| Tomato (Solalnum lycopersicum L.) is an important commercial crop. Fruit colour is an important indicator of the tomato fruit quality. The major carotenoid in tomato fruits was lycopene. High temperature adversely affects the fruit quality, such as fruit colour and delayed maturity. Carotenoids formation is highly regulated by multi-genes. Most structural genes and metabolic engineering of the pathway have been characterized, but the molecular basis was unknown.Polyamines are small ubiquitous compounds that have been implicated in the regulation of a variety of stress responses in plants. It has been suggested that PA involvement in abiotic stress adaptation could be due to their roles in osmotic adjustment, membrane stability, free-radical scavenging and regulation of stomatal movements. In our previous study, overexpression of heterologous SAMDC in tomato generally results in improving the tolerance to heat stress and carotene accumulation. But the relationship between polyamine and carotene is not sure. In addition, the carotene content affecting by high temperature, the tolerance improving by polyamine and the carotene content accumulating by polyamine, those suggest there is a positive relationship among high temperature, polyamine and carotene content. The objective of this study was to understand the respective impact of exogenous spermidine on ripening, fruit quality and carotene content with off-vine tomato under high temperature. The results are as follows:(1) Fruit mature and carotene biosynthesis is adversely affected by high temperature. The objective of this study was to understand the respective impact of exogenous spermidine on ripening, fruit quality and carotene content with off-vine tomato under high temperature. During ripening, TCI, reducing sugars, carotenes, soluble solids content and total ascorbate increased, whereas firmness and titratable acidity decreased. Exogenous spermidine and temperature can severely affect the ripening process and the final nutrient composition of tomato fruit. Sugars and acids were not considerably modified, but carotenoids and total antioxidants were very sensitive to polyamine and temperature. Under normal temperature, exogenous spermidine enhanced fruit TCI value, reducing sugars content, total carotene content, total antioxidant activity, and ethylene production and respiration rate, while soluble solids content, titratable acidity and total ascorbic were lower than untreated fruit. Increasing temperature from26to33℃, it reduced ascorbate, reducing sugars, soluble solids and lycopene content, but enhanced ethylene production and respiration rate and total antioxidant activity. Exogenous application of spermidine could partially alleviate the effect of high temperature, spermidine-treated fruits under higher temperature exhibited higher total antioxidants than untreated fruits. High temperature (38℃) significantly delayed fruit ripening, adversely affected the fruit quality, and spermidine can not alleviate the effects. Spermidine delayed the ripening process of tomato fruits under high temperature. Meanwhile, high temperature and exogenous spermidine treatment all increased endogenous level of Put and Spm. The regulation by spermidine and temperature of the carotene biosynthesis pathways is also discussed.(2) High temperature adversely affects quality and yield of tomato fruit. Polyamine can alleviate heat injury in plants. This study is aimed to investigate the effects of polyamine and high temperature on transcriptional profiles in ripening tomato fruit. Methods:An Affymetrix tomato microarray was used to evaluate changes in gene expresse in response to exogenous spermidine (Spd,1mmol/L) and high temperature (33℃) treatments in tomato fruits at mature green stage. Results:Of the10101tomato probe sets represented on the array,127loci were differentially expressed in high temperature-treated fruits, compared with those under normal conditions, functionally characterized by their involvement in signal transduction, defense response, oxidation reduction, and hormone responses. However, only34genes were up-regulated in Spd-treated fruits as compared with non-treated fruits, which were involved in primary metabolism, signal transduction, hormone responses, transcription factors, and stress response. Meanwhile,55genes involved in energy metabolism, cell wall metabolism, and photosynthesis were down-regulated in Spd-treated fruits. Functional categorization and the further analysis indicated that Spd might alleviate the heat stress injury during tomato fruit ripening.(3) To study how Spd works by MAPK cascade, and the function of SIMAPK3of tomato fruits in improving tolerance to heat stress, the35S:MAPK3, E8:MAPK3,35S:mapk3-RNAi and E8: mapk3-RNAi was transform to tomato. The35S:mapk3-RNAi plants can not grow normally, while the35S.MAPK3, E8:MAPK3, and E8:mapk3-RNAi plants development normally. The plant height, leaf length, fruit weight and fruit colour were mearsured. Real-time PCR was used to determine the expression pattern of SIMAPK1, MAPK2and MAPK3in35S.MAPK3plants treated with high temperature, low temperature, touch, wounding or salt tolerance. It confirmed that the expression raised firstly, to reach the highest value, then reduced in different stress. And it was expressed at higher levels in35S:MAPK3plants than WT plants. The35S:MAPK3plants showed higher tolerance to stress than WT plants. It confirmed that SIMAPK3play important role in tomato response to different stresses. |
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