3. Control of sex expression in conifers

Despite considerable progress in recent years in the promotion of flowering in conifers, relatively little is known about the endogenous control of sex expression or its practical manipulation to aid pollen and crop management in seed orchards. Well defined patterns of sexual zonation exist within the tree crown and shoot, and these appear to be associated with hormonal and possibly nutritional gradients. No firm conclusions, however, are possible regarding the specific role(s) of different PGRs in sex expression, this being as much as a problem of lack of critical study as the complexity of the process itself. Whether a PGR such as gibberellins or auxins, or a cultural treatment that itself may influence endogenous hormone levels, primarily promotes female or male flowering often depends on the position within the crown of the shoot being treated, and its timing in relation to stage of primordia development. Photoperiod also may be involved- short days favoring females and long days males, at least in some species- although its role in controlling sex expression is by no means clear. Practical manipulation of sex expression may be possible through selective crown pruning, different PGR combinations, treatment timing and/or photoperiod control, but the development of such techniques for operational use will require a better basic understanding of the endogenous regulatory mechanisms involved.     

Metabolism of [H]Gibberellin A(5) by Immature Seeds of Apricot (Prunus armeniaca L.)

Immature seeds of apricot (Prunus armeniaca L.) were fed the native gibberellin A₅ (GA₅) as 1- and 1,2-[³H]GA₅ (5.3 Curies per millimole to 16 milliCuries per millimole) at doses (42 nanograms to 10.6 micrograms per seed) 2 to 530 times the expected endogenous level. After 4 days of incubation, seeds were extracted and free [³H]GA-like metabolites were separated from the highly H₂O-soluble [³H]metabolites. For high specific activity feeds the retention times (Rts) of radioactive peaks were compared with Rts of authentic GAs on sequential gradient-eluted → isocratic eluted reversed-phase C₁₈ high performance liquid chromatography (HPLC) -radiocounting (RC). From high substrate feeds (530 and 230 × expected endogenous levels) HPLC-RC peak groupings were subjected to capillary gas chromatography-selected ion monitoring (GC-SIM), usually six characteristic ions. The major free GA metabolites of [³H] GA₅ were identified as GA₁, GA₃, and GA₆ by GC-SIM. The major highly water soluble metabolite of [³H]GA₅ at all levels of substrate GA₅ had chromatographic characteristics similar to authentic GA₁-glucosyl ester. Expressed as a percentage of recovered radioactivity, low substrate [³H]GA₅ feeds (2 × expected endogenous level) yielded a broad spectrum of metabolites eluting at the Rts where GA₁, GA₃, GA₅ methyl ester, GA₆, GA₂₂, GA₂₉ (17, 14, 1.6, 7, 1.1, 0.5%, respectively) and GA glucosyl conjugates of GA₁, GA₃, GA₅, and GA₈ (33, 11, 1, 0.1%, respectively) elute. Metabolites were also present at Rts where GA glucosyl conjugates of GA₆ and GA₂₉ would be expected to elute (8 and 0.1%, respectively). Only 5% of the radioactivity remained as GA₅. Increasing substrate GA₅ levels increased the proportion of metabolites with HPLC Rts similar to GA₁, GA₆, and especially GA₁ glucosyl ester, primarily at the expense of metabolites with HPLC Rts similar to GA₃, GA₃-glucosyl ester, and a postulated conjugate of GA₆. There was evidence that high doses of substrate GA₅ induced new metabolites which often, but not always, differed from GA₁, GA₃, and GA₆ in HPLC Rt. These same metabolites, when analyzed by GC-SIM yielded m/e ions the same as the M⁺ and other characteristic m/e ions of the above GAs, albeit at differing GC Rt and relative intensities.     

Identification of Gibberellins A(1), A(5), A(29), and A(32) from Immature Seeds of Apricot (Prunus armeniaca L.)

