BRANCHING MUTANT RMS-2 IN PISUM-SATIVUM - GRAFTING STUDIES AND ENDOGENOUS INDOLE-3-ACETIC-ACID LEVELS

Isogenic lines of pea (Pisum sativum L.) were used to determine the ph ysiological site of action of the Rms-2 gene, which maintains apical d ominance, and its effect on endogenous free indole-3-acetic acid (IAA) levels. In mutant rms-2 scions, which normally produce lateral branch es below node 3 and above node 7, apical dominance was almost fully re stored by grafting to Rms-2 (wildtype) stocks. In the reciprocal graft s, rms-2 stacks did not promote branching in wild-type shoots. Togethe r, these results suggest that the Rms-2 gene inhibits branching in the shoot of pea by controlling the synthesis of a translocatable (hormon e-like) substance that is produced in the roots and/or cotyledons and in the shoot. At all stages, including the stage at which aerial later al buds commence outgrowth, the level of IAA in rms-a shoots was eleva ted (up to 5-fold) in comparison with that in wild-type shoots. The in ternode length of rms-2 plants was 40% less than in wild-type plants, and the mutant plants allocated significantly more dry weight to the s hoot than to the root in comparison with wild-type plants. Crafting to wild-type stocks did not normalize IAA levels or internode length in rms-2 scions, even though it inhibited branching, suggesting that the involvement of Rms-2 in the control of IAA level and internode length may be confined to processes in the shoot.