Golden alga presence and abundance are inversely related to salinity in a high-salinity river ecosystem,Pecos River,USA

Prymnesium parvum (golden alga, GA) is a toxigenic harmful alga native to marine ecosystems that has also affected brackish inland waters. The first toxic bloom of GA in the western hemisphere occurred in the Pecos River, one of the saltiest rivers in North America. Environmental factors (water quality) associated with GA occurrence in this basin, however, have not been examined. Water quality and GA presence and abundance were determined at eight sites in the Pecos River basin with or without prior history of toxic blooms. Sampling was conducted monthly from January 2012 to July 2013. Specific conductance (salinity) varied spatiotemporally between 4408 and 73,786 μS/cm. Results of graphical, principal component (PCA), and zero-inflated Poisson (ZIP) regression analyses indicated that the incidence and abundance of GA are reduced as salinity increases spatiotemporally. LOWESS regression and correlation analyses of archived data for specific conductance and GA abundance at one of the study sites retrospectively confirmed the negative association between these variables. Results of PCA also suggested that at <∼15,000 μS/cm, GA was present at a relatively wide range of nutrient (nitrogen and phosphorus) concentrations whereas at higher salinity, GA was observed only at mid-to-high nutrient levels. Generally consistent with earlier studies, results of ZIP regression indicated that GA presence is positively associated with organic phosphorus and in samples where GA is present, GA abundance is positively associated with organic nitrogen and negatively associated with inorganic nitrogen. This is the first report of an inverse relation between salinity and GA presence and abundance in riverine waters and of interaction effects of salinity and nutrients in the field. These observations contribute to a more complete understanding of environmental conditions that influence GA distribution in inland waters.     

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.     

Interaction Between Mineral Nutrients, Cytokinin and Gibberellic Acid During Growth of Sorghum at High NaCI Salinity

Sorghum bicolor (L.) Moench, cv. 610, adapted to high salinitywas able to grow at 300 mol m^–3 NaCl only when half-strengthHoagland's solution was enriched with mineral nutrients. Theoptimal growth rate was observed in full strength Hoagland'ssolution; at higher or lower concentrations growth rates werelower. In contrast, growth rate of plants exposed to 150 molm^–3 NaCl was not affected by similar modification of theHoagland solution concentration. At high salinity, additionof cytokinin (CK) or gibberellic acid (GA), or a mixture ofboth, can induce the same effect on growth as the increasedmineral nutrient concentration. Phytohormones and increasedmineral concentration have similar effects, possibly becausean imbalance in phytohormones, rather than a mineral deficiency,limits growth at 300 mol m^–3 NaCl in the presence of half-strengthHoagland solution. The change in mineral concentration in thenutrient medium, in addition to its nutritional effect, alsoapparently acts as a signal involved in hormonal balance whichallows growth at high salinity. Exposure of Sorghum to 300 molm^–3 NaCl causes a decrease in the range of nutrient concentrationswhich can sustain growth. Adjustment of the nutrient concentrationmay induce the synthesis of endogenous CK and GA concentrationsrequired for growth. In contrast, addition of CK or GA at similarconcentrations during the adaptation (pretreatment) period inhibitsgrowth and prevents the adaptation process. The response tothe exogenous phytohormone treatments depends on the time elapsedfrom the beginning of salinization. Key words: Adaptation to salinity, cytokinin, gibberellic acid, mineral nutrition, growth, Sorghum, NaCl     

Species richness loss after nutrient addition as affected by N:C ratios and phytohormone GA3 contents in an alpine meadow community

