Endogenous Gibberellins of Pine Pollen: III. Conversion of 1,2-[H]GA(4) to Gibberellins A(1) and A(34) in Germinating Pollen of Pinus attenuata Lemm

Quantitation of Gibberellins A(1), A(3), A(4), A(9) and a Putative A(9)-Conjugate in Grafts of Sitka Spruce (Picea sitchensis) during the Period of Shoot Elongation

The levels of endogenous gibberellin A(1) (GA(1)), GA(3), GA(4), GA(9), and a cellulase hydrolyzable GA(9) conjugate in needles and shoot stems of mature grafts of Sitka spruce (Picea sitchensis [Bong.] Carr.) grown under environmental conditions that were either inductive, hot, and dry, or noninductive, cool, and wet, for flowering, were estimated by combined gas chromatography-mass spectrometry selected ion monitoring using deuterated [(2)H(2)]GA(1), GA(3), GA(4), and GA(9) as internal standards. The samples were taken when the shoots had elongated about 30, 70, and 95% of the final shoot length and 17 days after elongation had terminated. The concentration of putative GA(9)-conjugate, estimated by GCSIM of GA(9) after cellulase hydrolysis of the highly water soluble fraction, was 33 nanograms per gram fresh weight in the needles of both heat and drought- and cool and wet-treated plants sampled just after bud burst. The concentration gradually decreased to a final value of 13 nanograms per gram fresh weight in the heat and drought-treated grafts and 6 nanograms per gram fresh weight in the cool and wet-treated grafts. The stems contained no detectable putative GA(9) conjugate. Free GA(9) was highest in heat and drought-treated material. For plants subjected to this treatment, GA(9) increased from 22 to 32 nanograms per gram fresh weight in needles and from 1 to 22 nanograms per gram fresh weight in stems during the rapid stem elongation phase. By day 17, after cessation of shoot elongation, GA(9) had decreased to 12 nanograms per gram fresh weight in needles and 9 nanograms per gram fresh weight in the shoot stems. The cool and wet-treated material also showed an increase in GA(9) concentration during shoot elongation. However, the concentration was not as high and was also delayed compared with heat and drought-treated material. By day 17, after cessation of shoot elongation, GA(9) concentration was 9 nanograms per gram fresh weight in needles and 5 nanograms per gram fresh weight in stems for cool and wet treatment plants. The concentration of GA(4) was very low in tissue from both treatments. Fluctuation in concentration of the more polar gibberellins, GA(1) and GA(3), showed the same pattern as fluctuations in the content of GA(9). However, the heat and drought-treated material had lower amounts of GA(1) and GA(3) during the later phases of shoot elongation, than the cool and wet-treated material. These results imply differential metabolism between clones treated with conditions inductive and noninductive for flowering. Higher concentrations of putative GA(9) conjugate and free GA(9) in the hot and dry treatment indicate a higher capacity of synthesizing, for flowering, the physiologically important GA(4) in the heat and drought-treated material. This synthesis does not, however, result in a buildup of the GA(4) pool, probably because of a high turnover rate of GA(4). The cool and wet-treated material had higher amounts of GA(1) and GA(3), indicating that the differentiation was preferentially directed toward vegetative growth.

Quantitation of gibberellins A1, A 3, A 4, A 9 and an A 9-conjugate in good- and poor-flowering clones of Sitka spruce (Picea sitchensis) during the period of flower-bud differentiation

