Influx and efflux of inorganic phosphate in sweet potato slices. effects of abscisic acid on bi-phasic kinetics

Influx and efflux of inorganic phosphate was determined in freshly cut and “aged” slices of sweet potato tubers, in the presence or absence of abscisic acid. Slices aged in the phytohormone took up considerably less phosphate than did the control slices. No difference in the rates of uptake of phosphate by the fresh tissue was observed. Kinetics of uptake of the aged untreated slices, proved to be bi-phasic. This was not the case for the treated slices. Neither the treated nor the untreated uptake curves for the fresh slices were bi-phasic. Efflux of phosphate from the slices aged in abscisic acid was greater than from the untreated slices. The results strongly suggest an effect of abscisic acid on the cell membrane.     

Gibberellic acid improves water deficit tolerance in maize plants

The combination effects of water stress and gibberellic acid (GA₃) on physiological attributes and nutritional status of maize (Zea mays L. cv., DK 647 F1) were studied in a pot experiment. Maize plants were grown in the control (well watered WW) and water stress subjected to treated both water stress and two concentrations of gibberellic acid (GA₃ 25 mg L⁻¹, 50 mg L⁻¹). WS was imposed by maintaining the moisture level equivalent to 50 % pot capacity whereas the WW pots were maintained at full pot capacity. Water stress reduced the total dry weight, chlorophyll concentration, and leaf relative water content (RWC), but it increased proline accumulation and electrolyte leakage in maize plants and appears to affect shoots more than roots. Both concentrations of GA₃ (25 and 50 mg L⁻¹) largely enhanced the above physiological parameters to levels similar to control. WS reduced leaf Ca²⁺ and K⁺ concentrations, but exogenous application of GA₃ increased those nutrient levels similar or close to control. Exogenous application of GA₃ improved the water stress tolerance in maize plants by maintaining membrane permeability, enhancing chlorophyll concentration, leaf relative water content (LRWC) and some macro-nutrient concentrations in leaves.     

Effects of gibberellic Acid and sucrose on the growth of oat (Avena) stem segments

Gibberellic acid induced growth in Avena (oat) stem segments within 35 minutes after hormone application. The total elongation elicited by gibberellic acid was greater than 15 times the control growth. The sensitivity of the segments to low concentrations of gibberellic acid (1 pmole) and the specificity of the segments to the gibberellin class of hormones suggest that oat stem segments would be a valuable tool for gibberellin bioassays. Both gibberellic acid-induced growth and control growth are temperature-dependent and showed a Q₁₀ of two or greater. Although the most apparent effect of gibberellic acid was to promote the uptake of water into the internode, the hormone also promoted transport of endogenous substrate and the uptake of exogenous substrate into the growing region. The growth promotion was accomplished without an apparent increase in osmotic pressure.     

Studies on the physiology of hyacinth bulbs (Hyacinthus orientalis L.) the effect of plant growth regulators on metabolic activities in non-chilled hyacinth bulbs

The effect of gibberellic acid, benzyladenine and a mixture of these compounds on the activity of some hydrolytic enzymes was studied in hyacinth bulbs non-exposed to low temperatures. Plant growth regulators were applied on the heel of dormant bulbs in the middle of July. An intensive elongation of the inflorescence was observed only in the plants treated previously with GA₃ and grown in a warm greenhouse for 63 and 84 days. The activities of amylase, invertase and acid phosphatase were higher in the flower buds of unrooted bulbs treated with growth regulators than in the control plants, although growth regulators did not affect the level of extractable proteins. The elongation of the inflorescence in the plants treated with gibberellic acid was correlated with a sharp increase of invertase activity in this organ. The effect of GA₃ and BA on the activity of other enzymes in buds and scales varied with the period of plant growth.     

Light and nitrate induction of nitrate reductase in kinetin-and gibberellic acid-treated mustard cotyledons

Nitrate reductase activity in gibberellic acid and kinetin treated mustard (Brassica juncea Coss. cv. T-59 ‘Varuna’) seedlings, grown in the presence or absence of light and/or NO₃ was investigated. While both light and NO₃, alone could induce NR activity, their combination showed additive effects. Kinetin treatment significantly promoted both light- and NO₃- induced NR activities, assayed by either in vivo or in vitro techniques, whereas, gibberellic acid was almost ineffective. In the absence of both light and NO₃, however, phytohormones alone could not induce NR activity. Both light-induced and NO₃ induced NR fractions had a pH optima of 7.5, preferred NADH as an electron donor (NADH: NADPH ratio 2.5) and K_m values for NO₃ was 0.2 mM. Actinomycin D, cycloheximide and tungstate were equally effective in suppressing the development of NR activity after exposure to light or NO₃. These results indicate that two independent NR fractions operate, with apparently identical properties but separate control mechanisms.     

