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1.
Stem segments taken from Avena sativa plants grown at 10°, 20° or 30° varied in their phospholipid composition depending on the growth temperature; as temperature was lowered, there was a shift towards a greater proportion of unsaturated fatty acids. A significant increase was observed in the concentration of linolenic acid (18:3) as growth temperature was lowered. Although prolonged treatment of oat plants with GA3 produced marked changes in phospholipid composition of stem segments, these changes did not always accompany the GA3-induced growth response of segments. Treatment of stem segments with GA3 for only 20 hr produced a significant growth response with little or no effect on phospholipid composition over this time. The data support the hypothesis that GA3-induced growth in Avena stem segments can occur without a concomitant change in phospholipid composition.  相似文献   

2.
Of the three morphological subunits of Avena sativa stem segments (node, leaf-sheath and internode) examined, internodes constituted the richest source of phospholipids and sterols, yielding almost double the concentration of lipid found in the leaf-sheath. The phospholipid compositions of nodes and internodes were similar, comprising mostly phosphatidylcholine (PC) and phosphatidylethanolamine (PE), with linoleic, linolenic and palmitic acids as the predominant component fatty acids. Leaf-sheath tissue contained mainly PE, with equally high amounts of palmitic, linoleic and linolenic acids. β-Sitosterol and cholesterol were the major 4-desmethylsterols of the internode, while β-sitosterol was predominant in the node and leaf-sheath tissues. The growth temperature of segments prior to isolation produced its major effect on the concentration of stigmasterol, which decreased markedly with temperature. The sitosterol/stigmasterol ratio increased significantly as temperature decreased. Stem segments isolated from plants treated with gibberellic acid (GA3) for 3 weeks, showed a significant reduction in the amounts of 4-desmethyl sterols on a dry wt basis when compared with control segments. However, when stem segments were incubated with GA3 for 20 hr, no change in 4-desmethylsterol composition or concentration was observed, even though significant growth in response to GA3 occurred.  相似文献   

3.
Gibberellic acid (GA3) induces invertase activity within 6 hours in Avena stem segments that are incubated in the dark at 23°. The maximum amount of promotion is about 5 times that of invertase activity in untreated segments. GA3 causes significant promotion of invertase activity at concentrations as low as 3 × 10−5 μm GA3. The increase in invertase activity elicited by GA3 between 3 × 10−5 μm and 300 μm closely parallels the growth promotion that is caused by GA3 over this concentration range. In control segments, invertase activity rises steeply during the first 6 hours of incubation, then decays slowly between 12 and 48 hours. In GA3-treated segments, the invertase activity also rises during the first 6 hours, parallel to that in control segments and continues to rise during the next 42 hours. These changes in invertase activity during 48-hour incubation periods do not parallel the changes in growth that occur in control and GA3-treated segments. Cycloheximide at 10 μg/ml abolishes all GA3-promoted growth and invertase activity in these segments. Actinomycin D at 40 and 80 μg/ml decreases GA3-promoted growth by 20% and invertase activity by 38 and 44%, respectively. The data clearly support the idea that protein synthesis is necessary for GA3-promoted growth and invertase activity in Avena stem segments.  相似文献   

4.
The rate of acidification of media by Avena stem segments was studied with a titrimeter. GA3 increased this rate by an average of 17% if supplied to the segments 90 min prior to measurement. GA3 inhibited the rate by 15% if supplied 10 min prior to measurement. After 90 min incubation, stimulation of elongation had started; at 10 min, GA3 had not yet started to stimulate elongation in the segments.  相似文献   

5.
The relationship between temperature and sensitivity to gibberellin A3 (GA3) was studied in lettuce seedlings (Lactuca sativa L. cv. Arctic). Dose/response curves for hypocotyl elongation (10-4 mol l-1 to 10-8 mol l-1) were constructed for a range of temperatures and the slope of the linear portion of the plots used as an indication of the sensitivity to GA3. Hypocotyls were unresponsive to GA3 below 13°C but above this temperature sensitivity increased linearly. Plots of growth rate against temperature had inflexions between 12°C and 13°C, with slopes above this point which increased with increasing GA3 concentration. The Q10 value for response increased in a similar manner. Reaction rates of NAD-dependent malate dehydrogenase and peroxidase extracted from hypocotyls varied linearly with temperature whilst nonspecific tetrazolium reduction, a membrane based activity, showed an abrupt rate change above 14°C. Pre-exposure to GA3 had no effect on the temperature responses of soluble or particulate enzymes.Abbreviation GA3 gibberellin A3  相似文献   

