Showing papers on "Gibberellic acid published in 1972"

Plant growth substances produced by micro‐organisms of soil and rhizosphere

Abstract: Summary: Micro-organisms isolated from rhizospheres and rhizoplanes of wheat plants, and from root-free soil, produced growth regulating substances with the properties of gibberellins and indolyl-3-acetic acid (IAA). Substances inhibiting extensions of pea plant internodes and lettuce hypocotyls were also produced, especially by bacteria from the root region of seedlings 6 days old. Bacteria producing growth promoting substances were most abundant on roots of older plants. Seedlings grown aseptically with added gibberellic acid (GA3) and IAA, or grown with a soil inoculum, developed similarly and differed in their morphology from those grown aseptically without additives.

Adventive plants from ovules and nucelli in Citrus.

Abstract: 1- to 8-week-old ovules and nucelli from three Citrus cultivars—Shamouti and Valencia (Citrus sinensis) oranges and Marsh Seedless (C. paradisi) grapefruit—were cultured in vitro. No embryo differentiation was observed in the explants prior to culture. The Shamouti ovules had degenerated and were apparently unfertilized. Embryoids formed on Murashige and Tucker nutrient medium supplemented with 500 mg/l malt extract. Whole plants developed on the same basal medium supplemented with kinetin and indole-3-acetic acid (IAA), coconut milk or gibberellic acid (GA3). A higher kinetin/IAA ratio or the addition of coconut milk favoured stem elongation more than root formation while a lower kinetin/IAA ratio favoured root formation and inhibited stem elongation. The addition of GA3 to the basal medium stimulated rooting and stem elongation. These results can be of aid in mutation research, allowing irradiation at stages prior to embryonic development.

Xanthoxin, a Recently Discovered Plant Growth Inhibitor

Abstract: The naturally occurring plant growth inhibitor xanthoxin which was discovered in these laboratories has been prepared in vitro by the oxidation of the pigment violaxanthin with neutral zinc permanganate solution. By the use of chemical and spectroscopic techniques, xanthoxin has been characterized as a mixture of the 2- cis , 4- trans - and 2- trans , 4- trans -isomers of 5-(19, 29, -epoxy-49-hydroxy-29, 69, 69-tri-methyl-19-cyclohexy)-3-methyl-pentadienal. These are also obtained by similar oxidations of neoxanthin, antheraxanthin and lutein epoxide. Cis, trans -xanthoxin probably arises from the corresponding cis -xanthophyll and its conversion to ( + )-ABA by simple chemical procedures is reported. The biological activity of cis, trans -xanthoxin has been shown to be considerably greater than that of the trans, trans -isomer. It is comparable with that of ( ± )-ABA in the wheat coleoptile section, the lettuce hypocotyl and bean petiole abscission tests, but greater than that of ( ± )-ABA in the cress seed germination test. Xanthoxin is shown to antagonize the growth-promoting effects of the plant hormones 3-indolylacetic acid, gibberellic acid and kinetin. Other xanthoxin derivatives have been prepared and their activities in several tests are also reported. The uptake of xanthoxin by tomato shoots leads to a subsequent large increase in the ABA content of the tissue. Evidence is presented for a possible biogenetic conversion of cis, trans -xanthoxin into ( + )-ABA by plants.

Starch Metabolism, Respiration, and Shoot Formation in Tobacco Callus Cultures

Abstract: The starch content of shoot-forming and non-shoot-forming tobacco callus cultured in light and darkness was determined. A variety of carbohydrates and cytokinins incorporated into the culture medium were effective in bringing about starch accumulation and shoot formation in the tissue. In addition, the respiratory activity of the callus, grown in the presence or absence of gibberellic acid, was measured. A strong correlation between the starch content of the tissue, its rate of respiration, and shoot formation was observed.

