Thermoperiodic stem elongation involves transcriptional regulation of gibberellin deactivation in pea - PubMed (original) (raw)

Thermoperiodic stem elongation involves transcriptional regulation of gibberellin deactivation in pea

Jon Anders Stavang et al. Plant Physiol. 2005 Aug.

Abstract

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 degrees C. A day temperature/night temperature combination of 13 degrees C/21 degrees C reduced stem elongation after 12 d by 30% as compared to 21 degrees C/13 degrees 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 degrees C/21 degrees C (compared to 21 degrees C/13 degrees 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.

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Figures

Figure 1.

Simplified 13-hydroxylation pathway of GA biosynthesis in vegetative tissue of pea. The enzymes that are cloned and characterized in pea are underlined. Corresponding mutants are given in parentheses. Diurnal steady-state expression of the characterized genes in response to diurnal temperature alternations has been investigated in this study.

Figure 2.

Effect of different DT/NT combinations on the stem elongation rate of pea. Seedlings were grown for 6 d at constant temperature of 17°C prior to start of DIF treatments. The temperature regimes were negative DIF, 13°C/21°C; zero DIF, 17°C/17°C; and positive DIF, 21°C/13°C. Results are average of 18 plants ±

Figure 3.

Diurnal growth rhythms in pea as affected by different DT/NT combinations. Seedlings were grown for 6 d at constant temperature of 17°C prior to start of DIF treatments. The temperature regimes were negative DIF, 13°C/21°C; zero DIF, 17°C/17°C; and positive DIF, 21°C/13°C. Results are average of six individual plants and represent growth rhythms at day 12 to day 14 after start of DIF treatments.

Figure 4.

Effects of different DT/NT combinations on expression of late-stage GA metabolism genes in pea. Diurnal variation of PsGA20ox1, PsGA3ox1, PsGA2ox1, and PsGA2ox2 mRNA levels after 12 d of negative DIF, zero DIF, and positive DIF treatment. The mRNA levels are normalized to mRNA of actin. Results are average of two independent experiments ±

. In each independent experiment, the sample at each time point consisted of 18 plants. Note that the scale is logarithmic.

Figure 5.

Effects of different DT/NT combinations on expression of GA biosynthesis genes in pea. Diurnal variation of LS, LH, and NA mRNA levels after 12 d of negative DIF, zero DIF, and positive DIF treatment. The mRNA levels are normalized to mRNA of actin. Results are average of two independent experiments ±

. In each independent experiment, the sample at each time point consisted of 18 plants. Note that the scale is logarithmic and different from Figure 4.

Figure 6.

Effects of different DT/NT combinations on GA levels. Comparisons of diurnal variation of GA levels in pea after 12 d of negative, zero, and positive DIF treatments. Results are average of two independent experiments ±

, except from the third and sixth measurement in each series, where n = 1. In each independent experiment, the sample at each time point consisted of 18 plants.

Figure 7.

Effects of different DT/NT combinations on stem elongation of the sln mutant. Seedlings were grown for 6 d at constant temperature of 17°C prior to the start of DIF treatments. Negative DIF, 13°C/21°C; zero DIF, 17°C/17°C; and positive DIF, 21°C/13°C. Results are average ±

of 12 plants.

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Thermoperiodic stem elongation involves transcriptional regulation of gibberellin deactivation in pea - PubMed (original) (raw)