The rms7 Mutant of Pea Has Elevated Indole-3-Acetic Acid Levels and Reduced Root-Sap Zeatin Riboside Content

Rmsl i s one of the series of five ramosus loci in pea (Pisum sativum 1.) in which recessive mutant alleles confer increased branching at basal and aerial vegetative nodes. Shoots of the nonallelic rms l and rms2 mutants are phenotypically similar in most respects. However, we found an up to 40-fold difference in root-sap zeatin riboside ([9R]Z) concentration between rms l and rms2 plants. Compared with wild-type (WT) plants, the concentration of [9RIZ i n rms l root sap was very iow and the concentration in rms2 root sap was slightly elevated. To our knowledge, the rms l mutant is therefore the second ramosus mutant (rms4 being the first) to be characterized with low root-sap [9R]Z content. Like rms2, the apical bud and upper nodes of rms l plants contain elevated indole3-acetic acid levels compared with WT shoots. Therefore, the rms l mutant demonstrates that high shoot auxin levels and low root-sap cytokinin levels are not necessarily correlated with increased apical dominance in pea. A graft-transmissible basis of action has been demonstrated for both mutants from reciproca1 grafts between mutant and WT plants. Branching was also largely inhibited in rms l shoots when grafted to rms2 rootstocks, but was not inhibited in rms2 shoots grafted to rms l rootstocks. These grafting results are discussed, along with the conclusion that hormone-like signals other than auxin and cytokinin are also involved.