Meristematic Activity during Adventitious Root Primordium Development: Influences of Endogenous Auxin and Applied Gibberellic Acid

Abstract: Intact brittle willows (Salix fragilis L) were treated so that developing adventitious root primordia in the stems would be subjected to elevated gibberellic acid or reduced endogenous auxin levels Observations were made of primordia that were initiated during the experiments and of primordia that were established before the experiments began The results indicated that as primordia became older and contained more cells, auxin basipetally transported in the stem seemed to be of less importance in determining cell number per primordium Thus, established primordia depended upon this auxin to a lesser extent than primordia which were being initiated These observations were explained on the basis of differential contributions during primordium development of cell division in the cambium of the stem and in the primordia themselves As opposed to the effects of reduced auxin levels, applied gibberellic acid reduced the cell number per primordium most in established primordia Initiating primordia were least affected by gibberellic acid treatment Gibberellic acid treatment seemed mainly to reduce intraprimordium cell division, on which continued development of established primordia most depends Seemingly, at least in brittle willow, applied gibberellic acid blocks the action of auxin in primordium development subsequent to the initiation phase

Characteristics of the process of enzyme release from secretory plant cells.

Abstract: Secretion-the outward movement of molecules across the plasmalemma-of alpha-amylase by barley (Hordeum vulgare L. cv. Himalaya) aleurone layers is an energy-dependent process that is not directly dependent upon protein synthesis or RNA synthesis and does not appear to be under the direct control of gibberellic acid or abscisic acid. Release-the movement of the secreted alpha-amylase molecules through the walls into the surrounding medium-is apparently diffusion limited and is markedly dependent upon the presence of ions.

The Influence of Gibberellic Acid on the Permeability of Model Membrane Systems

Abstract: Gibberellic acid increases the permeability of model membranes composed of various plant-source lipids, a sterol, and dicetyl phosphate. As a result of hormone treatment, the flux of uncharged molecules such as glucose or sucrose, or charged ions such as chromate, through the model membranes (liposomes or micelles) is increased. The revelance of this finding to the in vivo effects of the hormone is briefly discussed.

Tannins as gibberellin antagonists.

Abstract: Fourteen chemically defined hydrolyzable tannins and six impure mixtures of either condensed or hydrolyzable tannins were found to inhibit the gibberellin-induced growth of light-grown dwarf pea seedlings. The highest ratio of tannins to gibberellic acid tested (1000: 1 by weight) inhibited from 80 to 95% of the induced growth for all tannins tested except for two monogalloyl glucose tannins which inhibited only 50% of the induced growth. The lowest ratio tested (10: 1) inhibited the induced growth by less than 25% except for the case of terchebin where 50% inhibition was found. The inhibition of gibberellin-induced growth was found to be completely reversed by increasing the amount of gibberellin in three cases tested. Tannins alone did not inhibit endogenous growth of either dwarf or nondwarf pea seedlings. Eight compounds related to tannins, including coumarin, trans-cinnamic acid, and a number of phenolic compounds were also tested as gibberellin antagonists. Most of these compounds showed some inhibition of gibberellin-induced growth, but less than that of the tannins. At the highest ratio (1000: 1) the greatest inhibition was 55%; at the lowest ratio (10: 1) no more than 17% was observed. These compounds did not inhibit endogenous growth, and the inhibition of gibberellin-induced growth could be reversed by increasing the amount of gibberellin in two cases tested.Six chemically defined tannins were found to inhibit hypocotyl growth induced by gibberellic acid in cucumber seedlings. Growth induced by indoleacetic acid in the same test was not inhibited. The highest ratio of tannin to promotor tested gave strong inhibition of gibberellic acid-induced growth, but actually enhanced the growth induced by indoleacetic acid. This difference in action suggests a specificity between the tannins and gibberellic acid.

Hormonal control of polyribosome formation in barley aleurone layers.

