Applied GA5 , GA4 , and GA4/7 increase berry number per bunch, yield, and grape quality for winemaking in Vitis vinifera L. cv. Malbec

BACKGROUND

The gibberellins (GAs) GA₅ (inhibitor of GA₃ -oxidase), GA₄ (biologically active), GA_4/7 (commercially available mixture of Ga₄ and GA₇ ) prohexadione-calcium (ProCa, inhibitor of dioxygenases that render GAs bioactive, negative control), and GA₃ (positive control) were applied to bunches of Vitis vinifera cv. Malbec. Different techniques, doses, and timings were used in a 3-year field experiment. In year 1, GA₅ , ProCa, and GA₃ were applied at 35, 20, and 0 days before veraison (DBV) by dipping bunches three times. In year 2, single applications of GA₅ and GA₃ , also by immersion, were tested at 60, 45, and 30 DBV. In year 3, applications at 60 and 30 DBV of GA₅ , GA₄ , and a mixture of GA_4/7 were evaluated by dipping or spraying the bunches.

RESULTS

Vegetative growth, berry weight, and sugar content were unaffected by treatments. ProCa did not affect the yield with respect to water control, although it reduced the levels of phenolics in berry skins, an undesirable effect for winemaking. GA₅ , in the dose range 5-50 mg L^-1 , raised berry numbers, thereby augmenting bunch weight and skin phenolics at harvest, so increasing berry quality for winemaking. GA₄ and GA_4/7 produced similar benefits to GA₅ , with similar doses.

CONCLUSION

The applications of GA₅ , GA₄ , and GA_4/7 to developing grape berry bunches, in a range of concentrations and by dipping or spraying, increased berry numbers per bunch at harvest. The method can be used as a viticultural practice to improve the production and quality of wine grapes. © 2021 Society of Chemical Industry.

Evaluating the use of plant hormones and biostimulators in forage pastures to enhance shoot dry biomass production by perennial ryegrass (Lolium perenne L.)

Fertilisation of established perennial ryegrass forage pastures with nitrogen (N)-based fertilisers is currently the most common practice used on farms to increase pasture forage biomass yield. However, over-fertilisation can lead to undesired environmental impacts, including nitrate leaching into waterways and increased gaseous emissions of ammonia and nitrous oxide to the atmosphere. Additionally, there is growing interest from pastoral farmers to adopt methods for increasing pasture dry matter yield which use 'natural', environmentally safe plant growth stimulators, together with N-based fertilisers. Such plant growth stimulators include plant hormones and plant growth promotive microorganisms such as bacteria and fungi ('biostimulators', which may produce plant growth-inducing hormones), as well as extracts of seaweed (marine algae). This review presents examples and discusses current uses of plant hormones and biostimulators, applied alone or together with N-based fertilisers, to enhance shoot dry matter yield of forage pasture species, with an emphasis on perennial ryegrass.

Stress-related hormones and glycinebetaine interplay in protection of photosynthesis under abiotic stress conditions

Plants subjected to abiotic stresses such as extreme high and low temperatures, drought or salinity, often exhibit decreased vegetative growth and reduced reproductive capabilities. This is often associated with decreased photosynthesis via an increase in photoinhibition, and accompanied by rapid changes in endogenous levels of stress-related hormones such as abscisic acid (ABA), salicylic acid (SA) and ethylene. However, certain plant species and/or genotypes exhibit greater tolerance to abiotic stress because they are capable of accumulating endogenous levels of the zwitterionic osmolyte-glycinebetaine (GB). The accumulation of GB via natural production, exogenous application or genetic engineering, enhances plant osmoregulation and thus increases abiotic stress tolerance. The final steps of GB biosynthesis occur in chloroplasts where GB has been shown to play a key role in increasing the protection of soluble stromal and lumenal enzymes, lipids and proteins, of the photosynthetic apparatus. In addition, we suggest that the stress-induced GB biosynthesis pathway may well serve as an additional or alternative biochemical sink, one which consumes excess photosynthesis-generated electrons, thus protecting photosynthetic apparatus from overreduction. Glycinebetaine biosynthesis in chloroplasts is up-regulated by increases in endogenous ABA or SA levels. In this review, we propose and discuss a model describing the close interaction and synergistic physiological effects of GB and ABA in the process of cold acclimation of higher plants.

Overexpression of gibberellin 20-oxidase1 from Pinus densiflora results in enhanced wood formation with gelatinous fiber development in a transgenic hybrid poplar

Gibberellins (GAs) are important regulators of plant shoot biomass growth, and GA 20-oxidase (GA20ox) is one of the major regulatory enzymes in the GA biosynthetic pathway. Previously, we showed that the expression levels of a putative GA20ox1 (i.e., PdGA20ox1) in stem tissue of 3-month-old seedlings of 12 families of Pinus densiflora were positively correlated with stem diameter growth across those same families growing in an even-aged 32-year-old pine forest (Park EJ, Lee WY, Kurepin LV, Zhang R, Janzen L, Pharis RP (2015) Plant hormone-assisted early family selection in Pinus densiflora via a retrospective approach. Tree Physiol 35:86-94). To further investigate the molecular function of this gene in the stem wood growth of forest trees, we produced transgenic poplar lines expressing PdGA20ox1 under the control of the 35S promoter (designated as 35S::PdGA20ox1). By age 3 months, most of the 35S::PdGA20ox1 poplar trees were showing an exceptional enhancement of stem wood growth, i.e., up to fourfold increases in stem dry weight, compared with the nontransformed control poplar plants. Significant increases in endogenous GA1, its immediate precursor (GA20) and its catabolite (GA8) in elongating internode tissue accompanied the increased stem growth in the transgenic lines. Additionally, the development of gelatinous fibers occurred in vertically grown stems of the 35S::PdGA20ox1 poplars. An analysis of the cell wall monosaccharide composition of the 35S::PdGA20ox1 poplars showed significant increases in xylose and glucose contents, indicating a qualitative increase in secondary wall depositions. Microarray analyses led us to find a total of 276 probe sets that were upregulated (using threefold as a threshold) in the stem tissues of 35S::PdGA20ox1 poplars relative to the controls. 'Cell organization or biogenesis'- and 'cell wall'-related genes were overrepresented, including many of genes that are involved in cell wall modification. Several transcriptional regulators, which positively regulate cell elongation through GA signaling, were also upregulated. In contrast, genes involved in defense signaling were appreciably downregulated in the 35S::PdGA20ox1 stem tissues, suggesting a growth versus defense trade-off. Taken together, our results suggest that PdGA20ox1 functions to promote stem growth and wood formation in poplar, probably by activating GA signaling while coincidentally depressing defense signaling.

Phenotypic plasticity of sun and shade ecotypes of Stellaria longipes in response to light quality signaling, gibberellins and auxin

Stellaria longipes plant communities (ecotypes) occur in several environmentally distinct habitats along the eastern slopes of southern Alberta's Rocky Mountains. One ecotype occurs in a prairie habitat at ∼1000 m elevation where Stellaria plants grow in an environment in which the light is filtered by taller neighbouring vegetation, i.e. sunlight with a low red to far-red (R/FR) ratio. This ecotype exhibits a high degree of phenotypic plasticity by increasing stem elongation in response to the low R/FR ratio light signal. Another Stellaria ecotype occurs nearby at ∼2400 m elevation in a much cooler alpine habitat, one where plants rarely experience low R/FR ratio shade light. Stem elongation of plants is largely regulated by gibberellins (GAs) and auxin, indole-3-acetic acid (IAA). Shoots of the prairie ecotype plants show increased IAA levels under low R/FR ratio light and they also increase their stem growth in response to applied IAA. The alpine ecotype plants show neither response. Plants from both ecotypes produce high levels of growth-active GA1 under low R/FR ratio light, though they differ appreciably in their catabolism of GA1. The alpine ecotype plants exhibit very high levels of GA8, the inactive product of GA1 metabolism, under both normal and low R/FR ratio light. Alpine origin plants may de-activate GA1 by conversion to GA8 via a constitutively high level of expression of the GA2ox gene, thereby maintaining their dwarf phenotype and exhibiting a reduced phenotypic plasticity in terms of shoot elongation. In contrast, prairie plants exhibit a high degree of phenotypic plasticity, using low R/FR ratio light-mediated changes in GA and IAA concentrations to increase shoot elongation, thereby accessing direct sunlight to optimize photosynthesis. There thus appear to be complex adaptation strategies for the two ecotypes, ones which involve modifications in the homeostasis of endogenous hormones.

