Effect of hot air treatment on organic acid- and sugar-metabolism in Ponkan (Citrus reticulata) fruit

Organic acid and sugar balance is an important trait for fruit quality. The mandarin, Ponkan (Citrus reticulata Blanco cv. Ponkan) is rich in organic acids even at maturity, thus the fruit provide good material for the study of organic acid degradation. In the present research, hot air (40 degrees C, 2 d) treatment (HAT) was found to have significant effects on both degradation of the organic acids, especially on citric acid, and accumulation of soluble sugars, especially on fructose and glucose. Genes related to citric acid degradation related (CitAco1,CitAco2,CitAco3,CitIDH1,CitIDH2,CitIDH3,CitGAD4,CitGAD5 and CitGS2) and sucrose metabolism (CitAI1,CitAI3,CitNI1 and CitNI3) were isolated and transcription analyzed. HAT significantly up-regulated CitAco3, CitIDH2/3 and CitGAD4 expression, while having little effect on CitGS2. Sucrose metabolism related genes also differentially responded to HAT, with CitAI genes were induced and CitNI genes were relatively unchanged. It is proposed that HAT drove citric acid degradation via the GABA shunt pathway (especially by modulating CitAco3-CitIDH2/3-CitGAD4 cascade), but not the glycolysis pathway. (C) 2012 Elsevier B.V. All rights reserved.