Gibberellins in seeds of Arabidopsis thaliana: biological activities, identification and effects of light and chilling on endogenous levels

Derkx, M.P.M.; Vermeer, E.; Karssen, C.M.

doi:10.1007/bf00029895

Cited by 74 publications

(52 citation statements)

References 27 publications

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“…Our in vitro enzyme assays have shown that the recombinant GA4H protein has enzymatic properties similar to GA4, including the substrate preference for GA 9 rather than GA 20 (Williams et al, 1998). This observation may reflect the predominance of non-13-hydroxylated GAs in Arabidopsis (Talon et al, 1990a(Talon et al, , 1990bDerkx et al, 1994) and is consistent with more efficient conversion of the non-13-hydroxylated substrate than the 13-hydroxylated precursor by the Arabidopsis GA 20-oxidases, which catalyze the formation of GA 9 and GA 20 (Phillips et al, 1995). In addition to the 3␤-hydroxylation of GA 9 and GA 20 , recombinant GA4 catalyzes 3␤-hydroxylation of C 20 GAs (GA 15 , GA 24 , and GA 44 ) and 2,3-epoxidation of 2,3-didehydrogibberellins with lower efficiencies (Williams et al, 1998).…”

Section: Ga4 and Ga4h Genes Are Differentially Expressed Although Thmentioning

confidence: 69%

“…In Arabidopsis, both the early 13-hydroxylation and the non-13-hydroxylation pathways are present in flowering shoots (Talon et al, 1990a(Talon et al, , 1990b and possibly in germinating seeds (Derkx et al, 1994). Therefore, we used both GA 9 and GA 20 as substrates to determine whether MBP-GA4H had 3 ␤ -hydroxylase activity (Figure 2A).…”

Section: In Vitro Functional Analysis Of the Ga4h Proteinmentioning

confidence: 99%

“…GA 4 is the major bioactive GA in germinating Arabidopsis seeds (Derkx et al, 1994) and has the highest germination-inducing activity among GAs examined thus far (Yang et al, 1995). In the presence of 100 M GA 4 , the ga1-3 seeds started to germinate at ‫63ف‬ hr ( Figure 8B), and 91% of the seeds had germinated at 48 hr after imbibition under continuous white light.…”

Section: Ga4 But Not Ga4h Is Under Feedback Regulation During Seed Gementioning

confidence: 99%

“…Studies using the phyB mutant, which is deficient in the PHYB apoprotein (Somers et al, 1991;Reed et al, 1993), indicated that R/FR-reversible induction of seed germination is primarily regulated by PHYB (Shinomura et al, 1994(Shinomura et al, , 1996. Derkx et al (1994) showed that the level of GA 4 (but not its precursor GA 9 ) in wild-type Arabidopsis seeds irradiated by continuous white light was higher than in dark-imbibed seeds. In addition, R light irradiation was shown to lower the concentration of applied GAs required to induce germination of both the GA-deficient ga1 mutant (Hilhorst and Karssen, 1988) and wild-type seeds treated with the GA biosynthesis inhibitor uniconazole (Yang et al, 1995).…”

mentioning

confidence: 99%

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Phytochrome Regulation and Differential Expression of Gibberellin 3b-Hydroxylase Genes in Germinating Arabidopsis Seeds