Enhancing crop yield with the use of N-based fertilizers co-applied with plant hormones or growth regulators

Crop yield, vegetative or reproductive, depends on access to an adequate supply of essential mineral nutrients. At the same time, a crop plant's growth and development, and thus yield, also depend on in situ production of plant hormones. Thus optimizing mineral nutrition and providing supplemental hormones are two mechanisms for gaining appreciable yield increases. Optimizing the mineral nutrient supply is a common and accepted agricultural practice, but the co-application of nitrogen-based fertilizers with plant hormones or plant growth regulators is relatively uncommon. Our review discusses possible uses of plant hormones (gibberellins, auxins, cytokinins, abscisic acid and ethylene) and specific growth regulators (glycine betaine and polyamines) to enhance and optimize crop yield when co-applied with nitrogen-based fertilizers. We conclude that use of growth-active gibberellins, together with a nitrogen-based fertilizer, can result in appreciable and significant additive increases in shoot dry biomass of crops, including forage crops growing under low-temperature conditions. There may also be a potential for use of an auxin or cytokinin, together with a nitrogen-based fertilizer, for obtaining additive increases in dry shoot biomass and/or reproductive yield. Further research, though, is needed to determine the potential of co-application of nitrogen-based fertilizers with abscisic acid, ethylene and other growth regulators.

Plant hormone-assisted early family selection in Pinus densiflora via a retrospective approach

In an even-aged pine forest trees can vary considerably in stem size. We examined the basis for this anomaly using a retrospective approach. Twelve open-pollinated families of Pinus densiflora Sieb. et Zucc. were deliberately chosen for their variation in stem volumes at age 32 years. Seedlings obtained from these families were grown to age 6 months under optimal nursery conditions. Endogenous levels of growth hormones (auxin [IAA] and gibberellins [GAs]) and expression of the GA biosynthesis gene, PdGA20ox1, all assessed at age 3 months, were significantly correlated, across family, with seedling stem and/or shoot dry biomass at age 6 months. Retrospective comparisons of seedling growth, seedling stem tissue GA(20) and seedling stem expression levels of PdGA20ox1 were then made, across family, with tree stem growth at age 32 years. Age 6 months length and shoot dry biomass at age 6 months showed positive and significant Pearson's correlations with age 32 years tree stem diameters and a tree stem volume index, as did seedling stem tissue GA(20). Even seedling stem PdGA20ox1 expression levels were positively and near significantly (P = 0.088) correlated with age 32 years tree stem diameters. Auxin and GAs control nursery growth of seedlings at the family level, and this control also extends, for GAs at least, to field growth of older trees. We propose that family differences in PdGA20ox1 gene expression, and thus endogenous GA levels, may explain much of the natural variation seen for tree stem size in even-aged pine forests. If our hypothesis is correct, then the heritable components of variation in tree stem growth capacity should be predictable by hormonal and gene expression profiling. Such profiling, combined with the measurement of seedling phenotypic growth characters, could have the potential to accelerate the early selection of those conifer families that possess traits for inherently rapid stem wood growth.

Light signaling and the phytohormonal regulation of shoot growth

Shoot growth of dicot plants is rigorously controlled by the interactions of environmental cues with several groups of phytohormones. The signaling effects of light on shoot growth are of special interest, as both light irradiance and light quality change rapidly throughout the day, causing profound changes in stem elongation and leaf area growth. Among the several dicot species examined, we have focused on sunflower (Helianthus annuus L.) because its shoots are robust and their growth is highly plastic. Sunflower shoots thus constitute an ideal tissue for assessing responses to both light irradiance and light quality signals. Herein, we discuss the possible roles of gibberellins, auxin, ethylene, cytokinins and brassinosteroids in mediating the stem elongation and leaf area growth that is induced by shade light. To do this we uncoupled the plant's responses to changes in the red to far-red [R/FR] light ratio from its responses to changes in irradiance of photosynthetically active radiation [PAR]. Reducing each of R/FR light ratio and PAR irradiance results in increased sunflower stem elongation. However, the plant's response for leaf area growth differs considerably, with a low R/FR ratio generally promoting leaf area growth, whereas low irradiance PAR inhibits it. The increased stem elongation that occurs in response to lowering R/FR ratio and PAR irradiance is accomplished at the expense of leaf area growth. In effect, the low PAR irradiance signal overrides the low R/FR ratio signal in shade light's control of leaf growth and development. Three hormone groups, gibberellins, auxin and ethylene are directly involved in regulating these light-mediated shoot growth changes. Gibberellins and auxin function as growth promoters, with auxin likely acting as an up-regulator of gibberellin biosynthesis. Ethylene functions as a growth-inhibitor and probably interacts with gibberellins in regulating both stem and leaf growth of the sunflower shoot.

Improving ryegrass-clover pasture dry matter yield and urea efficiency with gibberellic acid

BACKGROUND

The effects of spraying gibberellic acid (GA3) at 20 or 30 g ha(-1), with or without application of urea, on pasture dry matter (DM) yield, herbage nitrogen (N) concentration and feed quality were investigated in 2011 and 2012 for managed pastoral systems in New Zealand across a range of sites, in both autumn and spring.

RESULTS

On the Waikato site (autumn and spring, 2012), and at all five sites in 2011, liquid urea applied with GA3 at 20 or 30 g ha(-1) consistently produced significantly higher pasture shoot DM yield, relative to liquid urea alone. Application of GA3 alone reduced feed quality by lowering metabolizable energy, crude protein and organic matter digestibility values. However, a reduced feed quality was not observed when GA3 was applied together with liquid urea. Liquid urea applied with GA3 also reduced total N and nitrate-N concentration in herbage, relative to liquid urea applied alone.

CONCLUSION

Application of GA3 together with liquid urea provides an opportunity for the strategic use of urea to meet both production and environmental goals.

Phytohormonal basis for the plant growth promoting action of naturally occurring biostimulators

There is increasing interest in the use of naturally occurring 'biostimulators' for enhancing the growth of agricultural and horticultural crops. Bacteria, fungi and protozoa, as well as marine algae-based seaweed extracts, can produce or contain biostimulators. The activity of biostimulators to promote plant growth is often attributed to their ability to directly or indirectly provide mineral nutrients (mostly N, but also P, S and other macro- and micro-nutrients) to plants. Alternatively, biostimulators are postulated to increase the plant's ability to assimilate these mineral nutrients, often in return for photo-assimilates (as occurs with certain bacteria and fungi associations). Although optimal growth of plants depends on the availability of adequate mineral nutritients, that growth (and also development, including reproduction) is also regulated by plant hormones (phytohormones), including gibberellins, auxins and cytokinins. This review describes and discusses the evidence that the presence or application of biostimulators also increases plant growth directly via phytohormone action and also influences the plant's ability to control its own hormone biosynthesis and homeostasis. Finally, it discusses the need for a better understanding of the role(s) that are played by the naturally occurring biostimulators associated with the plant in the crop field. It is suggested that better understanding will allow for optimal crop yield returns, since disruptions of phytohormone homeostasis in plant organs and tissues can yield either beneficial or sub-optimal outcomes.

Gibberellin 3-oxidase gene expression patterns influence gibberellin biosynthesis, growth, and development in pea

Gibberellins (GAs) are key modulators of plant growth and development. PsGA3ox1 (LE) encodes a GA 3β-hydroxylase that catalyzes the conversion of GA20 to biologically active GA1. To further clarify the role of GA3ox expression during pea (Pisum sativum) plant growth and development, we generated transgenic pea lines (in a lele background) with cauliflower mosaic virus-35S-driven expression of PsGA3ox1 (LE). PsGA3ox1 transgene expression led to higher GA1 concentrations in a tissue-specific and development-specific manner, altering GA biosynthesis and catabolism gene expression and plant phenotype. PsGA3ox1 transgenic plants had longer internodes, tendrils, and fruits, larger stipules, and displayed delayed flowering, increased apical meristem life, and altered vascular development relative to the null controls. Transgenic PsGA3ox1 overexpression lines were then compared with lines where endogenous PsGA3ox1 (LE) was introduced, by a series of backcrosses, into the same genetic background (BC LEle). Most notably, the BC LEle plants had substantially longer internodes containing much greater GA1 levels than the transgenic PsGA3ox1 plants. Induction of expression of the GA deactivation gene PsGA2ox1 appears to make an important contribution to limiting the increase of internode GA1 to modest levels for the transgenic lines. In contrast, PsGA3ox1 (LE) expression driven by its endogenous promoter was coordinated within the internode tissue to avoid feed-forward regulation of PsGA2ox1, resulting in much greater GA1 accumulation. These studies further our fundamental understanding of the regulation of GA biosynthesis and catabolism at the tissue and organ level and demonstrate that the timing/localization of GA3ox expression within an organ affects both GA homeostasis and GA1 levels, and thereby growth.

