Decapitation-induced axillary bud outgrowth is a vital mechanism whereby shoots are able to continue normal growth and development. In many plants, including wild-type garden pea (Pisum sativum L.), this process can be inhibited by exogenous
auxin. Using the ramosus (rms) increased branching mutants of pea, we present evidence that this response to
auxin is dependent on graft-transmissible
substance(s) regulated by the genes Rms1 and Rms2. The response to exogenous
auxin is massively diminished in decapitated rms1 and rms2 mutant plants. However, basipetal
auxin transport is not reduced in intact or decapitated mutants. Grafting rms1 or rms2 shoots onto wild-type rootstocks restored the
auxin response, indicating that Rms1 and Rms2 gene action in the rootstock is sufficient to enable an
auxin response in mutant shoots. We conclude that Rms1 and Rms2 act in the rootstock and shoot to control levels of mobile
substance(s) that interact with exogenous
auxin in the inhibition of bud outgrowth after
decapitation. At least for rms1, the reduced
auxin response is unlikely to be due to an inability of
auxin to decrease xylem sap
cytokinin content, as this is already low in intact rms1 plants. Consequently, we have genetic evidence that
auxin action in decapitated plants depends on at least one novel long-distance signal.