柿果实采后氧化还原电位与乙烯合成和相关酶活性的关系

Oxidation reduction potential, ethylene biosynthesis, and enzyme activity of post-harvest persimmon

关键词:  柿, 氧化还原电位, 乙烯, 酶活性, 软化, 保鲜

Key words:  persimmon, oxidation reduction potential, ethylene, enzyme activity, soften, retain freshness

摘要:

该研究以广西特色柿品种‘恭城月柿'为材料,在采后贮藏过程中对其氧化还原电位(ORP)、乙烯生物合成量、硬度、色差、抗氧化酶及细胞壁降解酶活性的变化进行了测定,初步探讨柿果实氧化还原电位与乙烯生物合成和相关酶活性的关系。结果表明:贮藏期果实的硬度整体呈下降趋势,乙烯利处理果实的硬度从采后3 d即急速下降,至贮藏末期始终显著低于对照。贮藏前14 d果实转色较缓慢,采后15 d乙烯利处理果实的总色差ΔE值快速上升至29.6,转色完全,显著高于对照的11.9。在贮藏前期处理和对照果实的ORP均稳定在7.5 mv·g^-1,采后15 d乙烯利处理果实的ORP快速上升至11.9 mv·g^-1,是对照组的1.4倍。乙烯利处理果实的乙烯生物合成量在贮藏前期呈较低水平,采后15 d乙烯生成量急剧增加至0.372 μL·kg^-1·h^-1的高峰,对照乙烯生成量则始终维持在0.033 μL·kg^-1·h^-1的较低水平。可见,乙烯生成量的增加与ORP的上升关系密切。此外,抗氧化酶中的过氧化物酶(POD)和细胞壁降解酶中的β-D-半乳糖苷酶(β-D-Gal)活性与ORP呈极显著正相关,表明二者受果实ORP变化的影响。因此,经乙烯利处理柿果实的ORP贮藏末期显著上升,促进乙烯生物合成量的急剧增加,诱导抗氧化酶POD和细胞壁降解酶 β-D-Gal活性增强,导致果实急速后熟软化。柿果实ORP可能作为开关调控1-氨基环丙烷-1-羧酸(ACC)生成乙烯这一生物化学反应,即打破ORP的稳定状态引发乙烯合成的启动。

Abstract:

Ethylene is a common plant hormone which can accelerate the ripening of fruits. Post-harvest ripening involves a variety of complex metabolic processes such as ethylene biosynthesis, reactive oxygen species biosynthesis and cell wall degradation hydrolyses. ‘Gongcheng' persimmon is a distinctive variety of Guangxi Zhuang Autonomous Region, and was used as the research material to determine the changes of indexes e.g., oxidation reduction potential(ORP), ethylene biosynthesis, firmness, total chromatism, and related enzyme activities during the storing experiment. The results demonstrated that firmness decreased continuously during the whole storing period, the firmness of fruits were treated with ethephon were declining rapidly during the first three days of storage, and were significantly lower than the control at all times. During the first fourteen days of storage, the total color chromatism was rising slowly. Fifteen days after harvest, the color of fruits, which were treated with ethephon, had changed completely and delta E value rapidly increased to the maximum of 29.6 which is evidently higher than that of the control 11.9. The ORP changed within a smaller range and maintained at 7.5 mv·g^-1 in the prophase of storage. Fifteen days after harvest, the ORP of fruits which were treated with ethephon increased rapidly to 11.9 mv·g^-1, 1.4 times as much as that of the control. Additionally, ethylene biosynthesis did not change significantly during the first fourteen days. However, from the fifteenth days after harvest, the ethylene biosynthesis rate of fruits were treated with ethephon increased sharply to 0.372 μL·kg^-1·h^-1 and reached the maximum, but the control kept at a stable level of 0.033 μL·kg^-1·h^-1. Thus, the increase of ethylene biosynthesis was closely related to the rise of ORP. Furthermore, the activity of peroxidase(POD)belonging to the antioxidative enzymes and β-D-galactosidase(β-D-Gal)belonging to the cell wall degrading enzymes were also significantly and positively correlated to ORP, indicating that POD and β-D-Gal activities are affected by the ORP. Therefore, the ORP of persimmon fruits treated with ethephon increased observably at the end of storage, promoting a sharp biosynthesize of ethylene, increasing activities of POD and β-D-Gal, and finally resulting in the rapid softening and ripening of persimmon. It is proved that persimmon fruit ORP may act as a switch to control the biochemical reaction of ethylene biosynthesis, and breaking the ORP steady state can initiate ethylene synthesis.