The Function Of Trehalose On The Heat Resistance And The Role Of Plant Hormones On The Reproduction And Development Of Gracilariopsis Lemaneiformis

Gracilariopsis lemaneiformis is cultivated in both northern and southern seas of China,and is mainly used as raw material of agar extraction and as bait for abalone.With the expansion of its cultivation area and yield,Gp.lemaneiformis has become the second largest yield of cultivated seaweed in China.However,the cultivation cycle of Gp.lemaneiformis in southern sea area is restricted by high temperature in summer,which seriously affects its yield and economic benefit.In addition,the cultivation of Gp.lemaneiformis depends on nutrition and propagation,it will lead to the degradation of its germplasm in the long term,so the demand for good Gp.lemaneiformis germplasm is more urgent.As a signal molecule,non-reducing disaccharide trehalose plays an important role in the resistance to heat,drought and other stresses.Plant hormones also play an important role in the reproduction and development of higher plants.Based on the above background,this paper studied the role of trehalose in the resistance to heat stress and the role of plant hormones in the regulation of carpospores release and development of Gp.lemaneiformis.(1)Effects of trehalose addition on the growth,membrane damage related substances,endogenous plant hormones and metabolic pathway key enzymes of Gp.lemaneiformis under heat stress.The results showed that trehalose enhanced the respiration of Gp.lemaneiformis under heat stress,decreased the proportion of Gp.lemaneiformis rotting and whitening,promoted the growth of Gp.lemaneiformis(1.39 times),and increased the content of total phycobilin and proline contents(1.35 times).Meanwhile,trehalose alleviated the damage of heat stress to the cell membrane of Gp.lemaneiformis,and the malondialdehyde content and lipoxygenase activity of Gp.lemaneiformis at48 h were decreased by 30.94% and 17.28%(P<0.05),respectively.The addition of trehalose activated the activity of trehalose 6-phosphate synthase(TPS,2.91 times,24 h)and trehalase(1.43 times,24 h),the key enzymes in trehalose metabolic pathway,and the expression of 4 TPS genes.In addition,trehalose significantly increased the accumulation of salicylic acid(SA)and abscisic acid(ABA)(2.05 and 5.21 times).The activities of isochorismate synthase and phenylalanine ammonialyase,the two key enzymes of salicylic acid synthesis,increased.(2)Ultra-performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS)was used to detect the effects of trehalose supplementation on the contents of metabolites in Gp.lemaneiformis.A total of 405 metabolites were detected and 66 differential metabolites were screened.Among the differential metabolites,the contents of most amino acids,such as valine,threonine,cysteine,were decreased,which were verified by amino acid high performance liquid chromatography detection method with 84.62% consistency to the metabolome results.In addition,spermidine in the polyamine pathway,glycolytic intermediate of 3-phosphoglycerate,glucose-1-phosphoric acid and various phenolic acids were significantly enriched in the trehalose addition group.(3)Effects of salinity and plant hormones on the carpospores release and development of Gp.lemaneiformis.The results showed that the amounts of carpospores released and the percentage of branch at salinity 35 were 29.28 and 1.40 times of those at salinity 25,respectively.The addition of100 μmol/L SA promoted the releasing of carpospores(9.88 times)and the germination percentage of branch(2.18 times).0.25 mg/L gibberellin(GA3)could increase the amounts of carpospores(20.15 times),but had no effect on the number of branch germination from each discoidal body.The linear and relative growth rate of Gp.lemaneiformis seedlings were increased after 0.5 mg/L naphthoacetate(NAA)treatment.In conclusion,the exogenous addition of 10 mmol/L trehalose can promote the growth,photosynthesis,phycobilin content,proline content,reduce the content or activity of substances related to membrane damage,stimulate superoxide dismutase and key enzymes of trehalose metabolism,and promote the accumulation of stress resistance related hormones,which alleviated the adverse effects of heat-stressed Gp.lemaneiformis.Plant hormones played an important role in the breeding process of Gp.lemaneiformis.,100 μmol/L SA could promote the carpospores dispersion and the germination of branches.0.25 mg/L GA3 and 0.5 mg/L NAA were involved in carpospores releasing and seedling growth.These results provided a theoretical basis for using trehalose and plant hormones to improve the heat resistance,breeding and development of Gp.lemaneiformis.