A GENETIC SYNDROME AFFECTING LEAF DEVELOPMENT IN PISUM

A recessive foliage mutant of Pisum, designated ‘sinuate leaf’ (sil), was found to have two distinct forms of expression, depending on the background genotype. In an af/af background—wherein leaflets are converted to tendrils—sil/sil plants had adventitious tendrils arising from clefts in the distal portion of the stipule. These adventitious tendrils were morphologically modified, just as were the true tendrils on the same plant, by different allelic combinations at the tl locus. In the standard Af background, sil/sil plants had neither incised stipules nor adventitious tendrils, although they did have undulated and somewhat distorted leaflets and stipules. Because mutant expression was variable in an Af background, classification of segregating populations was uncertain. This uncertainty was removed by taking advantange of pleiotropic effects exerted by sil in the presence of one of the wax mutants, wlo, wb, or wsp. Homozygous wlo plants ordinarily have uniformly waxy stipule surfaces, but when the plants were also homozygous for sil the stipule tips were waxless. Conversely, wb/wb and wsp/wsp plants ordinarily have uniformly waxless stipules, but when wb/wb or wsp/wsp plants were also homozygous recessive for sil the stipule tips were waxy. However, sil had no observable effects of any kind on the stipule tips of plants with stipules reduced in size by the action of st/st. By their individual and combined effects, the foliage mutants used in this study revealed developmental relationships among leaf parts not otherwise evident in non-mutant plants.