The levels of endogenous gibberellin A1 (GA1), GA3, GA4, GA9 and a cellulase-hydrolysable GA9-conjugate in needles and shoot stems of Sitka spruce [Picea sitchensis (Bong.) Carr.] grafts with different coning or flowering histories were estimated by combined gas chromatography-mass spectrometry selected ion monitoring using deuterated GA3, GA4 and GA9 as internal standards. The samples were taken at the approximate time of the start of flower-bud differentiation, i.e. when the shoots had elongated approx. 95% of the final length. The needles of the good-flowering clones contained 11-12 ng per g fresh weight (FW) and 15-28 ng· (g FW) (-1) of GA9-conjugate and GA9, respectively. The shoot stems of the same material contained no detectable amounts of GA9-conjugate and 11-15 ng-(g FW)(-1) of GA9. The amounts of GA9-conjugate and GA9 were apparently lower in the poor-flowering clones, the needles containing 4-9 ng-(g FW)(-1) and 7-17 ng·(g FW)(-1), respectively. Also in this material the shoot stems contained no detectable amounts of GA9-conjugate. The amounts of GA4 were very small in both materials, ranging from 1-1.6 ng-(g FW)(-1). The good-flowering clones contained no detectable amounts of the more polar gibberellins, GA1 and GA3. The poor-flowering clones, on the other hand, contained high levels of GA15 17-19ng·(gFW)(-1) in the needles and 10-13 ng·(g FW) (-1) in the shoot stems, and also smaller amounts of GA3, 2-3 ng·(g FW)(-1) in the needles and approx. 1 ng·(g FW)(-1) in the shoot stems. The results demonstrate differences in GA-metabolism between the poor- and the good-flowering clones. The higher amounts of GA9-conjugate and GA9 might indicate a higher capacity for synthesizing GA4 in the good-flowering material. This synthesis does not, however, result in a build-up of the GA4-pool, maybe because of a high rate of turnover. Gibberellin A4 was apparently neither hydroxylated to GA1 nor converted to GA3 in the goodflowering material, as was the case in the poor-flowering material. This might indicate that gibberellin metabolism in the poor-flowering material is directed towards GA1 and GA3, GAs preferentially used in vegetative growth.

Gibberellins regulate seed germination in tomato by endosperm weakening: a study with gibberellin-deficient mutants

The germination of seeds of tomato [Lycopersicon esculentum (L.) Mill.] cv. Moneymaker has been compared with that of seeds of the gibberellin-deficient dwarf-mutant line ga-1, induced in the same genetic background. Germination of tomato seeds was absolutely dependent on the presence of either endogenous or exogenous gibberellins (GAs). Gibberellin A4+7 was 1000-fold more active than commercial gibberellic acid in inducing germination of the ga-1 seeds. Red light, a preincubation at 2°C, and ethylene did not stimulate germination of ga-1 seeds in the absence of GA4+7; however, fusicoccin did stimulate germination independently. Removal of the endosperm and testa layers opposite the radicle tip caused germination of ga-1 seeds in water. The seedlings and plants that develop from the detipped ga-1 seeds exhibited the extreme dwarfy phenotype that is normal to this genotype. Measurements of the mechanical resistance of the surrounding layers showed that the major action of GAs was directed to the weakening of the endosperm cells around the radicle tip. In wild-type seeds this weakening occurred in water before radicle protrusion. In ga-1 seeds a similar event was dependent on GA4+7, while fusicoccin also had some activity. Simultaneous incubation of de-embryonated endosperms and isolated axes showed that wild-type embryos contain and endosperm-weakening factor that is absent in ga-1 axes and is probably a GA. Thus, an endogenous GA facilitates germination in tomato seeds by weakening the mechanical restraint of the endosperm cells to permit radicle protrusion.

Metabolism of Tritiated Gibberellins A(4) and A(9) in Norway Spruce, Picea abies (L.) Karst. : Effects of a Cultural Treatment Known to Enhance Flowering

Shoots of mature grafted propagules of Picea abies (L.) Karst. metabolized [(3)H]gibberellin A(4) (GA(4)) to at least 14 acidic substances, two of which were tentatively identified by gas-liquid radiochromatography as GA(2) (possibly an artifact) and GA(34). [(3)H]GA(9) was converted into a number of metabolites, one of which was chromatographically similar to, but not identical with, GA(4). Metabolism was maximally 61 and 57% over 48 hours for GA(4) and GA(9), respectively, and was correlated with the rate of change (i.e. increase followed by decrease) in endogenous GA-like substances as shoot elongation progressed. Propagules covered with a clear plastic film, a treatment which promotes flowering, metabolized [(3)H]GA(4) more slowly than did control plants in the open. Inasmuch as a GA(4/7) mixture can also promote flowering in P. abies, the retarded metabolism of [(3)H]GA(4) may reflect the manner in which trees under plastic metabolize endogenous GA-like substances. If so, then the stimulating effect of this cultural treatment on flowering may come about through an increased level of endogenous, less polar GA-like substances.