THE RMS1 MUTANT OF PEA HAS ELEVATED INDOLE-3-ACETIC-ACID LEVELS AND REDUCED ROOT-SAP ZEATIN RIBOSIDE CONTENT BUT INCREASED BRANCHING CONTROLLED BY GRAFT-TRANSMISSIBLE SIGNAL(S)

Rms1 is one of the series of five ramosus loci in pea (Pisum sativum L .) in which recessive mutant alleles confer increased branching at bas al and aerial vegetative nodes. Shoots of the nonallelic rms1 and rms2 mutants are phenotypically similar in most respects. However, we foun d an up to 40-fold difference in root-sap zeatin riboside ([9R]Z) conc entration between rms1 and rms2 plants. Compared with wild-type (WT) p lants, the concentration of [9R]Z in rms1 root sap was very low and th e concentration in rms2 root sap was slightly elevated. To our knowled ge, the rms1 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 rms1 plants contain elevated i ndole-3-acetic acid levels compared with WT shoots. Therefore, the rms 1 mutant demonstrates that high shoot auxin levels and low root-sap cy tokinin levels are not necessarily correlated with increased apical do minance in pea. A graft-transmissible basis of action has been demonst rated for both mutants from reciprocal grafts between mutant and WT pl ants. Branching was also largely inhibited in rms1 shoots when grafted to rms2 rootstocks, but was not inhibited in rms2 shoots grafted to r ms1 rootstocks. These grafting results are discussed, along with the c onclusion that hormone-like signals other than auxin and cytokinin are also involved.