Abstract: The addition of abscisic acid to barley ( Hordeum vulgare L. cv. Himalaya) aleurone layers at the same time as gibberellic acid completely prevents the gibberellin-induced increases in the percentage of polysomes, the formation of polyribosomes, and the synthesis of α-amylase, even when the molar concentration of gibberellic acid is four times greater than the concentration of abscisic acid. The addition of abscisic acid to aleurone cells producing α-amylase (midcourse addition) inhibits the further synthesis of α-amylase and decreases the percentage of polysomes but does not change the number of ribosomes per cell. The removal of gibberellic acid from aleurone layers during the midcourse of α-amylase production arrests α-amylase synthesis and decreases the percentage of polysomes. Readdition of gibberellic acid causes the reinitiation of the synthesis of α-amylase and a return of the percentage of polysomes to the original level. The incubation of aleurone layers with 5-fluorouracil inhibits the secretion of α-amylase. The changes in polysomes isolated from cells treated with either fluorouracil or actinomycin D correlate with the changes in enzyme synthesis caused by the addition of these inhibitors. Gibberellic acid and abscisic acid affect both the conversion of monosomes to polysomes and the synthesis of new ribosomes. The gibberellin-stimulated increases in the number of ribosomes and the percentage of polysomes are probably a prerequisite for the hormone induction of enzyme synthesis.

De Novo Synthesis of Ribonuclease and β-1,3-Glucanase by Aleurone Cells of Barley

Abstract: When isolated aleurone layers of barley are incubated they produce a number of hydrolytic enzymes which can be divided into three groups. The synthesis and the secretion of the hydrolases in the first group is greatly enhanced by gibberellic acid. Using the density labeling technique of Filner and Varner (3) it has been shown that the increase in enzymatic activity of two of the enzymes in this group (a-amylase and protease) is due to de novo synthesis (3, 6). The marked effect of gibberellic acid on the rate of enzyme synthesis makes this an ideal system to study hormonal control of protein synthesis (10). The total enzymatic activity of hydrolases in the second group (e.g., ribonuclease and B-glucanase) does not show the same response to GA. There is a considerable increase in enzymatic activity during imbibition of the seeds, but the addition of GA to the isolated aleurone layers causes only a small increase in the total amount of enzyme activity (2, 7). However, release of these enzymes in the medium is dependent on GA, and this system has been used to study hormonal control of enzyme secretion (2, 7). Whether or not the increase in enzymatic activity which occurs during imbibition of the halfseeds and incubation of the aleurone layers is due to de novo synthesis has never been determined. Finally, the enzymatic activity of at least one hydrolase, /3-amylase, increases in the presence of GA, but this is due to release of preformed enzyme and not to de novo synthesis (5). We now present evidence consistent with the idea that two enzymes in the second group are also synthesized de novo.

The role of roots, cytokinins and apical dominance in the control of lateral shoot form in Solanum andigena

Abstract: The lateral bud of Solanum andigena has the potentiality to develop as a stolon or as a leafy, orthotropic shoot. Natural stolons are normally only produced from underground nodes, but aerial stolons can be induced to form by the application of a combination of indole-3-acetic acid and gibberellic acid (IAA/GA3) paste to the cut surface; under some conditions both natural or induced stolons are converted to upright, leafy shoots. The presence of roots was found to be necessary for the conversion of a natural stolon to a leafy shoot, but this root effect could be replaced by the synthetic cytokinin, 6-benzylaminopurine (BAP). By using α-14C-BAP it was demonstrated that cytokinin accumulates in the tip of an induced stolon, prior to its conversion to a leafy shoot caused by withdrawal of the IAA/GA3 paste. The application of IAA/GA3 to decapitated plants was shown to influence both the distribution and metabolism of the cytokinin. The possibility that the role of auxin in apical dominance, at least in part, is to control the distribution and metabolism of cytokinins is discussed.

Enzyme formation, cellular breakdown and the distribution of gibberellins in the endosperm of barley.

Abstract: The α-amylase contents of the dorsal and ventral sides of the endosperm of barley grains increase approximately equally during germination. Aleurone tissue from all locations in the grain is equally able to make α-amylase in response to gibberellic acid, so the distribution of this enzyme reflects the distribution of endogenous gibberellins.

