Relationship Between Toxin β-ODAP Accumulation And Carbon,nitrogen Metabolism In Grass Pea (Lathyrus Sativus L.) Under Drought Stress

Basic metabolic processes in the process of plant growth,i.e.carbon and nitrogen metabolism have a great significance on plant growth and physiology.However,researches on the carbon and nitrogen metabolism of grass pea is scarce.Therefore,the relationship betweenβ-ODAP accumulation,carbon and nitrogen metabolism of grass pea under drought stress is poorly understood.In this study,we used Lathyrus sativus L.as test material.The pot experiment was conducted at Yuzhong Campus of Lanzhou University from 2016 to 2017 with three water gradients namely,35%,50%and 80%FWC.The data of the indicators such as biomass allocation,grain yield,photosynthetic index,water use efficiency,soluble sugar,β-ODAP content,soluble protein,starch,free amino acids,sucrose,glutamine synthetase amylase,sucrose phosphate synthase and photosynthetic pigments were analyzed and compared statistically.The main objectives of our research were:1)to reveal the variation trend ofβ-ODAP accumulation,the main substances and key enzymes of carbon and nitrogen metabolism under drought stress;2)to explore the possible influence of carbon and nitrogen metabolism on the accumulation ofβ-ODAP and;3)to explain the reason of the variation ofβ-ODAP content in the treatment of drought stress from the perspective of carbon and nitrogen metabolism.Here are the main results:1.In this experiment,it was found that the growth parameters,biomass and yield formation of grass pea at podding stage,full bloom and mature stage decreased with the increase of water stress.Compared with full water supply（80%FWC）,the yield under moderate drought stress decreased by 60%and 47%and the drought tolerance index was 40.25%and 52.56%in 2017 and2016,respectively.Severe drought stress decreased the yield by 76%and 84%in 2017 and 2016and the drought tolerance index was 24.05%and 16.02%,respectively.There was a significant difference（p<0.05）in water use efficiency among treatments in 2017 with 50%FWC and 35%FWC decreasing by 31%and 39%,respectively.In 2016,50%FWC showed no significant difference（p<0.05）compared with the control（80%FWC）,while 35%FWC had significantly lower water use efficiency.It can be concluded that drought stress reduced yield and water use efficiency.2.The concentration and content ofβ-ODAP in leaf and stem of grass pea at branching and flowering,in the seeds and pods at the maturity period were increased by drought stress.The amount ofβ-ODAP in leaves and stems increased with increasing drought stress at the branching,flowering and podding stages.Severe drought stress（35%FWC）significantly increased the concentration and content ofβ-ODAP in pods and seeds.According to PCA,Chlorophyll b,carotenoids,starch,amylase,amino acid and soluble protein were greatly associated with concentration and content ofβ-ODAP.3.Drought stress has different effects on the photosynthetic pigments of different periods of the grass pea,and results in a significant change in the gas exchange parameters of grass pea,which have no significant correlation with the changes ofβ-ODAP.Drought stress forced reduction of photosynthetic parameters,which ultimately weakened photosynthesis of grass pea.Drought stress decreased chlorophyll a,chlorophyll b,chlorophyll and carotenoid in branching stage,and increased the content of photosynthetic pigments in flowering stage.In the podding period,chlorophyll a,chlorophyll b,chlorophyll and carotenoid content increased significantly under moderate drought stress,and significantly decreased under severe drought stress.Correlation analysis showed that there was no significant correlation between photosynthetic pigments and toxinβ-ODAP.Principal component analysis showed that photosynthesis rate,transpiration rate,stomatal conductance and intercellular CO₂ concentration were significantly correlated with each other,but rendered no significant correlation with the concentration and content ofβ-ODAP.Therefore,gas exchange parameters and photosynthetic pigments had no direct effect on the accumulation ofβ-ODAP.4.Drought stress led to changes in main indexes and key enzymes of sugar metabolism,and was significantly correlated with the change ofβ-ODAP.At the same time,drought stress increased the content of soluble sugar and sucrose in leaves and stems.In addition,drought stress had different effects on photosynthetic pigments,sucrose phosphate synthase and amylase in different growth stages of grass pea.The correlation analysis showed that the soluble sugar,sucrose in the leaf of grass pea were positively correlated with toxinβ-ODAP（P<0.01）.Amylase,sucrose phosphate synthase was positively correlated with toxinβ-ODAP,starch negative correlation with toxinβ-ODAP.Principal component analysis（PCA）showed that there was a significant correlation between sucrose and soluble sugar in the leaves of grass pea.Starch and amylase were highly correlated with the concentration and content ofβ-ODAP.There was a significant correlation between sucrose,soluble sugar and starch in the stems of grass pea.Besides,soluble sugar,starch,amylase,sucrose were significantly correlated with the concentration and concent ofβ-ODAP.Drought stress could affect the accumulation of toxinβ-ODAP by reducing the content of starch and increasing the content of soluble sugar,sucrose,amylase,sucrose phosphate synthetase and so on.5.The drought stress promoted the nitrogen metabolism of leaves and stems of grass pea,the major indexes and key enzymes of nitrogen metabolism were significantly correlated with the change ofβ-ODAP.Additionally,the soluble protein content in leaves and stems increased at flowering and full blooming stages.In addition,drought stress reduced the C/N ratios in leaves,pods and grains of grass pea.The correlation analysis showed that,under severe drought stress,the free amino acids in the stem of grass pea in branching stage were significantly positively correlated with toxinβ-ODAP（P<0.01）,and soluble protein in the stem of the flowering period was positively correlated with the toxinβ-ODAP（P<0.05）.Principal component analysis showed that the indexes correlated with the concentration and concent ofβ-ODAP were free amino acids and soluble proteins.Drought stress could affect the accumulation of toxinβ-ODAP by increasing the content of free amino acid and soluble protein,but glutamine synthetase has no direct effect on the accumulation of toxinβ-ODAP.