Yamaguchi¹,

Smith²,

Brown³

et al. 1998

The Plant Cell

131

182

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Despite extensive studies on the roles of phytochrome in photostimulated seed germination, the mechanisms downstream of the photoreceptor that promote germination are largely unknown. Previous studies have indicated that light-induced germination of Arabidopsis seeds is mediated by the hormone gibberellin (GA). Using RNA gel blot analyses, we studied the regulation of two Arabidopsis genes, GA4 and GA4H (for GA4 homolog), both of which encode GA 3 ␤ -hydroxylases that catalyze the final biosynthetic step to produce bioactive GAs. The newly isolated GA4H gene was expressed predominantly during seed germination. We show that expression of both GA4 and GA4H genes in imbibed seeds was induced within 1 hr after a brief red (R) light treatment. In the phytochrome B-deficient phyB-1 mutant, GA4H expression was not induced by R light, but GA4 expression still was, indicating that R light-induced GA4 and GA4H expression is mediated by different phytochromes. In contrast to the GA4 gene, the GA4H gene was not regulated by the feedback inhibition mechanism in germinating seeds. Our data demonstrate that expression of GA 3 ␤ -hydroxylase genes is elevated by R light, which may result in an increase in biosynthesis of active GAs to promote seed germination. Furthermore, our results suggest that each GA 3 ␤ -hydroxylase gene plays a unique physiological role during light-induced seed germination. INTRODUCTIONGibberellins (GAs) are a group of diterpenoids, some of which are growth regulators in higher plants. Studies using GA-deficient mutants have shown that active GAs control many aspects of plant development, including seed germination, stem elongation, flowering, and seed development (for a recent review, see Ross et al., 1997). In the major GA biosynthetic pathway in higher plants, GA 3 ␤ -hydroxylase catalyzes the conversion of both GA 9 to GA 4 and GA 20 to GA 1 (Hedden and Kamiya, 1997). Several GA-deficient dwarf mutants with reduced 3 ␤ -hydroxylase activities have been isolated. These include dwarf1 in maize (Fujioka et al., 1988), le in pea (Ingram et al., 1984), dy in rice (Kobayashi et al., 1989), and ga4 in Arabidopsis (Talon et al., 1990a). Biochemical studies using these mutants have shown that only GA 4 and GA 1 , but not their precursors GA 9 and GA 20 , are biologically active in stimulating stem elongation. Therefore, GA 3 ␤ -hydroxylase catalyzes the final step of the biosynthetic pathway to produce active GAs in these plant species.Based on their function in GA biosynthesis, expression of GA 3 ␤ -hydroxylase genes is likely to play a key regulatory role in controlling the appropriate levels of active GAs during plant growth. Recently, the Arabidopsis GA4 and pea LE genes have been cloned and shown to encode GA 3 ␤ -hydroxylase (Chiang et al., 1995;Lester et al., 1997;Martin et al., 1997;Williams et al., 1998). The transcript levels of both GA4 and LE are controlled by a feedback inhibition mechanism, that is, they are upregulated in the GA-deficient mutant background and downregulated by applied GAs (Chi...

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Section: Ga4 and Ga4h Genes Are Differentially Expressed Although Thmentioning

confidence: 69%

Section: In Vitro Functional Analysis Of the Ga4h Proteinmentioning

confidence: 99%

Section: Ga4 But Not Ga4h Is Under Feedback Regulation During Seed Gementioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Phytochrome Regulation and Differential Expression of Gibberellin 3b-Hydroxylase Genes in Germinating Arabidopsis Seeds

Yamaguchi¹,

Smith²,

Brown³

et al. 1998

The Plant Cell

131

182

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“…PAC totally repressed radicle protrusion. The addition of GA 4ϩ7 (Derkx et al, 1994) to the germination medium reversed this PAC inhibition. However, under these conditions, seed germination was somewhat more heterogeneous (T 50 Ϸ 2.2 d) than in the absence of PAC (Table I).…”

Section: Preparation Of Seed Samplesmentioning

confidence: 94%

Proteomics of Arabidopsis Seed Germination. A Comparative Study of Wild-Type and Gibberellin-Deficient Seeds

