Preliminary Study On The Morphology And Physiological Mechanism Of Silver Leaf Sunflower Inresponse To Salt Stress

Helianthus argophyllus,is known as silver leaf sunflower,has propensity to grow in drought and saline-alkali prone areas,and has shown salt tolerance tendency.Therefore,study on the salt tolerant morphology,physiological mechanism of silver leaf sunflower and identification of salt tolerant genes will be excavated to improve the salt tolerance sunflower cultivars.In this study,we used silver leaf sunflower（Wt）as the test material,and cultivated sunflower as control materials to determine their growth characteristics,photosynthetic physiology,redox system,ion absorption and distribution.We analyzed the physiological mechanism of silver leaf sunflower（Wt）to adapt at salt stress condition.The full-length cDNA sequence of sunflower epidermis related genes was cloned,and then the expression pattern of epidermal hair-related genes in different sunflowers was analyzed.The main results are as follows:1.The plant height,leaf area and biomass of tested Wt were not significantly increased as compared to those of the untreated plants（control,CK）,but the plant height,leaf area and biomass of cultivated sunflower were significantly different at NaCl stress of 250mmol·L^-1.It indicates that Wt is relatively stable adaptability to salt stress in terms of plant morphology.2.Under salt stress,the chlorophyll content,photosynthetic rate and stomatal conductance,proline（Pro）content,malondialdehyde（MDA）content and superoxide dismutase（SOD）activity of Wt and cultivated sunflower decreased significantly,but peroxidase（POD）activity,catalase（CAT）activity,electrolyte permeability increased significantly,and the sensitivity of different tissues of Wt seedlings to salt stress:root>stem>leaf,sensitivity of cultivated sunflower seedlings to salt stress:leaf>stem>root.3.Without stress condition,the stomatal density,stomatal length,stomatal width and stomatal area of Wt were significantly lower（P<0.05）than that of cultivated sunflower,but,the length and density of epidermal hair on the surface leaves of Wt were significantly higher than that of cultivated sunflower.The relative water contents of leaves of Wt and cultivated sunflowers（sk02M,sk02R）were 86.2%,88.0%,and 87.0%,respectively,but their difference was not significant.Under the salt stress conditions,the stomatal density of Wt and cultivated sunflower increased with different degrees,but the stomatal length,stomatal width and stomatal area were significantly decreased（P<0.05）.The surface of Wt leaves were still tightly covered with epidermis,and its length and density did not change significantly,but the epidermis hair shapes were obviously collapsed.The numbers of epidermal hairs of cultivated sunflowers were reduced and the length was shortened.Moreover,the relative water content of Wt leaves was the highest（76.6%）,which was significantly lower than that of cultivated sunflower.The leaf water loss rate was still the slowest.One of the possible reasons for high water retention capacity of Wt is that its surface is densely covered with epidermis,which makes it salt-tolerant.4.Without stress condition,the total wax content of Wt was significantly higher（P<0.05）than that of cultivated sunflower,and the proportion of primary alcohol in the wax component was 48.751%and alkane was 41.646%of the total wax.In cultivated sunflower,the proportion of alkane of total wax was the largest.Under salt stress,the total wax content of Wt was significantly higher（P<0.05）than that of cultivated sunflower.The proportion of alkane of total wax was increased,and the proportion of alcohol was decreased as compared with the control.5.Epidermal hair-related genes Hair1（HanXRQChr13g0398371）,GL1（HanXRQC hr16g0532031）,MYB16（HanXRQChr17g0545981）and MYB107（HanXRQChr17g0559401）have the highest expression in Wt young leaves,indicating that these four genes may be involved in the development of Wt young leaves.