A basic peroxidase isoenzyme from the grape pedicel is induced by gibberellic acid

Abstract

Soluble peroxidase activity from pedicels of seedless table grape cv. Sultana was highly stimulated by post-bloom applications of gibberellic acid (GA₃) to vines. The increase in peroxidase activity was mainly due to the induction of a basic peroxidase isoenzyme (pI > 9; BPrx-HpI). The activity of two other peroxidase isoenzymes of pI 6.5 and 3.2 was not altered by the hormone treatment. BPrx-HpI was induced by GA₃ in pedicels and rachis but not in berries, although in berries peroxidase activity was also stimulated by post-bloom GA₃ applications. BPrx-HpI oxidised guaiacol and ortho-phenylenediamine (o-PDA), while the others peroxidases found in the pedicel and in the berry oxidised only o-PDA. Hence, BPrx-HpI was characterised as a guaiacol-peroxidase showing no activity towards ascorbic acid (ASC). The possible role of BPrx-HpI in pedicel lignification and berry-drop caused by GA₃ applications to cv. Sultana vines is discussed.