Stamenless, a tomato mutant with homeotic conversions in petals and stamens

A tomato (Lycopersicon esculentum Mill.) monogenic semidominant mutation, s tamenless (sl), which results in homeotic conversions in two adjacent flora l whorls, was studied. When grown at standard temperature, flowers of sl/sl plants showed sepaloid petals in the second whorl and strong transformatio n of stamens to carpels in whorl three. These transformed carpels were fuse d with each other and with the genuine carpels in the fourth whorl to form a unique gynoecium. The mutation is semidominant since heterozygous plants showed a phenotype intermediate between that of the wild type (WT) and that of homozygous mutant plants, with nearly WT petals but with feminized stam ens bearing naked ovules on the base of their adaxial face. The initiation and position of organ primordia in sl/sl flowers were not altered when comp ared with WT primordia although development of organ primordia in the secon d and third whorls deviated from WT at an early stage as observed by scanni ng electron microscopy. The mutant phenotype is temperature sensitive and w hen sl/sl plants were cultured at low temperature, the morphology of some f lowers resembled that of the WT. This reversion of the mutant phenotype is also induced by treatment of young sl/sl plants with gibberellic acid, prov iding evidence that gibberellin synthesis or sensitivity could mediate the effect of low temperature on the mutant phenotype. Southern blot analyses u sing a Deficiens-homologous gene from Solanum tuberosum as a probe showed a restriction-fragment-length polymorphism (RFLP) linked to the sl mutation. This result indicates that the mutation affects a Deficiens-like gene that controls the identity of petals and stamens.