HYDROXYPROLINE-RICH GLYCOPROTEINS IN CELL-WALLS OF PERICARP FROM MAIZE

Hydroxyproline-rich glycoprotein accumulation in maize (Zea mays L.) pericarp cell walls was assayed by determining total hydroxyproline and by assessing protein extracts on western blots. Whole kernel dry weight and pericarp cell wall dry weight increased throughout kernel development of the three varieties studied, Golden x Bantam (GXB), Japanese Hulless (JHL) and South American Yellow (SAY). Total hydroxyproline per mg dry weight and per pericarp increased throughout kernel development: a major increase occurred between 10 and 20 days after pollination. Soluble proteins from all three varieties were assayed on western blots reacted with a monoclonal antibody raised against PC-1, the major maize hydroxyproline-rich glycoprotein purified from GXB pericarp. Each of the maize varieties contained one major band that cross reacted with anti-PC-1 antibodies. This protein was a major part of the salt soluble proteins of the pericarp walls from all developmental times studied. PC-1 differed in electrophoretic mobility on native gels among the three varieties, and the popcorn proteins showed heterogeneity at different times after pollination as well. These maize wall proteins are strongly correlated with development and maturation of kernel pericarp, indicating a functional role for them in mechanical support and protection of the embryo and endosperm.