Induction of defence responses in zucchini (Cucurbita pepo) by Anabaena sp water extract

Abstract

The induction of systemic defence responses in zucchini leaves treated by a water extract of Anabaena sp. BEA0300B strain was studied firstly through a bioassay under Podosphaera xanthii (Castagne) U. Braun and Shishkoff challenge. In a second experiment, enzyme activities correlated to induced systemic resistance were assayed 1, 2 and 3 days after treatment (DAT) with BEA0300B on untreated cotyledonar leaves. Endochitinase, beta-N-acetylhexosaminidase, chitin 1,4-beta-chitobiosidase, beta-1,3-glucanase and peroxidases were spectrophotometrically determined. Enzyme isoforms were detected after isoelectric focusing. The extract reduced Podosphaera xanthii symptoms by 25%, similarly to chitosan, the positive control. BEA0300B treatment caused systemic accumulation of all the enzymes. In particular, the treatment provoked an early increase of total chitinase activity (15-38%) and of the expression of two constitutive chitinase isoforms, pI 4.4 (159%) and pI 4.6 (433%). The total beta-1,3-glucanase and peroxidase activities were transiently increased. The expression of two constitutive isoforms of these enzyme increased, particularly pI 5.0 glucanase (148%, 1 DAT) and pI 4.9 peroxidase (181%, 2 DAT). BEA0300B water extract also showed a direct antifungal activity on pathogen sporulation.