Near-lethal heat treatment induced metabolic changes associated with endodormancy release of Superior Seedless grapevine cv. (Vitis vinifera L.) buds

Abstract

Abstract To assess the efficacy of near lethal heat stress for endodormancy release of Superior Seedless grapevine buds, single-node cuttings were soaked for 1 h in hot water (50°C) and then forced for one month. The effects of hot water treatment (HWT) on budburst, metabolic changes of carbohydrates, proline, free polyamines PAs (putrescine (Put), spermidine (Spd) and spermine (Spm)) and antioxidant enzymes' activity were investigated in bud under forcing conditions. Near-lethal heat stress caused a transient increase in starch hydrolysis, leading to an abrupt accumulation of soluble sugars, especially sucrose concentration during the first 3 days after treatment. This accumulation of soluble sugars coincided with a brief stimulation of the antioxidant system represented by ascorbate peroxidase (APX; EC 1.11.1.11), peroxidase (POD; EC 1.11.1.7) as well as an increase in the concentration of proline and free polyamines, especially putrescine (Put) and spermidine (Spd). These changes, which occurred immediately upon treatment, appear to be related with a process leading to endodormancy release. These results support the argument that a temporary and acute oxidative stress is involved in the mechanism leading to dormancy release and budbreak. Furthermore, it is possible that the stimulation of both peroxidases' activity and proline biosynthesis activated the pentose phosphate pathway (PPP) which helped the bud to overcome endodormancy. After this initial period and towards budbreak initiation, there was a rapid decline in the concentration of soluble sugars, proline and Put, while, Spm and Spd became abundant. Such post stress changes appear to be associated with the reactivation of growth leading to an earlier and more vigorous budbreak. The metabolic response to HWT was compared to those observed after bud chilling or the application of restbreaking agents such as hydrogen cyanamide (HC). The similarity in the response to these various stimuli suggests the presence of common regulatory pathways involved in bud dormancy release and subsequent sprouting