Impact of eastern dwarf mistletoe (Arceuthobium pusillum) on host white spruce (Picea glauca) development, growth and performance across multiple scales

Infection by eastern dwarf mistletoe (Arceuthobium pusillum) modifies needle and branch morphology and hastens white spruce (Picea glauca) mortality. We examined potential causal mechanisms and assessed the impacts of infection-induced alterations to host development and performance across scales ranging from needle hormone contents to bole expansion. Needles on infected branches (IBs) possessed higher total cytokinin (CK) and lower abscisic acid contents than needles on uninfected branches (UBs). IBs exhibited greater xylem growth than same-aged UBs, which is consistent with the promotive effect of CKs on vascular differentiation and organ sink strength. Elevated CK content may also explain the dense secondary and tertiary branching observed at the site of infection, i.e. the formation of 'witches' brooms' with significantly lower light capture efficiencies. Observed hormone perturbations were consistent with higher rates of transpiration, lower water use efficiencies (WUEs) and more negative needle carbon isotope ratios observed for IBs. Observed reductions in needle size allowed IBs to compensate for reduced hydraulic conductivity. Severe infections resulted in dramatically decreased diameter growth of the bole. It seems likely that the modifications to host hormone contents by eastern dwarf mistletoe infection led white spruce trees to dedicate a disproportionate fraction of their photoassimilate and other resources to self-shaded branches with low WUE. This would have decreased the potential for fixed carbon accumulation, generating a decline in the whole-tree resource pool. As mistletoe infections grew in size and the number of IBs increased, this burden was manifested as increasingly greater reductions in bole growth.

Ethylene involvement in silique and seed development of canola, Brassica napus L

A wide range of plant hormones, including gibberellins (GAs) and auxins are known to be involved in regulating seed and fruit growth and development. Changes in ethylene biosynthesis are also associated with seed and fruit development, but ethylene's role in these processes is poorly understood, as is its possible interaction with the other plant hormones. A major complication of investigating ethylene-induced regulation of developmental processes is ethylene's biphasic mode of action. To investigate ethylene's actions and interactions we used a 1-amino-cyclopropane-1-carboxylic acid (ACC) deaminase transgenic canola line. This line evolves significantly less ethylene from its siliques and seeds, relative to plants from a wild type (WT) background. Plants of the transgenic line also had smaller siliques which were associated with reductions in both seed size and seed number. Application of ethephon, a compound that produces ethylene, to plants of the transgenic line restored the WT phenotype for both siliques and seeds. Application of the same dose of ethephon to WT plants diminished both silique and seed development, showing ethylene's biphasic effect and effectively producing the ACC deaminase transgenic phenotype. There were significant decreases in endogenous concentrations of GA(1) and GA(4) and also of indole-3-acetic acid (IAA), between WT seeds and seedless siliques and seeds and siliques from the transgenic line plants. These differences were emphasized during early stages (10-20 days after pollination) of seed and silique development. The above results strongly suggest that ethylene interacts with other endogenous plant hormones in regulating silique and seed development and growth in WT lines of canola.

Flowering in snow tussock (Chionochloa spp.) is influenced by temperature and hormonal cues

Snow tussocks (Chionochloa spp.) in New Zealand exhibit extreme mast (episodic) seeding which has important implications for plant ecology and plant-insect interactions. Heavy flowering appears to be triggered by very warm/dry summers in the preceding year. In order to investigate the physiological basis for mast flowering, mature snow tussock plants in the field and younger plants in a glasshouse and shadehouse were subjected to a range of manipulative treatments. Field treatments included combinations of warming, root pruning and applications of two native gibberellins (GAs) GA3, which is known to be highly floral inductive and GA4, which is associated with continued floral apex development in another long-day grass. Warming, GA3 alone and especially warming+GA3, significantly promoted flowering, as did applications of GA4 alone and GA4+CCC (2-chloroethyltrimethylammonium chloride, which is a known synergist of GA3-induced flowering in the annual grass, Lolium temulentum L.). Our results provide support for the concept that mast flowering events in tussock species are causally related to high temperature-induced increases in endogenous gibberellin levels. It is likely that GAs (endogenous or applied) promote the continued development of a previously long-day induced floral apex. In addition to the promotion of flowering, applied GA3 also disturbed the plant's innate resource threshold requirements, as shown by the death, over winter, of many non-flowering tillers. Applied GA4 did not show this effect, likely due to its rapid catabolic metabolism to an inactive form. High temperature-induced flowering mediated by elevated levels of endogenous floral-promotive GAs could have important implications for regulating the evolutionary interaction between these masting plants and their seed predators.

Tissue-specific regulation of gibberellin biosynthesis in developing pea seeds

Previous work suggests that gibberellins (GAs) play an important role in early seed development. To more fully understand the roles of GAs throughout seed development, tissue-specific transcription profiles of GA metabolism genes and quantitative profiles of key GAs were determined in pea (Pisum sativum) seeds during the seed-filling development period (8-20 d after anthesis [DAA]). These profiles were correlated with seed photoassimilate acquisition and storage as well as morphological development. Seed coat growth (8-12 DAA) and the subsequent dramatic expansion of branched parenchyma cells were correlated with both transcript abundance of GA biosynthesis genes and the concentration of the growth effector GA, GA(1). These results suggest GA(1) involvement in determining the rate of seed coat growth and sink strength. The endosperm's PsGA20ox transcript abundance and the concentration of GA(20) increased markedly as the endosperm reached its maximum volume (12 DAA), thus providing ample GA(20) substrate for the GA 3-oxidases present in both the embryo and seed coat. Furthermore, PsGA3ox transcript profiles and trends in GA(1) levels in embryos at 10 to 16 DAA and also in embryo axes at 18 DAA suggest localized GA(1)-induced growth in these tissues. A shift from synthesis of GA(1) to that of GA(8) occurred after 18 DAA in the embryo axis, suggesting that deactivation of GA(1) to GA(8) is a likely mechanism to limit embryo axis growth and allow embryo maturation to proceed. We hypothesize that GA biosynthesis and catabolism are tightly regulated to bring about the unique developmental events that occur during seed growth, development, and maturation.

Gibberellins: a phytohormonal basis for heterosis in maize

Four commercially important maize parental inbreds and their 12 F(1) hybrids were studied to investigate the role of the phytohormone gibberellin (GA) in the regulation of heterosis (hybrid vigor). All hybrids grew faster than any inbred. In contrast, all inbreds showed a greater promotion of shoot growth after the exogenous application of GA(3). Concentrations of endogenous GA(1), the biological effector for shoot growth in maize, and GA(19), a precursor of GA(1), were measured in apical meristematic shoot cylinders for three of the inbreds and their hybrids by gas chromatography-mass spectrometry with selected ion monitoring; deuterated GAs were used as quantitative internal standards. In 34 of 36 comparisons, hybrids contained higher concentrations of endogenous GAs than their parental inbreds. Preferential growth acceleration of the inbreds by exogenous GA(3) indicates that a deficiency of endogenous GA limits the growth of the inbreds and is thus a cause of inbreeding depression. Conversely, the increased endogenous concentration of GA in the hybrids could provide a phytohormonal basis for heterosis for shoot growth.

Photoperiod, light quality, and irradiance effects on flowering in the alpine and prairie ecotypes of Stellaria longipes

Plants growing in vegetative shade are subjected to reductions in both red to far-red (R/FR) light ratio and in irradiance levels of photosynthetically active radiation (PAR). In this report we have attempted to uncouple the reduced R/FR ratio- and low PAR-mediated effects of shade on flowering in the ramets of Stellaria longipes Goldie s.l. (Caryophyllaceae) ecotypes collected from alpine “sun” and lower elevation prairie “shade” habitats. Both ecotypes were also tested for their flowering response (defined as the number of open flowers per ramet) to daylength. The alpine ecotype plants can best be classified as day-neutral, whereas prairie ecotype plants require long-days (LD). Under a low PAR of 115 μmol m–2·s–1 given under LD conditions at a reduced (0.7) R/FR ratio, alpine ecotype plants flowered significantly later relative to plants grown under the low PAR at a normal (1.22) R/FR ratio. In contrast, plants of the prairie ecotype flowered earlier under the reduced R/FR ratio combined with the same low PAR. Flower number per ramet differed significantly between the two ecotypes, with alpine ecotype plants developing fewer flowers under a low PAR (109 μmol m–2·s–1 irradiance) relative to a high PAR of 611 μmol m–2·s–1 (both given at a normal R/FR ratio). The prairie ecotype plants responded differently and had similar flower numbers under both low and high PARs at the normal (1.22) R/FR ratio. However, growing the prairie ecotype plants under a reduced R/FR ratio at a low PAR showed a significant increase in number of flowers. In contrast, plants grown under high (2.7) and normal (1.9) R/FR ratios combined with low PAR produced many more flowers than the alpine ecotype. Thus, the two components of shade, reduced R/FR ratio and low PAR can cause distinctly different flowering responses in sun and shade plants of S. longipes.

