DOSAGE EFFECTS OF THE LANCEOLATE GENE IN TOMATO

Abstract

In contrast to the odd‐pinnately compound leaf of the normal (+/+) tomato plant (Lycopersicon esculentum), the single‐gene mutant lanceolate (La/+) generally has a simple leaf. Lanceolate plants, also, have small fruits and flowers, weak apical dominance, and exhibit variation in the position and fusion of cotyledons. Homozygous mutants (La/La) appear in 3 different phenotypes, 1 of which, narrow, has narrow simple leaves, sterile inflorescences, and extremely weak apical dominance. The other 2, modified, and reduced, lack an organized shoot. After selfing La/ + plants for 9 generations, autotetraploids were produced with the aid of colchicine. In addition, several triploid plants arose spontaneously. The study of diploid, triploid, and tetraploid material with various proportions of the La allele revealed in many characters a graded series as a function of the La dosage. With increasing La dose, there was a gradual reduction in: (1) total leaf length; (2) the number and size of primary and secondary lateral leaflets; (3) the number and size of marginal lobes of the terminal leaflet, associated with an increase in the proportional length of the terminal leaflet. Many leaves were found with the basal lobes of the terminal leaflet resembling incompletely separated lateral leaflets. The differences in leaf shape between different genotypes came about before the leaf primordium was 3 mm long. There was a progressive delay in the initiation of lateral primordia with increasing La dosage. It is proposed that the gradual changes from compound to simple leaves with increasing La dosage are produced by successively greater restrictions of meristematic activity after the terminal leaflet is formed. With increasing proportion of La alleles, the reproductive structures showed: (1) a decrease in the number of flowers per inflorescence; (2) a decrease in the length of the sepals; (3) an increase in the proportion of flowers with dialytic anthers. Dialytic anthers had narrow adaxial lobes and were frequently twisted along their main axes. The common denominator for most trends affected by the La allele seems to be a general reduction of growth, but more so in lateral than in longitudinal growth. Histological data suggest that the reduction in lateral growth is mainly brought about by a reduction of cell division in lateral meristems.