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 eve nts in the inflorescence, flower and floral organ meristems. WT peas h ave a late flowering, quantitative long day habit. The photoperiod res ponse results from production of a flower inhibitor under short days. The phytochrome system controls inhibitor production via two mechanism s - a red (R) activated switch and a far-red (FR) mechanism involving extended exposure. The phyB deficient mutant, 1v, is early flowering u nder long or short days. Thus the iv mutation may prevent R activation of the inhibitor synthesis pathway. The long term FR mechanism probab ly involves phyA and we suggest a phyA defective pen would be unable t o down regulate inhibitor synthesis and would thus flower late in long or short days. The 1w mutant shows delayed flower initiation and enha nced response to photoperiod, traits indicative of an enlarged respons e to phyB. The phytochrome chromophore deficient mutant, pcd1, shows a small flowering delay render all photoperiods. Three genes Sn, Dne an d Ppd act synthesis pathway and two genes E and Hr control ontogenetic expression of the system. Evidence of an additional gene which may re gulate inhibitor synthesis has recently been obtained following identi fication of a dominant day neutral mutant, A23. The primary action of the graft-transmissible inhibitor may be to direct assimilate flow. Th e 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 (I-1) inflorescence meristem and V eg2 identity of the lateral (I-2) inflorescence meristem. It is yet cl ear whether Veg1 determines I-1 or I-2 identity. Mutants veg1 and veg2 -1 never flower Five mutants pim, A324, uni, M175 and leflo show flora l 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 a nd in two cases stamens are replaced by petals. In the k mutant, the c hange is within the petal whorl itself and the two wing petals express keel-lihe traits.