6.
Auxin-Gibberellin Interactions in Pea: Integrating the Old with the New   总被引:4,自引:1,他引:3  
Recent findings on auxin-gibberellin interactions in pea are reviewed, and related to those from studies conducted in the 1950s and 1960s. It is now clear that in elongating internodes, auxin maintains the level of the bioactive gibberellin, GA1, by promoting GA1 biosynthesis and by inhibiting GA1 deactivation. These effects are mediated by changes in expression of key GA biosynthesis and deactivation genes. In particular, auxin promotes the step GA20 to GA1, catalyzed by a GA 3-oxidase encoded by Mendel’s LE gene. We have used the traditional system of excised stem segments, in which auxin strongly promotes elongation, to investigate the importance for growth of auxin-induced GA1. After excision, the level of GA1 in wild-type (LE) stem segments rapidly drops, but the auxin indole-3-acetic acid (IAA) prevents this decrease. The growth response to IAA was greater in internode segments from LE plants than in segments from the le-1 mutant, in which the step GA20 to GA1 is impaired. These results indicate that, at least in excised segments, auxin partly promotes elongation by increasing the content of GA1. We also confirm that excised (light-grown) segments require exogenous auxin in order to respond to GA. On the other hand, decapitated internodes typically respond strongly to GA1 application, despite being auxin-deficient. Finally, unlike the maintenance of GA1 content by auxin, other known relationships among the growth-promoting hormones auxin, brassinosteroids, and GA do not appear to involve large changes in hormone level.  相似文献   

7.
In near-isogenic lines of winter wheat (Triticum aestivum L. cv. Maris Huntsman) grown at 20° C under long days the reduced-height genes, Rht1 (semi-dwarf) and Rht3 (dwarf) reduced the rate of extension of leaf 2 by 12% and 52%, respectively, compared with corresponding rht (tall) lines. Lowering the growing temperature from 20° to 10° C reduced the rate of linear extension of leaf 2 by 2.5-fold (60% reduction) in the rht3 line but by only 1.6-fold (36% reduction) in the Rht3 line. For both genotypes, the duration of leaf expansion was greater at the lower temperature so that final leaf length was reduced by only 35% in the rht3 line and was similar in the Rht3 line at both temperatures. Seedlings of the rht3 (tall) line growing at 20° C responded positively to root-applied gibberellin A1 (GA1) in the range 1–10 μM GA1; there was a linear increase in sheath length of leaf 1 whereas the Rht3 (dwarf) line remained unresponsive. Gibberellins A1, 3, 4, 8, 19, 20, 29, 34, 44 and 53 were identified by full-scan gas chromatography-mass spectrometry in aseptically grown 4-d-old shoots of the Rht3 line. In 12-d-old seedlings grown at 20° C, there were fourfold and 24-fold increases in the concentration of GA1 in the leaf expansion zone of Rht1 and Rht3 lines, respectively, compared with corresponding rht lines. Although GA3 was present at a similar level to GA1 in the rht3 (tall) line it accumulated only fivefold in the Rht3 (dwarf) line. The steady-state pool sizes of endogenous GAs were GA19 ? GA20 = GA1 in the GA-responsive rht3 line whereas in the GA non-responsive Rht3 line the content of GA19≈ GA20 ? GA1. It is proposed that one of the consequences of GA1 action is suppression of GA19-oxidase activity such that the conversion of GA19 to GA20 becomes a rate-limiting step on the pathway to GA1 in GA-responsive lines. In the GA-non-responsive Rht lines it is suggested that GA19 oxidase is not downregulated to the same extent and GA1 accumulates before the next rate-limiting step on the pathway, its 2β-hydroxylation to GA8. The steady-state pool sizes of GA19, 20, 1, 3 and 8 were similar in developmentally equivalent tissues of the rht3 (tall) line growing at 10° C and 20° C despite a 2.5-fold difference in the rate of leaf expansion. In contrast, in the Rht3 (dwarf) line, the extent of accumulation of GA1 reflected the severity of the phenotype at the two temperatures with slower growing tissues accumulating less, not more, GA1. These results are interpreted as supporting the proposed model of regulation of the GA-biosynthetic pathway rather than previous suggestions that GA1 accumulates in GA-insensitive dwarfs as a consequence of reduced growth rates.  相似文献   

