Hydroxyproline-rich glycoproteins accumulate in pearl millet after seed treatment with elicitors of defense responses against Sclerospora graminicola

The accumulation of hydroxyproline-rich glycoproteins (HRGPs) was investigated after induction of resistance in pearl millet against downy mildew caused by Sclerospora graminicola. Treatment of susceptible pearl millet seeds with various biotic and abiotic elicitors resulted in increased HRGP content in the cell walls of coleoptiles at 9 h after inoculation. Similar results with increased accumulation at 4–6 h after inoculation were obtained in suspension cells of pearl millet. Maximum HRGP accumulation was observed in seedlings raised from susceptible seeds treated with chitosan and Pseudomonas fluorescens. Western blot analysis with MAC 265 (a rat monoclonal antibody raised against pea HRGP) identified three proteins of 27, 17 and 14 kDa in resistant cultivars. The absence of the 14 kDa HRGP was observed in susceptible cultivars as reported earlier. The induced accumulation of the 14 kDa HRGP upon elicitor treatments was observed in the present study. Peroxidase and hydrogen peroxide, essential components for HRGP cross-linking, were also increased in samples treated with these elicitors. A tissue specific increase in HRGP at the regions around vascular bundles was observed upon chitosan treatment. The results presented will have a presumed importance in identifying the susceptible pearl millet varieties and improving those using elicitors of defense for field applications.