Eco-physiological Effect Of24-epibrassinolide Onβ-ODAP Biosynthesis And Drought Adaptability And Its Mechanism In Grass Pea(Lathyrus Sativus L.)

In this study, pot-culture experiments with soil medium were conducted using grass pea (Lathyrus sativus L.) as test material under environment-controlled conditions. Dynamics of toxin β-N-oxalyl-L-α, β-diaminopropionic acid (β-ODAP) concentrations were continuously tracked and determined in leaves of grass pea seedlings using exogenous application methods with0.1mg/L24-epibrassinolide (EBL) including seed priming (sp), foliar application (fa) and seed priming and foliar application (sf). Other parameters including growth, water status, gas exchange index, proline contents and activities of antioxidant enzymes were also synchronously measured. Drought stress gradients were designed as field water capacity (FWC) of80%,50%,40%and30%respectively. In a separate experiment, the effects of EBL exogenous application on biomass distribution, grain yield and β-ODAP concentrations in seeds were tracked and measured in grass pea in three gradients of water supply including80%FWC,50%FWC and30%FWC respectively. Mathematical statistics methods were employed to elucidate eco-physiological effects of EBL application on β-ODAP biosynthesis and drought adaptability and its mechanism in grass pea. The major results were achieved as follows:(1) EBL was observed to significantly enhance drought tolerance of grass pea. It alleviated the adverse effect and promoted the growth of plant height and leaf area in grass pea seedlings under drought stress. Sp, fa and sf treatment increased plant height by12.9%,11.9%and17.4%, leaf area by52.3%,47.7%and56.8%under50%FWC; plant height by14.3%,13.7%and14.7%, leaf area by59.2%,28.5%and47.7%under40%FWC; plant height by16.7%,11.9%and19.5%, leaf area by29.2%,9.7%and24.3%under30%FWC. EBL also slowed down the rate of decrease in leaf relative water content, stomatal conductance, increased the survival days and decreased the withering soil water content for grass pea seedlings from sufficient water supply to permanent withering point.(2) The results of synchronous tracking indicated that exogenous application of EBL improved the abilities of osmotic adjustment and antioxidant adjustment in grass pea seedlings. There was an increase in the leaf proline content and activity of antioxidant enzymes(SOD, APX, CAT) of treated seedlings. Compared to untreated ones, the sf treatment under30%FWC increased the proline content by60.4%, activity of SOD by68.3%, activity of APX by26.4%, activity of CAT by238.7%.(3) In general, EBL played a role to promote biomass accumulation and yield information in grass pea, but it varied from application treatments of EBL and drought stress gradient. EBL could increase the total biomass of grass pea under different water conditions, especially under50%FWC. Under80%FWC, sp and sf treatment increased the total biomass through improving the growth of vegetative and productive organs of grass pea, such as root, stem, leaf and pod dry weight; while fa treatment increased the biomass by increasing the vegetative organs including root, stem and leaf dry weight. Under50%FWC, EBL could improve pod, leaf, stem and root dry weight, and the increase in pod and leaf dry weight reached a significant level. Under35%FWC, sp and sf treatment could increase the total biomass by increasing the stem, leaf and root dry weight; while fa treatment increase the biomass by improving the stem, leaf, root and pod dry weight.(4) Strategic variation in energy distribution for vegetative growth and productive growth was observed under the regulation of EBL, however the effects of different application treatments were different. Sp treatment could promote the vegetative and productive growth of grass pea under80%FWC and50%FWC, and more increase vegetative growth under35%FWC. Fa treatment could promote the vegetative growth under80%FWC, and more increase productive growth under50%FWC and35%FWC. Sf could promote the productive growth under80%FWC, and more increase vegetative growth under50%FWC and35%FWC.(5) Regulatory effects of on the P-ODAP biosynthesis relied on drought stress gradients. There was no obvious effect on P-ODAP in the leaves of grass pea seedling under80%FWC,50%FWC and40%FWC. EBL could decrease the β-ODAP content under30%FWC, the P-ODAP content of the control under30%FWC was4.52mg/g, but sp, fa and sf treatment was4.43mg/g,3.80mg/g and3.2mg/g. We saw that EBL could improve drought tolerance but decrease the P-ODAP content under30%FWC, and sf is the best effective treatment. EBL had little effect on P-ODAP content in grass pea seeds under80%FWC, but increased β-ODAP content under50%FWC. The β-ODAP content of the control under50%FWC was4.59mg/g, but sp, fa and sf treatment was5.53mg/g,5.23mg/g and4.61mg/g. Fa treatment could significantly reduce the content of β-ODAP under35%FWC, the p-ODAP content of the control was5.96mg/g, but fa treatment was5.14mg/g.In summary, exogenous EBL application could significantly regulate the adaptability of grass pea to drought, but different treatment and drought stress gradient had different effect on β-ODAP biosynthesis. We speculated that EBL could reduce the β-ODAP content by improving the drought adaptability of grass pea, but the mechanism was very complex and closely related with energy allocation of vegetable growth and reproductive growth of grass pea.