Light effects on endogenous levels of gibberellins in photoblastic lettuce seeds

Abstract

Gibberellin A 1 (GA1), 3-epi-GAl, GA17, GA19, GA2o, and GA77 were identified by Kovats retention indices and full-scan mass spectra from gas chromatography-mass spectrometry analysis of a purified extract of mature seeds of photoblastic lettuce (Lactuca sativa L. cv. Grand Rapids). Non-13-hydroxylated GAs such as GA 4 and GA 9 were not detected even by highly sensitive radioimmunoassay. These results show that the major biosyn-

Photomorphogenesis and phyfohormones

“…Several studies have examined the relationships between light and GAs, in these processes, and provided strong, but somewhat contrasting, arguments for an involvement of GAs in the light-signalling pathway. Toyomasu et al (1993) described R-inducible, FR-reversible induction of GAl accumulation in lettuce seeds, which correlates with the R/FR reversible induction of germination. These results led to the hypothesis of a sequential relationship between R treatment, active GAl gibberellin accumulation and germination induction (the ABA inactivation described previously would be a consequence of GAl accumulation).…”

Phytochrome Regulates Gibberellin Biosynthesis during Germination of Photoblastic Lettuce Seeds

“…Furthermore, endogenous levels of GA 20 and its direct precursor, GA 19 ( Fig. 1), are much higher than that of GA 1 and are not greatly affected by light treatment (Toyomasu et al, 1993). These results suggest that conversion of GA 20 to GA 1 is a likely key step that is regulated by phytochrome in GA biosynthesis.…”

“…This early 13-hydroxylation pathway ( Fig. 1) has been shown to be present in lettuce seeds (Toyomasu et al, 1993).…”

“…The germination-inducing activity of GA 20 (Fig. 1), the immediate precursor of GA 1 , is less than one-thousandth that of GA 1 in the dark (Toyomasu et al, 1993). Furthermore, endogenous levels of GA 20 and its direct precursor, GA 19 ( Fig.…”

“…1) is an endogenous bioactive GA in lettuce seed: GA 1 was identified by full-scan GC-MS analysis, and treatment with 10 Ϫ6 m GA 1 induced germination in the dark (Toyomasu et al, 1993). The endogenous content of GA 1 increased after red-light treatment, and this effect was canceled by subsequent far-red-light treatment (Toyomasu et al, 1993). Here we have focused on the mechanism by which GA 1 levels increase as a result of red-light treatment.…”