Physiological-genetics of flowering in Pisum

The physiological genetics of flowering in the pea (Pisum sativum L.) is examined starting with events in the leaves and concluding with events in the inflorescence, flower and floral organ meristems. WT peas have a late flowering, quantitative long day habit. The photoperiod response results from production of a flower inhibitor under short days. The phytochrome system controls inhibitor production via two mechanisms - a red (R) activated switch and a far-red (FR) mechanism involving extended exposure. The phyB deficient mutant, lv, is early flowering under long or short days. Thus the lv mutation may prevent R activation of the inhibitor synthesis pathway. The long term FR mechanism probably involves phyA and we suggest a phyA defective pea would be unable to down regulate inhibitor synthesis and would thus flower late in long or short days. The 1w mutant shows delayed flower initiation and enhanced response to photoperiod, traits indicative of an enlarged response to phyB. The phytochrome chromophore deficient mutant, pcd1, shows a small flowering delay under all photoperiods. Three genes Sn, Dne and Ppd act in the inhibitor synthesis pathway and two genes E and Hr control ontogenetic expression of the system. Evidence of an additional gene which may regulate inhibitor synthesis has recently been obtained following identification of a dominant day neutral mutant, A23. The primary action of the graft-transmissible inhibitor may be to direct assimilate flow. The gi mutation blocks synthesis of the floral stimulus. The Lf alleles appear to determine apical reception of the flowering signal. Gene Det determines identity of the primary (I1) inflorescence meristem and Veg2 identity of the lateral (I2) inflorescence meristem. It is not yet clear whether Veg1 determines I1 or I2 identity. Mutants veg1 and veg2-1 never flower. Five mutants pim, A324, uni, M175 and leflo show floral proliferation and aberrant flowers; these genes may determine floral (F) meristem identity. In addition, five mutants with floral homeotic changes are described. In two cases stamens are replaced by pistils and in two cases stamens are replaced by petals. In the k mutant, the change is within the petal whorl itself and the two wing petals express keel-like traits.