Tolerance Of Vetiver To High Manganese Stress

In order to investigate the manganese tolerance of vetiver grass?Vetiveria zizanioides?and its physiological response,and to explore the mechanism of silicon-enhanced resistance to high manganese stress,Seedlings were treated for 60 day with 1/2 Hogland nutrient solution containing normal Mn?CK?or 15,30,60,120mmol·L^-1MnSO₄.Morphology parameters,photosynthesis,chlorophyll fluorescence parameters,the contents of mineral element and the activity of antioxidant enzymes were measured.Or Seedlings were cultured in nutrient solution containing normal Mn?CK?or high Mn(120 mmol·L^-1),both with or without Si supply at 1,4,10 mmol·L^-1,accumulation,subcellular distribution and chemical forms of Mn and other physiological parameters were investigated.The main results are presented as follows:1.The results showed that SPAD,leaf water content,plant height,dry weight of plants,potassium content,net photosynthetic rate?Pn?and potential maximum electron conductivity(ETR_max)showed a decreasing trend with increasing Mn-treated concentration.Under 15-60 mmol·L^-1Mn treatments,the dry weight of plants were 77.6%-88.1% of that of the control.Also,F_v/F_m and SPAD were not observed significant changes.The content of Mn in roots and leaves were 14393-18845 mg·kg^-1 and 4118-4782 mg·kg^-1.Accumulation coefficient of Mn in roots was above1.Besides,the content of Mn in roots showed no significant changes,but accumulation coefficient of Mn decreased under 30-120 mmol·L^-1 Mn treatments.The content of Mn and translocation coefficient in leaves presented no significant changes under 15-60mmol·L^-1Mn treatments.The results suggested that vetiver grass has Mn tolerance and accumulation in high Mn stress(below 60mmol·L^-1Mn),which indicated that vetiver grass could be used for phytoremediation of Mn pollution.2.Under Mn stress,non-regulatory passive energy dissipation[Y?NO?]remained stable,but the regulatory active energy dissipation[Y?NPQ?]increased with increasing light intensity.The activity of superoxide dismutase?SOD?,peroxidase?POD?and catalase?CAT?also increased,Especially,these increased greatly under low concentrations of Mn treatments in roots.K contents in leaves decreased slightly,while Mg and Fe contents relatively remained stable.However,K and Mg contents in roots decreased significantly,while the contents of Fe increased significantly.The results indicated that increasing PSII regulatory active energy dissipation and improving the activity of antioxidant and keeping stable Mg and Fe contents in leaves might be the adaptive responses of Vetiveria zizanioides to high Mn stress.3.Supply with Si increased SPAD,F_v/F_m,ETR_max,Y?NPQ?and the activity of CAT,and it decreased Y?NO?and wilting rate of leaves at high Mn(120 mmol·L^-1).At the same time,it also significantly increased the activity of SOD and CAT at roots.Compared to Mn treatment without Si,as for roots,the content of Mn showed no significant changes,but the contents and proportion of Mn in the soluble fraction significantly increased,and the proportion of Mn increased in the 80% ethanol extraction but decreased in the extraction of deionized water.As for leaves,the total and each subcellular components of Mn contents significantly decreased,and the proportion of Mn lower in cell wall.Furthermore,the proportion of Mn increased in the 80% ethanol extraction and the deionized water extraction,and the proportion of Mn decreased in the NaCl extraction.The results suggested that the addition of Si can alleviate high Mn Stress in Vetiveria zizanioides by limiting the absorption and translocation of Mn at leaves,increasing the proportion of Mn in the soluble fraction and in the 80% ethanol extraction at leaves and roots,improving the activity of SOD,CAT at roots and CAT at leaves.