BRANCHING IN PEA - ACTION OF GENES RMS3 AND RMS4

The nonallelic ramosus mutations rms3-2 and rms4 of pea (Pisum sativum L.) cause extensive release of vegetative axillary buds and lateral g rowth in comparison with wild-type (cv Torsdag) plants, in which axill ary buds are not normally released under the conditions utilized. Craf ting studies showed that the expression of the rms4 mutation in the sh oot is independent of the genotype of the rootstock. In contrast, the length of the branches at certain nodes of rms3-2 plants was reduced b y grafting to wild-type stocks, indicating that the wild-type Rms3 gen e may control the level of a mobile substance produced in the root. Th is substance also appears to be produced in the shoot because Rms3 sho ots did not branch when grafted to mutant rms3-2 rootstocks. However, the end product of the Rms3 gene appears to differ from that of the Rm s2 gene (C.A. Beveridge, J.J. Ross, and I.C. Murfet [1994] Plant Physi ol 104: 953-959) because reciprocal grafts between rms3-2 and rms2 see dlings produced mature shoots with apical dominance similar to that of rms3-2 and rms2 shoots grafted to wild-type stocks. Indole-3-acetic a cid levels were not reduced in apical or nodal portions of rms4 plants and were actually elevated (up to 2-fold) in rms3-2 plants. It is sug gested that further studies with these branching mutants may enable si gnificant progress in understanding the normal control of apical domin ance and the related communication between the root and shoot.