Aims From the light-competition hypothesis, competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light. Greater plant height provides pre-emptive access to light and produces increased height differences among species. The question is what produces these differences in plant height or height growth response among species in response to fertilization.Methods In 2009, a field experiment of N, P and N + P enrichments at three levels each was initiated in an alpine meadow on the northeast Qinghai-Tibet Plateau. Effects of fertilization on species richness, aboveground net primary production (ANPP), relative light intensity and plant height of different plant functional groups were determined. Festuca ovina (grass), Kobresia humilis (sedge), Oxytropis ochrocephala (legume), Taraxacum lugubre (rosette forb) and Geranium pylzowianum (upright forb) were selected as exemplars of each of the indicated functional groups. The N:C ratios in aboveground biomass, gibberellic acid (GA 3) concentrations in leaves, plant heights and height relative growth rate (RGR) of these exemplar species were analyzed in detail.Important findings Species richness of grasses significantly increased with increasing N + P levels. Species richness of legumes and upright forbs decreased after N and N + P additions. P addition had no significant effect on species richness. The effects of N + P addition on species richness and ANPP were consistently stronger than those of the single N or P fertilization. Reductions in species richness caused by nutrient addition paralleled the increases in ANPP and decreases in light intensity under the canopies, indicating indirect effect of nutrient addition on species richness via ANPP-induced light competition. The exemplar species that responded most positively to fertilization in height and RGR also displayed stronger increases in their GA 3 content and N:C ratios. GA 3 concentrations and N:C ratios were positively correlated with height RGR when the data were pooled for all species. The tallest and the fastest-growing grass, F. ovina, had the largest increase in N:C ratios and the highest leaf GA 3 concentrations after nutrient addition. These results indicated that differential responses of GA 3 concentrations and N:C ratios to fertilization were related to the inequality in plant heights among species.     

COMPARATIVE EFFECTS OF GIBBERELLIN AND INDOLE COMPOUNDS ON THE INDUCTION OF PARTHENOCARPY IN SEXUALLY INCOMPATIBLE PERESKIA ACULEATA

Sachar , R. C. (U. Delhi, India.) Comparative effects of gibberellin and indole compounds on the induction of parthenocarpy in sexually incompatible Pereskia aculeata. Amer. Jour. Bot. 49(9): 913–917. Illus. 1962.—The effects of indoleacetic acid (IAA), indolebutyric acid (IBA), gibberellin (G) and gibberellic acid (GA) were studied on the fruit growth of the sexually incompatible Pereskia. Under natural conditions, this plant did not produce any fruits and seeds, and the flowers abscised a week after anthesis. IAA (50–500 ppm) delayed the formation of an abscission layer by another 2 weeks, but it was ineffective in inducing parthenocarpy. IBA (50–500 ppm) induced fruit-set in only 15% of the flowers. Best response was achieved by G (100–500 ppm), or GA (100–500 ppm), which gave 100% fruit-set. The effect of GA in inducing parthenocarpy was not inhibited when used in conjunction with IAA. Maximum size of the fruits was obtained with 2 sprayings of GA, and subsequent sprays were of no consequence. Further, fruit size was the largest when GA or G was sprayed at anthesis, or on old flower buds, but it was much less when the chemicals were sprayed on young flower buds. There was no stimulation of the growth of ovules; instead, a translucent mucilaginous placental tissue developed within the cavity of the fruit wall. Attempts were made to culture ovules and the placental tissue on artificial nutrient medium, but without success.     

Growth and Nitrogen Accumulation in Young Tomato Plants Treated with Gibberellic Acid

The effects of foliar sprays of gibberellic acid (GA) on thegrowth of tomato plants cv. Potentate were studied in growthrooms and a glasshouse. Four sprays of GA (5 ppm) increasedleaf area and whole plant weight relative to water controlsgrown at constant temperatures (7, 17, 22, and 27 °C) for12 days, the largest plants being obtained with 5 ppm. Experimentsmade at four photoperiods (5, 10, 15, and 20 h) and at two lightintensities (7000 and 10 750 lx) showed that GA increased leafand whole plant weight at 15 h, leaf area at 10 and 15 h andstem height at all photoperiods; area, height, and weight increaseswere obtained at both light intensities, leaf growth being increasedmore by GA at 7000 lx and stem growth more at 10 750 lx. Four foliar sprays of GA (5 ppm) were combined with N supplementsapplied via leaf and/or root to plants in sand culture. Withlow supply to the roots (20 ppm N) GA failed to increase growth,but increased it at higher levels. Total N in leaf and stemwas increased by GA or by NH₄NO₃ (10 sprays 280 ppm N) at alllevels of N supplied to roots, but when applied together theeffect on total leaf N was more than additive except at thehighest level (540 ppm) GA increased the concentration of N(as per cent dry matter) in leaf and stem at all levels of Nsupplied to roots. GA and NH₄NO₃ together resulted in a greateramount and a higher concentration of N in the shoots (and usuallyalso in roots) than did NH₄NO₃ alone. Leaf thickness (as freshweight/unit area) could only be increased appreciably by sprayingwith a complete nutrient solution which reduced leaf area butnot dry weight. Growth increases induced by GA were detectable 43 days afterthe first of four sprays in the glasshouse and after 30 daysin the growth room. The persistence of GA effects was comparedwith those induced by sprays of NH₄NO₃.     

