Molecular analysis of the improvement in rachis quality by high CO₂ levels in table grapes stored at low temperature.

摘要

Rachis browning is one of the main factors reducing the quality of table grapes during storage at low temperature. To better understand the effect of a 3-day CO₂ pretreatment (20% CO₂ plus 20% O₂) on maintaining the rachis quality of table grapes (Vitis vinifera cv. Cardinal) at 0 degrees C, we analyzed the expression of genes codifying enzymes related to the synthesis and oxidation of phenolic compounds (phenylalanine ammonia-lyase, VcPAL; and polyphenol oxidase, GPO) and the detoxification of reactive oxygen species (catalase, GCAT; and ascorbate peroxidase, VcAPX) in rachis of treated and non-treated bunches. Furthermore, due to their role in senescence, the implication of ethylene and abscisic acid (ABA) was also investigated by studying the expression pattern of key regulatory genes for these hormones such as ACC synthase (ACS1) and oxidase (ACO1), VvNCED1 and 2. To determine whether these changes in gene expression were specifically related to rachis deterioration, their expression pattern in pulp and skin of treated and non-treated grapes were evaluated. The appearance of browning in non-treated rachis was associated with an increase in GPO and VcPAL mRNA levels, whereas high CO₂ levels arrested this accumulation. In pulp, even though browning was not evident, a slight increase in GPO1 mRNA accumulation in non-treated bunches was detected. Moreover, lipid peroxidation level revealed lower oxidative stress in rachis of CO₂-treated bunches than in non-treated ones, which seemed to be regulated by VcAPX and GCAT gene expression induction. This regulation was specific to rachis, showing a different pattern in pulp and skin. Regarding phytohormones, the effect of high CO₂ levels reducing rachis browning seems to be linked to the modulation of ethylene biosynthesis genes. On the other hand, neither VvNCED1 nor VvNCED2 expression levels were altered in rachis, but NCED1 was induced specifically by low temperature in pulp. Overall, our results suggest a specific response of rachis to high levels of CO₂ that could be related to the mitigation of rachis browning