8.
Pulvini of excised segments from oats (Avena sativa L. cv Victory) were treated unilaterally with indoleacetic acid (IAA) or gibberellic acid (GA3) with or without gravistimulation to assess the effect of gravistimulation on hormone action. Optimum pulvinus elongation growth (millimeters) and segment curvature (degrees) over 24 hours were produced by 100 micromolar IAA in vertical segments. The curvature response to IAA at levels greater than 100 micromolar, applied to the lower sides of gravistimulated (90°) pulvini, was significantly less than the response to identical levels in vertical segments. Furthermore, the bending response of pulvini to 100 micromolar IAA did not vary significantly over a range of presentation angles between 0 and 90°. In contrast, the response to IAA at levels less than 10 micromolar, with gravistimulation, was approximately the sum of the responses to gravistimulation alone and to IAA without gravistimulation. This was observed over a range of presentation angles. Also, GA3 (0.3-30 micromolar) applied to the lower sides of horizontal segments significantly enhanced pulvinus growth and segment curvature, although exogenous GA3 over a range of concentrations had no effect on pulvinus elongation growth or segment curvature in vertical segments. The response to GA3 (10 micromolar) plus IAA (1.0 or 100 micromolar) was additive for either vertical or horizontal segments. These results indicate that gravistimulation produces changes in pulvinus responsiveness to both IAA and GA3 and that the changes are unique for each growth regulator. It is suggested that the changes in responsiveness may result from processes at the cellular level other than changes in hormonal sensitivity.  相似文献   

9.
The lipid composition of Avena sativa stem segments was manipulated using BASF 13-338 (formerly Sandoz 9785) and growth temperature, in order to establish whether there were correlations between responsiveness of the tissue to gibberellic acid (GA3) and the presence, before hormone treatment, of specific lipid components. High correlations were obtained between GA3-induced growth and total phospholipid, individual phospholipids, and fatty acids (except for linolenic acid), total saturated fatty acids, stigmasterol content, and the unsaturated/saturated fatty acid ratio. It was concluded that, although the lipid composition, and particularly the total saturated fatty acid content, seem to be important contributory determinants of the GA3-induced growth response in this system, they may not be obligatory prerequisites, nor the only endogenous factors capable of influencing the response. However, the results are consistent with the hypothesis that membranes are involved in the hormonal mechanism and/or very early stages of the mode of GA3 action in this tissue.  相似文献   

10.
The purpose of this study was to analyze the nature of the interaction between gibberellic acid (GA3) and abscisic acid (ABA) in the regulation of growth in excised Avena (oat) stem segments. Growth, compared to sucrose controls, was inhibited by ABA in the range of 10?4 to 10?6M. GA3-promoted growth was also inhibited by ABA in the same concentration range. A Lineweaver-Burk analysis of the interaction between GA3 and ABA indicated that ABA acts in a non-competitive fashion with GA3. This same result was obtained previously with GA3-indoleacetic acid (IAA) and GA3-kinetin interactions with Avena stem sections. Our results indicate that ABA can inhibit GA3-promoted growth within physiological concentrations, and that it is probably acting at a different physiological site from that for GA3.  相似文献   

