Arabidopsis superman (sup, also referred to as floral mutant10) mutants have previously been shown to have flowers with supernumerary stamens and reduced carpels as a result of ectopic expression of the floral homeotic gene APETALA3 (AP3). Here, we report that sup mutations also cause specific alterations in ovule development. Growth of the outer integument of wild-type ovules occurs almost exclusively on the abaxial side of the ovule, resulting in a bilaterally symmetrical hoodlike structure. In contrast, the outer integument of sup mutant ovules grows equally on all sides of the ovule, resulting in a nearly radially symmetrical tubular shape. Thus, one role of SUP is to suppress growth of the outer integument on the adaxial side of the ovule. Genetic analyses showed that the effects of sup mutations on ovule development are independent of the presence or absence of AP3 activity. Thus, SUP acts through different mechanisms in its early role in ensuring proper determination of carpel identity and in its later role in asymmetric suppression of outer integument growth.

Arabidopsis superman (sup, also referred to as floral mutant70) mutants have previously been shown to have flowers with supernumerary stamens and reduced carpels as a result of ectopic expression of the floral homeotic gene APETALA3 (AP3). Here, we report that sup mutations also cause specific alterations in ovule development. Growth of the outer integument of wild-type ovules occurs almost exclusively on the abaxial side of the ovule, resulting in a bilaterally symmetrical hoodlike structure. In contrast, the outer integument of sup mutant ovules grows equally on all sides of the ovule, resulting in a nearly radially symmetrical tubular shape. Thus, one role of SUP is to suppress growth of the outer integument on the adaxial side of the ovule. Genetic analyses showed that the effects of sup mutations on ovule development are independent of the presence or absence of AP3 activity. Thus, SUP acts through different mechanisms in its early role in ensuring proper determination of carpel identity and in its later role in asymmetric suppression of outer integument growth.

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The INNER NO OUTER (INO) and AINTEGUMENTA (ANT) genes are essential for ovule integument development in Arabidopsis thaliana. Ovules of ino mutants initiate two integument primordia, but the outer integument primordium forms on the opposite side of the ovule from the normal location and undergoes no further development. The inner integument appears to develop normally, resulting in erect, unitegmic ovules that resemble those of gymnosperms. ino plants are partially fertile and produce seeds with altered surface topography, demonstrating a lineage dependence in development of the testa. ant mutations affect initiation of both integuments. The strongest of five new ant alleles we have isolated produces ovules that lack integuments and fail to complete megasporogenesis. ant mutations also affect flower development, resulting in narrow petals and the absence of one or both lateral stamens. Characterization of double mutants between ant, ino and other mutations affecting ovule development has enabled the construction of a model for genetic control of ovule development. This model proposes parallel independent regulatory pathways for a number of aspects of this process, a dependence on the presence of an inner integument for development of the embryo sac, and the existence of additional genes regulating ovule development.

Shoots of the lazy-2 (lz-2) gravitropic mutant of tomato (Lyco- There are severa1 reports in the literature of an interaction between light and the gravity response of higher plants. The clearest and best-studied example of such an interaction is the phytochrome-regulated switch from a diagravitropic growth habit of dark-grown roots of the Merit variety of com to a positive gravitropic growth habit after R irradiation (Mandoli et al., 1984). The same response has been reported in other varieties of corn (Johnson et al., 1991) and in Convolvulus arvensis (Tepfer and Bonnett, 1972). Feldman and Briggs (1987) demonstrated that the phytochrome response of Merit was a VLFR.Data on the interactions between phytochrome and the gravitropic response of shoots are conflicting. Kang and Burg (1972) reported a stimulation of the gravitropic response of peas after R irradiation. On the other hand, there are reports of R irradiation resulting in an inhibition of gravitropic curvature in peas (McArthur and Briggs, 1979) and watercress (Hart and MacDonald, 1980). Another study (Britz and Galston, 1982) concluded that R pretreatment enhanced gravity perception but that, ultimately, the kinetics and extent of the gravitropic response were identical in R-irradiated and darkgrown control plants. Thus, although it appears that phytochrome can modulate the shoot gravitropic response in some plants, the exact nature of the light/gravity interaction is unclear.Here we report on the 12-2 gravitropic mutant of tomato (Lycopersicon esculentum Mill.), for which exposure to light results in a specific reversal in the direction of the shoot gravitropic response. In the dark, 12-2 plants exhibit a typical gravitropic response: differential growth leads to an upward reorientation of the shoot apex and a downward reorientation of the root apex. However, when plants canying the 22-2 mutation are placed in the light, the stem response is reversed so that the shoot apex becomes reoriented downward (Roberts, 1987) but the root response is unchanged (Gaiser and Lomax, 1992). If the 12-2 plants are retumed to the dark, they revert to the wild-type phenotype, exhibiting upward reorientation of the shoot apex (Roberts, 1987).We have previously shown that light-induced downward curvature in 12-2 is a directed response to gravity rather than simply a failure to grow upright (Gaiser and Lomax, 1992). Shoots of 12-2 seedlings apparently sense the gravitropic vector normally, but respond in the opposite direction than do wild-type plants. 12-2 seedlings show no variation from wild type in their elongation response to exogenous IAA and are able to carry out B-mediated phototropic curvature in the proper direction (Gaiser and Lomax, 1992).Light-induced downward growth of 12-2 stems is enhanced by R as compared with W (Gaiser and Lomax, 1992;Roberts and Gilbert, 1992). We demonstrate here that this downward growth is regulated by the photoreceptor phytochrome. Our data from experiments with dark-grown 12-2 seedlings suggest that (a) whereas R is capable of ind...