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DEVELOPMENT AND HORMONE ACTION

Thermoperiodic Stem Elongation Involves Transcriptional Regulation of Gibberellin Deactivation in Pea¹

Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, N1432 Ås, Norway (J.A.S., S.E.L., R.M., J.E.O.); and Department of Biology, University of Tromsø, N9037 Tromsø, Norway (B.L., A.E.)

The physiological basis of thermoperiodic stem elongation is as yet poorly understood. Thermoperiodic control of gibberellin (GA) metabolism has been suggested as an underlying mechanism. We have investigated the influence of different day and night temperature combinations on GA levels, and diurnal steady-state expression of genes involved in GA biosynthesis (LS, LH, NA, PSGA20ox1, and PsGA3ox1) and GA deactivation (PsGA2ox1 and PsGA2ox2), and related this to diurnal stem elongation in pea (Pisum sativum L. cv Torsdag). The plants were grown under a 12-h light period with an average temperature of 17°C. A day temperature/night temperature combination of 13°C/21°C reduced stem elongation after 12 d by 30% as compared to 21°C/13°C. This was correlated with a 55% reduction of GA₁. Although plant height correlated with GA₁ content, there was no correlation between diurnal growth rhythms and GA₁ content. NA, PsGA20ox1, and PsGA2ox2 showed diurnal rhythms of expression. PsGA2ox2 was up-regulated in 13°C/21°C (compared to 21°C/13°C), at certain time points, by up to 19-fold. Relative to PsGA2ox2, the expression of LS, LH, NA, PSGA20ox1, PsGA3ox1, and PsGA2ox1 was not or only slightly affected by the different temperature treatments. The sln mutant having a nonfunctional PsGA2ox1 gene product showed the same relative stem elongation response to temperature as the wild type. This supports the importance of PsGA2ox2 in mediating thermoperiodic stem elongation responses in pea. We present evidence for an important role of GA catabolism in thermoperiodic effect on stem elongation and conclude that PsGA2ox2 is the main mediator of this effect in pea.

² Recently passed away.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.063149.

^* Corresponding author; e-mail jorunn.olsen{at}umb.no; fax 47–64–94–78–02.

Received March 22, 2005; returned for revision May 21, 2005; accepted May 31, 2005.

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