Gibberellins (GAs) A₁, A₅, and A₂₉ were identified, and also GA₃₂ was confirmed, as endogenous GAs of immature seeds (3-4 weeks after anthesis, 0.25-0.5 gram fresh weight) of apricot (Prunus armeniaca L.) based on capillary gas chromatography (GC), retention time (Rt), and selected ion monitoring (SIM), in comparison with authentic standards. Fractions subjected to GC-SIM were purified and separated using sequential solvent partitioning → paper chromatography → reverse phase C₁₈ high performance liquid chromatography (HPLC) → bioassay on dwarf rice cv Tan-ginbozu. Two other peaks of free GA-like bioactivity (microdrop and immersion dwarf rice assays) were eluted from C₁₈ HPLC at Rts where GA_4/7 and GA₈ (or other GAs with similar structures) would elute. Also, three unidentified GA glucoside-like compounds (based on bioactivity on the immersion assay, and no bioactivity on the microdrop assay) were noted. There were very high amounts of GA₃₂ (112 ng of GA₃ equivalents per gram fresh weight), and minor amounts (0.5 ng of GA₃ equivalents) for each of GA₁ and GA₅, respectively, based on the microdrop assay.     

Metabolism of [3H]gibberellin A4 in somatic suspension cell cultures of carrot

The native gibberellin A₄ (GA₄), in radioactive form ([1,2-³H]GA₄, 1.06 Ci/mmol), was fed to carrot somatic cell cultures (suspension and immobilized cell systems) and its metabolism over a 48 hr period was investigated. It was found that the [³H]GA₄ was metabolized to at least two GAs, [³H]GA₁ and [³H]GA₈, six GA glucosyl conjugates, [³H]GA₁-0(3)-glucoside, [³H]GA₁-0(13)-glucoside, [³H]GA₁-glucosyl ester, [³H]GA₄-glucoside, [³H]GA₄-glucosyl ester, a [³H]GA₈ glucosyl conjugate(s) and a previously unknown [³H]GA₁ glucosyl conjugate ([³H]GA₁-0(3,13)-diglucoside-like compound). The GA₁-diglucoside-like compound was found only in extracts of cells and was present in significant amounts (33 % of total extractable radioactivity). All other metabolites were present in both cells and medium. For extracts of the medium, no differences between the suspension and immobilized cultures existed in types of [³H]GA₄ metabolites although quantitative differences were apparent.     

Gibberellin structure and florigenic activity in Lolium temulentum,a long-day plant

Structural requirements for florigenic activity among gibberellins (GAs) and GA derivatives, including several new ones, applied once to leaves of Lolium temulentum, were examined. The compounds were applied to plants kept either in non-inductive short days (SD) or exposed to one inductive long day (LD). Inflorescence initiation and stem-elongation responses were assessed three weeks later. Among the GAs used, the range in effective dose for inflorescence initiation was more than 1000-fold, but substantially less for stem elongation. Some GAs promoted both stem elongation and inflorescence initiation, some promoted one without the other, and some affected neither. The structural features enhancing florigenic activity were often different from those enhancing stem elongation. Except in the case of 2,2-dimethyl GA₄, a double bond in the A ring at either C-1,2 or C-2,3 was essential for high florigenic activity, though not for stem elongation. A free carboxy group was needed for both. Inflorescence initiation in Lolium was enhanced by hydroxylation at C-12, ?13 and ?15, whereas hydroxylation at C-3 reduced the effect on inflorescence initiation but increased that on stem elongation. A 12β-hydroxyl was more effective than the α epimer for inflorescence initiation whereas the reverse was true for stem elongation. Although such differential effectiveness of GAs for inflorescence initiation and for stem elongation could reflect differences in uptake, transport or metabolism, we suggest that it is indicative of specific structural requirements for inflorescence initiation.     

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A₉ (GA₉) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA₉ could completely substitute for a transfer to a long photoperiod. When [³H]GA₉ or [²H₂]GA₉ was injected into a leaf, no [³H]GA₉ was detected in the elongating apex and only traces of [³H]GA₉ were found in the shoot above the treated leaf. By the use of gas chromatography-mass spectrometry (GC-MS), [²H₂]GA₂₀ was identified as the main metabolite of [²H₂]GA₉ in both the shoot and the treated leaf. In addition, [²H₂]GA₁ and [²H₂]GA₂₉ were also identified as metabolites of [²H₂]GA₉. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA₂₀ and GA,.     

