Floral mutants in tomato: development, physiology, and evolutionary implications

Developmental and experimental studies on two floral mutants of tomato (Lycopersicon esculentum) are presented. These studies have provided insights into the gene-regulated physiological, biochemical, and structural processes that affect flower morphology. In the stamenless-2 (sl-2/sl-2) mutant, plant growth regulators and temperature conditions affect the development of stamens, and these effects are mediated through changes in proteins, including some specific enzymes. Stamen primordia can be induced to form either normal stamens or carpels, which suggests the possibility of another mechanism by which unisexuality may have evolved. In the solanifolia (sf/sf) mutant, the nonfusion of stamens and carpels is associated with an increase in the size of the apex and the number of organs. The fusion of these organs is also affected by plant growth regulators and temperature conditions. It is proposed that during the course of evolution plants with small floral apices that produce few stamens and carpels were selected and that the reduction in apex size was achieved by mutations that affect endogenous plant growth regulators. Key words: floral mutants, Lycopersicon esculentum, plant growth regulators, temperature, tomato, evolution.