GA Metabolic Pathways Research Articles

Isolation and characterization of a novel mutation that confers gibberellin-sensitive dwarfism inArabidopsis thaliana

Gibberellins (GAs) regulate diverse aspects of plant growth and development. Despite extensive analysis of the GA-metabolic pathway, only a few genes have been identified as regulatory components of GA metabolism. In searching for those genes, we screened and isolated a novel dominant mutant,GA-sensitive dwarf1-1D (gsd1-1D), fromArabidopsis thaliana. This mutant exhibited the characteristic phenotypes of GA-deficient mutants, including semi-dwarfism, dark-green leaves, late-flowering, and reduced fertility. Exogenously applied GA rescued thegsd1-1D mutant phenotypes, implying that this phenomenon was likely due to a reduced level of GA. Likewise, transcripts of GA-responsive genes were affected by thisgsd1-1D mutation, which genetic analysis showed to be semi-dominant and monogenic. Chromosomal mapping of theGSD1 locus indicated that it resides on the middle of Chromosome 3, where no loci related to GA metabolism exist. These results suggest that theGSD1 locus encodes a novel regulatory component controlling the bioactive GA level inA. thaliana.

Identification of endogenous gibberellins, and metabolism of tritiated and deuterated GA4, GA9 and GA20, in Scots pine (Pinus sylvestris) shoots

The application of gibberellin A4/7 (GA4/7) to the stem of previous‐year (1‐year‐old) terminal shoots of Scots pine (Pinus sylvestris) seedlings has been observed to stimulate cambial growth locally, as well as at a distance in the distal current‐year terminal shoot, but the distribution and metabolic fate of the applied GA4/7, as well as the pathway of endogenous GA biosynthesis in this species, has not been investigated. As a first step, we analysed for endogenous GAs and monitored the transport and metabolism of labelled GAs 4, 9 and 20. Endogenous GAs from the elongating current‐year terminal shoot of 2‐year‐old seedlings were purified by column chromatography and high‐performance liquid chromatography and analysed by combined gas chromatography‐mass spectrometry (GC‐MS). GAs 1, 3, 4, 9, 12 and 20 were identified in the stem, and GAs 1, 3 and 4 in the needles, by full‐scan mass spectrometry (GAs 1, 3, 4, 9 and 12) or selected‐ion monitoring (GA20) and Kovats retention index. Tritiated and deuterated GA4, GA9 or GA20 were applied around the circumference at the midpoint of the previous‐year terminal shoot, and metabolites were extracted from the elongating current‐year terminal shoot, the application point, and the 1‐year‐old needles and the cambial region above and below the application point. After purification, detection by liquid scintillation spectrometry and analysis by GC‐MS, it was evident that, for each applied GA, unmetabolised [2H2]GA and [3H]radioactivity were present in every seedling part analysed. Most of the radioactivity was retained at the application point when [3H]GA9 and [3H]GA20 were applied, whereas the largest percentage of radioactivity derived from [3H]GA4 was recovered in the current‐year terminal shoot. It was also found that [2H2]GA9 was converted to [2H2]GA20 and to both [2H2]GA4 and [2H2]GA1, [2H2]GA4 was metabolised to [2H2]GA1, and [2H2]GA20 was converted to [2H2]GA29. The data indicate that for Pinus sylvestris shoots (1) GAs applied laterally to the outside of the vascular system of previous‐year shoots not only are absorbed and translocated extensively throughout the previous‐year and current‐year shoots, but also are readily metabolised, (2) the GA metabolic pathways found are closely related to the endogenous GAs identified, and (3) GA9 metabolism follows two distinctly different routes: in one, GA9 is converted to GA1 through GA4, and in the other it is converted to GA20, which is then metabolised to GA29. The results suggest that the late 13‐hydroxylation pathway is an important route for GA biosynthesis in shoots of Pinus sylvestris, and that the stimulation of cambial growth in Scots pine by exogenous GA4/7 may be due to its conversion to GA1, rather than to it being active per se.

Identification of endogenous gibberellins in immature seeds of loquat (Eriobotrya japonica Lindl.).

Gibberellins (GAs) A9, A15, A19, A20, A29, A35, A44, A50 and A61 were identified by capillary gas chromatography/selected ion monitoring (GC/SIM) in immature seeds of loquat (Eriobotrya japonica Lindl). Furthermore, five unknown GA-like compounds with apparent parent ions of m/z 418, 504 or 506 (as methyl ester trimethylsilyl ether derivatives) were found by GC/mass spectrometry (GC/MS) in the biologically active fractions. The m/z 418 and 504 compounds may have been C-11β hydroxylated GA9 and dehydro-GA35, respectively. The bioassay and GC/MS results suggest that the major GAs were GA50 and the five unknown GA-like compounds. In the immature seeds, at least two GA metabolic pathways may thus exist, one being the non-hydroxylation pathway of GA15→GA24→GA9, and the other, the early C-13 hydroxylation pathway of GA44→GA19→GA20→GA29. A late C-11β hydroxylation pathway is also possible.

Photoperiod Modification of [14C]Gibberellin A12 Aldehyde Metabolism in Shoots of Pea, Line G2

In G2 peas (Pisum sativum L.) apical senescence occurs only in long days (LD), and indeterminate growth is associated with elevated gibberellin (GA) levels in the shoot in short days (SD). Metabolism of GA(12) aldehyde was investigated by feeding shoots grown in SD or LD with [(14)C]GA(12) aldehyde through the cut end of the stem for 0.5 to 6 hours in the light and analyzing the tissue extract by high performance liquid chromatography. More radioactive products were detected than can be accounted for by the two GA metabolic pathways previously known to be present in peas. Three of the major products appear to be GA conjugates, but an additional pathway(s) of GA metabolism may be present. The levels of putative C(20) GAs, [(14)C]GA(53), [(14)C]GA(44), [(14)C]GA(19), and/or [(14)C] GA(17), were all elevated in SD as compared to LD. Putative [(14)C]GA, was slightly higher in LD than in SD. Putative [(14)C]GA(53) was a major metabolite after 30 minutes of treatment in SD but had declined after longer treatment times to be replaced by elevated levels of putative [(14)C] GA(44) and [(14)C]GA(19/17). Metabolism of GA(20) was slow in both photoperiods. Although GA(20) and GA(19) are the major endogenous GAs as determined by gas chromatography-mass spectrometry, putative [(14)C]GA(20) and [(14)C]GA(19) were never major products of [(14)C]GA(12) aldehyde metabolism. Thus, photoperiod acts in G2 peas to change the rate of GA(53) production from GA(12) aldehyde, with the levels of the subsequent GAs on the 13-OH pathway being determined by the amount of GA(53) being produced.