The Effect of Phytohormones on Chlorophyll(ide), Protochlorophyll(ide) and Carotenoid Formation in Greening Dark Grown Wheat Leaves

The influence of phytohormones on chlorophyll and carotenoid formation during the greening of irradiated dark grown wheat leaves (Triticum aestivum L. cv. Starke II Weibull) was studied. Leaves were floated on solutions of abscisic acid, gibberellic acid and kinetin for 24 h. The chlorophyll and carotenoid contents were determined during a subsequent period of 48 h of continuous irradiation. Leaves treated with abscisic acid showed a longer lag phase and a lower rate of accumulation of chlorophyll as compared to the control than did leaves treated with gibberellic acid and kinetin. The carotenoid content was low both in leaves treated with abscisic acid and in those treated with gibberellic acid. Treatment with abscisic acid lowered the protochlorophyllide regeneration after a saturating light flash while gibberellic acid as well as kinetin had no effect. The influence of ABA was partly dependent on an increase of the wounded part of the cut leaf segments. The accumulation of protochlorophyllide in leaves treated with δ-aminolevulinic acid was not affected by the different hormonal treatments. These results suggest that the main effect of abscisic acid is probably outside the chloroplast, i.e. on the formation or transport of δ-aminolevulinic acid.     

Germination responses of <Emphasis Type="Italic">Erica andevalensis</Emphasis> to different chemical and physical treatments

Erica andevalensis Cabezudo & Rivera is a threatened edaphic endemic species of Andalusia (SW Spain). Under natural conditions, the plants produce a very large number of small seeds (0.3–0.4 mm) but very few seedlings survive. Different treatments (high temperature, cold pre-treatment, nitrogen salts, and gibberellic acid applications) were tested to assess germination patterns in different populations and to determinate the most favorable conditions for germination. Gibberellic acid was provided in five different concentrations from 0 to 400 ppm GA₃, while nitrogen was applied as 10 mM of either KNO₃ or NH₄NO₃. The effect of pH on germination was also tested. The species always showed a low germination rate (6.50–22%) that was not stimulated either by 1 or 4 months in dry cold pre-treatment, nitrogen application, acid pH medium, or by high temperature (80°C for 10 min); although gibberellic acid application (100–400 ppm) significantly enhanced germination. The highest percentage of germination (41.6%) was achieved with a mean germination time to start germination (t ₀) of 7.6 ± 0.54 days when the seeds were subjected to 400 ppm gibberellic acid treatment. The population origin did not have a significant effect on germination percentage.     

Effects of gibberellic acid and uniconazole on the activities of some enzymes of anthocyanin biosynthesis in carrot cell cultures

Gibberellic acid (GA₃) inhibition of anthocyanin accumulation by carrot cell-suspension cultures was reversed by supplying dihydroquercitin or naringenin to the culture and not by supplying 4-coumaric acid or malonic acid. This suggested that gibberellic acid was inhibiting chalcone synthase, chalcone isomerase, or acetyl CoA carboxylase. Acetyl-CoA-carboxylase specific activity was the same in GA₃-treated and untreated cultures and was not detected in cultures treated with uniconazole, an inhibitor of gibberellic acid biosynthesis. Chalcone-isomerase specific activity was lower in GA₃-treated cultures than in untreated cultures and was lower in uniconazole-treated cultures than in the GA₃-treated cultures. The total chalcone synthase activity in extracts from GA₃- and from uniconazole-treated cells was not significantly different from that in extracts of untreated tissue. When these extracts were chromatographed on a Mono Q column, three peaks of chalcone synthase activity were found in extracts of nontreated cells, whereas only two of these peaks were detected in extracts of GA₃-treated cells. The extracts from GA₃-treated cells did not contain the peak of chalcone synthase activity that, in untreated cells, preceded the main peak. The correlation between the absence of this peak and the inhibition of anthocyanin accumulation suggests that this form of chalcone synthase is responsible for anthocyanin synthesis and that GA₃ prevents this form from appearing in the cells.     

