Phytochrome A (phyA) is an important photoreceptor controlling many processes throughout the plant life cycle. It is unique within the phytochrome family for its ability to mediate photomorphogenic responses to continuous far-red light and for the strong photocontrol of its transcript level and protein stability. Here we describe a dominant mutant of garden pea (Pisum sativum) that displays dramatically enhanced responses to light, early photoperiod-independent flowering, and impaired photodestruction of phyA. The mutant carries a single base substitution in the PHYA gene that is genetically inseparable from the mutant phenotype. This substitution is predicted to direct the replacement of a conserved Ala in an N-terminal region of PHYA that is highly divergent between phyA and other phytochromes. This result identifies a region of the phyA photoreceptor molecule that may play an important role in its fate after photoconversion.

control plants. To investigate whether the accumulation ofThe lh-2 mutation in garden pea (Pisum sati7um L.) blocks an ABA is partly responsible for causing the observed seed early step in the gibberellin (GA) biosynthesis pathway, the abortion in lh-2 plants, we constructed a double mutant three-step oxidation of ent-kaurene to ent-kaurenoic acid. As between the lh-2 allele and wil. The wil mutation blocks ABA a result, only low levels of GAs, including the bioactive GA 1 , biosynthesis, and reduces ABA levels in young seeds by 10-are found in shoots and seeds of lh-2 plants. Mutant plants are dwarf in stature, and show increased seed abortion and fold. Introduction of the wil mutation reduces the endogenous ABA levels in young lh-2 seeds, but fails to rescue the seeds decreased seed weight, compared with seeds of the tall wildfrom abortion. This indicates that the effects of lh-2 on seed type (WT) progenitor (cv. Torsdag). The aberrant seed develdevelopment are not mediated through increased ABA levels, opment of lh-2 plants is associated with reduced levels of GA 1 and GA 3 , and with an accumulation of abscisic acid (ABA) in and is consistent with previous evidence that GAs are the controlling factor underlying the lh-2 seed phenotype in pea. young seeds (pre-contact point). This ABA accumulation is typically 3-to 4-fold, and can be up to 6-fold, compared with

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The veg1 (vegetative) mutant in pea (Pisum sativum L.) does not flower under any circumstances and gi (gigas) mutants remain vegetative under certain conditions. gi plants are deficient in production of floral stimulus, whereas veg1 plants lack a response to floral stimulus. During long days in particular, these non-flowering mutant plants eventually enter a stable compact phase characterised by a large reduction in internode length, small leaves and growth of lateral shoots from the upper-stem (aerial) nodes. The first-order laterals in turn produce second-order laterals and so on in a reiterative pattern. The apical bud is reduced in size but continues active growth. Endogenous hormone measurements and gibberellin application studies with gi-1, gi-2 and veg1 plants indicate that a reduction in gibberellin and perhaps indole-3-acetic acid level may account, at least partially, for the compact aerial shoot phenotype. In the gi-1 mutant, the compact phenotype is rescued by transfer from a 24- to an 8-h photoperiod. We propose that in plants where flowering is prevented by a lack of floral stimulus or an inability to respond, the large reduction in photoperiod gene activity during long days may lead to a reduction in apical sink strength that is manifest in an altered hormone profile and weak apical dominance.