Figure 3.

gai-t6 confers increased resistance to PAC. Bolt stem elongation of gai-t6 (rear two plants) and GAI (front two plants) plants grown on 10⁻⁶ m PAC is shown. The plants were photographed 57 days after sowing. Because PAC inhibits GA biosynthesis both classes of plant are dwarfed and darker green than when grown on medium lacking PAC. However, gai-t6 plants grow taller than the GAI plants and, therefore, are more resistant to the effects of 10⁻⁶ m PAC. As shown, the gai-t6 plants have open flowers, with the petals clearly visible, whereas the flowers on the GAI plants are not open (retarded petal and stamen elongation is characteristic of severe GA deficiency; Koornneef and van der Veen 1980). gai-d1 and gai-d5 mutants behave like gai-t6 under these conditions, and not like GAI. When grown on medium lacking PAC, gai-t6, gai-d1, and gai-d5 are indistinguishable from GAI.