Growth and stomata development of Arabidopsis hypocotyls are controlled by gibberellins and modulated by ethylene and auxins

The plant hormones gibberellin (GA), ethylene and auxin can promote hypocotyl elongation of Arabidopsis seedlings grown in the light on a low nutrient medium (LNM). In this study, we used hypocotyl elongation as a system to investigate interactions between GA and ethylene or auxin and analysed their influence on the development of stomata in the hypocotyl. When applied together, GA and ethylene or auxin exerted a synergistic effect on hypocotyl elongation. Stimulated cell elongation is the main cause of hypocotyl elongation. Furthermore, hypocotyls treated with GA plus either ethylene or auxin show an increased endoreduplication. In addition, a small but significant increase in cell number was observed in the cortical cell files of hypocotyls treated with ethylene and GA together. However, studies with transgenic seedlings expressing CycB1::uidA genes revealed that cell division in the hypocotyl occurs only in the epidermis and mainly to form stomata, a process strictly regulated by hormones. Stomata formation in the hypocotyl is induced by the treatment with either GA or ethylene. The effect of GA could be strongly enhanced by the simultaneous addition of ethylene or auxin to the growth medium. Gibberellin is the main signal inducing stomata formation in the hypocotyl. In addition, this signal regulates hypocotyl elongation and is modulated by ethylene and auxin. The implication of these three hormones in relation to cell division and stomata formation is discussed.     

Shoot growth in willow (Salix viminalis) in relation to abscisic acid, plant water status and photoperiod

The decline in growth rate of field-grown willow trees in Aberystwyth, U.K., began in mid-summer and was followed by the senescence and abortion of shoot tips. These events were not triggered by a decline in the length of the natural photoperiod but were coincident with low leaf water potentials that developed in summer. Transient increases in the abscisic acid (ABA) content of shoot tips were observed during the period of declining water potential. These increases were roughly coincident with the onset of growth decline and preceded abortion and senescence of shoot tips. Under controlled conditions growth of both rooted cuttings and potted plants was arrested by short days (8 h) without any increase in tip ABA levels. Growth of rooted cuttings under long days (16 h) was inhibited by exogenous ABA; this inhibition could be relieved by addition of gibberellic acid (GA3) to the nutrient solution. Growth of aseptically cultured apices was also inhibited by ABA; this inhibition was relieved by joint application of GA9 and zeatin riboside.     

The effect of growth regulators on the growth and pigmentation of "Baccara" rose flowers

"Baccara" rose buds were treated with various growth regulatorsduring late stages of bud development. The effect of these substanceson growth and pigmentation were determined. Growth regulatorswere applied by spray or injection or as a lanolin paste, alsoin the nutrient media on which petals were cultured in vitro.Injection of GA into the base of the receptacle caused elongationof the bud whereas IAA, K, ABA, AMO-1618, CCC, and SADH hadlittle or no effect. CCC and MeCl-F did not reduce the elongationcaused by GA. GA treatments also enhanced flower weight andpetal pigmentation and MeCl-F decreased the gibberellin effecton pigmentation. GA treatments of intact flowers and excisedpetals cultured in vitro, were only effective at low temperatures. Gibberellin treatments increased the size of petals, the receptacleand the pedicel only if applied directly to the receptacle.Treatments at lower positions on the flowering shoot eitherhad no effect at all, or caused elongation of only the receptacle. Endogenous gibberellin levels are higher in the receptacle thanin petals or in the pedicel. Injection of GA into the receptaclesignificantly increased gibberellin activity in all flower partswhereas injection into the flowering-shoot base increased gibberellinactivity only in the receptacle. The possibility is discussed that GA, which is exogenously supplieddirectly to the receptacle, enhances flower dimensions and pigmentationby drawing photosynthates to the flower as a consequence ofintensification of the sink. (Received August 17, 1973; )     