11.
Acanthostachys strobilacea Link, Klotzsch, & Otto is an ornamental bromeliad native to Brazilian Atlantic Forest that naturally exhibits a rosette growth pattern. According to the temperature conditions of the in vitro culture, this species can exhibit stem elongation, facilitating the isolation of the nodal segments to be applied in its micropropagation. The rosette morphology is reestablished when this species is maintained under low temperature, thus allowing the maintenance of a germplasm collection (slow growth storage). Gibberellins (GA) are usually applied to stimulate stem elongation in micropropagated plants. Thus, our aim here was to verify the influence of temperature over the stem elongation of A. strobilacea when GA3 is applied to the medium, thus estimating the use of this phytoregulator in slow growth cultures at low temperatures. Physiological and anatomical studies were performed on plants obtained from nodal segments maintained at 10, 15, 20, and 25 °C. Regardless of the applied treatment, no segments developed at 10 °C. Stem elongation occurred at 25 and 30 °C, and was not seen for plants grown under 15 and 20 °C. The application of 50 µM of GA3 restored stem elongation in plants at 20 but not at 15 °C. The influence of gibberellins on stem elongation of this tropical bromeliad depends on the cultivation temperature, in which low temperature preponderates over the stem elongation effects of GA3. In addition, the optimum temperature for the slow growth of this species depends on the starting temperature of the explant used in the micropropagation.  相似文献   

12.
Four gibberellins, GA53, GA19, GA20, and GA1, were detected by bioassay, chromatography in two HPLC systems, and combined gas chromatography-mass spectroscopy-selected ion monitoring (GC-MS-SIM) in etiolated soybean (Glycine max [L.] Merr.) hypocotyls. GC-MS-SIM employed [2H2]-labeled standards for each endogenous gibberellin detected, and quantities estimated from bioassays and GC-MS-SIM were similar. This result plus the tentative detection of GA44 and GA8 (standards not available) indicates that the early-C-13-hydroxylation pathway for gibberellin biosynthesis predominates in soybean hypocotyls. Other gibberellins were not detected. Growth rates decreased after transfer to low water potential (ψw) vermiculite and were completely arrested 24 hours after transfer. The GA1 content in the elongating region of hypocotyls had declined to 38% of the 0 time value at 24 hours after transfer to low ψw vermiculite, a level which was only 13% of the GA1 content in control seedlings at the same time (24 hours posttransfer). Rewatering seedlings following 24 hours growth in low ψw vermiculite resulted in a complete recovery in elongation rate, an increase in GA1 (20% at 2 hours, two-fold at 8 hours, eightfold at 24 hours), and a decrease in ABA levels (tenfold at 2 hours). Treatment of well-watered seedlings with the GA-synthesis inhibitor tetcyclacis (TCY) resulted in lowered GA1 levels and increased ABA levels. When seedlings grown 24 hours in low ψw vermiculite were rewatered with TCY, recovery of the elongation rate was delayed and reduced, and the decline in ABA levels was slowed. Addition of GA3 restored the elongation rate inhibited by TCY. Seedlings were growth responsive to exogenous GA3, and this GA3-promoted growth was inhibited by exogenous ABA. The data are consistent with the hypothesis that changes in GA1 and ABA levels play a role in adjusting hypocotyl elongation rates. However, the changes observed are not of sufficient magnitude nor do they occur rapidly enough to suggest they are the primary regulators of elongation rate responses to rapidly changing plant water status.  相似文献   

13.
The rice pathogen Fusarium fujikuroi is known for producing a wide range of secondary metabolites such as pigments, mycotoxins, and a group of phytohormones, the gibberellic acids (GAs). Bioactive forms of these diterpenes are responsible for hyperelongation of rice stems, yellowish chlorotic leaves, and reduced grain formation during the bakanae disease leading to severely decreased crop yields. GAs are also successfully applied in agriculture and horticulture as plant growth regulators to enhance crop yields, fruit size, and to induce earlier flowering. In this study, six F. fujikuroi wild-type and mutant strains differing in GA yields and the spectrum of produced GAs were cultivated in high-quality lab fermenters for optimal temperature and pH control and compared regarding their growth, GA production, and GA gene expression levels. Comparative analysis of the six strains revealed that strain 6314/ΔDESPPT1, holding mutations in two GA biosynthetic genes and an additional deletion of the 4'-phosphopantetheinyl transferase gene PPT1, exhibits the highest total GA amount. Expression studies of two GA biosynthesis genes, CPS/KS and DES, showed a constantly high expression level for both genes under production conditions (nitrogen limitation) in all strains. By cultivating these genetically engineered mutant strains, we were able to produce not only mixtures of different bioactive GAs (GA3, GA4, and GA7) but also pure GA4 or GA7. In addition, we show that the GA yields are not only determined by different production rates, but also by different decomposition rates of the end products GA3, GA4, and GA7 explaining the varying GA levels of genetically almost identical mutant strains.  相似文献   