A Comparative Study of the Changes in Root Growth, Induced by Coumarin, Auxin, Ethylene, Kinetin and Gibberellic Acid

Abstract: The effect of coumarin, IAA, ethylene, kinetin and gibberellic acid on roots of maize and wheat was investigated. Sterile attached and detached roots and isolated elongation zones were used. In some experiments a semi-sterile procedure was followed. The effects of the different regulators separately or in various combinations together with coumarin were studied on the root growth with regard to division, elongation and swelling of the cells. The ethylene production in isolated elongation zones was measured after treatment with coumarin, IAA, PCIB, kinetin, colchicine and dinitrophenol. The results show the following: 1) Each substance produces a specific morphologic pattern. 2) Changes in polarity were demonstrated for auxin-induced swelling in cell divisions and cell expansion and for coumarin-induced swelling in cell divisions. Other cell expansion in swollen parts was due to cylindric cells increasing in width while retaining their cylindric form. 3) Coumarin-induced inhibition could not be counteracted by IAA, PCIB, carbon dioxide, kinetin, gibberellic acid or Cycocel. 4) The ethylene production in isolated elongation zones increases noticeably after kinetin treatment, less strongly after auxin treatment and least after coumarin treatment. The production of ethylene does not seem to be correlated with the morphogenetic effect of the different substances. 5) The isolated elongation zones reacted to a) IAA and kinetin with an increase in length in some cases and b) gibberellic acid with a reduction of their width. 6) The inhibitory effect of coumarin on the growth in length of the elongation zones was diminished by kinetin. The swelling produced by coumarin in these zones was reduced by gibberellic acid. The effects just mentioned of kinetin and gibberellic acid were considered as indirect ones. - From the present findings it was concluded that concomitant effects of auxin, ethylene, cytokinins and gibberellins are not obligatory for coumarin to exert its morphogenetic effects on root growth. In discussing the results some pitfalls in studies of growth reactions after application of hormones to roots containing meristem were emphasized.

Interaction of cytokinin, auxin, and gibberellin on peroxidase isoenzymes in tobacco tissues cultured in vitro

Abstract: Peroxidase in tobacco callus tissue (Nicotiana tabacum, cv. White Gold) was resolved into three groups of isoenzymes by polyacrylamide gel electrophoresis, and a combined action of cytokinin, auxin, and gibberellin in their formation was clearly demonstrated. The most significant change was in a group of fast-migrating isoperoxidases, the development of which required both kinetin and indoleacetic acid. Kinetin was most stimulatory at 0.2 μM but became inhibitory with increasing concentrations. Indole acetic acid was effective at concentrations from 0.1 to 100 μM with an optimum at 10 μM. With both kinetin and indoleacetic acid at optimal concentrations, addition of gibberellic acid further increased the contents of the fast migrating isoperoxidases, but it was inactive in the absence of indoleacetic acid or in the presence of kinetin in 5 μM or higher concentrations. Cycloheximide, actinomycin D, and abscisic acid inhibited the formation of the fast-migrating peroxidases. Formation of the fast-migrating ...

Hormonal control of weed seed germination

Abstract: Freshly-harvested seeds of several common weeds showed little or no promotion of germination by light. However, after burial for 6 months, germination becomes entirely dependent on exposure to light. Red light promoted the germination of the buried seeds, and this promotion was reversed by far-red light, indicating phytochrome involvement. Freshly-harvested seeds were made light-requiring by treatment with mannitol. The germination of these light-requiring seeds was promoted by red light, gibberellic acid (GA), acetylcholine (ACh), and adenosine 3′,5′-monophosphate (cyclic AMP). The phytochrome response may trigger ACh synthesis which causes the release of GA from a bound form and/or GA synthesis which enhances the production of cyclic AMP which initiates the germination response.

Seed dormancy in Acer: Endogenous germination inhibitors and dormancy in Acer pseudoplatanus L

Abstract: Dormant seeds of Acer pseudoplatanus L. contain two zones of inhibition on paper chromatograms in “10:1:1” as detected by the lettuce and cress seed germination, and the wheat coleoptile bioassays. One zone at Rf 0.6–0.8 was partitioned into ethyl acetate at acid pH and was shown to contain ABA by its behaviour on GLC and isomerization under ultra-violet light. The other zone at Rf 0.9 was detected only in the germination bioassays and was partitioned into ethyl acetate over a range of pH indicating the presence of one or more neutral compounds.

