Effects Of 2,4-epbrassinolide Priming On Drought-resistant Physiology And Leaf Cuticle Of Sweet Sorghum And Silage Maize

The production of forage crops is the basis to ensure the healthy development of our country’s livestock farming.As high-quality gramineous forage crops,sweet sorghum and silage corn have the characteristics of rich nutritional value,aromatic smell,and easy digestion,and are widely planted and used.However,environmental factors such as drought caused by climate change directly affect the production of forage crops,reducing their output,and in severe cases,it will cause a reduction in production or even no harvest.Therefore,improving the drought resistance of forage crops is an urgent task now.Plant cuticle is a protective structure covering the surface of plants.It plays a vital role in preventing germs from infecting plants,protecting plants from ultraviolet stress,and preventing non-stomata water loss.A large number of studies have shown that seed priming is a technology that treats seeds before sowing to improve seed vigor and stress resistance.In this paper,2,4-epibrassinolide（EBR）was used to priming the seeds of sweet sorghum Mule 8000 and silage corn Quchen 11.And the effects of EBR priming on the germination and drought resistance of two forage crops and their drought resistance at the seedling stage were analyzed.The impact of cuticular wax and cutin are also analyzed.The main findings are as follows:1.EBR solution concentration and priming treatment time have different effects on seed germination.Based on radicle length,germ length,radicle dry weight,germ dry weight,germination rate and germination potential,as well as their responses under normal germination conditions and simulated drought（PEG-6000）conditions,priming seeds with 0.01μM EBR solution priming treatment for 24 h was the best,and it could promote seed germination and the elongation of radicle and bud under normal water conditions and simulated drought.2.The physiological indicators of the two forage crops are greatly affected by drought.Photosynthetic parameters（net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO₂ concentration）,malondialdehyde（MDA）content,osmotic adjustment substances（soluble protein and proline）,as well as the activity of antioxidant enzymes（SOD,POD,CAT,APX）,all have significant changes due to drought.EBR-induced forage crops are more resistant to the adverse effects of drought on crops.Under drought stress,plant height,stem diameter and net photosynthetic rate of sweet sorghum and silage maize decreased significantly.However,sweet sorghum and silage maize after EBR priming were less affected by drought than water-induced and unpriming control.The EBR priming treatment also reduced the malondialdehyde content of the plants after drought stress.The MDA content of sweet sorghum and silage corn treated by the EBR was significantly lower than that of the untreated control under drought condition.However,after drought stress,the soluble protein content of sweet sorghum and silage maize treated with EBR increased by 48.87%and 75.4%,which were significantly higher than the 28.07%and 33.88%of the untreated control.In addition,the antioxidant enzyme activity of sweet sorghum and silage corn treated with EBR increased after drought,and the increase range was 59.29%～178.62%,which was much higher than the untreated control（3.4%～54.3%）.3.Sweet sorghum and silage corn cuticular wax is mainly composed of alkanes,aldehydes,alcohols and triterpenoids.Among these components,the content of alkanes is the highest,and its relative content is 46.65%～63.42%in sweet sorghum and39.88%～64.16%in silage corn.The wax content of sweet sorghum and silage corn cuticle treated by EBR was much lower than that of the unprimed control under normal and drought conditions.EBR priming increased the relative content of C₂₈ and C₃₀aldehydes in sweet sorghum and silage corn under drought conditions,as well as the relative content of C₂₉ alkanes in sweet sorghum,and the relative content of C₃₀ and C₃₂alkanes in silage corn under drought conditions.Sweet sorghum and silage corn cutin mainly include alkane acid and epoxy fatty acid.The total leaf cutin of sweet sorghum and silage corn after EBR priming treatment was 3,5009.13 ng/g and 8441.83 ng/g,which were significantly higher than those of the unprimed control,which were 5611.9ng/g and 3975.65 ng/g.On the whole,the total leaf cutin of the two crops after drought treatment was significantly higher than that of the control.Both forage crops are dominated by alkane acids,and the EBR priming treatment significantly increased the alkane acid content of the two crops.4.We screen several genes involved in sweet sorghum cuticular wax and cutin synthesis,and perform fluorescence quantitative expression analysis on them.The results showed that EBR induced changes in the gene expression levels of forage crops.Under normal moisture conditions,the expression levels of SBWIN1,MYB77,CER1and KCS12 genes were 1/2 of those of the untreated control.After drought treatment,except for cytochrome P450,the gene expression levels were significantly lower than the unprimed control.It shows that EBR induces a decrease in the expression level of genes related to wax synthesis.The expression of four cutin-related genes（ALDH2B7,AT5G42250,CYP86A2,FDH）increased significantly after EBR priming.For example,the expression level of FDH after the EBR priming is 3 times that of the control after drought treatment,indicating that the EBR priming induces an increase in the expression level of cutin genes.Comprehensive analysis suggests that EBR priming treatment can promote the germination of forage crop seeds and improve their drought resistance in seedling stage.EBR priming mainly reduces the synthesis of wax in the stratum corneum,but improves the synthesis of cutin.The specific regulation mechanism needs to be further studied in the future.