Effect of growth regulators and ethylmethane sulphonate on growth,and chlorophyll,sugar and proline contents in <Emphasis Type="Italic">Dracaena sanderiana</Emphasis> cultured <Emphasis Type="Italic">in vitro</Emphasis>

A high efficient four step protocol (callus initiation, regeneration, shoot elongation and rooting) for in vitro propagation of Dracaena sanderiana Sander ex Mast was developed. Callusing was achieved from nodal stem segment explants treated with various concentrations of ethylmethane sulphonate (EMS) on MS medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D; 1.5 g m⁻³). A significant increase in callus induction percentage and biomass production was noticed from lower EMS treated lines (ET₁ and ET₂) comparatively to control and other (ET₃, ET₄ and ET₅) lines. Calli of ET₁ line showed high regeneration potential on MS medium with N ⁶-benzylaminopurine (BAP; 1.75 g m⁻³). Length of microshoots, which was reduced by EMS, restored by addition of gibberellic acid (GA₃; 0.4 g m⁻³). A marked increase in rooting with increasing EMS concentration was noticed on MS medium fortified with 3-indolebutyric acid (IBA; 1.5 g m⁻³).     

An endogenous RNA-synthesis-promoting oligopeptide from Cucurbita pepto var. patissonina

The effect of CPPTI (Cucurbita pepo patissonina trypsin inhibitor) on the growth of Cucurbita pepo var patissonina (White bush) was examined. Plants treated with CPPTI grew faster than untreated plants and similarly to those treated with gibberellic acid. Isolated cell nuclei from plants treated with CPPTI showed that of the three DNA-dependent RNA polymerases assayed, RNA polymerase I (EC2.7.7.6) activity was preferentially elevated.Abbreviations CPPTI Cucurbita pepo patissonina trypsin inhibitor - GA₃ gibberellic acid - IAA indole-3-acetic acid - kDa kilodalton - RP I DNA-dependent RNA polymerase I     

Effect of photoperiod and gibberellic acid on the plasma membrane H+ATPase activity of spinach leaves

Plasma membrane H⁺ATPase extracted from leaves of spinach plants induced to flower by gibberellic acid treatments or by a transfer to a photoperiod of 24 h had a lower Km_app than that from vegetative plants grown in short days. The Km_app obtained after inhibition by vanadate was decreased in vegetative plants and increased in induced ones showing a differential effect of this inhibitor on the kinetic properties of the enzyme between vegetative and induced plants. The phospholipid fatty acid analysis of the purified plasma membrane showed an increase of C18:1/C18:2 fatty acid ratio upon induction by light or by gibberellic acid treatments, whereas the saturated to unsaturated fatty acid ratio was kept constant. The decrease in the Km_app observed after induction may be thus interpreted in terms of the observed changes in lipid environment.     

Gibberellic Acid Treatment Reduces the Tolerance of Field-Grown Common Bean to Leaf Removal

I studied the influence of gibberellic acid (GA₃) treatment in a field population of common bean on plant tolerance to leaf removal. Individual bean seedlings were treated with a foliar application of 10 μM GA₃ on day 7 and day 14 after emergence, which led to a significant increase in height in GA₃-treated plants. Twenty-eight days after emergence, either zero, one, two, or three leaflets from each trifoliate leaf were removed from each of 20 GA₃-treated and 20 control plants. All pods were harvested from each plant after plants became senescent 6 weeks later. Multivariate analyses revealed that leaf removal produced significant reductions in several yield components in both GA₃-treated and control plants, although the effects were not pronounced until at least two leaflets from each trifoliate leaf (67% of the total leaf area) were removed. However, GA₃-treated plants suffered greater reductions in total pod wall mass and total seed number than control plants after 33 and 67% leaf area removal. These results indicate that GA₃ treatment may have altered the assimilatory capacity or resource allocation pattern of treated plants in such a way as to decrease their ability to tolerate leaf removal, a negative consequence of the hormonal alteration of traits important to plant compensation for biotic stressors. Received December 6, 1996; accepted March 5, 1997     

