Endogenous gibberellin A₁ levels control thermoperiodic stem elongation in Pisum sativum

Abstract

Gibberellin (GA) is believed to be involved in thermoperiodic stem elongation. With this in mind, we studied the correlation between gibberellin A1 (GA1) levels and stem elongation affected by alternating day (DT) and night temperature (NT) in 5 genotypes of Pisum sativum differing in their degree of dwarfism. The endogenous GA content in the tissue of two of the genotypes was determined by combined gas chromatography and mass spectrometry. The wild genotype developed 40 to 50% shorter stems and internodes under a low DT and high NT combination (negative difference [DIF] between DT and NT, DT/NT 15.5/21.5 or 14/24°C) than under the opposite regime of high DT and low NT (positive DIF, DT/NT 22.5/16.5 or 24/14°C). The GA biosynthetic mutants ls and le, and the auxin and brassinosteroid mutant lkb responded in a similar way, but not as strongly as the wild type. The stem length of the GA‐insensitive slender mutant (la crys) was reduced by only 8% under negative compared to positive DIF. In the wild type endogenous GA levels decreased by 60% from positive to negative DIF in the upper part of the stem. Further, there was a corresponding decrease in the levels of precursors to GA1, i.e. GA53, GA44, GA19 and GA20, while 2β‐hydroxylated GA20 and GA1, GA29 and GA8, respectively, were unaffected by DIF. A similar increase in the ratios of GA29 to GA20 and GA8 to GA1 from positive to negative DIF was seen in the stem tissue of the le mutant as in the wild type. The temperature regimes affected the levels of GA1 and its precursors in combined leaf and petiole samples and in the shoot tip in a similar manner as in the stem tissue. However, the different temperature regimes did not affect the ratio of GA8/GA1 in the shoot tip. The results indicate that altered stem elongation of the pea plants in response to diurnal temperature alternations may be mediated by changes in endogenous levels of GA1. The GA1 levels may be controlled by an effect of DIF on both biosynthetic and inactivation steps.

The highs and lows of plant life: temperature and light interactions in development

“…The enhanced inhibition of internode elongation correlated with a marked reduction in GA1 levels in these seedlings suggesting that regulation of GA biosynthesis is a major control point for this response. Further analysis showed that pea plants dwarfed by paclobutrazol had a higher rate of 2β-hydroxylation of GA1, leading to lower levels of endogenous GA1 and shorter stems and internodes under negative DIF (Grindal, 1998a). Together these results indicate that, for pea at least, thermoperiodic responses are mediated by changes in the endogenous levels of GA1, via GA biosynthetic and inactivation steps.…”

“…Particularly in the horticultural industry, plant morphology is routinely manipulated by altering day length (photoperiod) and temperature of the growth conditions. Plant development can also be influenced by the topical application of hormones, for example, GA, is known to control stem elongation and is often applied to control crop morphology (Grindal et al, 1998a). However, as chemical applications are becoming increasingly less acceptable for use in a commercial environment, thermoperiodic manipulation, i.e.…”

“…Auxin levels increase as ambient temperature rises, therefore, auxin-mediated effects on elongation growth are highly temperature-dependent (Gray et al, 1998). Furthermore, GA biosythesis and signaling have been shown to be altered in plants exposed to differing day time and night temperatures (Myster and Moe, 1995;Grindal et al, 1998a;1998b). This has a marked impact on plant stature as adjustment of this pathway can have considerable affects on stem elongation.…”

Thermoperiodic Stem Elongation Involves Transcriptional Regulation of Gibberellin Deactivation in Pea

“…Jensen et al (1996) reported higher levels of GA 1 in Campanula isophylla grown under positive DIF than negative DIF. It has been suggested that altered stem elongation of pea (Pisum sativum) plants in response to diurnal temperature alternations may be mediated by changes in the endogenous levels of GA 1 (Grindal et al, 1998a). GA 1 levels were found reduced by almost 60% under a temperature regime with low DT and high NT compared to a temperature regime with high DT and 1 This work was supported by the Norwegian Research Council (grant no.…”

“…GA 1 levels were found reduced by almost 60% under a temperature regime with low DT and high NT compared to a temperature regime with high DT and low NT, with both temperature treatments having the same daily average temperature. The study of GA metabolites suggested that thermoperiodicity could affect both biosynthesis and inactivation steps of GA 1 (Grindal et al, 1998a). Furthermore, based on experiments with GA biosynthesis inhibitors and applications of GA 1 and GA 3 (GA 3 is protected from deactivation by enzymatic 2-oxidation), it has been hypothesized that reduced GA 1 levels in stem tissue under negative DIF are caused by enhanced inactivation of GA 1 by 2-oxidation in pea (Grindal et al, 1998b).…”