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Abstract
Summary We tested the hypothesis that GA3, like red light (Zhang et al., 1994), enhances activity of a Ca-calmodulin- dependent isozyme of NAD kinase and causes lower levels of NAD+ and higher levels of NADP+ in half-seeds of Grand Rapids lettuce (Lactuca sativa L.). Half-seeds containing hypocotyl/radicle sections were imbibed for 1 h in H2O or 560 μM GA3, treated with far-red light, then kept in darkness for various times up to 17 h. NAD kinase activity from crude extracts was measured, and activities of a partially purified Ca-calmodulin-independent and a Ca-calmodulin-dependent isozyme were determined. In all experiments kinase activity increased with time after treatment. GA3 enhanced activity in crude extracts and of the Ca-calmodulin-dependent isozyme 30 min after irradiation, but it had no effect on the Ca-calmodulin-independent isozyme at any time period. GA3 caused increased amounts of NADP+ and NADPH and decreased amounts of NAD+, all effects significant 30 min after irradiation. Although these results might be explained partially by GA3-enhanced formation of Ca-calmodulin in vivo, it appears that GA3 additionally or alternatively induced formation of the Ca-calmodulin-dependent isozyme of NAD kinase. These effects of GA3 are similar to those of red light, and they support the hypothesis that Pfr somehow promotes synthesis of a gibberellin as it overcomes photodormancy of the seeds.
Published Version
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