Regulation Of Hydrogen Sulfide Signal On Photosynthesis Of Brassicaceae Plants Under Drought Stress

Photosynthesis is vital for plant growth and development,and its efficiency is the fundamental determinant of plant productivity and crop yield.Drought stress,one of the major adversities,effects on crop production.It can reduce the whole yield by inhibiting photosynthesis in leaves.The inhibition of photosynthesis can be divided into two aspects: stomatal factors and non-stomatal factors.In recent years,research on the physiological function of new gasotransmitter hydrogen sulfide?H₂S?in higher plants had been deepened,revealed that H₂S signal plays an important role in regulating plant growth and environmental adaptability.Previous researches had found that H₂S involved in induced stomatal closure and enhanced photosynthesis.What confused us is that stomatal closure may be a limiting factor for photosynthesis.How could H₂S ensure efficient photosynthesis at the same time? Is it achieved by regulating certain non-stomatal factors? To answer the above questions,model plants Arabidopsis thaliana and important cash crop Chinese cabbage were used as experimental materials in this paper.From two aspects: stomatal factors and non-stomatal factors,we explored the effect of H₂S signal on cruciferous plants respond to drought stress,and how to regulate their photosynthetic efficiency to maximize under drought stress.The research results based on this paper have very important theoretical significance and application prospects for crop yield and quality control.One part of this paper,Arabidopsis thaliana wild type?WT?and mutant defective in the gene encoding H₂S-producing enzyme?lcd/des1?were used as experimental materials.Based on the previous report that H₂S could promote K+ flux outflow,which induced stomatal closure in Arabidopsis,we mainly studied the regulation of endogenous and exogenous H₂S on a non-stomatal factor,the key enzyme of photosynthetic,Ribulose-1,5-bisphosphate carboxylase/oxygenase?RuBisCo?.The main results as followed:?1?Under normal conditions,in the presence of exogenousphysiological concentrations of H₂S,stomatal conductance?Gs?and net photosynthetic rate?Pn?decreased significantly,intercellular carbon dioxide concentration?Ci?increased significantly in WT.Under drought stress,Gs and Pn decreased significantly,Ci increased significantly in WT.After the treatment of exogenous H₂S in WT under drought conditions,Gs and Ci decreased while Pn increased.Under drought conditions,AtRuBisCo large and small subunit coding genes were significantly down-regulated;while exogenous H₂S treatment could up-regulate its expression level and enhance the carboxylation activity of At RuBisCo to normal levels.?2?During the same growth cycle,lcd/des1 had a slow growth.After the treatment of exogenous H₂S,its Gs decreased,Ci decreased significantly,and Pn increased significantly.Under drought stress,compared with WT,Gs in lcd/des1 increased and Pn decreased significantly.In particular,after the treatment of exogenous H₂S under drought conditions,the expression levels of At RuBisCo coding genes in lcd/des1 were up-regulated and the activity of At RuBisCo was significantly improved.?3?Large and small subunits of Arabidopsis RuBisCo: The own S-sulfhydration level of At RBCL,At RBCS1 A,At RBCS1 B,At RBCS2 B and At RBCS3 B could all be detected.Especially,At RBCL and At RBCS1 A,At RBCS3 B could be further S-sulfhydration by 150 mmol/L and 50 mmol/L Na HS,respectively.Another part of this paper,Chinese cabbage“aiqing 1” were used as experimental materials.This part focuses on H₂S signal affecting non-stomatal and stomatal factors to regulate photosynthesis of Chinese cabbage under drought stress.Below are key research findings.?1?Under drought conditions,Gs,Ci as well as Pn decreased significantly in Chinese cabbage;after the treatment of exogenous H₂S,Gs decreased more and had a significant different,Ci decreased while Pn significantly increased;after the treatment of HT,cleaning endogenous H₂S in plants,its Pn decreased significantly.?2?By compared with AtRuBisCo,we obtained one large subunitcoding gene?RBCL?and seven small subunit coding genes?RBCS?of Br RuBisCo.At present,we had cloned one Br RBCL and three Br RBCS from Chinese cabbage “aiqing 1”.Under drought stress,treated with exogenous H₂S,Br RBCLS24 expression level was up-regulated significantly,but there was no effect on the expression of Br RBCL;the expression of Br RBCL and Br RBCS74 could be significantly down-regulated by physiological concentration of HT,at the same time,the expression of Br RBCS24 had some down-regulation.Under normal conditions,the carboxylation activity of Br RuBisCo with HT treatment significantly reduced.H₂S treatment could alleviate the inhibition of enzyme activity under drought stress.?3?Under normal conditions,the stomatal aperture of Chinese cabbage narrowed significantly by exogenous physiological concentrations of H₂S.Under drought stress,the stomatal aperture narrowed,and the difference was significant;and Non-invasive Micro-test Technology?NMT?was used to analyze the reasons,it was found that the H⁺ influx in guard cells of Chinese cabbage “aiqing 1” under drought stress,and Cl-massively efflux,with the depolarization of guard cells plasma membrane,K⁺ efflux,causing stomatal closure;Under drought stress,with physiological concentration of H₂S treatment,Cl^- efflux was promoted significantly;H⁺ efflux was slow at a very small flow rate value;K⁺ remained efflux,and the flow rate value was almost unchanged;which eventually led to a further reduction in stomatal aperture.Among them,Cl^- efflux might be the main reason that H₂S signal promoted Chinese cabbage stomatal closed.In summary,H₂S signal not only activate ion channel proteins?especially Cl^-?of leaf guard cell membranes,induce stomatal closure,but also regulate the transcription and carboxylation activity of non-stomatal RuBisCo,to enhance leaf photosynthetic efficiency,so that the Brassicaceae plants under drought stress maintain high-efficiency photosynthesis during the stomatal closure,and resist drought as well ensure yield..