Synergism between Gibberellin and Auxin in the Growth of Intact Tomato

Gibberellin A_4&7 was more effective than gibberellic acid in increasing shoot elongation when applied to the apex of intact Lycopersicum esculentum seedlings of Tiny Tim, a dwarf cultivar, and Winsall, a tall cultivar. After 14 days, gibberellic acid and gibberellin A_4&7 stimulated growth of the dwarf more than the tall tomato. In tall tomato the application of indole-3-acetic acid alone (6.1 μg/plant) showed an inhibitory growth effect, but when applied with 17.5 μg per plant of gibberellic acid, it had a synergistic effect at 7 days but not at 14 days. When the auxin concentration was reduced to 0.61 μg per plant a synergistic effect was observed on tall plants at 7 and 14 days between indole-3-acetic acid and gibberellic acid. Application of gibberellin A_4&7 with auxin did not give a synergistic response in tall or dwarf tomato.     

Lignin Deposition and Effect of Postharvest Treatment on Lignification of Green Asparagus (Asparagus officinalis L.)

To understand how lignin synthesis is regulated after harvest, detached green asparagus stalks (Asparagus officinalis L.) were treated with 1 μl l⁻¹ of 1-methylcyclopropene (1-MCP), 50 μg l⁻¹ gibberellic acid (GA₃), 2% (v:v) ethanol or 1 μl l⁻¹ ethylene. The results showed that lignin concentration in asparagus stalks stored at room temperature rapidly increased. Three conventional precursors of lignin, 4-hydroxycinnamic acid (coumaric acid), 3,4-dihydroxycinnamic acid (caffeic acid) and 4-hydroxy-3-mythoxycinnamic acid (ferulic acid), were found to be the major phenolics in the asparagus stalks. Furthermore, the concentrations of O₂⁻ in asparagus stalks steadily increased during the storage. Deposition of lignin in harvested asparagus was significantly reduced by treating the stalks with GA₃, 1-MCP or ethanol. The concentration of lignin in stalks treated with GA₃, 1-MCP or ethanol was 32, 20 or 27% lower, respectively, than in controls 3 days after treatment. Treating stalks with ethylene enhanced lignin synthesis (p<0.05). The concentration of total phenol in stalks was also significantly reduced by GA₃, 1-MCP and ethanol, but was enhanced by ethylene treatment. However, the concentration of active oxygen (O₂^−⋅) in stalks was significantly reduced by treatment with GA₃, 1-MCP and ethanol, but was enhanced by treatment with ethylene. Our study show that postharvest treatment with 1-MCP, GA₃ or ethanol may be applied to improve the quality of green asparagus.     

INDUCTION OF MORPHOGENETIC CHANGES AND ACCELERATION OF LEAF INITIATION BY GIBBERELLIC ACID IN XANTHIUM PENNSYLVANICUM

One application of gibberellic acid (GA₃) to young internodes significantly accelerated the rate of leaf initiation and caused an increase in the number of internodes in shoots of Xanthium pennsylvanicum. The average duration of one plastochron was reduced from 3.3 to 1.9 days. The rate of growth of the GA₃-treated internodes, and also of those positioned above and below, was at least twice that of the control. It appeared that the growth substance was translocated both acropetally and basipetally from the locus of application and that it significantly accelerated the rate of stem elongation. Gibberellic acid also had a pronounced morphogenetic effect on the leaves. It induced the development of lanceolate leaves instead of typical deltoid leaves. The area and the leaf length of the treated plants were both significantly reduced. Each response may be regulated by increasing or decreasing the concentration of gibberellic acid. The induced morphogenetic changes were not permanent. A reversion to the original condition was noticeable about 8 wk after treatment.     

Influence of GA3, sucrose and solid medium/bioreactor culture on in vitro flowering of Spathiphyllum and association of glutathione metabolism

Hormonal control of flower induction and inflorescence development in vitro was investigated in Spathiphyllum. The effects of gibberellic acid (GA₃) and sucrose on inflorescence development were studied in plantlets regenerated in tissue culture. GA₃ was mandatory for the shift from the vegetative to the reproductive stage. The effect of sucrose concentration on inflorescence bud development was studied in plantlets cultured in MS medium supplemented with 10 mg l⁻¹ GA₃. Sucrose concentration at 3 or 6% induced inflorescence development in, respectively, 83–85% of the plantlets. The effect of GA₃ and sucrose on inflorescence differentiation and development were also recorded in liquid culture using air-lift bioreactor. The best response was found in the same medium which was standardized as an optimum for solid culture, but the results were better than solid culture. In order to study the relationship between glutathione (GSH) and flowering, we also measured the oxidized and reduced GSH content in leaves throughout the culture period on 2 weeks interval. The GSH accumulation was more after 4 weeks until 6 weeks in GA₃ treated plantlets. Similarly, glutathione reductase which is involved in the recycling of reduced GSH providing a constant intracellular level of GSH, was also higher in GA₃ treated plantlets. The transient increase in GSH contents also correlated with the changes in measured γ-glutamylcysteine synthetase (γ-ECS) activity over the same period. The antioxidant enzyme activity in GA₃ treated plantlets also suggests that the plants suffered increased oxidative stress during the period of GA₃ treatment which subsequently increases GSH synthesis through activation of γ-ECS and this promotes flowering by increasing endogenous GSH.     