Metabolism of gibberellins A1 and A3 in fruits and shoots of Prunus avium

Isotope-labelled GA metabolites were identified by GC--MS, following HPLC fractionation of extracts derived from fruits or shoots, that had been incubated with [2H]- and [3H]- GA1 or [2H]- and [3H]- GA3. GA1 (1) was converted into GA8 (10) by developing fruits and vegetative shoots of sweet cherry (Prunus avium cv. 'Stella'), while GA3 (4) was converted into GA3-isolactone (17). Other metabolites of each GA were detected but were not identified unequivocally. These included a metabolite of GA1 (1) in fruitlets that was more polar (by reverse phase HPLC) than GA8 (10) and a metabolite of similar polarity to GA87 (6), was obtained after incubating fruitlets with GA3 (4). However, no evidence was obtained to suggest that GA87 (6) was a metabolite of GA3 (4) or that GA85 (2) was a metabolite of GA1 (1) in these tissues, under the conditions used. The pattern of metabolites obtained from vegetative tissues was similar to that from fruitlets. However, the results suggested that GA1 (1) and GA3 (4) were metabolised at a greater rate in shoots from mature trees than in shoots from seedlings, and that GA1 (1) was metabolised more rapidly than GA3 (4) in juvenile and mature shoots. We conclude from these observations that GA3 (4) is not a precursor of GA87 (6) and GA32 (5), also, that GA1 (1) is not a precursor of GA85 (2) and GA86 (3) in developing fruits or in vegetative shoots of sweet cherry.     

Effects of Growth Retardants on Norway Spruce (Picea abies)

Young seedlings of Picea abies Karst, grown in nutrient solution were treated with the growth retardants Amo-1618, B-995, and CCC. These were added to the nutrient medium. B-995 and CCC retarded root and shoot growth in the concentrations 100, 10, and 1 mg/l. Growth was almost entirely inhibited by 300 mg/l, obviously due to toxicity. The effects of Amo-1618 were similar but more varying. GA counteracted the effects of all the retardants on shoot growth, but not on root growth.     

A florigenic effect of sucrose in Fuchsia hybrida is blocked by gibberellin-induced assimilate competition

The use of gas chromatography-mass spectrometry-selected ion monitoring along with a (13)C internal standard has allowed sensitive measurements of the sucrose (Suc) content of individual shoot apices of Fuchsia hybrida. With intact plants, as the photosynthetic irradiance increased, so did shoot apex Suc content, reaching saturation at about 500 micromol m(-2) s(-1). These same plants flowered at the higher irradiances, remaining vegetative in 10-h short days at an irradiance of 230 micromol m(-2) s(-1). The strong correlation (r = 0.93) in these studies between flowering and shoot apex Suc content indicates a role for Suc as a stimulus to flowering in this species. However, Suc is not the long-day (LD) "florigen" of F. hybrida because 2 to 4 LD given as a 14-h low-irradiance photoperiod extension (10-15 micromol m(-2) s(-1)) induced flowering but without increase in shoot apex Suc content. Flowering induced by either pathway, the LD- or the Suc-mediated one, was inhibited by applying gibberellin (GA) to the shoot tip. Such inhibition of flowering by GA, at least for the LD pathway, was associated with a reduced apex Suc content, enhanced elongation of subapical stem tissue, and a reduced import into the shoot apex of leaf-sourced assimilate. Thus, our findings show how GA inhibits flowering of F. hybrida and confirm the importance of nutrient diversion in regulating flowering.     

穗花牡荆花芽分化过程中形态和生理指标变化

以穗花牡荆为研究材料,通过探究其花芽分化进程和生理特性,为花期调控技术提供成花机理。采用物候期观察和石蜡切片相结合的方法并测定花芽分化过程中相关生理指标,研究花发育过程中的形态和生理变化。结果表明,穗花牡荆花芽分化为一年多次分化型,其进程可划分为七个时期：未分化期、总轴花序原基分化期、初级分轴花序原基分化期、次级分轴花序原基分化期、小花原基分化期、花器官分化前期和花器官分化后期。同一植株不同位置花芽及同一花序中不同单花分化的进程不同,第一季花期后各阶段的花芽分化形态常存在重叠。花芽分化过程中不同时期叶片和花芽的可溶性糖和可溶性蛋白质含量均有上升下降的变化,总体上叶片中营养物质含量高于花芽保证营养供应。花芽分化过程中,IAA、ABA、CTK和GA3整体水平上先升后降有利于花芽分化进行。研究认为,花芽中大量的可溶性糖和蛋白质积累及较高的碳氮比,有利于穗花牡荆花芽形态分化顺利完成。低水平的GA3/ABA和IAA/CTK有利于花序的形成,ABA/CTK和ABA/IAA比值升高促进小花原基和小花萼片原基的分化, GA3/CTK、GA3/ABA和GA3/IAA比值升高促进花瓣原基、雄雌蕊原基发育。     