The interaction of light quality and irradiance with gibberellins, cytokinins and auxin in regulating growth of Helianthus annuus hypocotyls

A reduced red to far-red (R/FR) light ratio and low photosynthetically active radiation (PAR) irradiance are both strong signals for inducing etiolation growth of plant stems. Under natural field conditions, plants can be exposed to either a reduced R/FR ratio or lower PAR, or to a combination of both. We used Helianthus annuus L., the sunflower, to study the effect of reduced R/FR ratio, low PAR or their combination on hypocotyl elongation. To accomplish this, we attempted to uncouple light quality from light irradiance as factors controlling hypocotyl elongation. We measured alterations in the levels of endogenous gibberellins (GAs), cytokinins (CKs) and the auxin indole-3-acetic acid (IAA), and the effect of exogenous hormones on hypocotyl growth. As expected, both reduced R/FR ratio and lower PAR can significantly promote sunflower hypocotyl elongation when given separately. However, providing the reduced R/FR ratio at a low PAR resulted in the greatest hypocotyl growth, and this was accompanied by significantly higher levels of endogenous IAA, GA1, GA8, GA20 and of a wide range of CKs. Providing a reduced R/FR ratio under normal PAR also significantly increased growth and again gave significantly higher levels of endogenous IAA, GAs and CKs. However, only under the de-etiolating influence of a normal R/FR ratio did lowering PAR significantly increase levels of GA1, GA8 and GA20. We thus conclude that light quality (e.g. the R/FR ratio) is the most important component of shade for controlling hypocotyl growth and elevated growth hormone content.

Uncoupling light quality from light irradiance effects in Helianthus annuus shoots: putative roles for plant hormones in leaf and internode growth

An attempt has been made to uncouple the effects of the two primary components of shade light, a reduced red to far-red (R/FR) ratio and low photosynthetically active radiation (PAR), on the elongation of the youngest internode of sunflower (Helianthus annuus) seedlings. Maximal internode growth (length and biomass) was induced by a shade light having a reduced R/FR ratio (0.85) under the low PAR of 157 micromol m(-2) s(-1). Reducing the R/FR ratio under normal PAR (421 micromol m(-2) s(-1)) gave similar growth trends, albeit with a reduced magnitude of the response. Leaf area growth showed a rather different pattern, with maximal growth occurring at the higher (normal) PAR of 421 micromol m(-2) s(-1)), but with variable effects being seen with changes in light quality. Reducing the R/FR ratio (by enrichment with FR) gave significant increases in gibberellin A(1) (GA(1)) and indole-3-acetic acid (IAA) contents in both internodes and leaves. By contrast, a lower PAR irradiance had no significant effect on GA(1) and IAA levels in internodes or leaves, but did increase the levels of other GAs, including two precursors of GA(1). Interestingly, both leaf and internode hormone content (GAs, IAA) are positively and significantly correlated with growth of the internode, as are leaf levels of abscisic acid (ABA). However, changes in these three hormones bear little relationship to leaf growth. By implication, then, the leaf may be the major source of GAs and IAA, at least, for the rapidly elongating internode. Several other hormones were also assessed in leaves for plants grown under varying R/FR ratios and PARs. Leaf ethylene production was not influenced by changes in R/FR ratio, but was significantly reduced under the normal (higher) PAR, the irradiance treatment which increased leaf growth. Levels of the growth-active free base and riboside cytokinins were significantly increased in leaves under a reduced R/FR ratio, but only at the higher (normal) PAR irradiance; other light quality treatments evoked no significant changes. Taken in toto, these results indicate that both components of shade light can influence the levels of a wide range of endogenous hormones in internodes and leaves while evoking increased internode elongation and biomass accumulation. However, it is light quality changes (FR enrichment) which are most closely tied to increased hormone content, and especially with increased GA and IAA levels. Finally, the increases seen in internode and leaf GA content with a reduced R/FR ratio are consistent with FR enrichment inducing an overall increase in sunflower seedling GA biosynthesis.

Involvement of gibberellins in the stem elongation of sun and shade ecotypes of Stellaria longipes that is induced by low light irradiance

Plants from two ecotypes of Stellaria longipes, alpine (an open, sunny habitat) and prairie (where adjacent plants provide a shaded habitat), were grown under normal and reduced levels of photosynthetically active radiation (PAR). Growth under low PAR is significantly promoted in both ecotypes. When quantified by the stable isotope dilution method, endogenous gibberellins (GAs) (GA1, GA8, GA20, GA19) were significantly elevated under low PAR in both 'sun' and 'shade' ecotypes, as was GA53 in the shade ecotype. Changes in endogenous GA1 levels were significantly correlated with stem growth during a 28 d growth cycle and with relative growth rate (RGR) for height under low PAR for both ecotypes. Interestingly, under low irradiance PAR, changes (both increases and decreases) in GA8, the 2beta-hydroxylated 'inactive' catabolite of GA1, closely parallel bidaily stem growth changes for both ecotypes. Because the significantly greater stem elongation of both ecotypes in response to low irradiance PAR is associated with significant increases in the endogenous levels of five GAs (GA53, GA19, GA1, GA8) in the early 13-hydroxylation GA biosynthesis pathway (measured at days 7,14 and 21), we conclude that the low irradiance PAR has very likely induced an overall increase in GA biosynthesis.

Possible roles for ethylene and gibberellin in the phenotypic plasticity of an alpine population of Stellaria longipes

Four phenotypically different genotypes from an alpine population of Stellaria longipes Goldie s.l. (Caryophyllaceae) were collected from neighbouring sites at the top of the Plateau Mountain in southeastern Alberta, Canada, to examine a possible hormonal basis for their differences in stem length, leaf size, and flowering characteristics. All four genotypes had a dwarf shoot phenotype, compared with the low-elevation ecotype. Among the four genotypes, PMI-D was the tallest and had the largest leaves and flowers as well as more flowers per plant. PMI-D also maintained the flowering state, upon repropagation, without low temperature, short-day vernalization. Under controlled long-day warm conditions, the PMI-D genotype had a higher rate of ethylene evolution, but contained levels of endogenous gibberellin A1 that were similar to the other three (smaller) alpine genotypes. PMI-D was more sensitive to exogenously applied ethylene and growth-active gibberellins than other alpine genotypes. In contrast, the other three genotypes were smaller, had fewer (and smaller) flowers, and exhibited low ethylene evolution and a reduced sensitivity to applied ethylene and growth-active gibberellins. Speculatively, this behaviour may indicate an adaptation within this unique population of “dwarf” phenotypes that involves enhanced sensitivity to endogenous ethylene and gibberellins.

Growth and ethylene evolution by shade and sun ecotypes of Stellaria longipes in response to varied light quality and irradiance

Plants growing in the shade receive both low light irradiance and light enriched in far red (FR) (i.e., light with a low red (R) to FR ratio). In an attempt to uncouple the R/FR ratio effects from light irradiance effects, we utilized Stellaria longipes because this species has two distinct natural population ecotypes, alpine (dwarf) and prairie (tall). The alpine population occupies the open, sun habitat. By contrast, the prairie population grows in the shade of other plants. Both 'sun' and 'shade' ecotypes responded with increased stem elongation responses under low irradiance, relative to growth under 'normal' irradiance, and this increased growth was proportionally similar. However, only the shade ecotype had increased shoot elongation in response to a low R/FR ratio. By contrast, the sun ecotype showed increased stem elongation in response to increasing R/FR ratio. Varying the R/FR ratios had no significant effect on ethylene evolution in either sun or shade ecotype. Under low irradiance, only the sun ecotype showed a significantly changed (decreased) ethylene evolution. We conclude that R/FR ratio and irradiance both regulate growth, and that irradiance can also influence ethylene evolution of the sun ecotype. By contrast, R/FR ratio and irradiance, while having profound influences on growth of the shade ecotype, do not appear to regulate these growth changes via effects on ethylene production.

Storage Behavior of Chionanthus retusus Seed and Asynchronous Development of the Radicle and Shoot Apex during Germination in Relation to Germination Inhibitors, Including Abscisic Acid and Four Phenolic Glucosides

Studies on seed storage of Chionanthus retusus Lindl. & Paxt. revealed an orthodox behavior, one which showed both desiccation and freezing tolerance. An epicotyl after-ripening dormancy was expressed in C. retusus seeds by slow growth of the shoot apex relative to more rapid growth of the radicle when seeds were germinated at 30/20 degrees C. Although these seeds exhibit radicle protrusion, they must be after-ripened for another 8-10 weeks at 30/20 degrees C in order to obtain normal shoot growth. Removal of the endosperm, however, quickly stimulated cotyledon and shoot emergence without the additional after-ripening. Water-soluble glucoside phenolics, GL-3, Nuzhenide, ligustroside and oleoside dimethyl ester are present at relatively high levels in endosperm of freshly harvested seeds. These glucoside phenolics are excreted from the endosperm during subsequent after-ripening. Embryo and endosperm tissue from seed germinating at 30/20 degrees C (germination being defined by protrusion of the radicle) had a 10 times lower abscisic acid (ABA) content than similar tissues from freshly harvested mature seed. However, no shoot growth occurred even with the 10-fold reduction in ABA and a concomitant increase in endogenous gibberellins A1, A4 and A20. Thus, epicotyl dormancy during the first 8 weeks of after-ripening at 30/20 degrees C may be controlled by factors other than high ABA, i.e., the slow development of the shoot apex following radicle protrusion may be controlled more by high levels of glucoside phenolics than by diminished ABA and elevated GA levels.

