Mechanism Underlying Acetic Acid Affecting Heat Tolerance Of Rice During Flowering

Acetic acid（HAc）is a small molecule organic acid.It is widely distributed in nature and directly participates in the growth and development of animals and plants.Under abiotic stress,acetic acid is reported as the initial signal molecule in the regulation network of plants to connect plant metabolism and hormone signal pathway.This can alleviate the damages on the plant growth and development caused by high temperature.In this experiment,two early indica cultivars with obvious differences in heat tolerance,Zhongjiazao 17（ZJZ17）and Zhongzao 39（ZZ39）,were used as the materials to reveal the mechanism underlying acetic acid improving the heat resistance of rice at anthesis,and the effect of the compound application of acetic acid and other plant growth regulators on heat tolerance of rice are also discussed.The main results are as follows:1.Heat stress at the flowering stage led to a significant decrease in the seed setting rate of rice,and the decrease degree of ZZ39 was much greater than that of ZJZ17.There was no obvious difference in pollen viability,pollen numbers and pollen germination on stigma between control and heat stress in either rice plants.However,the ratio of pollen tube growth into ovule was higher showed in ZJZ17 than that of ZZ39 under heat stress compared with their respective control.According to the transcriptome analysis,the metabolism of carbohydrates,amino acids and lipids were involved in heat tolerance between these two rice cultivars.The acetyl-Co A which derived from acetate regulating the synthesis of methyl jasmonate and quercetin in these processes.Further,higher decreases in contents of acetate,quercetin and methyl jasmonate were found in spikelets of ZZ39 than those of ZJZ17 under heat stress compared with their respective controls.Thus,it was inferred that the difference in heat tolerance between these two rice plants might be mainly ascribed to the difference response of acetate to heat stress.2.Under heat stress,acetate extraneously sprayed onto rice plants at anthesis could enhance the spikelet fertility,contents of acetate contents,quercetin and methyl jasmonate and antioxidant enzyme activity as well as inhibit the H₂O₂and MDA contents compared with those of plants treated with H₂O.Accordingly,rice plants sprayed with quercetin or methyl jasmonate could enhance the spikelet fertility of rice under heat stress.Importantly,rice plants treated with combination of acetate and quercetin or methyl jasmonate as well as acetate and quercetin or methyl jasmonate attain higher spikelet fertility than those plants treated with acetate,quercetin or methyl jasmonate alone under heat stress.This suggested that acetate could enhance pollen tube elongation in pistil into ovule to confer heat tolerance in rice plants via interacting with both quercetin and methyl jasmonate.3.In order to reveal the effect of combination of acetate and other chemical such as Jinggangmycin,the combinations of potassium acetate,Jinggangmycin,naphthalene acetic acid,and leucine were sprayed onto rice plants under heat stress at anthesis.the results showed that the spikelet fertility,kernel weight,total dry matter weight,panicle dry matter weight,and ratio of panicle dry matter weight to the total dry matter weight in the treatments of Jinggangmycin+potassium acetate+naphthalene acetic acid,Jinggangmycin+potassium acetate+leucine and Jinggangmycin+potassium acetate+methyl jasmonate were higher than those of control treatment under heat stress.This suggested that potassium acetate combined with the chemicals could also improve the heat tolerance in rice.