Molecular Basis For Increased 2-acetyl-1-pyrroline Contents Under Alternate Wetting And Drying And Nutrition Management In Fragrant Rice

Factors affecting rice aroma biosynthesis have been well documented previously,however the molecular mechanism lies behind the regulations 2-acetyl-1-pyrroline（2-AP）biosynthesis under water and nutrition management remained largely unexplored.The three experiments were conducted at South China Agricultural University’s College of Agriculture,Teaching and Experimental Farm as following.Experiment 1,the pot experiments were carried out using Meixianzghan2 and Xiangyaxiangzhan as planting materials.At grain filling stage,three irrigation regimes viz.,（i）conventional irrigation（CI）,（ii）alternate wetting and moderate soil drying（WMD）,when the soil water potential reached-15±5k Pa,and then was flooded with 2–3 cm water depth,and（iii）alternate wetting and severe soil drying irrigation（WSD）,the soil water potential reached-25±5 k Pa,and then was flooded with 2–3 cm water depth.Soil moisture meter hermetically sealed with vacuum gauge was used to measure the soil water potential with the depth of 10–15 cm below the soil surface.Previous studies have focused on whether can increase the content of 2-AP in fragrant rice under alternate wetting and drying,but there is still a lack of research on the molecular mechanism of how alternate wetting and drying affects the accumulation of 2-AP in fragrant rice.In this study,the expression of 2-AP synthesis related genes were measured by q PCR,the activities of related enzymes were determined at the same time,and other physiological and biochemical indexes in fragrant rice under alternate wetting and drying.Experiment 2,the pot experiments were carried out using Meixianzghan2 and Xiangyaxiangzhan as planting materials.From three different nitrogen fertilizer treatments at heading stage,（1）no fertilizer（N0）,（2）low nitrogen fertilizer 0.43 g urea per pot（N1）,（3）high nitrogen fertilizer 0.86 g urea per pot（N2）,the other cultivation management is the same.The effects of different nitrogen fertilizer treatments on the content of 2-AP,genes,enzyme activity and other physiological and biochemical indexes on the accumulation of 2-AP,as well as the yield of aromatic rice were studied.Experiment 3,the pot experiments were carried out using Meixianzghan2 and Xiangyaxiangzhan as planting materials.Zn solution was applied as a foliar spray solution using a manual sprayer at the heading stage.Zinc chloride was used as the Zn source for all treatments.Three different zinc fertilizers（Zncl₂）were sprayed on the leaf surface at heading stage,Z0:no fertilizer,Z1:Zn concentration of 14mg g^-1,Z2:Zn concentration of 30.1mg g^-1,and the other cultivation management was the same.Previous studies have found that exogenous zinc application in fragrant rice varieties can increase the 2-AP content of fragrant rice grains,but there is no explanation at molecular level.Therefore,this study attempts to construct the relationship between zinc and 2-AP from transcriptology,in order to understand the molecular mechanism of spraying zinc fertilizer at heading stage to increase 2-AP content in fragrant rice grains.The main results are as follows:（1）The grain filling stage alternate wetting and drying treatments（WMD and WSD）was good for scented rice mature grains at 2-AP content accumulation,mainly lies in induced genes expression（PRODH,P5CS2,DAO）and enzyme activities（PRODH,P5CS,DAO）,and up-regulation of P5C andΔ1-pyrroline under alternate wetting and drying treatments,and inhibition of BADH2 and down-regulation of GABA.Furthermore,this study provides the theoretical evidence for high yield,good quality and water saving cultivation of fragrant rice and further suggests that the evaluation and adoption of alternate wetting and drying treatments（within safe limits）at field level could be alternative option to flooded rice.（2）There was no significant difference in mature grains at 2-AP content accumulation and related physiological indexes between different nitrogen grain fertilizer treatments at heading stage.Different nitrogen treatments at heading stage increased the expression of P5CS gene and decreased the expression of BADH2 gene in mature grains.The heading stage different nitrogen treatments（N1 and N2）was good for the accumulation of the aroma of scented rice leaves 2-AP content,lies mainly in,higher proline dehydrogenase activity,pyrroline-5-carboxylic acid synthase,pyrroline-5-carboxylic acid content,Δ1-pyrroline content,Methylglyoxal content,and lower GABA levels.The heading stage to high nitrogen（N2）enhanced the yield of Meixiangzhan2 and Xiangyaxiangzhan.（3）The heading stage different zinc fertilizer treatments（Z1 and Z2）was good for scented rice mature grains at 2-AP content accumulation,mainly lies in up-regulation of P5C,Δ1-pyrroline and Methylglyoxal under different zinc fertilizer treatments results in enhanced2AP biosynthesis in both rice cultivars through induced genes expression（PRODH,P5CS2,DAO）and enzyme activities（PRODH,P5CS,DAO）,and through inhibition of BADH2.The heading stage different zinc fertilizer treatments（Z1 and Z2）increased the yield of Meixiangzhan2.