Changes in Gibberellin A1 Levels and Response during De-Etiolation of Pea Seedlings

Abstract

The level of gibberellin A1 (GA1) in shoots of pea (Pisum sativum) dropped rapidly during the first 24 h of de-etiolation. The level then increased between 1 and 5 d after transfer to white light. Comparison of the metabolism of [13C3H] GA20 suggested that the initial drop in GA1 after transfer is mediated by a light-induced increase in the 2β-hydroxylation of GA1 to GA8. A comparison of the elongation response to GA1 at early and late stages of de-etiolation provided strong evidence for a change in GA1 response during de-etiolation, coinciding with the return of GA1 levels to the normal, homeostatic levels found in light- and dark-grown plants. The emerging picture of the control of shoot elongation by light involves an initial inhibition of elongation by a light-induced decrease in GA1 levels, with continued inhibition mediated by a light-induced change in the plant's response to the endogenous level of GA1. Hence the plant uses a change in hormone level to respond to a change in the environment, but over time, homeostasis returns the level of the hormone to normal once the ongoing change in environment is accommodated by a change in the response of the plant to the hormone.

DELLAs Contribute to Plant Photomorphogenesis

“…Previous studies have shown GAs promote skotomorphogenetic growth of Arabidopsis and pea (Pisum sativum) seedlings grown in darkness (Cowling and Harberd, 1999;Alabadí et al, 2004). Furthermore, a rapid decrease in the levels of bioactive GA 1 has been observed upon transfer of etiolated pea seedlings into light (Ait-ali et al, 1999;Gil and García-Martinez, 2000;O'Neill et al, 2000). Here we have shown that Arabidopsis GA metabolism gene transcript levels change rapidly in response to changes in the light environment.…”

Light Regulation of Gibberellin Biosynthesis in Pea Is Mediated through the COP1/HY5 Pathway

“…Effects of light on levels of bioactive GA were first reported in lettuce (Lactuca sativa) (Toyomasu et al, 1992) and have been firmly established for GA 1 in pea (Ait-Ali et al, 1999;Gil and García-Martinez, 2000;O'Neill et al, 2000). Similar changes have also been inferred to occur in Arabidopsis from measurements of GA biosynthesis gene expression (Achard et al, 2007;Alabadí et al, 2008), and this has recently been confirmed by direct measurements of GA 4 Symons et al, 2008).…”

“…Transfer of etiolated pea seedlings to light is rapidly followed by a dramatic decrease in the content of the active gibberellin GA 1 (O'Neill et al, 2000;Symons and Reid, 2003), and we next tested whether LONG1 was also required for this response. Figure 5A shows that when 7-d-old wild-type seedlings were transferred to continuous W for 4 h, the GA 1 content of the apical portion (including the apical bud and 20 mm of expanding internode) dropped by more than 95%, consistent with the recent report of Symons et al, (2008).…”

“…However, the clearest example of light-regulated hormone biosynthesis during deetiolation comes from pea (Pisum sativum), where transfer of etiolated pea seedlings to light induces a rapid drop in levels of the active GA (GA 1 ), to <10% of dark levels within 4 h (Ait-Ali et al, 1999;Gil and García-Martinez, 2000;O'Neill et al, 2000;Symons and Reid, 2003). This drop is associated with changes in transcript levels of GA biosynthesis genes and depends on the activity of the phyA and cry1 photoreceptors (Reid et al, 2002;Foo et al, 2006).…”

Synergistic Substrate Inhibition of ent-Copalyl Diphosphate Synthase: A Potential Feed-Forward Inhibition Mechanism Limiting Gibberellin Metabolism

“…Genes in the GA metabolic pathway are quickly upregulated during germination (Yamaguchi et al, 2001) and a high level of GA is maintained until seedlings reach light, which triggers a drop in the level of bioactive GA (Ait-Ali et al, 1999;Gil and Garcia-Martinez, 2000;O'Neill et al, 2000;Reid et al, 2002;Symons and Reid, 2003). This initial drop in active GA levels is needed for deetiolation (i.e.…”