Regulation of the Krebs cycle and pentose phosphate pathway activities in the control of dormancy of Avena fatua

Abstract: Malonic acid (10−2 M) promoted germination of excised dormant embryos of Avena fatua L. but inhibited germination of non-dormant embryos. Malonate inhibited oxygen consumption and carbon dioxide evolution of dormant embryos which resulted in an increased respiratory quotient and a decrease in the glucose C6/C1 ratio. Germination is oxygen-dependent, and malonate-sensitive oxygen consumption decreased during afterripening. Succinic acid (5 × 10−2 M) promoted germination of dormant embryos. Gibberellic acid (GA) (1.0 ppm) and succinate (5 × 10−2 M) interacted synergistically in promoting germination. Adenosine diphosphate also promoted germination but only after a considerable lag period. Germination of non-dormant embryos was inhibited by 2,4-dinitrophenol indicating the importance of adenosine triphosphate for germination. Storage of caryopses in various gaseous environments indicated that the response of dormant embryos to GA treatment was dependent on the operation of oxidative processes during afterrip...

Transport of Materials from the Cotyledons during Germination of Seeds of the Garden Pea (Pisum sativum L.)

Abstract: The transport of total dry matter, nitrogen, phosphorus, sulphur, potassium, and calcium from the cotyledons into the developing axis of young pea (Pisum sativum L.) seedlings has been studied under a variety of growth conditions. It is shown that the duration of transport increased when the plants were grown in distilled water, or in the dark, or upon removal of the shoot ; all these treatments delayed senescence of the cotyledons. On the other hand, the rate of transport was increased by treatments, such as the supply of calcium and phosphate in the medium, or darkness, which stimulate growth of the axis. Treatment of the seeds before germination with gibberellic acid (GA3) did not affect the movement of materials from the cotyledons although it changed the pattern of growth of the axis. After the first week of germination the relationship between the amounts of total dry matter, nitrogen, phosphorus, sulphur, and potassium transferred to the axis from the cotyledons in the intact plant remained approximately constant irrespective of the conditions of growth. It is proposed that the ratio in which the individual elements are transported is determined by the proportions in which they are released by the storage cells. Deviation from this ratio during the first week of germination, and over a longer period in deshooted plants is attributed to competition for the available nutrients between actively metabolizing cells in the cotyledons and axis. It is demonstrated by steam-girdling that movement of materials from the cotyledons into the shoot probably occurs via the phloem. Calcium is mobile in the phloem during the early stages of germination, possibly because the amount of free calcium in the cotyledons is high.

A distinction between the actions of abscisic acid, gibberellic acid and cytokinins in light-sensitive lettuce seed.

Abstract: Using isolated lettuce seed embryos it can be shown that the inhibitory effect of abscisic acid upon germination is reversed solely by cytokinin In the intact seed, however, gibberellic acid is also required for this reversal to be manifested in germination

Does Gibberellic Acid Stimulate Seed Germination via Amylase Synthesis

Abstract: Gibberellic acid is known to break dormancy of several types of seeds: (a) light-promoted seeds, such as Grand Rapids lettuce seed (Lactuca sativa L. var. Grand Rapids); (b) lightinhibited seeds, such as the seed of the honey-bee plant (Phacelia tanacetifolia Benth; (c) seeds requiring stratification (storage at low temperatures in a moist condition), such as the hazel nut (Corylus avellana L.); (d) seeds requiring after-ripening (storage at room temperature in dry condition), such as the wild oat (Avena fatua L.). Recent findings indicate that when dormant hazel nut seeds are soaked at 5 C for 28 days, which is a natural means of breaking dormancy, the gibbereilin-synthesizing mechanism is activated and that actual synthesis of gibberellins takes place when the seeds are transferred to a suitably higher temperature. Accumulation of GA results in germination (10). It has also been suggested that in the phytochrome-controlled germination of Grand Rapids lettuce seeds, the role of Pfr is to activate GA biosynthesis (8). One biochemical reaction known to be enhanced by GA is the synthesis of hydrolases (especially a-amylase) in the endosperm of cereal grains, such as barley (2, 9, 13). Since starch is a major food reserve in the cereal grains, its breakdown is generally assumed to be an essential process of germination. Many writers have implied that GA stimulates seed germination via amylase synthesis (1, 7, 12). Drennan and Berrie (5) compared the time course of amylase development in dormant and nondormant wild oats (Avena spp.). Their results indicated that both types of seeds contained traces of amylases. When dormant seeds were soaked, there was neither germination nor a change in the level of amylases. When nondormant seeds were soaked (in water), they germinated in 4 days and from the 6th day, amylase activity increased. Thus, they concluded that buildup of amylases is a postgermination phenomenon, and a lack of amylase synthesis must be eliminated as a possible cause of dormancy. We have investigated the time course relationship of GAinduced germination and amylase development in an attempt to find out if GA-induced germination is mediated by amylase production. The seeds of Avena fatua L. (wild oat) type Montana were obtained from Dr. G. M. Simpson of the University of Saskatchewan. These seeds were field-harvested in 1968 and stored at -15 C prior to use. Dry storage at low temperatures

