No abstract

Gibberellins A12 (GAI2), GA53, GA44, GA19, GA,7, GA20, GA29, GA1, and GAB have been identified from extracts of vegetative shoots of normal (wild type) maize using full scan capillary gas chromatography-mass spectrometry and Kovats retention indices. Seven of these gibberellins (GAs) have been quantified by capillary gas chromatography-selected ion monitoring using internal standards of 114C41GA53, I'4C41GA44, 12H21 GA1I, 113C,IGA2o, 1'3C,IGA29, 113C,IGAI, and 1'3C,JGA8. Quantitative data from extracts of normal, dwarf-1, dwarf-2, dwarf-3, and dwarf-5 seedlings support the operation of the early 13-hydroxylation pathway in vegetative shoots of Zea mays. These data support the positions in the pathway blocked by the mutants, previously assigned by bioassay data and metabolic studies. The GA levels in dwarf-2, dwarf-3, and dwarf-5 were equal to, or less than, 2.0 nanograms per 100 grams fresh weight, showing that these mutants are blocked for steps early in the pathway. In dwarf-1, the level of GA, was very low (0.23 nanograms per 100 grams fresh weight) and less than 2% of that in normal shoots, while GA20 and GA29 accumulated to levels over 10 times those in normals; these results confirm that the dwarf-1 mutant blocks the conversion of GA20 to GA,.Since the level of GAs beyond the blocked step for each mutant is greater than zero, each mutated gene probably codes for an altered gene product, thus leading to impaired enzyme activities. (8,19), and GA20 to GA, (19); third, bioassay data, using the dwarf-l (dl), dwarf-2 (d2), dwarf-3 (d3) and dwarf-5 (d5) mutants indicate that these single-gene, nonallelic mutants block specific steps in the early 13-hydroxylation pathway. The pattern of response suggests the position in the pathway blocked by each mutant. For example, GA20 and GA, are both highly active when assayed on d5 whereas GA20 is 1% as active as GA, when assayed on dl. Thus, the d5 mutant blocks a step before GA20, and the dl mutant the late step, GA20 to GA,. In addition, the GA precursor ent-kaurene is active on d5, suggesting that the d5 block is before ent-kaurene (Fig. 1) (6).In this paper, evidence is presented for the presence of GA12, GA53, GA44, GA,9, GA17, GA20, GA29, GA,, and GA8 in the seedling shoots of normal maize (Fig. 1). The data are based on full scan mass spectra and Kovats retention indices (14) from capillary GC-MS. In addition, quantitative data are presented for the levels of specific endogenous GAs in normal, dl, d2, d3, and d5 seedlings using labeled internal standards and GC-SIM.3 These data provide additional support for the positions of the steps in the metabolic pathway blocked by the mutant genes (Fig. 1).The early 13-hydroxylation pathway (Fig. 1) for GA biosynthesis was first established for seeds of Pisum sativum (1 1, 17). This pathway has also been proposed for shoots of Zea mays (7,16). Four lines of evidence support the presence of this pathway and its operation in the control of shoot elongation in maize.First, eight members of the pathway, GA53, GA44, GA,9...

No abstract

GENETICS: B. 0. PHINNEY required to reduce the methylene blue. It is clear that the long lag phase observed when methylene blue was present before all the oxygen was removed is due to an inhibition by methylene blue of the systems of the cell which consume oxygen.Summary. Hemming4 that slow-growing varieties of peas (Pisum) will respond more than fastgrowing varieties to applications of gibberellic acid. They also reported a similar differential growth response to applications of gibberellic acid between tall and dwarf varieties of broad bean (Vicia) and French bean (Phaseolus), concluding that VOL. 42, 1956 185

In plants, gibberellin (GA)-responding mutants have been used as tools to identify the genes that control specific steps in the GA-biosynthetic pathway. They have also been used to determine which native GAs are active per se, i.e., further metabolism is not necessary for bioactivity. We present metabolic evidence that the Dl gene of maize (Zea mays L.) controls the three biosynthetic steps: GA20 to GA1, GA20 to GA5, and GA5 to GA3. We also present evidence that three gibberellins, GA1, GA5, and GA3, have per se activity in stimulating shoot elongation in maize. The metabolic evidence comes from the injection of [17-13C,3H]GA20 and [17-13C,3H] GA5 into seedlings of dl and controls (normal and d5), followed by isolation and identification of the 13C-labeled metabolites by full-scan GC-MS and Kovats retention index.For the controls, GA20 was metabolized to GA1, GA3, and GA5; GA5 was metabolized to GA3. For the dl mutant, GA20 was not metabolized to GA1, GA3, or to GA5, and GA5 was not metabolized to GA3. The bioassay evidence is based on dosage response curves using dl seedlings for assay. GA1, GA3, and GA5 had similar bioactivities, and they were 10-times more active than GA20.linear and there is no evidence for a metabolic grid with the other pathways, as has been shown for cell-free preparations obtained from seeds of bean, cucumber, and pea (for review, see ref.3).The biological significance of the metabolic studies in maize comes from the use of GA mutants that exhibit a dwarf phenotype, yet respond by normal growth to applied GAs. Thus, the relative responses of the mutants to specific GAs together with information on the role of the genes in controlling specific steps in the pathway have led to the conclusion that only a limited number of GAs in the pathway are active per se, i.e., they do not require further metabolism to be bioactive (for reviews, see refs. 10-12).The purpose of the present study was to examine the metabolic steps, GA20 to GA5, GA5 to GA3 and GA20 to GA1 in relation to the dl mutation (blockage after GA20). To this end, [17-13C,3H]GA2o and [17-13C,3H]GAs were fed to dl seedlings and to controls (normal and d5 seedlings) and the metabolites from the feeds were analyzed by full-scan GC-MS. In addition, the bioactivities of GA20, GA1, GA5, and GA3 were determined using dl seedlings for assay.The gibberellins (GAs) are tetracarbocyclic diterpenes that occur naturally in higher plants (1). There is continued interest in the biosynthetic origin of the GAs since some of them are known to act as native regulators controlling a range of growth responses, including seed germination, floral development, and shoot elongation (for reviews, see refs. 2 and 3).All GAs are biosynthesized from trans-geranylgeranyl diphosphate (GGDP) via ent-copalyl diphosphate (CDP) and the tetracyclic hydrocarbon, ent-kaurene. ent-Kaurene is sequentially oxidized to ent-7a-hydroxykaurenoic acid, which is then rearranged to GA12-aldehyde and oxidized to GA12. At least three pathways diverge from GA12-aldehyde and ...