Gibberellin structure and function: biological activity and competitive inhibition of gibberellin 2- and 3-oxidases

Some gibberellin (GA) analogues, especially with C-16,17 modifications of GA(5), can inhibit growth of plants apparently by acting as competitors with the endogenous substrate of GA biosynthetic enzymes. Here, we directly confirm the competitive action of GA derivatives but also show that some analogues may retain significant bioactivity. A recombinant 3-oxidase from pea, which converts GA(20) to bioactive GA(1), was inhibited by GA(5), and 16,17-dihydro-GA(5) derivatives, especially if the C-17 alkyl chain length was increased by up to three carbons or if the C-13 hydroxyl was acetylated. Genetic confirmation that GA(5) analogues target 3-oxidases in vivo was provided by comparing the growth response of a WT (LE) pea with a 3-oxidase mutant (le-1). Two pea 2-oxidases that inactivate bioactive GAs, were inhibited by GA(1) and GA(3) but were generally insensitive to GA(5) analogues. alpha-Amylase production by barley half-seeds in response to GA analogues provided a method to study their action when effects on GA biosynthesis were excluded. This bioactivity assay showed that 16,17-dihydro GA(5) analogues have some inherent activity but mostly less than for GA(5) (5-50-fold), which in turn was 100-fold less active than GA(1) and GA(3). However, although C-17 alkyl derivatives with one or two added carbons showed little bioactivity and were purely 3-oxidase inhibitors, adding a third carbon (the 17-n-propyl-16,17-dihydro GA(5) analogue) restored bioactivity to that of GA(5). Furthermore, this analogue has lost its capacity to inhibit stem elongation of Lolium temulentum (Mander et al., Phytochemistry 49:1509-1515, 1998a), although it strongly inhibits the 3-oxidase. Thus, the effectiveness of a GA derivative as a growth retardant will reflect the balance between its bioactivity and its capacity to inhibit the terminal enzyme of GA biosynthesis. The weaker growth inhibition in dicots including pea (approximately 10%) than in monocots such as L. temulentum (>35%) is suggestive of taxonomic differences in the bioactivity of GAs and/or their effects on GA biosynthesis.     

Immunomodulation of gibberellin biosynthesis using an anti-precursor gibberellin antibody confers gibberellin-deficient phenotypes

Immunomodulation is a means to modulate an organism's function by antibody production to capture either endogenous or exogenous antigens. We have recently succeeded in obtaining gibberellin (GA)-deficient phenotypes in Arabidopsis thaliana by using anti-bioactive GA antibodies. In this study, a single-chain antibody (scFv) against GA(24), a precursor GA, was utilized to repress the biosynthesis of bioactive gibberellins. Stable accumulation of the scFv in endoplasmic reticulum (ER) was achieved by being produced as a fusion with GFP as well as KDEL ER-retention signal. The transgenic plants showed GFP fluorescence in the reticulate cortical ER network in epidermal cells. The GFP-scFv fusion produced in plants maintained its binding activity. The transgenic plants showed GA-deficient phenotypes, including reduced rosette leaf development, delayed flower induction and reduced stem elongation of the main culm, especially in the early stage of inflorescence growth. Contrarily, stem elongation of the main culm at a later stage, or that of lateral shoots was much less affected by scFv production. These phenotypes were different from anti-bioactive GA scFv-producing lines, whose stem elongation was continuously repressed throughout the inflorescence development. The GA-deficient phenotypes were recovered by treatment with GA(24) and bioactive GA(4), the latter being more effective. The transgenic lines contained conspicuously higher endogenous GA(24) and clearly less GA(4) than wild-type plants. The expression of GA 20-oxidase and GA 3-oxidase genes, which are feedback-regulated by GA signaling, were up-regulated in those plants. These results demonstrate that the scFv trapped GA(24) in ER and inhibited metabolism of GA(24) to bioactive GA(4).