Hormonal Control of Nuclease Level in Excised Avena Leaf Tissues1

Abstract: In excised Avena leaves, kinetin and benzyladenine decreased, while abscisic acid and benzimidazole increased the over-all nuclease level. Significant effects were observed as early as 2 h after treatment. Not all the nucleases of the Avena leaf were affected by the growth regulators. Changes in over-all nuclease activity were accounted for almost entirely by changes in the amount of a relatively purine-specific endo-ribonuclease, which produces 2', 3'-cyclic phosphates as breakdown products. Slight changes induced by the growth regulators were also detected in the amount of a sugar non-specific endo-nuclease which produces 5'-nucleotides and has a relative specificity for adenylic acid. The level of an alkaline phosphodiesterase, an exo-nuclease which produces 5'-nucleotides, was not affected by any of the growth regulators tested. Gibberellic acid and indol-3yl-acetic acid did not influence the level of Avena nucleases.

Studies in terpenoid biosynthesis. Part IX. The sequence of oxidation on ring B in kaurene–gibberellin biosynthesis

Abstract: The formation of 7β-hydroxy-(–)-kaur-16-en-19-oic acid and its incorporation into gibberellic acid and the kauranoid metabolites of Gibberella fujikuroi are described. The results of incubation of 7β-hydroxy-[6β-3H,17-14C]-(–)-kaur-16-en-19-oic acid have shown that the 6β-hydrogen atom is lost in the formation of gibberellic acid. However 6β,7β-dihydroxy-(–)-kaur-16-en-19-oic acid is not incorporated into gibberellic acid. Experiments with [1-3H2,1-14C]geranyl pyrophosphate suggest that the 6β-hydrogen atom migrates to C-7 during ring contraction.

A Correlation between a Ribonucleic Acid Fraction Selectively Labeled in the Presence of Gibberellic Acid and Amylase Synthesis in Barley Aleurone Layers.

Abstract: The effects of gibberellic acid on the incorporation of radio-active uridine and adenosine into RNA of barley aleurone layers were investigated using a double labeling method combined with acrylamide gel electrophoresis. After 16 hours of incubation, gibberellic acid stimulated the incorporation of label into all species of RNA, but the effects were very small (0-10%) for ribosomal and transfer RNA and comparatively large (up to 300%) for RNA sedimenting between 5S and 14S. This result was obtained for both isolated aleurone layers and for layers still attached to the endosperm. A similar but less marked pattern occurred in layers incubated for 8 hours, but the effect was not observed after 4 hours. The gibberellic acid-enhanced RNA labeling was not due to micro-organisms. The following evidence was obtained for an association between the gibberellic acid-enhanced RNA synthesis and α-amylase synthesis: (a) synthesis of α-amylase took place in parallel with incorporation of label into gibberellic acid-RNA; (b) actinomycin D inhibited amylase synthesis and gibberellic acid-RNA by similar percentages; (c) 5-fluorouracil halved incorporation of label into ribosomal RNA but had no effect on amylase synthesis and gibberellic acid-RNA; and (d) abscisic acid had little effect on synthesis of RNA in the absence of gibberellic acid, but when it was included with gibberellic acid the synthesis of both enzyme and gibberellic acid-RNA was eliminated. We conclude that large changes in the synthesis of the major RNA species are not necessary for α-amylase synthesis to occur but that α-amylase synthesis does not occur without the production of gibberrellic acid-RNA. Gibberellic acid-RNA is probably less than 1% of the total tissue RNA, is polydisperse on acrylamide gels, and could be messenger species for α-amylase and other hydrolytic enzymes whose synthesis is under gibberellic acid control.

