The Morphological Characteristics And Physiological Mechanism Of Sedum Aizoon L.response To Drought Stress

Sedum aizoon L.has the advantages of strong resistance and easy cultivation,which belongs to Crassulaceae Sedum Perennial herbs,China’s arid area accounts for about half of the land area,and drought severely restricts the growth of plants.Research on the drought resistance of plants has become a hot topic.This experiment adopts the method of potted drought stress water control,set up four gradient,respectively control（CK,moisture content 75%⁸0%of field maximum moisture capacity）,mild stress（T1,55%⁶0%）,moderate stress（T2,40%⁴5%）and severe stress（T3,20%²5%）.The growth index,membrane peroxidation,membrane permeability and protective enzyme activity were measured by 10 d.The anatomic structure,ultrastructure,photosynthetic and chlorophyll fluorescence parameters were observed under stress 30d.In order to study the morphological characteristics and physiological mechanism of drought-resistant drought,the following conclusions are drawn:（1）Sedum aizoon L.has strong drought resistance and can grow normally under mild stress.The effects of moderate stress and severe stress on plant growth after 30 d and 20 d were observed.And with the increase of stress and stress time,the effect is more significant.Especially in severe stress,40 d,plant growth almost stalled,basal leaves yellow,leaf relative water content was significantly lower than other treatment,leaf softening,thinner after a large number of water loss,the growth of aboveground and underground part are severely suppressed.（2）The fleshy leaf structure of Sedum aizoon L.is special.There is no obvious tissue differentiation,mesophyll cell arranged loosely,intercellular gap is big,water storage organization developed,cell wall thickening of keratinization in the leaf of the control group.This special structure has the effect of reducing transpiration of leaves and effectively preserving water,which is the characteristic of drought-tolerant plants.（3）Drought stress can induce the change of Sedum aizoon L.CO₂ assimilation mode.There was no significant difference between stoma and photosynthetic parameters in mild stress.Under moderate and severe stress,stomatal opening and closing ratio decreased,especially in severe stress,the stoma of Sedum aizoon L was closed during the day and opened at night.In addition,Gs,Ci,Tr significantly decreased,Ls significantly increased,and the photosynthetic capacity decreased,showing the characteristics of the concurrent CAM plants,The photosynthetic pathway was transformed from C3 to CAM cycle,and the plant life activity was slowed down,the stomatal transpiration loss decreased,and the blade cuticle was thickened with the stress,weaken leaf surface evaporation loss,improve plant drought tolerance;（4）There was no significant difference in the ultrastructure of the Sedum aizoon L.leaves of control and mild stress under TEM.Moderate and severe stress caused a certain degree of change in its cellular structure.Moderate stress:the chloroplast is concentrated in the middle of the cell.Severe stress:The chloroplast shriveled and rounded,and the chloroplast granule laminae appeared to fracture.The chloroplast membrane was slightly dissolved,and the density of the osmiophilic globules increased,while the starch grain decreased,and the outer wall was blurred.The inner layer of the mitochondria dissolved and the swelling became white;（5）The decrease of chlorophyll content was caused by drought stress,but there was no significant difference between mild stress and control.Although moderate stress inhibited the accumulation of chlorophyll,it did not significantly affect photosynthesis.The chlorophyll content Fm、Fv/Fm、ΦPSⅡ、qP and NPQ were significantly lower than the control group under severe stress.Through the observation and analysis of its ultrastructure,the results show that in the 30d of severe drought stress,the chloroplast and mitochondrial structure of Sedum aizoon L.are destroyed,which can cause light suppression or light destruction,and weaken photosynthesis of plants.（6）The content of Sedum aizoon L.Pro with mild and moderate stress increased,soluble sugar,trehalose and soluble protein decreased slightly in the later stage of severe stress,but all significantly higher than the control,indicating that under the drought stress Sedum aizoon L.initiative to increase the secretion of osmotic regulation substances and improve the osmotic regulation ability of plants to reduce the osmotic potential of plant cells,so as to improve the ability of plants to absorb and retain water;（7）The activity of SOD,POD and CAT was significantly increased under mild and moderate stress.In the 40 d of severe stress,autioxidant enzyme activities decreased.However,the relative conductivity and MDA content of the blades were significantly higher than that of other treatments,and the 30 d tended to be stable.Indicating that SOD,POD and CAT can effectively remove the active oxygen and protect the cell membrane within a certain rang and the cell membrane is damaged but40d is the tolerance limit.