Elongation of the First Internode of the Pea Seedling during Etiolation

In the present study, 40 lines of peas, Pisum sativum L., from the Weibullsholm collection were examined for elongation response of the first internode to growth in soil, sand, or in darkness in air. The results obtained establish that appearance of the first (lowest) node of the epicotyl at the surface of soil was usual in only a few of the lines tested (L25, L1088, L1570). By contrast, appearance of the first node at the surface of sand as a result of enhancement of first internode extension occurred in 80% of the lines tested. In many lines, extension in sand or soil was more than in darkness in air, a surprising observation given that the known response of the pea epicotyl to pressure is to produce the extension inhibitor, ethylene. Results of two crosses, one of tallxdwarf and one of tallxtall, point to the conclusion that the Le/le locus exercises only partial control over first internode extension and that other, as yet unknown, loci are implicated.