14.
Kinetin at physiological concentrations causes significant reduction of GA3-promoted growth in excised Avena stem segments. Kinetin is therefore considered to be a gibberellin-antagonist in this system. A Lineweaver-Burke plot reveals that kinetin acts non-competitively with GA3. The kinetin inhibition of GA3-promoted growth can be seen within 6 hours. It was found that soluble protein is markedly increased by kinetin in the tissue during the first 3 hours, thus preceding the inhibition of GA3-promoted growth by several hours. At the cellular level, kinetin negated the blocking effect of GA3 on cell division in the intercalary meristem portions of these segments. In fact, kinetin promotes both lateral and longitudinal cell divisions in intercalary meristem cells.  相似文献   

15.
Corolla expansion inIpomoea nil appears to be triggered by changes in gibberellin concentration and ethylene production during development. We investigated the role of responsiveness to GA and ethylene in corolla expansion. The effects of growth regulators applied in vitro were measured as a change in area of corolla segments from younger (15–17 mm) and older (18–20 mm) whole corollas. Applied gibberellic acid (GA3) significantly (p < 0.05) promoted growth in the younger segments but was less effective in the older segments. Moreover, applications of the GA biosynthesis inhibitors, PP333 (paclobutrazol) AMO1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride), chlorocholine chloride, and tetcyclasis had little effect on younger segments but inhibited growth of older segments. The older corollas have apparently synthesized and accumulated enough GA-like substances to become less responsive to additional applied GA3. The amount of growth induced by applied or endogenous GA depended on the amount of ethylene simultaneously produced in the tissue. The younger corollas rapidly produced ethylene from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) and did not respond to applied ACC whereas the older corollas naturally produced much less ethylene and were significantly (p < 0.05) inhibited by applied ACC. When ethylene production was inhibited by applying aminoethoxyvinylglycine (AVG), growth was promoted in all segments. However, only the growth of the younger segments was further stimulated by simultaneously applied AVG and GA3 over the GA3 control. Thus the differential responses of segments from 15- to 20-mm long corollas to applied growth regulators reflect developmental changes in responsiveness of the developing corolla. The change in responsiveness is attributed in part to the changes in production of endogenous growth regulators and to the effect of one endogenous plant growth regulator (PGR) on the responsiveness of the corolla to another PGR.  相似文献   

16.
Chilling depresses seed germination and seedling establishment, and is one major constraint to grain yield formation in late sown winter wheat. Seeds of winter wheat (Triticum aestivum L.) were separately pre-soaked with sodium nitroprusside (SNP, as nitric oxide donor) and Gibberellic acid (GA3) before germination and then germinated under low temperature. SNP and GA3 pre-treatment increased seed germination rate, germination index, weights and lengths of coleoptile and radicle, while they decreased mean germination time and weight of seeds germinating under low temperature. Exogenous NO and GA3 increased seed respiration rate and promoted starch degradation along with increased amylase activities. In addition, efficient antioxidant systems were activated by NO, and which effectively reduced concentrations of malondialdehyde and hydrogen peroxide (H2O2). Seedling growth was also enhanced by exogenous NO and GA3 as a result of improved seed germination and maintenance of better reactive oxygen species homeostasis in seedling growing under chilling temperatures. It is indicated that exogenous NO was more effective than GA3 in alleviating chilling stress during seed germination and seedling establishment in wheat.  相似文献   

