Grape Berries Turn Ripe Physiological Mechanism Study

This paper, submitted as a Ph.D. dissertation, reports a series of studies on the formation of expansion foroe, hormonal regulation, ultra-struotural ohanges of berry skin cells and the differences and ohanges in respiratory patterns of different tissues in Golden Musoat grape (Vitis vinifera × V. labrusoa) during its physiologioal phase ohanges of "veraison"*.The results obtained are as follows.1. A physioal mode of the start of expansion growth in post-veraison grape berries, being oonoeptualized as a "Two-step theory", has been put forward. In this mode, it is elucidated that the berry expansion foroe originates from the difference of water potentials(△Ψw) built up between within and without a berry rather than from the turgor pressure as has been commonly assumed. In this oase, the drop of berry Ψw is essential ly the major element related to the build-up of expansion foroe. The realization of berry expansion growth is bound to undergo the following two steps: The first step — the simultaneous occurrenoe of sugar accumulation (Ψs↓) and cell wall loosening in the flesh resulting in an abrupt berry softening and a rapid inorease of skin-carried turgor.The second step--cell wall loosening in the berry skin resulting inthe release of turgor pressure (Ψp) and the consequent drop of Ψw, which leads to a burst of berry expansion growth. The potentiality of expansion growth originating from sugar accumulation and cell wall loosening of the flesh oould not be expressed until the constraint is finally relieved by cell wall loosening in the skin. The comparison proposed for a whole grape berry as a "large cell", and for the berry skin as the corresponding "cell wall" is not appropriate for a berry being in the pre-veraison state when its cell walls in the flesh are still rigid.2. Ametabolic mode has been establ ished to unravel the nature of metabolic water uptake for the post-veraison berries. The cellular metabolism is involved in the sugar accumulation and the cell wall loosening processes.leading to the drop of Ψ(?) and Ψp and thus to the drop of Ψw. Consequently, a greater water uptake foroe is built up and rapid berry exp(?)n(?)ion growth is thus resulted. In this oase, plasma membrane ATPase-H+ pump plays the key role in the formation of expansion foroe.3. The reappraisal of the role of ethylene and a hypothesis of the oo-effeot of ethylene and ABA on the triggering of grape veraison: based on the transient ethylene peak deteoted prior to veraison, and the significant depressive effeot of ethylene aotion inhibitor (STS) treatment resulting in a 10 days delay of the inoeption of veraison, it is suggested that ethylene is essential in the regulation of veraison with ABA aoting synergistioally and/or differentially on separate components of the veraison syndrome.4. Grape seeds have been found to be important in the modification of hormonal balance in the berry. Its role in veraison is suggested. Seeds in a post-veraison berry secret a large amount of ABA, and the surfaoe of the seeds is a site where strong IAA oxidizing activities exist and increase towards berry maturity.5. It has been established that the skin and the flesh are two separate metabolic systems . The respiration patterns of both the two systems have obvious ohanges with the advent of veraison, and the rate in the skin being much higher than that in the flesh. Respiration in the skin of a pre-veraison berry has been shown dominated by EMP-TCAC, with a RQ value <1.0, obviously a result of CO2 dark fixation being involved in the malic formation. In the skin, PPP though weak, its funotion to provide NADPH and carbon skeletons for the synthesis of such compounds as organio acids and phenols accumulated before veraison could be replaced by the photosynthesis in ohloroplasts in the skin cells. The flesh of a pre-veraison berry is characterized by a RQ value near 1.0, a weak EMP-TCAC with a dominating PPP being related to the accumulation of organio acids and phenols before veraison. The shift of its RQ to >1.0 after veraison signifies that organic acids either are transformed to sugar through the reversed EMP pathway (gluoogenesis) or oxidized by respiration per se.6. Based on the involvement of ethylene and qualitative respiratory...