Effect of exogenous gibberellin A4/7 on tracheid production, longitudinal growth and the levels of indole‐3‐acetic acid and gibberellins A4, A7 and A9 in the terminal shoot of Pinus sylvestris seedlings

Synchronously dividing cultures of the unicellular green alga Scenedesmus obtusiusculus were cultivated for 24 or 70 h in medium high (1000 μM) or low (60 μM) in phosphorus. Aliquots of AlCl₃ (0, 37, 74, 111, 148, 185, or 222 μmol) were added daily to 1 l cell suspension at the end of the cell division phase. Algae were also grown in media with different pH, adjusted with HCl, in the absence of AlCl₃.
Effects of Al on cell metabolism vary with the intracellular Al concentration and with the concentration of Al available per cell. When the concentration of phosphorus is low, internal concentrations of Al are high and the chlorophyll content and the net dry matter production per cell increase, whereas the photosynthesis and the cell division are increased. Presence of Al in a low P medium decreases the pH of the medium down to 4.5. There are only small effects of Al in the presence of P, due to precipitation of most of the Al with P in the medium.
Despite the Al-induced decrease of the pH of the culture medium, effects caused by Al cannot be explained as a pH effect. Instead, the Al effect may, at least to some extent, be related to a decrease in availability of P in the metabolism, due to formation of aluminium phosphate inside the cell.     

Brassinosteroid-Induced Bending of the Leaf Lamina of Dwarf Rice Seedlings: An Auxin-Mediated Phenomenon

A synthetic brassinosteroid (BR), 2,3,22ß,23ß-tetrahydroxy-24ß-methyl-B-homo7-oxa-5-cholestan-6-one, an isomer of the growth promoter brassinolide,when applied to seedlings of dwarf rice Oryza sativa var. Tan-ginbozuand Waito-C, induced a significant bending of the second leaflamina at 100 ng/plant and higher dosages. Promotion of thesecond leaf sheath elongation, the characteristic response ofdwarf rice varieties to gibberellins, was significantly butmodestly enhanced by BR at a dosage of 10,000 ng/plant, fiveorders of magnitude higher than the minimal dosage responseto GA₃. Gibberellin A₃ had no significant effect on the bendingof the second leaf lamina, nor did any synergism exist betweenBR and GA₃ in leaf lamina bending or leaf sheath elongation.Neither ethylene nor (2-chloroethyl)phosphonic acid (ethephon)caused the bending of the second leaf lamina, and neither synergizedthe BR effect. However, IAA and -naphthaleneacetic acid causedsignificant bending at 5,000 ng/plant, and both auxins significantlysynergized the effect of BR on the bending, IAA being effectiveat 500 ng/ plant in this regard. The antiauxins, 2,3,5-triiodobenzoicacid (TIBA) and -(p-chlorophenoxy)isobutyric acid (PCIB) completelynullified both the BR-induced bending and the BR$IAA-synergizedbending. The BR-induced bending response may thus be mediatedthrough endogenous auxin. (Received May 11, 1982; Accepted August 25, 1982)     

The endogenous gibberellins of vegetative and reproductive tissue of G2 peas

The gibberellins (GAs) of both vegetative (leaves and stems) and reproductive (pods and seeds) tissue of the G2 strain of peas Pisum sativum L. were characterized in purified extracts by a combination of sequential silicic-acid partition column chromatography, and gas chromatography-mass spectrometry. Gibberellins A₁₉, A₂₀, A₂₉ and an A₂₉ catabolite were identified in both types of tissue. Gibberellins A₉, A₁₇ and A₄₄ were also found in pods and seeds.Abbreviations FID Ilame ionization detector - GA(s) gibberellin(s) - GC gas chromatograph(y) - HPLC high performance liquid chromatograph(y) - LD long day - MS mass spectrum(a) or mass spectrometer(ry) - SD short day     

Changes of Endogenous Gibberellin-like Substances with Sex Reversal of the Apical Inflorescence of Corn

In developing apical meristems of corn, the level of acidic, ethyl acetate-soluble gibberellin (GA)-like substances increased to a maximum of 108 micrograms GA₃-equivalents per kilogram dry weight of tissue at inflorescence initiation, and then fell rapidly. At anthesis, only a trace (0.2 microgram per kilogram) of GA-like activity remained in the apical (male) inflorescences, whereas moderate activity (32 micrograms per kilogram), mostly of a nonpolar nature, was present in lateral, female, inflorescences.