β-amino butyric acid-induced resistance in pearl millet to downy mildew is associated with accumulation of defence-related proteins

Earlier studies had indicated that beta-amino butyric acid (BABA) treatment of pearl millet seeds influenced seedling vigor and protected seedlings from downy mildew disease caused by the oomycetous biotrophic fungus Sclerospora graminicola. Application of 50 mM BABA reduced disease severity and offered protection against S. graminicola of similar to 74%. The protection induced was durable and operative during the vegetative and reproductive growth periods of the crop. In the present study an attempt was made to understand the biochemical basis for this protection. A close association was found between BABA-induced protection and increased accumulation of defence-related proteins like phenylalanine ammonia lyase, peroxidase, beta-1,3-glucanase and cell wall hydroxyproline-rich glycoproteins (HRGP). Isoelectric focusing of beta-1,3-glucanases indicated the presence of several isoforms, of which isoforms of pI 9.6 and 8.8 were markedly increased in BABA-treated seedlings upon S. graminicola infection. Increased accumulation of hydroxyproline-rich glycoproteins was also observed at 9 h after inoculation in these samples. Western blots with MAC 265, a monoclonal antibody against pea HRGP identified a 17-kDa HRGP molecule that significantly increased in concentration in BABA-treated pearl millet seedlings as a response to S. graminicola infection. The postinfectional protection offered by BABA involved induction of defence responses which were comparable to the highly resistant cultivar.