THE EFFECTS OF SHAM AND CN ON GERMINATION OF LETTUCE SEEDS

CAROLYN ANNE BROOKS, Purdue University

Abstract

Inhibitors of the CN-sensitive respiratory pathway have an unexpected ability to stimulate germination of dormant seeds. This phenomenon has led to speculation regarding the role of oxidative metabolism in the dormancy-breaking mechanism. As a means of gaining insight into the mechanism of dormancy breaking, the effect of respiratory inhibitors on germination and potentiation of dormant lettuce seeds was characterized, and the morphological site of action determined. Salicylhydroxamic acid (SHAM) potentiated germination when present for either the first 8 or 24 hours of a 72 hour incubation, with 24 hours stimulating germination more. However, the continuous presence of SHAM during the 72 hour period when germination would normally occur, did not stimulate germination. There was an interaction between respiratory inhibitors. Continuous treatment of seeds with SHAM + CN('-) during the 72 hour incubation stimulated germination as much as did 8 hours of pretreatment with SHAM alone. SHAM stimulated germination maximally at pH 4. Oxygen was required for SHAM or SHAM + CN('-) to potentiate germination. Studies were conducted to determine whether SHAM stimulated embryo growth potential or induced weakening of the endosperm. Radicle growth of embryos from seeds pretreated with SHAM for 24 hours was not different from controls thus indicating that SHAM had no effect on embryo growth potential. SHAM weakened endosperm strength in the micropylar region, but not in the lateral cotyledonary region. SHAM also caused weakening in the micropylar region of isolated endosperms. In summary, the ability of SHAM and CN to stimulate germination is influenced by timing and pH of chemical treatment. The requirement of O(,2) during SHAM or SHAM + CN('-)-induced potentiation supports the hypothesis that a shift in oxidative metabolism is involved in the dormancy mechanism. Studies on the effect of SHAM on the embryo and endosperm indicate that SHAM specifically weakens the endosperm in the micropylar region, thereby reducing the restriction to growth imposed by the endosperm and allowing germination to proceed.

Degree

Ph.D.

Subject Area

Botany

COinS