Phenovariation induced in Streptocarpus prolixus (Gesneriaceae) by β-glucosyl Yariv reagent

Streptocarpus prolixus C.B. Clarke is a species in the family Gesneriaceae characterized by an acaulescent vegetative body. Instead of a stem bearing leaves developing from a shoot apical meristem, its vegetative body derives from the continued, intercalary growth of one of its cotyledons. β-glucosyl Yariv phenyglycoside (β-D-Glc)3 selectively binds a class of cell surface associated proteoglycans and glycoproteins known as arabinogalactan-proteins (AGPs). Treating seeds and seedlings of S. prolixus with (β-D-Glc)3 induced phenovariants considered phyogenetically significant because they copied morphological features (phenocopied) characteristic of other, presumably more primitive species of Streptocarpus as well as species in other genera in the family to which it belongs. These results paralleled those obtained in earlier experiments with S. prolixus using antimetabolites of hydroxyproline-containing proteins (Hyp-proteins). Treatment with α-galactosyl phenylglycoside, a Yariv reagent that does not bind AGPs, did not induce phenovariants. The finding that (β-D-Glc)3 produced the same “phyletic phenocopies” as Hyp-protein antagonists strongly suggests that the morphoregulatory Hyp-proteins that were antagonized in the earlier experiments were AGPs and that AGPs play a pivotal role in pattern formation and pattern change during plant morphogenesis.