Exploring the mechanism of Akebia trifoliata fruit cracking based on cell-wall metabolism

Akebia trifoliata fruit cracks easily, but little is known about the underlying mechanism of this process. In this study, the changes in minerals contents, water distribution, phytohormone levels, and reactive oxygen species (ROS) metabolism were investigated to explore the effects of cell-wall metabolism in A. trifoliata fruit cracking. The micro-morphological observation confirmed that A. trifoliata fruit cracking was closely related to the cell-wall metabolism. After cracking, the higher polygalacturonase, β-1,4-endoglucanase, and β-glucosidase activities resulted in the depolymerization of covalently bound pectin (from 9.69% to 7.70%) and cellulose (from 57.91% to 38.05%). Moreover, the disordered ROS homeostasis resulted from the lower superoxide dismutase and ascorbate peroxidase activities, which led to cellular oxidative damage. These modifications, together with the decreases in Ca, K, and B, degradation of starch, and the movement of water, decreased cell-wall strength and degraded the cellulose network, and thus resulted in A. trifoliata cracking. The above processes were regulated by phytohormones through increased indole-3-acetic acid, salicylic acid, and jasmonic acid levels, as well as decreased cytokinin content. The findings of this study will be beneficial for further research into the preservation of A. trifoliata fruit, which is of great significance to the development of the A. trifoliata industry.