Pleiotropic effects of the male sterile33 (ms33) mutation in Arabidopsis are associated with modifications in endogenous gibberellins, indole-3-acetic acid and abscisic acid

Earlier, we reported that mutation in the Male Sterile33 (MS33) locus in Arabidopsis thaliana causes inhibition of stamen filament growth and a defect in the maturation of pollen grains [Fei and Sawhney (1999) Physiol Plant 105:165-170; Fei and Sawhney (2001) Can J Bot 79:118-129]. Here we report that the ms33 mutant has other pleiotropic effects, including aberrant growth of all floral organs and a delay in seed germination and in flowering time. These defects could be partially or completely restored by low temperature or by exogenous gibberellin A4 (GA4), which in all cases was more effective than GA3. Analysis of endogenous GAs showed that in wild type (WT) mature flowers GA4 was the major GA, and that relative to WT the ms33 flowers had low levels of the growth active GAs, GA1 and GA4, and very reduced levels of GA9, GA24 and GA15, precursors of GA4. This suggests that mutation in the MS33 gene may suppress the GA biosynthetic pathway that leads to GA4 via GA9 and the early 13-H C20 GAs. WT flowers also possessed a much higher level of indole-3-acetic acid (IAA), and a lower level of abscisic acid (ABA), relative to ms33 flowers. Low temperature induced partial restoration of male fertility in the ms33 flowers and this was associated with partial increase in GA4. In contrast, in WT flowers GA1 and GA4 were very much reduced by low temperature. Low temperature also had little effect on IAA or ABA levels of ms33 flowers, but did reduce (>2-fold) IAA levels in WT flowers. The double mutants, ms33 aba1-1 (an ABA-deficient mutant), and ms33 spy-3 (a GA signal transduction mutant) had flower phenotypes similar to ms33. Together, the data suggest that the developmental defects in the ms33 mutant are unrelated to ABA levels, but may be causally associated with reduced levels of IAA, GA1 and GA4, compared to WT flowers.

16,17-dihydro gibberellin A5 competitively inhibits a recombinant Arabidopsis GA 3beta-hydroxylase encoded by the GA4 gene

Ring D-modified gibberellin (GA) A5 and A20 derivatives are structurally similar to GA20 and GA9 (the precursors to growth-active GA1 and GA4) and, when applied to higher plants, especially grasses, can reduce shoot growth with concomitant reductions in levels of growth-active GAs and increases in levels of their immediate 3-deoxy precursors. The recombinant Arabidopsis GA 3beta-hydroxylase (AtGA3ox1) protein was used in vitro to test a number of ring D-modified GA structures as possible inhibitors of AtGA3ox1. This fusion protein was able to 3beta-hydroxylate the 3-deoxy GAs, GA9 and GA20, to GA4 and GA1, respectively, and convert the 2,3-didehydro GA, GA5, to its 2,3-epoxide, GA6. Michaelis-Menten constant (Km) values of 1.25 and 10 microM, respectively, were obtained for the GA9 and GA20 conversions. We utilized the enzyme's ability to convert GA20 to GA1 in order to test the efficacy of GA5, 16,17-dihydro GA5 (dihydro GA5), and a number of other ring D-modified GAs as inhibitors of AtGA3ox activity. For the exo-isomer of dihydro GA5, inhibition increased with the dose of dihydro GA5, with Lineweaver-Burk plots showing that dihydro GA5 changed only the Km of the enzyme reaction, not the V(max), giving a dissociation constant of the enzyme-inhibitor complex (Ki) of 70 microM. Other ring D-modified GA derivatives showed similar inhibitory effects on GA1 production, with 16,17-dihydro GA20-13-acetate being the most effective inhibitor. This behavior is consistent with dihydro GA5, at least, functioning as a competitive substrate inhibitor of AtGA3ox1. Finally, the recombinant AtGA3ox1 fusion protein may be a useful screening tool for other effective 3beta-hydroxylase inhibitors, including naturally occurring ones.

Structure-Activity Studies of Brassinosteroids and the Search for Novel Analogues and Mimetics with Improved Bioactivity

A number of novel brassinosteroid analogues were synthesized and subjected to the rice leaf lamina inclination bioassay. Modified B-ring analogues included lactam, thiolactone, cyclic ether, ketone, hydroxyl, and exocyclic methylene derivatives of brassinolide. Those derivatives containing polar functional groups retained considerable bioactivity, whereas the exocyclic methylene compounds were devoid of activity. Analogues containing normal alkyl and cycloalkyl substituents at C-24 (in place of the isopropyl group of brassinolide) showed an inverse relationship between activity and chain length or ring size, respectively. The corresponding cyclopropyl and cyclobutyl derivatives were significantly more active than brassinolide and appear to be the most potent brassinosteroids reported to date. When synergized with the auxin indole-3-acetic acid (IAA), their bioactivity can be further enhanced by 1-2 orders of magnitude. The cyclopropyl derivative, when coapplied with the auxin naphthaleneacetic acid, gave a significant increase in yield of wheat in a field trial. Certain 25- and 26-hydroxy derivatives are known metabolites of brassinosteroids. All of the C-25 stereoisomers of 25-hydroxy, 26-hydroxy, and 25,26-dihydroxy derivatives of brassinolide were prepared and shown to be much less active than brassinolide. This indicates that they are likely metabolic deactivation products of the parent phytohormone. A series of methyl ethers of brassinolide was synthesized to block deactivation by glucosylation of the free hydroxyl groups. The most significant finding was that the compound where three of the four hydroxyl groups (at C-3, C-22, and C-23) had been converted to methyl ethers retained substantial bioactivity. This type of modification could, in theory, allow brassinolide or 24-epibrassinolide to resist deactivation and thus offer greater persistence in field applications. A series of nonsteroidal mimetics of brassinolide was designed and synthesized. Two of the mimetics showed significant bioactivity and one had bioactivity comparable to brassinolide, but only when formulated and coapplied with IAA. They thus represent the first nonsteroidal analogues possessing brassinosteroid activity.

Inhibition of growth of microcultured Hancornia speciosa shoots by 3beta-hydroxylated gibberellins and one of their C-3 deoxy precursors

Gibberellins (GAs) A(1), A(3), A(4) and A(7), all 3beta-hydroxylated, growth-active GAs, significantly inhibited shoot elongation and the formation of nodes in in vitro-grown Hancornia speciosa, as did GA(20), a 3-deoxy precursor of GA(1). Ancymidol, an early-stage inhibitor of GA biosynthesis, significantly retarded shoot elongation without affecting the formation of nodes. Co-application of ancymidol and GA(1 )did not overcome the ancymidol-induced growth retardation. Trinexapac-ethyl, which can inhibit 3beta-hydroxylation (GA activation) and 2beta-hydroxylation (GA inactivation), gave no significant response on either shoot elongation or node formation, while two isomers of 16,17-dihydro GA(5), also inhibitors of GA 3beta-hydroxylation, significantly inhibited both shoot growth and the formation of nodes. These unusual results may indicate a unique metabolism for GAs in microcultured shoots of H. speciosa.

Synthesis of gibberellin GA6 and its role in flowering of Lolium temulentum

The induction of flowering by one long day (LD) in the grass Lolium temulentum is most closely mimicked by application of the gibberellins (GAs) GA(5) or GA(6), both of which occur naturally. These gibberellins promote floral development but have little effect on stem elongation. Endogenous GA(5) and GA(6) contents in the shoot apex double on the day after the LD and, for GA(5) (and we presume for GA(6) as well) reach a concentration known to be inductive for the excised shoot apex in vitro. They are, therefore, strong candidates as LD floral stimuli in this grass. The synthesis of GA(6) and an examination of its florigenic properties in L. temulentum are described.

