Effect of Light Source and Quality on Endogenous Gibberellin Level and GA₃ Response of Petunia (Petunia × hybrida Vilm.)

Abstract

Petunia (Petunia X hybrida Vilm.) 'Baccarat Blue' under high pressure sodium lamp (HPS) exhibits, dwarfism compared with one grown under a daylight type metal halide lamp (MH). The role of gibberellin (GA) in this growth change, caused by artificial lighting was investigated. The amounts of GA₂₀ and GA₁ were lower in petunia grown under HPS than those under MH, but, the levels of GA₁₉ were similar in both treatments. Plant height of petunia was decreased by treatment with uniconazol, but the difference in plant height between treatments was small. GA₃ application promoted stem elongation of uniconazol-treated petunia; the magnitude of stem elongation was independent of light source. These results indicate that dwarfism in petunia under HPS is caused by lower GA₂₀ and GA₁ contents, but not by GA sensitivity. The GA biosynthesis step of GA₁₉ to GA₂₀ may be affected by the light quality of these lamps.