Effects of Ethylenediaminetetraacetic Acid, Auxin and Gibberellic Acid on Phytochrome Controlled Nyctinasty in Albizzia julibrissin

Abstract: Nyctinastic closure of Albizzia julibrissin pinnules is inhibited by 5 × 10−2M ethylenediaminetetraacetic acid. At least two hours of incubation are required for maximum inhibition and destruction of the phytochrome effect. Concentrations of 10−3 to 10−5M naphthaleneacetic acid reduced the nyctinastic closure of pinnules but not the phytochrome response. Similar results were obtained with indoleacetic acid and gibberellic acid. No appreciable differences in pinnule movements could be attributed to pH. Chelation or the inhibition of ion transport resulting in, or caused by, changes in membrane permeability are suggested as possible mechanisms involved in these effects.

Effect of Chilling on Budbreak in `Thompson Seedless' and `Carignane' Grapevines

Abstract: Shortly before leaf fall (November 10), potted `Thompson Seedless9 and `Carignane9 vines were put in a coldroom (35 ± 2°F) for various periods ranging up to 77 days. They were then removed to a heated greenhouse for determination of rate and amount of budbreak. Respective times to initial budbreak of `Thompson Seedless9 and `Carignane9 were reduced from 5 and 6 weeks in unchilled vines to 2 and 3 weeks in vines chilled 9 weeks. The buds that broke per vine on `Thompson Seedless9 were 2-3 times as numerous on vines that received one or more weeks of chilling as on unchilled vines. For `Thompson Seedless9, 7 or more weeks of chilling resulted in maximum percentage of budbreak per vine and minimum time between first and last bud to break. Gibberellic acid prolonged the time required for the first bud to break dormancy on vines that received 0 or 7 days of chilling, but had little effect on vines that were chilled longer. Neither benzyladenine nora 1:1 mixture of gibberellin and benzyladenine significantly affected the time or amount of budbreak.

The Relationship between Exogenous Growth Inhibitors and Endogenous Levels of Ethylene, and Tuberization of Dahlias

Abstract: Treatments with abscisic acid (ABA), succinic acid-2,2-dimethylhydrazide (SADH), or 2 chlorethyl phosphonic acid (ethephon) promoted the tuberization of dahlia plants in long-days. This effect was smaller, however, than the effect short days have on tuberization. In contrast, gibberellic acid (GA) treatments inhibited tuberization. SADH and ethephon treatments of budless leaf-cuttings inhibited tuberization whereas ABA treatments slightly enhanced it. Evolution of endogenous ethylene reached a peak between the second and third week after the start of short-day treatments, and then decreased to the low level found in plants growing under long days. The peak in ethylene evolution occurred one week before the onset of tuberization.

The Induction of Amylase Synthesis in Barley Aleurone Layers by Gibberellic Acid I. RESPONSE TO TEMPERATURE

Abstract: The lag phase between application of gibberellic acid to barley aleurone layers and the beginning of amylase synthesis is at a minimum at 30 °C. This temperature is also the optimum for enzyme synthesis. Incubation temperature has little effect on the background activity found in the absence of gibberellic acid, or on the concentration of enzyme retained in the tissue in the presence of hormone. When aleurone layers spend only 2 h of the lag period at 30 °C, and the remainder of the incubation at 25 or 15 °C, the lag period is considerably reduced. Short-term incubation at 30 °C is most effective in reducing the lag period at 25 °C when given for the first 2 h after gibberellic-acid addition. Under these conditions ('tempera ture stepdown incubation') the lag period is reduced to that with the whole incubation at 30 °C. The temperature stepdown incubation has a sharp pH optimum of 5-00-5-05 and its effectiveness is increased by the presence of iron in the medium. There are thus two rate limiting reactions during the lag period, the first highly temperature sensitive, the second relatively temperature insensitive.