The metabolism of soluble nucleotides in wheat aleurone layers treated with gibberellic Acid

The metabolism of soluble nucleotides was investigated in wheat (Triticum aestivum var. Olympic) aleurone layers treated with gibberellic acid. Whereas nucleotide levels were relatively unaffected by the treatment, a transient increase was observed in the incorporation of ³²P. The effect was maximal 30 to 60 minutes after gibberellic acid was administered, and by 180 minutes incorporation was lower than in the control. The greatest changes were detected in the nucleoside triphosphates, particularly in cytidine triphosphate. The findings are discussed in relation to the mode of action of gibberellic acid.     

Chloroplastic activity in response to gibberellic acid treatment of dwarf and normal cultivars of pea (Pisum sativum L.)

Levels of ferricyanide reduction, cyclic and non-cyclic photophosphorylation were measured in chloroplasts of two cultivars of pea and a comparison of their P/2e⁺ ratios were made. No differences were observed in cyclic photophosphorylation or ferricyanide reduction but non-cyclic photophosphorylation was lower in chloroplasts from the dwarf than the normal cultivar. Thus the P/2e⁺ ratio of the dwarf was lower than the normal. Dwarf seedlings treated with gibberellic acid (GA₃) had similar rates of cyclic photophosphorylation as the untreated dwarf but non-cyclic photophosphorylation was lower as was ferricyanide reduction. This resulted in P/2e⁺ ratios that were higher in chloroplasts from the GA₃ treated dwarf seedlings than the untreated, and were the same as the untreated normal. Addition of GA₃ directly to the chloroplasts did not alter the activity in any way. Hence gibberellins do not directly affect changes in chloroplastic activity but may conceivably be involved in a feed-back control system.     

Effect of exogenous gibberellic acid,abscisic acid,and benzylaminopurine on epicotyl dormancy of cultured herbaceous peony embryos

Epicotyl dormancy was broken in cultured peony (Paeonia lactiflora Pall.) embryos after topical application of agarose gels containing gibberellic acid, with optimum growth at 1.5 mM gibberellic acid. Addition of 100 M abscisic acid to the medium resulted in complete inhibition of gibberellic acid-stimulated promotion of dormant epicotyls. Epicotyl dormancy was also broken in embryos by culture on media containing 1 or 10 M benzylaminopurine. A highly significant increase in leaf number occurred when embryos were both cultured on medium containing benzylaminopurine and treated topically with gibberellic acid. Anatomical and morphological studies indicated that the increase in shoot growth was due to the development and growth of 1) buds formed at the cotyledonary node, 2) axillary buds, and 3) adventitious meristems originating from subepidermal parenchymatous tissue.Abbreviations ABA abscisic acid - BA N⁶-benzylaminopurine - DMSO dimethyl sulfoxide - GA₃ gibberellic acid - LS Linsmaier and Skoog     

Localization of gibberellic acid-induced acid phosphatase activity in the endoplasmic reticulum of barley aleurone cells with the electron microscope

A metal-salt precipitation method with p-nitrophenyl phosphate as substrate has been used to localize in the electron microscope acid phosphatase activity in isolated aleurone layers of barley (Hordeum vulgare L.), treated for 16 h in the presence or absence of gibberellic acid (GA₃). The paper confirms results obtained earlier with an azo-dye precipitation method of enzyme localization. In addition the results show for the first time that in GA₃-treated tissue enzyme activity is associated with the endoplasmic reticulum (ER), there being reaction product deposited in the ER cisternae. It is suggested that this activity represents new enzyme synthesized on ER in response to GA₃ and probably destined for secretion.Abbreviation ER endoplasmic reticulum