Exploration Of Mechanism Of Miscanthus Lutarioriparius Adaptation To Cadmium Stress

Miscanthus spp.has a high tolerance to heavy metal stress and can be utilized to remediate heavy metal-contaminated soils effectively.The restoration potential of the present screened wild Miscanthus resources has not been fully realized.The genetic improvements to the existing resources are required to increase their restoration capabilities.However,there is a lack of comprehensive knowledge on the heavy metal tolerance mechanism of Miscanthus species.It is important to figure out the heavy metal tolerance mechanism to provide scientific guidance for future genetic improvement.In the present study,we determined the response characteristics of rhizomes and leaves of Miscanthus lutarioriparius in tissue morphology,anatomical structure,cell and subcellular level changes under cadmium stresses.The objective of the study aims to reveal the tolerance and detoxification strategies of M.lutarioriparius under cadmium stresses.To explore the strategies of root exudates involved in the process of cadmium uptake and accumulation under cadmium stress;to explore the contribution of fixation and passivation of different parts and subcellular components of the plant to the tolerance to cadmium of M.lutarioriparius;Contribution of root cell wall barrier protection tissue to Cd-tolerant ability of M.lutarioriparius under cadmium stress;to explore whether M.lutarioriparius has the function of secreting cadmium salt under cadmium stress.It initially revealed the"absorption-transport-efflux"process mechanism of M.lutarioriparius adapting to cadmium stress at the level of tissue structure and cell changes,providing direction and theoretical support for subsequent variety improvement.The results showed as the following:（1）Compared with CK,the content of citric acid in root exudates under low-concentration cadmium treatment was significantly decreased,while the content of citric acid in root exudates under high-concentration cadmium treatment had no significant difference,and even increased under T4 treatment.10.48%.The concentration of citric acid and the content of cadmium in plant organs increased significantly with the increase of cadmium concentration.The proportion of oxidizable cadmium in the culture medium gradually increased with the increase of cadmium concentration.The distribution ratio of residual cadmium first increased and then leveled off.The distribution ratios of both exchangeable cadmium and reducible cadmium showed no obvious variance.（2）With the increase of cadmium treatment concentration,in the underground organs（roots and rhizomes）of M.lutarioriparius,The distribution ratio of ethanol-extracted state（F_E）and deionized water-extracted state（F_W）,which have strong migration ability,showed an overall downward trend.The distribution ratios of weak sodium chloride extract(F_{Na Cl}),acetic acid extract(F_HAc),hydrochloric acid extract(F_HCl)and residue state（F_R）showed an overall upward trend.At the same time,the distribution ratio of cadmium content in cell wall components in the root of Miscanthus lutarioriparius increased with the increase of cadmium treatment concentration and then became flat,and the distribution of cadmium content in nuclear components,chloroplast components,mitochondrial components and soluble sugar components The ratio decreased with the increase of cadmium treatment concentration and then leveled off.And under each treatment,the distribution ratio of cadmium content of cell wall components was the largest,followed by soluble sugar components,while the distribution ratio of cadmium content of organelle（nucleus,chloroplast and mitochondria）components was the smallest.（3）The analysis of chemical forms and subcellular distribution characteristics of cadmium in stems and leaves of M.lutarioriparius is not the same as the trend of underground organs,and the main chemical forms of cadmium are not static.Among them,the cadmium with weak mobility was mainly in the form of sodium chloride extraction under different cadmium stresses.The distribution ratio of the sodium chloride extracted state in stems was higher than that in leaves;T1)was the main form in deionized water extraction state,with the increase of cadmium treatment concentration（T2～T4）,the main form was in ethanol extraction state,and its distribution ratio reached the highest under T3 treatment.In addition,compared with CK,the distribution ratio of cadmium content in chloroplast components,mitochondrial components and soluble sugar components increased significantly（p<0.01）,and the distribution ratio of cell wall components was extremely significant under Tm treatment in the stems of D.decreased（p<0.01）,while the nuclear fractions were not significantly different.Compared with CK,the distribution ratios of cadmium content in the nuclear fraction,chloroplast fraction,mitochondria fraction and soluble sugar fraction were significantly increased under Tm treatment（p<0.01）.The proportion was extremely significantly lower（p<0.01）.（4）Sectioning was used to examine the barrier structure and components.The outer cortex,cortical parenchyma cells near the outer cortex,and cortical parenchyma cells around the poisoned cells were all lignified in the root of M.lutarioriparius,which lignifies the phloem of vascular bundles in leaves.In comparison with the low cadmium stress,the contents of cellulose,hemicellulose,and lignin in the underground organs（i.e.,roots and rhizomes）under the high cadmium stress increased by 0.54%,0.87%,and 2.16%,respectively,while the content of pectin in stems decreased by 0.14%.The cellulose,hemicellulose,and lignin contents in stems increased by 4.20%,4.39%,and 6.70%,respectively,while the pectin content decreased by 0.07%.（5）Compared with CK,the cadmium excretion rates of M.lutarioriparius under Tm at the day and night time were significantly increased by 73.80%and 544.55%（p<0.01）.With the increase of cadmium concentration,the cadmium secretion rate of leaves increased first and then decreased.The daytime cadmium excretion rate of M.lutarioriparius leaves under T3 reached the maximum(14.81 ug·m^-2·h^-1·10^-3)at the daytime.The cadmium secretion rate of M.lutarioriparius leaves under T2 reached the maximum(3.70 ug·m^-2·h^-1·10^-3)at night at the nighttime.Overall,the cadmium secretion rate of M.lutarioriparius leaves was0.58-11.98 times higher at the daytime than at the nighttime.