Effects Of Exogenous 2,4-epibrassinolide On Cotton Under Low Temperature Stress

Cotton is a thermophilic crop that originated in the subtropical zone and the most suitable growth temperature is 20-30?.Cotton is sensitive to low temperature.It is injured when the average temperature is below 15 degrees.Cotton seedling is vulnerable to low temperature damage by late spring coldness especially.Brassionolid is a steroid plant hormone,which plays an important role in the growth and development of plants and is involved in the adaptation of plants to adversity.We studied the effects of 2,4-Epibrassinolide on the physiological and transcriptional levels of cotton under low temperature stress.The following conclusions are drawn according to the experimental results:?1?CCRI 60 and Lumianyan 28 were sprayed with 0.05 mg·L^-1,0.1 mg·L^-1,0.2 mg·L^-1,0.5 mg·L^-1,1 mg·L^-1 EBR and distilled water before low temperature treatment.The content of MDA and relative conductivity of Cottons under low temperature stress increased significantly compared with the control after 24 hours.Under low temperatures,the exogenous EBR can significantly reduce the increase of MDA content and the relative conductivity.At the same time,the proline content,net photosynthetic rate,stomatal conductance and maximum photochemical efficiency and performance index based on the absorption of light energy,plant fresh weight and dry weight of Cottons spraying with suitable EBR increased significantly.The best concents of alleviating chilling injury is that CCRI 60 and Lumianyan28 were sprayed with 0.1 mg·L^-1 and 0.2 mg·L^-1EBR,respectively.?2?Under field conditions,Lumianyan 28 and CCRI 60 were sprayed with 0.1 mg·L^-11 and 0.2 mg mg·L^-1 EBR and distilled water respectively before cold stress.After 3 days,the relative conductivity of Cottons spraying with EBR were found to be significantly lower than those of spraying with distilled water.The chlorophyll content and the maximum photochemical efficiency and the performance index based on absorbed light energy PI_ABSBS and photoreactive center activity and electron transfer ability were significantly increased.As a result,the fresh weight and dry weight of cotton plants increased by7.8%-33.6%and 30.9%-41.5%,respectively.The treatment effect of 0.1 mg·L^-1EBR in CCRI 60 was better,and that of Lumianyan 28 was 0.2 mg·L^-1.?3?Lumianyan 28 was treated with 0.2 mg·L^-1EBR and distilled water before low temperature treatment at 4?,and the leaves were measured after 6h,12h and 24h.There were 282,85 and 4000differentially expressed genes of Lumianyan28 spraying with EBR compared with spraying with distilled water at 6h,12h and 24h.GO annotation of different expression genes at 24h were mainly enriched in response stress,defense response,protein folding,transcription factor and ADP binding.KEGG is enriched in 17 metabolic pathways,including amino acid biosynthesis,plant hormone signal transduction,amino acid sugar and nucleic acid sugar metabolism,glutathione metabolism and so on.The genes related to chlorophyll,thylakoid and light system I of cotton spraying with EBR were up regulated.The expression level of genes encoding ACOase which participate in the ethylene synthesis pathway and ERFs participating in the ethylene signaling pathway and the expression level of SLY participating in the gibberellin signaling pathway were all significantly down-regulated.The expression level of genes encoding glutathione-S-transferases?GSTs?,dehydroascorbate peroxides and the enzymes?DHAR2,DHAR3?and ascorbate reductase?GXP6,GXP1?were up-regulated.The analysis found that the effect of exogenous EBR on cotton anti-low temperature may be achieved by inhibiting ethylene synthesis and signal transduction,increasing antioxidant capacity and protecting photosynthesis.