GTP binding activity of membrane proteins in isolated barley embryo is enhanced by abscisic acid

Pharmacological studies showed that an inhibitor (pertussis toxin) or activ ator (mastoparan) of the Ga-subunit of heterotrimeric GTP binding proteins can counteract the effect of the plant hormone abscisic acid (ABA) in the i nhibition of barley embryo germination. The presence of several GTP binding proteins (ranging from 15 to 48 kDa) in membrane fractions of barley embry os was demonstrated by specific [alpha-P-32]GTP labeling of proteins and by Western blotting using antibodies against highly conserved G protein a-sub unit or Ras protein. GTP binding was enhanced in protein fractions from ABA -treated embryos, especially concerning poly-peptides of Mr 42, 29, 28, 27, and 25 kDa. Our data suggest that GTP-binding proteins are involved ABA-in duced responses in barley embryo. (C) 1999 Elsevier Science Ireland Ltd. Al l rights reserved.