The role of gibberellins in embryo axis development

The role of gibberellins (GAs) during early embryo development was examined using microspore-derived embryos (MDEs) of Brassica napus. At the globular stage of development, 10 d after initial culture (DAC) when endogenous GA(1) levels are increasing rapidly, a triazole, uniconazole, was used at 1, 33 and 100 microM to inhibit GA biosynthesis. Within this dose range there was no apparent effect of the inhibitor on embryo growth through to the early torpedo stage. However, by 25 DAC uniconazole-treated MDEs showed significantly reduced (50%) axis elongation. Addition of GA(1) at 33 microM on 14 DAC to embryos pretreated with 1 microM uniconazole on 10 DAC prevented this reduction in axis length, giving axis elongation equivalent to untreated MDEs. Application of GA(1) alone, however, did not significantly increase axis elongation. The reduced axis growth seen with uniconazole treatment was due to reduced cell elongation, but not cell number, and the co-applied GA(1) thus prevented the uniconazole-induced reduction in cell length. The elongating axis of MDEs may thus be a useful tool for examining the role of GAs in cell elongation.

Abscisic acid, phaseic acid and gibberellin contents associated with dormancy and germination in barley

Analyses of abscisic acid (ABA), ent-kaurenoids and gibberellins (GAs) showed that there were major changes in the contents of these compounds associated with germination of after-ripened barley (Hordeum vulgare cv. Schooner and cv. Proctor) grain but not in hydrated dormant grain. Embryos from dormant and after-ripened dry grain contained similar amounts of ABA, of ent-kaurenoids and of GAs, determined by gas chromatography-mass spectrometry-selected ion monitoring. In embryos of after-ripened grain, ABA content decreased rapidly after hydration and ABA appeared to be metabolized (inactivated) to phaseic acid (PA) rather than diffusing into the endosperm or the surrounding medium as previously thought. Similar changes in ABA occurred in hydrated dormant grain during germination in darkness. Accumulation of ent-kaurenoids and GAs, including GA1, the first biologically active GA in the early 13-hydroxylation biosynthetic pathway, occurred to a much greater extent in after-ripened than in dormant grain and these changes occurred mainly after 18 h of hydration when ABA had already decreased and germination was occurring. The block in ent-kaurenoid and GA synthesis in dormant grain appeared to occur prior to ent-kaurene in the biosynthetic pathway. These results are consistent with the view that ABA is the primary effector of dormancy and that after-ripening involves the development of the ability to reduce the amount of ABA quickly following hydration. Accumulation of GAs does not appear to be causally related to loss of dormancy but it does appear to be related to germination.

Dormancy in peach (Prunus persica) flower buds. VI. Effects of gibberellins and an acylcyclohexanedione (trinexapac-ethyl) on bud morphogenesis in field experiments with orchard trees and on cuttings

The effects of several gibberellins (GAs), exo-16,17-dihydro GA5, 2,2-dimethyl GA4, and GA3, and trinexapac-ethyl (an acylcyclohexanedione inhibitor of late-stage GA biosynthesis), were assessed for their effects on flower bud development during and after winter dormancy in peach (Prunus persica (L.) Batsch.) in three field trials and one experiment using cuttings. At late developmental stages, GA3 hastened floral bud development and shortened the time to anthesis, whereas early-stage applications of GA3 either had no effect or delayed floral bud development. In contrast, an exceptionally growth-active GA, 2,2-dimethyl GA4, promoted floral bud development (tested only on cuttings) across a range of application dates. However, it also induced a high percentage of bud abscission and remaining buds had a necrotic gynoecium and alterations in the androecium. Surprisingly, trinexapac-ethyl also promoted floral bud development, although it was not as effective as GA1. Trinexapac-ethyl-treated buds also showed morphological alterations and gynoecium necrosis. However, the best and most consistent treatment for enhancing floral bud development and hastening flower anthesis was 16,17-dihydro GA5. It stimulated floral bud development in up to 80% of the treated buds. Further, the promotive effect of 16,17-dihydro GA5 was maintained through to anthesis across three years of field experiments on intact trees, as well as with cuttings. Whether 16,17-dihydro GA5, a competitive inhibitor of the 3β-hydroxylation step in GA biosynthesis, acts per se, acts via a metabolite (such as 16,17-dihydro GA3), or acts by modifying endogenous GA metabolism is not yet known.Key words: gibberellins, trinexapac-ethyl, floral bud morphogenesis, peach.

Dormancy in peach (Prunus persica) flower buds. V. Anatomy of bud development in relation to phenological stage

Anatomical changes in the peach (Prunus persica (L.) Batsch.) flower buds were defined and then assessed and correlated with the phenological stage from early dormancy through to flower opening. The peach flower bud, unlike the vegetative bud, shows a continuous anatomical development during the late autumn and winter dormancy period, even though there are no obvious macroscopic changes. Sterile whorls differentiate rapidly in late summer through early autumn. In contrast, fertile whorls develop very slowly during winter; their rapid development begins in late winter and continues through early spring. The androecium develops throughout the winter, while the gynoecium develops in late winter. By late winter, the anthers begin to undergo microsporogenesis and microgametogenesis and the ovaries have formed ovules. Vascular connections between flower primordia and branch wood are complete by late winter, when rapid phenological changes begin. At this point in time, the peach floral bud enters a "rapid maturation phase" that ends in flower opening. Thus, for the peach flower bud at least, the concept of dormancy as "a temporary suspension of visible growth of any plant structure containing a meristem" that was proposed by earlier researchers appears inappropriate. Rather, cell division, enlargement, and differentiation, which lead to organogenesis, take place throughout the entire "dormancy" period.Key words: dormancy, floral bud anatomy, floral bud phenology, peach, Prunus persica.

Synthesis and bioactivity of C-2 and C-3 methyl ether derivatives of brassinolide

The following six novel methyl ether derivatives of brassinolide were prepared and their brassinosteroid activity was measured by means of the rice leaf lamina inclination bioassay: 2-O-methylbrassinolide, 3-O-methylbrassinolide, 2,22,23-tri-O-methylbrassinolide, 3,22,23-tri-O-methylbrassinolide, 2-O-methyl-25-methoxybrassinolide and 3-O-methyl-25-methoxybrassinolide. Brassinolide was used as a standard for comparison. All six compounds were also tested in the presence of 1000 ng of indole-3-acetic acid (IAA), an auxin that synergizes the effects of brassinosteroids. The 2-O-methyl- and 3-O-methylbrassinolide derivatives showed weak activity at high doses, which was enhanced by IAA, especially in the case of the 3-O-methyl derivative. Similarly, the 2,22,23-tri-O-methyl- and 3,22,23-tri-O-methyl derivatives displayed weak bioactivity on their own, but significantly stronger activity when applied with IAA. The 3-O-methyl and 3,22,23-tri-O-methyl analogues plus IAA were comparable in bioacivity to brassinolide alone, but were less active than brassinolide plus IAA. In each case, O-methylation at C-2 resulted in a greater loss of activity than O-methylation at C-3 under the same conditions. The relatively strong activity of 3,22,23-tri-O-methylbrassinolide in the presence of IAA is especially noteworthy as it indicates that free hydroxyl groups at C-3, C-22, and C-23 are not essential for bioactivity. Finally, 2-O-methyl- and 3-O-methyl-25-methoxybrassinolide were essentially inactive alone, and showed only a modest increase in bioactivity when coapplied with IAA.

Bioactivity of 25-hydroxy-, 26-hydroxy, 25,26-dihydroxy- and 25,26-epoxybrassinolide

The bioactivity of 25-hydroxybrassinolide, (25S)- and (25R)-26-hydroxybrassinolide, (25S)- and (25R)-25,26-dihydroxybrassinolide, and of (25R)-25,26-epoxybrassinolide was tested in the rice leaf lamina inclination assay. The 25- and (25S)-26-hydroxy derivatives are known metabolites of the naturally-occurring phytohormone brassinolide, whereas the other compounds are novel, but closely related, congeners. When tested alone, all showed either no activity or only weak activity at relatively high doses. When coapplied with indole-3-acetic acid (IAA), an auxin that synergizes the effects of brassinosteroids, enhanced bioactivity was observed for each compound. However, even when applied together with IAA, none of the compounds proved more bioactive than brassinolide with or without IAA. We conclude from these results that enzymatic hydroxylation of endogenous brassinolide at C-25 and/or C-26 does not enhance brassinosteroid activity, and so does not comprise an activation pathway in brassinolide biosynthesis. Instead, these hydroxylations result in modest to appreciable metabolic deactivation.

Design, synthesis, and bioactivity of the first nonsteroidal mimetics of brassinolide

Ten novel compounds, each consisting of two subunits and a linker, were designed with the aid of molecular modeling to resemble the natural steroidal phytohormone brassinolide. The mimetics were synthesized and subjected to the rice leaf lamina inclination bioassay to test for brassinosteroid activity. Most of the mimetics displayed very weak or no bioactivity, but two were strongly active when coapplied with the auxin indole-3-acetic acid (IAA), which synergizes the activity of brassinosteroids. Thus, 1-(4,6 alpha,7 alpha-trihydroxy-5,6,7,8-tetrahydronaphthyl)-2-(6 alpha',7 alpha'-dihydroxy-5',6',7',8'-tetrahydronaphthyl)ethyne (4) and (E)-1,2-bis[trans-(4a alpha,8a beta)-4-oxo-6 alpha,7 alpha-dihydroxy-4a,5,6,7,8,8a-hexahydro-(3H)-naphthyl]ethylene (11) showed exceptional activity at doses as low as 0.01 ng and 0.001 ng/plant, respectively. These compounds are the first biologically active nonsteroidal brassinolide mimetics.

