| Hydrogen sulfide?H2S?,as the third gas signal molecule other than nitric oxide and carbon monoxide,has been a hot spot in recent years,both in biology and in medicine.Initial research found that it can regulate important physiological functions in animals: protect the cardiovascular system,improve neurodegenerative diseases,relieve diabetes,relieve asthma,etc.With the deepening of research on H2 S in plants,it has been shown to have an indispensable role in all stages of plant growth and development.Until now,the results showd that H2 S is involved in the entire life process of plants from germination to aging;the endogenous H2 S could enhance the photosynthesis of plants and improve the tolerance of plants in harsh environments.However,there are few reports about the regulation mechanisms of endogenous H2 S in plant photosynthesis under heavy metal stress.To study the function of H2 S on photosynthetic physiology of plants under cadmium?Cd?stress,Chinese cabbage?Brassica pekinensis?Lour.?Rupr.?seedling are used as materials,we examined the effects of Cd stress and H2 S on the photosynthetic characteristics,the activity of Rubp carboxylase?ribulose-1,5-hisphpsphate carboxylase?,as well as the expression levels of CDes?cysteine desulfhydrases coding genes?and RBCSes?small subunits of Rubp?using physiological,biochemical and RT-q PCR analyses.Results demonstrated that:1.The leaves of Chinese cabbage seedlings showed obvious chlorosis,wilting and curling,and the leaf width decreased significantly under Cd(the concentration of Cd ? 2.5 mmol·L-1)stress.The chlorophyll content,photosynthetic fluorescence parameters?such as Fv/F0,Fv/Fm,PIabs?,net photosynthetic rate?Pn?,activity of Rubp carboxylase and the expression levels of RBCSes were inhibited considerably under Cd(the concentration of Cd ? 5 mmol·L-1)stress.After going through the stress,the content of endogenous H2 S content increases,which matched well with the related genes up-regulation of major H2 S generation enzymes such as LCD,DCD and DES.It indicated that H2 S may be involved in the response of Chinese cabbage seedlings to Cd stress.2.The cabbage seedlings pretreatment with 5 ?mol·L-1 Na HS showed obvious advantages in the growth state and leaf width under Cd stress.5 ?mol·L-1 Na HS pretreatment could notably alleviate the effects of Cd stress the chlorophyll content,Fv/F0,Fv/Fm,PIabs,Pn and up-regulate the m RNA levels of RBCSes under Cd stress.Furthermore,H2 S could also promote the activity of the Rubp carboxylase of seedlings under normal growth conditions.On the contrary,the presence of 0.1 mmol·L-1 hypotaurine aggravated the inhibition effects of Cd stress on seedlings.All these results indicated that H2 S could enhance the photosynthesis of seedlings to alleviate the damages caused by Cd stress and maintain the growth of Chinese cabbage under Cd stress. |
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