Arabinogalactan-Proteins, Place-Dependent Suppression and Plant Morphogenesis

Experiments in which several antagonists of the synthesis of Hyp-containing proteins (Hyp-proteins) induced profound changes in the morphogenetic patterns exhibited by five different species of leafy liverworts led to a hypothesis that some of the Hyp-proteins had a morphoregulatory function (Basile 1980, Basile and Basile 1982). The class to which the morphoregulatory Hyp-proteins belonged could not be known from the methods used. Two main classes of Hyp-proteins had been distinguished in plants by the time the series of experiments was completed. One class was referred to as “extensins” (Lamport 1963) and the other as arabinogalactan-proteins (AGPs) (Clarke et al 1979). Although there is no direct evidence to exclude “extensins”, available evidence obtained in subsequent studies suggested that the type of Hyp-protein modified would be characterized as AGPs (Basile et al 1986). What follows are some examples of how by antagonizing Hyp-protein synthesis at different stages of plant ontogeny, three separate aspects of plant morphogenesis are modified. In each case the experimentally induced changes in plant morphogenesis could be correlated with quantitative and/or qualitative differences in AGPs.