Design, synthesis, and bioactivity of the first nonsteroidal mimetics of brassinolide

Ten novel compounds, each consisting of two subunits and a linker, were designed with the aid of molecular modeling to resemble the natural steroidal phytohormone brassinolide. The mimetics were synthesized and subjected to the rice leaf lamina inclination bioassay to test for brassinosteroid activity. Most of the mimetics displayed very weak or no bioactivity, but two were strongly active when coapplied with the auxin indole-3-acetic acid (IAA), which synergizes the activity of brassinosteroids. Thus, 1-(4,6 alpha,7 alpha-trihydroxy-5,6,7,8-tetrahydronaphthyl)-2-(6 alpha',7 alpha'-dihydroxy-5',6',7',8'-tetrahydronaphthyl)ethyne (4) and (E)-1,2-bis[trans-(4a alpha,8a beta)-4-oxo-6 alpha,7 alpha-dihydroxy-4a,5,6,7,8,8a-hexahydro-(3H)-naphthyl]ethylene (11) showed exceptional activity at doses as low as 0.01 ng and 0.001 ng/plant, respectively. These compounds are the first biologically active nonsteroidal brassinolide mimetics.

Screening the foods of an endangered parrot, the kakapo (Strigops habroptilus), for oestrogenic activity using a recombinant yeast bioassay

In recent years the possibility of environmental oestrogens affecting the reproduction of vertebrates has become an issue of both public and scientific interest. Although the significance of such chemicals remains controversial there is clear evidence that, in some contexts, environmental oestrogens can influence the fertility of vertebrates. Highly endangered species represent a situation in which even modest reductions in the fertility of key individuals may have implications for the survival of the entire species. This paper reports the screening of both natural and supplementary foods of the kakapo (Strigops habroptilus), a critically endangered New Zealand nocturnal parrot, for oestrogenic activity using a recombinant yeast based bioassay. Low levels of oestrogenic activity were detected in one of the 'chick-raising' foods, but no oestrogenic activity was detected in the adult supplementary foods. The oestrogenicity of a range of phytochemicals possibly associated with the kakapo natural diet was also examined. Two such phytochemicals, podocarpic acid and its reduced derivative podocarpinol, showed weak oestrogenic activity (approximately 10(-6) and 10(-4) of the activity of 17-beta-oestradiol, respectively).

Endogenous gibberellins in immature seeds of Prunus persica L.: identification of GA(118), GA(119), GA(120), GA(121), GA(122) and GA(126)

The endogenous gibberellins in immature seeds of Prunus persica were analyzed by gas chromatography-mass spectrometry. Eleven known gibberellins, GA(3), GA(9), GA(17), GA(19), GA(30), GA(44), GA(61), GA(63), GA(87), GA(95) and GA(97) were identified. Additionally, several hitherto unknown gibberellins were detected and their putative structures were verified by synthesis of the authentic gibberellins. These gibberellins were then assigned trivial numbers, e.g. 1alpha-hydroxy GA(20) (GA(118)), 1alpha-hydroxy GA(9) (GA(119)), 1,2-didehydro GA(9) (GA(120)), 1,2-didehydro GA(70) (GA(121)), 1,2-didehydro GA(69) (GA(122)) and 1,2-didehydro GA(77) (GA(126)). GA(118) and GA(119) were the first 1alpha-hydroxy gibberellins identified from higher plants. The above profile of 1,2-didehydro gibberellins suggests that 1,2-dehydrogenation might occur prior to 3beta-hydroxylation in biosynthesis of GA(3), GA(30) and GA(87) in immature seeds of P. persica.

Reduced de-etiolation of hypocotyl growth in a tomato mutant is associated with hypersensitivity to, and high endogenous levels of, abscisic acid

A recessive single gene mutant, 7B-1, in tomato was originally selected for its photoperiod-dependent male sterility. The 7B-1 mutant also has some pleiotropic effects including reduced light-induced inhibition, i.e. de-etiolation, of the hypocotyl in long days (LD), increased seed size and weight, and reduced transpiration rate. These traits led us to investigate the sensitivity of 7B-1 to exogenous hormones and the interaction of these responses with daylength. In LD, but not in short days (SD), 7B-1 was more sensitive than wild-type (WT) to exogenous abscisic acid (ABA) for inhibition of seed germination, root elongation and transpiration rate. 7B-1 mutant also exhibited reduced responses to exogenous gibberellin (GA(3)) for hypocotyl elongation, and to inhibitors of GA biosynthesis for seed germination and root and hypocotyl elongation. 7B-1 hypocotyls contained a higher level of endogenous ABA than WT in both photoperiods, although ABA levels were higher in LD than in SD. In contrast, growth-active GAs, i.e. GA(1), GA(3) and GA(4), and IAA were low in the mutant hypocotyls. The 7B-1 mutant appears to be an ABA-overproducer, and the photoperiod-regulated ABA levels may be responsible for the hypersensitivity of the mutant to exogenous ABA.

Role of ethylene in cotyledon development of microspore-derived embryos of Brassica napus

Ethylene production during seed development in Brassica napus occurs first at 20 d after pollination (DAP), while a second greater peak occurs at 35 DAP. Because of the inaccessible location of the embryo within the maternal tissue, microspore-derived embryos (MDEs) of B. napus were used as a model for studying the role of ethylene during embryo development. The MDEs also produced a peak in ethylene evolution at 20 DAC (i.e. the early cotyledonary stage), dropping to minimal levels by 25-30 DAC. At 20 DAC the excised cotyledon evolved 85% of the ethylene found in the whole MDE. To determine the role of ethylene, MDEs were treated with aminoethoxyvinylglycine (AVG, an inhibitor of ethylene biosynthesis), CoCl(2) (an inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase), and silver thiosulphate (STS, an inhibitor of ethylene action). An inhibition in ethylene production or action at 20 DAC resulted in diminished lateral cotyledon expansion, due to a reduction in the lateral expansion of cells within the cotyledon. Recovery to 'control-type' levels of cotyledon cell expansion was achieved by application of ACC (the metabolic precursor of ethylene) to AVG-treated MDEs. Thus, ethylene production at 20 DAP likely controls cotyledon expansion during embryo development.

Synthesis and bioactivity of 6alpha- and 6beta-hydroxy analogues of castasterone

The reduction of castasterone with sodium in ethanol produced chiefly the known 6alpha-hydroxy stereoisomer, whereas reduction with sodium orohydride in methanol afforded mainly the novel 6beta-epimer. Both compounds showed variable bioactivity through four separate assays via the rice leaf lamina inclination bioassay. However, when treated with an appropriate statistical program to remove outliers, the averaged results clearly indicated that the two 6-hydroxy epimers possess comparable and significant bioactivity, which is, however, lower than that of castasterone or brassinolide. When applied together with 1000 ng of the auxin, indole-3-acetic acid (IAA), the activity of both the 6alpha and 6beta hydroxy epimers was enhanced by ca. one order of magnitude across a wide range of doses.

Effect of chain length and ring size of alkyl and cycloalkyl side-chain substituents upon the biological activity of brassinosteroids. Preparation of novel analogues with activity exceeding that of brassinolide

A series of brassinosteroids with different alkyl or cycloalkyl substituents in place of the isopropyl group at C-24 of brassinolide (1) were prepared by the CuCN-catalyzed addition of Grignard reagents to (threo-2R,3S,5alpha,22R,23R,24S)-23,24-epoxy-6, 6-(ethylenedioxy)-2,3-(isopropylidenedioxy)-26, 27-dinorcholestan-22-ol (9), followed by deketalization and Baeyer-Villiger oxidation. Compound 9 was employed as part of a 70:30 threo/erythro mixture of epoxides 9 and 10, from which the erythro-epoxide 10 was recovered intact after the Grignard additions. Thus, the corresponding n-dodecyl, n-hexyl, n-propyl, tert-butyl, cyclohexyl, cyclopentyl, cyclobutyl, and cyclopropyl analogues of brassinolide were obtained. A rearrangement byproduct was observed during the preparation of the cyclopropyl-substituted brassinosteroid when ether was used as the solvent in the Grignard reaction, but could be avoided by the use of THF. A method for recycling the undesired erythro-epoxide 10 was developed on the basis of deoxygenation with tellurium and lithium triethylborohydride. The rice leaf lamina inclination assay was then used to measure the bioactivity of the products. In general, increasing activity was observed as the length or ring size of the C-24 hydrocarbon substituent decreased. The novel cyclobutyl- and cyclopropyl-substituted analogues of brassinolide (1) were ca. 5-7 times as active as 1 and thus appear to be the most potent brassinosteroids reported to date. Further enhancement of the bioactivity of all of the above brassinosteroids, except that of the inactive n-dodecyl derivative, was observed when the brassinosteroid was applied together with an auxin, indole-3-acetic acid (IAA). The synergy between the brassinosteroids and IAA thus increased the bioactivity of the brassinosteroids, including the cyclopropyl and cyclobutyl derivatives, by ca. 1-2 orders of magnitude.