17.
The effect of application of GA3 on hypocotyl growth, the endogenous GAs, and the metabolism of applied 3H-GA1 were investigated in relation to dwarfism and light-mediated growth inhibition in the normal (tall) strain Violet and the dwarf strain Kidachi of Japanese morning glory (Pharbitis nil). GA3 applied in a wide concentration range (10−9 to 10−3m) to 4-day-old seedlings caused great extension of the hypocotyls in light-grown plants of both the normal and the dwarf strain. However, the dwarf strain did not attain the same length as the normal one at any given GA3 concentration, even when saturation was reached. Dark-grown plants of the dwarf strain responded to GA3, although relatively much less than light-grown ones; dark-grown plants of the normal strain showed no GA3 response at all.  相似文献   

18.
J. L. Stoddart  E. J. Lloyd 《Planta》1986,167(3):364-368
High-resolution growth measurements were conducted using a linear variable displacement transformer in conjunction with a temperature-programmed meristem-cooling collar. Chilling and rewarming profiles were determined for a range of Gramineae, in the presence and absence of varying concentrations of gibberellic acid (GA3). In wheat (Triticum aestivum L.) seedlings, the growth-constraining temperature (Pe) was progressively lowered by increasing GA3 concentration, with a difference of-4.8°C between controls and material treated with 10–4 M GA3. Dwarf-5 maize (Zea mays L.) seedlings had a higher Pe than tall segregates and the difference was markedly reduced by exposure to a saturating concentration of GA3. A similar effect was observed with Tanginbozu dwarf rice (Oryza sativa L.). The growth ratetemperature responses of Rht3 gibberellin-insensitive dwarf wheat seedlings were unaffected by GA3 and the Pe values for these segregates were around 5° C higher than for normals. Slender (s1) barley (Hordeum vulgare L.) genotypes had Pe values of-7° C, compared with +4° C for wild-type material, and did not show positive hysteresis for growth rate during the rewarming phase. These studies indicate that GA3 modifies the thermal sensitivity of meristem function in Gramineae in a manner which enhances low-temperature growth.Abbreviations GA gibberellin - GA3 gibberellic acid - LVDT linear variable displacement transducer  相似文献   

19.
A significant depression of callus growth resulted from low concentrations of abscisic acid (ABA) added to the medium recommended by Linsmaier and Skoog. Low concentrations also decreased the chlorogenic acid and lignin content of the callus, and generally decreased amounts of scopolin and scopoletin in the tissue. Gibberellic acid (GA3) stimulated callus growth in a low concentration (0.1 mg/1) and inhibited growth at a high concentration (10.0 mg/1). Both levels of GA3 increased scopoletin accumulation in tobacco callus. A high concentration of GA3 increased the accumulation of scopolin and chlorogenic acids, whereas a low concentration decreased the amounts of these two phenolic compounds. In comparison with the control, lignin synthesis was stimulated by a low GA3 concentration, but a high GA3 concentration did not have a significant effect. Both low and high concentrations of GA3 overcame ABA inhibition of growth and lignin synthesis, and partially reversed ABA inhibition of scopoletin production. However, GA3 did not reverse the inhibitory effect of ABA on scopolin production. The low concentration of GA3 overcame the inhibition of chlorogenic acid production resulting from a 0.01 mg/1 concentration of ABA, but this was the only reversal of chlorogenic acid inhibition resulting from addition of GA3 to the medium.  相似文献   

20.
Gibberellin response in lettuce hypocotyl sections   总被引:9,自引:7,他引:2       下载免费PDF全文
Silk WK  Jones RL 《Plant physiology》1975,56(2):267-272
Excised lettuce (Lactuca sativa L.) hypocotyl sections retain the ability to elongate in response to gibberellic acid (GA3) addition. In 48 hr at 30 C a GA3-treated segment more than doubles while a control segment elongates less than 50%. Auxin has no detectable effect on this system. Sensitivity to GA3 is not decreased by apex or root removal. Of the experimental variables tested, temperature, sucrose, and preincubation in water affect growth both with and without GA3. Blue and far red light inhibit growth without GA3; this inhibition is reversed by GA3. Potassium chloride stimulates growth of illuminated sections treated with GA3 but has no effect on control growth. When sections are incubated in the dark, KCl has a promotive effect on elongation.  相似文献   

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