BIOCHEMICAL AND HISTOLOGICAL CHANGES ASSOCIATED WITH DOWNY MILDEW (Plasmopara halstedii (Farl.) Berl. and de Toni) INFECTION IN SUNFLOWER (Helianthus annuus L.) / MODIFICACIONES BIOQUIMICAS E HISTOLOGICAS RELACIONADAS CON LA INFECCION DEL GIRASOL (Helianthus annuus L.) POR EL AGENTE DE MILDIU (Plasmopara halstedii (Farl.) Berl. y de Toni) / CHANGEMENTS BIOCHIMIQUES ET HISTOLOGIQUES ASSOCIÉS À L’INFECTION DU TOURNESOL (Helianthus annuus L.)

Abstract

SUMMARY Biochemical changes associated with downy mildew infection in sunflower revealed an increase in the total soluble proteins, 0-40% ammonium sulfate fractionated proteins and total soluble sugars. Molecular sieve chromatography of 0-40% ammonium sulphate fraction revealed for presence of a high molecular weight protein and polysaccharide in the downy mildew infected sunflower leaves. Antibodies raised against the high molecular weight protein and polysaccharide were used in the western blot/dot blot analysis. It has been shown that the downy mildew disease also induces PR proteins, which have antigenic homology with PR-S protein, a member of the PR-5 class of proteins. An increase in iPA (isopentenyl adenosine) content in the infected sample was observed. A positive correlation exists between iPA level, 0-40% protein and total sugar content. Histological studies revealed that the downy mildew fungal mycelium extensively proliferates, ramifies extensively the leaf tissue and forms a nutritional link with the host cell by producing the intracellular haustorium.