Physiological and biochemical characterization of bud dormancy: Evolution of carbohydrate and antioxidant metabolisms and hormonal profile in a low chill peach variety

Abstract

In this work, we studied the interplay among the levels of starch, sugars, abscisic acid (ABA) and bioactive gibberellins (GAs), and the antioxidant metabolism during bud dormancy release in a low chill peach variety. The experiments were performed in two consecutive years and two geographical areas with different annual media temperature.In the cold area, peach plants accumulated more starch and soluble sugars than in the temperate area, sorbitol and sucrose being the most abundant sugars.The enzymatic activities of the ascorbate-glutathione (ASC-GSH) cycle and the ROS-scavengers enzymes superoxide dismutase (SOD), catalase and peroxidase (POX) were measured. The increased activity of the ASC-GSH cycle enzymes and POX suggested a mild oxidative stress at endodormancy and at dormancy release periods. In this sense, the presence of H2O2-sensitive antioxidant enzymes, including Fe-SOD, Cu,Zn-SOD, POX and APX in the floral buds could trigger the oxidative signaling leading to dormancy release. Interestingly, the induction of a new POX isoenzyme occurred at dormancy release, suggesting its use as a marker for this event in low chill peach varieties.GAs levels decreased at the end of the dormancy period, whereas ABA levels showed a strong decline throughout the dormancy period, especially in buds from the cold area. As a consequence, a sharp decrease in the ABA/GAs ratio was observed, a phenomenon closely related to dormancy release. This response was more evident in the cold area. Results suggested that a decrease in ABA levels, as well as in the ABA/GAs ratio, may be necessary for the bud dormancy release in peach, at least in low chill varieties. Overall, we observed an interaction among sugars, antioxidant enzymes and plant hormones in the dormancy period. Glucose levels correlated with chill accumulation, peaking at ecodormancy and dormancy release. This response was parallel with increases in some antioxidant enzymes, the induction of a new POX isoenzyme and the decline in ABA levels and the ratio ABA/GAs.