et al. 2002

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We examined the role of gibberellins (GAs) in germination of Arabidopsis seeds by a proteomic approach. For that purpose, we used two systems. The first system consisted of seeds of the GA-deficient ga1 mutant, and the second corresponded to wild-type seeds incubated in paclobutrazol, a specific GA biosynthesis inhibitor. With both systems, radicle protrusion was strictly dependent on exogenous GAs. The proteomic analysis indicated that GAs do not participate in many processes involved in germination sensu stricto (prior to radicle protrusion), as, for example, the initial mobilization of seed protein and lipid reserves. Out of 46 protein changes detected during germination sensu stricto (1 d of incubation on water), only one, corresponding to the cytoskeleton component ␣-2,4 tubulin, appeared to depend on the action of GAs. An increase in this protein spot was noted for the wild-type seeds but not for the ga1 seeds incubated for 1 d on water. In contrast, GAs appeared to be involved, directly or indirectly, in controlling the abundance of several proteins associated with radicle protrusion. This is the case for two isoforms of S-adenosyl-methionine (Ado-Met) synthetase, which catalyzes the formation of Ado-Met from Met and ATP. Owing to the housekeeping functions of Ado-Met, this event is presumably required for germination and seedling establishment, and might represent a major metabolic control of seedling establishment. GAs can also play a role in controlling the abundance of a ␤-glucosidase, which might be involved in the embryo cell wall loosening needed for cell elongation and radicle extension.Maturation drying is the normal terminal event in the vast majority of seeds, after which they pass into a metabolically quiescent state where they may remain for many years and still retain their viability (Hoekstra et al., 2001). Upon hydration under suitable conditions, the seed, if not dormant, reactivates its metabolism and commences germination, giving rise to a new plant.Seed germination can be divided into three phases, imbibition, increased metabolic activity, and initiation of growth, which loosely parallel the triphasic water uptake of dry mature seeds. Morphologically, initiation of growth corresponds to radicle emergence; subsequent growth is generally defined as seedling growth. By definition, germination sensu stricto incorporates those events that start with the uptake of water by the quiescent dry seed and terminate with the protrusion of the radicle and the elongation of the embryonic axis (Bewley, 1997). From physiological studies on a wide variety of species, including a number of mutants, it appears that gibberellins (GAs) play a key role in late stages of seed germination Karssen, 1988, 1992;Karssen et al., 1989;Hilhorst and Toorop, 1997; Yamaguchi et al., 1998; Richards et al., 2001). Thus, in plant species such as Arabidopsis and tomato (Lycopersicon esculentum), the strong alleles of GA-deficient mutants are unable to complete germination without exogenous GAs (Koornneef and van der Veen,...

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Seed Germination

Kermode¹

2004

Handbook of Plant Biotechnology

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Seeds control the survival and reproductive capacity of plants and therefore occupy a critical position in the life history of higher plants. The successful establishment of the new plant both temporally and spatially, as well as the vigour of the young seedling, is largely determined by physiological and biochemical processes that occurred earlier, i.e. during seed development. At dispersal, the quiescent mature seed upon encountering favourable environmental conditions (that can include light of a given wavelength, sufficient water, optimal temperatures and adequate oxygen) commences germination. However, as will be discussed, under conditions that are not optimal for a transition from germination to seedling growth, seeds express genes that impose a transient ‘quiescence’ until those conditions become optimal. The agricultural and forest industries rely upon seeds that exhibit high germinability and vigorous, synchronous growth after germination; hence dormancy is generally considered an undesirable trait. Some of the problems unique to the forest industry in relation to the deep dormancy of conifer species will be discussed. Functional genomic approaches hold promise for elucidating genes and proteins that control seed dormancy and germination. The understanding of molecular and physiological mechanisms underlying seed dormancy, particularly of angiosperms, has been accelerated through the analysis of mutants that are disrupted in their development (including dormancy inception and maintenance) as a result of a deficiency in hormone biosynthesis or response. These and other biotechnological approaches for manipulating germination will be discussed.

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Gibberellins in seeds of Arabidopsis thaliana: biological activities, identification and effects of light and chilling on endogenous levels

Cited by 74 publications

References 27 publications

Phytochrome Regulation and Differential Expression of Gibberellin 3b-Hydroxylase Genes in Germinating Arabidopsis Seeds

Phytochrome Regulation and Differential Expression of Gibberellin 3b-Hydroxylase Genes in Germinating Arabidopsis Seeds

Proteomics of Arabidopsis Seed Germination. A Comparative Study of Wild-Type and Gibberellin-Deficient Seeds

Seed Germination

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