbage

Tip-burn has seriously affected the yield, quality and commodity value of mini Chinese cabbage. Calcium (Ca2+) deficiency is the main cause of tip-burn. In order to investigate whether exogenous brassinosteroids (BRs) can alleviate tip-burn induced by calcium (Ca2+) deficiency and its mechanism, in this study, Ca2+ deficiency in nutrient solution was used to induced tip-burn, and then distilled water and BRs were sprayed on leaves to observe the tip-burn incidence of mini Chinese cabbage. The tip-burn incidence and disease index, leaf area, fluorescence parameters (Fv/Fm, NPQ, qP andφPSII) and gas exchange parameters (Tr, Pn, Gs and Ci), pigment contents, cell wall components, mesophyll cell ultrastructure and the expression of genes related to chlorophyll degradation were measured. The results showed that exogenous BRs reduced the tip-burn incidence rate and disease index of mini Chinese cabbage, and the tip-burn incidence rate reached the highest on the ninth day after treatment. Exogenous BRs increased the contents of cellulose, hemifiber, water-soluble pectin in Ca2+ deficiency treated leaves, maintaining the stability of cell wall structure. In addition, BRs increased photosynthetic rate by increasing the activities of Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and fructose 1,6-bisphosphatase (FBPase) related to Calvin cycle, maintaining relatively complete chloroplast structure and higher chlorophyll content via down-regulating the expression of BrPPH1 and BrPAO1 genes related to chlorophyll degradation. In conclusion, exogenous BRs alleviated calcium deficiency-induced tip-burn by maintaining cell wall structural stability and higher photosynthesis

BR-Mediated Protein <i>S</i>-Nitrosylation Alleviated Low-Temperature Stress in Mini Chinese Cabbage (<i>Brassica rapa</i> ssp. <i>pekinensis</i>)

Brassinosteroids (BRs), a novel plant hormone, are widely involved in plant growth and stress response processes. Nitric oxide (NO), as an important gas signaling molecule, can regulate target protein activity, subcellular localization and function in response to various stresses through post-translational S-nitrosylation modifications. However, the relationship between BR and NO in alleviating low-temperature stress of mini Chinese cabbage remains unclear. The hydroponic experiment combined with the pharmacological and molecular biological method was conducted to study the alleviating mechanism of BR at low temperature in mini Chinese cabbage. The results showed that low temperature inhibited the growth of mini Chinese cabbage seedlings, as evidenced by dwarf plants and yellow leaves. Treatment with 0.05 mg/L BR and 50 µM NO donor S-nitrosoglutathione (GSNO) significantly increased the leaf area, stem diameter, chlorophyll content, dry and fresh weight and proline content. Meanwhile, the malondialdehyde (MDA) content in 0.05 mg/L BR- and 50 µM GSNO-treated leaves were significantly lower than those in other treated leaves under low-temperature conditions. In addition, BR and GSNO applications induced an increase in NO and S-nitrosothiol (SNO) levels in vivo under low-temperature stress. Similarly, spraying BR after the elimination of NO also increased the level of S-nitrosylation in vivo, while spraying GSNO after inhibiting BR biosynthesis decreased the level of NO and SNO in vivo. In contrast, the S-nitrosoglutathione reductase (BrGSNOR) relative expression level and GSNOR enzyme activity were downregulated and inhibited by BR treatment, GSNO treatment and spraying BR after NO clearance, while the relative expression level of BrGSNOR was upregulated and GSNOR enzyme activity was also increased when spraying GSNO after inhibiting BR synthesis. Meanwhile, the biotin switch assay showed that exogenous BR increased the level of total nitrosylated protein in vivo under low-temperature stress. These results suggested that BR might act as an upstream signal of NO, induced the increase of NO content in vivo and then induced the protein S-nitrosylation modification to alleviate the damage of mini Chinese cabbage seedlings under low-temperature stress

Hydrogen Sulfide Promotes Adventitious Root Development in Cucumber under Salt Stress by Enhancing Antioxidant Ability

As a gas signal molecule, hydrogen sulfide (H2S) can enhance plant stress resistance. Here, cucumber (Cucumis sativus &lsquo;Xinchun NO. 4&rsquo;) explants were used to investigate the role of H2S in adventitious root development under salt stress. The results show that sodium chloride (NaCl) at 10 mM produced moderate salt stress. The 100 &micro;M sodium hydrosulfide (NaHS) treatment, a H2S donor, increased root number and root length by 38.37% and 66.75%, respectively, indicating that H2S effectively promoted the occurrence of adventitious roots in cucumber explants under salt stress. The results show that under salt stress, NaHS treatment reduced free proline content and increased the soluble sugar and soluble protein content during rooting. Meanwhile, NaHS treatment enhanced the activities of antioxidant enzymes [peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT)], increased the content of ascorbic (ASA) and glutathione (GSH), reduced the content of hydrogen peroxide (H2O2) and the rate of superoxide radical (O2&minus;) production, and decreased relative electrical conductivity (REC) and the content of malondialdehyde (MDA). However, the NaHS scavenger hypotaurine (HT) reversed the above effects of NaHS under salt stress. In summary, H2S promoted adventitious root development under salt stress through regulating osmotic substance content and enhancing antioxidant ability in explants

A Crystallographic Study on the Growth of Partially Faceted MnSn2 Phase during Solidification Process

The growth of MnSn2 phase during the solidification process of Sn-Mn alloy was crystallographically investigated. The results show that the non-faced spherical caps of the MnSn2 crystals follow the continuous growth mechanism to grow rapidly along the &lt;001&gt; direction, while the side surfaces the two-dimensional nucleation mechanism to form the low index {100} and {110} facets. An interface structure analysis indicates that the atom planes within the {100} interplanar spacing period (IPSP) has a lower average reticular density than those within the {011} IPSP. This leads to the faster growth rates and thus the shortening and disappearance of the {100} side facets. As a consequence, the partially faceted (i.e., non-faceted spherical caps and faceted side surfaces) MnSn2 crystals follow an octagonal-base/spherical-cap geometric model (few crystals possess square bases) in three dimensions