Role of gibberellins in the development of floral organs of the gibberellin-deficient mutant, ga1-1, of Arabidopsis thaliana

The gibberellin-deficient mutant, ga1-1 (NG5) of Arabidopsis thaliana, when induced by 16-h-long days, will form floral buds. However, the flower stalk is very short and floral organs within the flowers remain undeveloped; petal growth is arrested, with the petals being scaly and translucent, the stamens are abortive, the filaments do not elongate, and the pollen does not mature. Sepals and pistils are also underdeveloped. All of the above defects of this mutant can be completely eliminated if certain gibberellins (GAs) are applied to the young floral buds. That is, the applied GA acts to normalize not only plant height but also development of floral organs, thereby yielding good seed set from self-pollination. There were appreciable differences in the efficacy of different GA structures in normalizing the various floral organs. For seed production, the order of efficacy was 2,2-dimethyl GA4 > GA7 > GA3 = GA4 > GA1 > GA5 = GA9. When 2,2-dimethyl GA4 was used to determine an optimal GA dose, the following pattern emerged: filament elongation and pollen development, 1-10 ng; petal and pistil growth, 1 ng; sepal growth, 0.1 ng; papilla elongation, 0.01 ng. However, one application at these doses was insufficient to normalize the flowers, which were formed one after another, and a continuing supply of GA at the optimal dose was required for normal flower development and seed set. We conclude from this work that GAs play an essential role in the development of floral organs of Arabidopsis and that petals and stamens (filaments and pollen) in particular develop normally only when GAs are present at the optimal level.Key words: Arabidopsis thaliana, floral organ development, gibberellin, gibberellin-deficient mutant, petal and pollen development, reproductive function.

Synthesis and Biological Activity of 25-Methoxy-, 25-Fluoro-, and 25-Azabrassinolide and 25-Fluorocastasterone: Surprising Effects of Heteroatom Substituents at C-25

The CuCN-catalyzed addition of 2-propenylmagnesium bromide to (threo-2R,3S,5alpha,22R,23R,24S)-23,24-epoxy-6,6-(ethylenedioxy)-2,3-(isopropylidenedioxy)-26,27-dinorcholestan-22-ol (11a) afforded the corresponding Delta(25)-22,23-diol 12. This was converted into 25-methoxybrassinolide (7) by protection as the 22,23-acetonide 13, oxymercuration in methanol, Baeyer-Villiger oxidation, and deprotection. Similarly, the addition of pyridinium poly(hydrogen fluoride) to 13 and deprotection afforded 25-fluorocastasterone (8), which was converted into 25-fluorobrassinolide (9) by Baeyer-Villiger oxidation. Treatment of threo-epoxide 11a with Me(2)NMgBr, followed by Baeyer-Villiger oxidation of the corresponding tetraacetate and saponification, provided 25-azabrassinolide (10). Epoxide 11a is therefore a versatile intermediate for the synthesis of side-chain analogues of brassinolide (1). 25-Methoxybrassinolide (7) displayed strong activity in the rice leaf lamina inclination bioassay, which was significantly enhanced by the simultaneous application of an auxin, indole-3-acetic acid (IAA). Thus, the presence of a 25-methoxy substituent, like that of the previously reported 25-hydroxy group in the 24-epibrassinolide series, yields a molecule with potent biological activity. On the other hand, 8-10 showed no bioactivity with or without IAA. This suggests that either the 25-fluoro and 25-aza substituents interfere with binding to a putative brassinosteroid receptor or that they prevent the in vivo enzymatic oxidation at C-25 that is required for bioactivity.

Embryo-specific gene expression in microspore-derived embryos of brassica napus. An interaction between abscisic acid and jasmonic acid1,2

The induction of napin and oleosin gene expression in Brassica napus microspore-derived embryos (MDEs) was studied to assess the possible interaction between abscisic acid (ABA) and jasmonic acid (JA). Napin and oleosin transcripts were detected sooner following treatment with ABA than JA. Treatment of MDEs with ABA plus JA gave an additive accumulation of both napin and oleosin mRNA, the absolute amount being dependent on the concentration of each hormone. Endogenous ABA levels were reduced by 10-fold after treatment with JA, negating the possibility that the observed additive interaction was due to JA-induced ABA biosynthesis. Also, JA did not significantly increase the uptake of [3H-ABA] from the medium into MDEs. This suggests that the additive interaction was not due to an enhanced carrier-mediated ABA uptake by JA. Finally, when JA was added to MDEs that had been treated with the ABA biosynthesis inhibitor fluridone, napin mRNA did not increase. Based on these results with the MDE system, it is possible that embryos of B. napus use endogenous JA to modulate ABA effects on expression of both napin and oleosin. In addition, JA could play a causal role in the reduction of ABA that occurs during late stages of seed development.

Metabolism of deuterium- and tritium-labeled gibberellins in cambial region tissues of Eucalyptus globulus stems

Deuterium- and tritium-labeled gibberellins (GAs) were applied to stems of 3-year-old Eucalyptus globulus Labill. saplings and 9-month-old potted seedlings. Cambial region tissues surrounding the application point were collected 6, 24 or 48 h later. Twenty-four hours after application of 5 &mgr;g of [(2)H(2)]GA(20), 7% of the cambial region GA(20) pool, 7% of the GA(1) pool and 58% of the GA(29) pool were labeled with deuterium based on selected ion monitoring of purified extracts subjected to gas chromatography-mass spectrometry. The relatively low percent dilution of endogenous GAs by [(2)H(2)]GAs suggests that the exogenous application of [(2)H(2)]GA(20) did not result in substrate overloading, indicating that these conversions probably occur naturally within cambial region tissues. Extracts from similar cambial region tissues fed tritium-labeled GAs were sequentially fractionated by SiO(2) partition chromatography, C(18) reversed phase HPLC and N(CH(3))(2) HPLC. The radioactivity profiles indicated metabolism of GA(20) to GA(1) and GA(29), GA(1) conversion to GA(8), GA(4) to GA(34) and GA(9) to GA(51). Gibberellins GA(34), GA(51) and GA(29) are C-2beta-hydroxylated catabolites of low biological activity, whereas GA(1) and GA(4) are probably effectors of growth in the Eucalyptus stem and shoot. Evidence for C-13 hydroxylation of GA(4) to GA(1), GA(9) to GA(4) or GA(9) to GA(20) in the stem was inconclusive. Thus, although GA(4) and GA(9) are native to cambial region tissues, GA(1) is probably not produced from them in significant quantities. We conclude that the early C-13-hydroxylation pathway; i.e., conversion of GA(19) to GA(20) to GA(1), is the major pathway of GA(1) biosynthesis.

Far-red light stimulates internode elongation, cell division, cell elongation, and gibberellin levels in bean

The contributions of cell division and cell elongation and the potential role of gibberellins in the far-red light stimulation of bean internode elongation were investigated. When bean plants, Phaseolus vulgaris cv. Kentucky Wonder, were grown in white light supplemented with far-red light a significant increase, up to threefold, in internode elongation was observed. Microscopic examination revealed that cell lengths were also increased but by a lower magnitude than internode length. Cell-labeling studies with [3H]thymidine showed that nuclei labeling was increased in internodes receiving supplemental far-red light. Thus far-red light induced increased internode elongation is a result of both increased cell elongation and increased cell division. Gibberellins A1, A20, A19, A44, and A4 and kaurenoic acid were identified in extracts of internode tissue by gas chromatography – mass spectroscopy using [2H2]-labeled internal standards for quantification. It thus appears that the early C-13 hydroxylation pathway is operative in the elongating internode. Endogenous GA1 and GA20 were approximately twofold higher in the first internodes of plants receiving supplemental far-red light. A comparison of the metabolism of exogenously supplied [2H2]GA19 suggested that GA turnover was greater in tissues exposed to supplemental far-red light. These results indicate that both cell division and elongation contribute to the enhanced elongation response of bean internodes to far-red light and that these processes are correlated with an increase in GA levels and (or) metabolism. Keywords: Phaseolus, gibberellins, phytochrome, far-red light.