半定量RT-PCR研究氮素形态对樱桃番茄果实中有机酸代谢相关酶基因表达的影响

摘要

研究了全硝(100%NO3-)、铵硝配施(75%NO3-:25%NH4+)及全铵(100%NH4+)营养对樱桃番茄果实有机酸含量的影响,测定了与有机酸合成相关的磷酸烯醇式丙酮酸羧化酶(PEPC)、柠檬酸合成酶(CS)、苹果酸脱氢酶(MDH)活性变化,并利用RT-PCR检测了相应的基因在转录水平上的表达差异.结果表明,1)全硝和铵硝配施处理下果实柠檬酸含量在整个生育期均显著高于全铵处理,而铵硝配施处理下果实中柠檬酸和苹果酸含量在成熟期均显著低于全硝处理.2)不同形态氮素及配施处理下,果实中柠檬酸含量与CS活性的变化趋势均呈单峰型,但到达峰值的时间不同.全铵处理下果实苹果酸含量与PEPC活性呈显著正相关,全硝、铵硝配施处理下果实苹果酸和柠檬酸含量都与MDH活性呈显著正相关.3)在膨大期和成熟期,全硝处理和铵硝配施处理下PEPC基因(PPC1、PPC2)表达显著高于全铵处理;线粒体苹果酸脱氢酶(mMDH)的表达对果实苹果酸脱氢酶活性和苹果酸积累起主要作用,表明适当比例的铵硝配施可能通过影响果实中PEPC和MDH的活性和基因表达从而显著降低成熟果实有机酸的含量.%Cherry tomatoes were grown in a matrix-nutrient solution co-culture systems with 100％ nitrate (NO3-), 100％ ammonium (NH4+) and 75％ NO3-:25％ NH4+ as the N source. The effects of the nitrogen (N) forms on the contents of organic acids, the activities of phosphoenolpyruvate carboxylase ( PEPC), citrate synthase (CS) and malate dehydrogenase (MDH), and their transcriptional expression patterns were investigated during the development of the fruit. The results are as follows: 1 ) During the development of the fruit, citrate contents under the treatments of 100％ NO3-and 75％ NO3-:25％ NH4+ are always significantly higher than that under the treatment of 100％ NH4+, while the contents of citrate and malate in mature fruits under the 75％ NO3-:25％ NH4+ treatment are lower than those of the 100％ NO3- treatment. 2) During the development of the fruit, the citrate content is related to the activity of CS under all treatments and shows the tendency with a single peak, although the peak values are different at the different stages. The content of malate is positively correlated with PEPC activity under the 100％ NH4+, in contrast, the contents of malate and citrate are positively correlated with MDH activity under the 100％ NO3- and 75％NO3-:25％ NH4+. 3) At the enlargement stage and mature stage, the expression of PEPC genes (PPC1 and PPC2) supplied by 100％ NO3- and combined 75％ NO4+ with 25％ NH4+ are both significantly higher than that of the 100％ NH4+. The activity of MDH is related to the mMDH expression level and the malate accumulation during the development of the fruit. Our results suggest that an appropriate ratio of NO3-/NH4+ could reduce organic acid contents in ripe fruits of tomato, and different exogenous N forms have different effects on the activities of PEPC and MDH and the expression pattern of corresponding genes.