Shoot Ethylene Research Articles

Epinasty Accompanies Potassium Nitrate-Induced Flower Bud Break in 'Carabao' Mango [RESEARCH NOTE

The hypothesis that potassium nitrate application promotes epinasty in ‘Carabao’ mango through increased ethylene production was investigated. The degree of drooping, apical primordium growth as affected by shoot ethylene and levels after potassium nitrate spraying were monitored. Evidence presented established for the first time in ‘Carabao’ mango that epinasty occurred just before flower emergence, coinciding with visible bud break, and extended up to 18 days, marking floral anthesis. The possible reasons could be the higher levels of ethylene at 0.31% and earlier increase of ethylene in the shoot apex at 4 hours and apical primordium growth. Increased ethylene levels at 0.21% were observed 2 hours from spraying of potassium nitrate, peaking between 4 to 5 hours both in the leaves and shoot apex and eventually declined at 0.11% thereafter while apical primordium growth started three days from potassium nitrate spray which the emerging buds pushes the side of the apex causing partial bending of apical leaves.

Drought and re-watering modify ethylene production and sensitivity, and are associated with coffee anthesis

Coffee flowering requires a period of water deficit followed by rainfall to break flower bud dormancy and promote anthesis. Since drought followed by re-watering can increase shoot ethylene production, we investigated changes in root, leaf and flower bud ethylene production and expression of genes within the ethylene biosynthesis and signalling pathways and their relationship to coffee flowering. Drought decreased foliar and flower bud ethylene production without changing root ethylene production, even though all tissues likely accumulated the ethylene precursor ACC (1-aminocyclopropane-1-carboxylic acid), since ACS gene expression was maintained while ACO gene expression decreased. The ethylene receptor CaETR4-like was not differentially expressed in leaves under water deficit, but it was downregulated in roots. Re-watering restored shoot ethylene production, which seems important in promoting anthesis. 1-MCP (1- Methylcyclopropene), an ethylene action inhibitor, triggered coffee anthesis without re-watering the plants, which hitherto was considered essential to allow flowering. 1-MCP positively regulated foliar and flower bud ethylene biosynthesis genes (CaACS1-like and CaACO1-like), similar to re-watering, and downregulated CaETR4-like, suggesting that changes in ethylene levels and sensitivity are required to promote coffee anthesis. Thus, drought and re-watering-induced changes in ethylene levels and sensitivity allow coffee flowering, while the growth regulator 1-MCP can potentially regulate anthesis time and intensity.

Light Signaling Regulates Tulip Organ Growth and Ethylene Production in a Tissue-Specific Manner

Premise of research. Plants growing under physical or leaf canopy shade often exhibit increases in shoot growth that allow for additional exposure to irradiance from sunlight. These shaded plants also usually exhibit an accelerated flowering, though the effect of shade light on growth of flower organs has not been well studied. These growth changes in shoot organs induced by shade light signaling are regulated in a negative manner by ethylene in a number of plant species; that is, shading reduces shoot ethylene production, thereby increasing shoot growth.Methodology. Tulip (Tulipa gesneriana L., Liliaceae) plants were selected as a model system, one where floral organ development occurs in the bulb before exposure to shade light. This allows any effects of shade light signaling on floral organ growth to be uncoupled from effects on development. Therefore, following a period of low temperature, tulip bulbs were exposed to simulated sunlight with and without physical or canopy shade.Pivotal results. Both a ...

Ammonium-induced shoot ethylene production is associated with the inhibition of lateral root formation in Arabidopsis

Foliar NH4(+) exposure is linked to inhibition of lateral root (LR) formation. Here, the role of shoot ethylene in NH4(+)-induced inhibition of LR formation in Arabidopsis was investigated using wild-type and mutant lines that show either blocked ethylene signalling (etr1) or enhanced ethylene synthesis (eto1, xbat32). NH4(+) exposure of wild-type Arabidopsis led to pronounced inhibition of LR production chiefly in the distal root, and triggered ethylene evolution and enhanced activity of the ethylene reporter EBS:GUS in the shoot. It is shown that shoot contact with NH4(+) is necessary to stimulate shoot ethylene evolution. The ethylene antagonists Ag(+) and aminoethoxyvinylglycine (AVG) mitigated LR inhibition under NH4(+) treatment. The decrease in LR production was significantly greater for eto1-1 and xbat32 and significantly less for etr1-3. Enhanced shoot ethylene synthesis/signalling blocked recovery of LR production when auxin was applied in the presence of NH4(+) and negatively impacted shoot AUX1 expression. The findings highlight the important role of shoot ethylene evolution in NH4(+)-mediated inhibition of LR formation.

The roles and interactions of ethylene with gibberellins in the far-red enriched light-mediated growth of Solanum lycopersicum seedlings

Wild type (WT) tomato seedlings responded to a low red to far-red (R/FR) ratio with increased stem elongation, similar leaflet area expansion and lower shoot ethylene levels. The levels of endogenous growth-active GA1 and its immediate precursor GA20 were decreased by low R/FR ratio, whereas the levels of GA1 catabolite, GA8, increased. To examine the interaction of ethylene with GAs in regulating tomato shoot growth under low R/FR ratio, transgenic (T) seedlings bearing Le-ACS2 and Le-ACS4 antisense mRNA were utilized. Low R/FR ratio increased stem elongation and decreased ethylene levels in T tomato shoots, as it did in WT shoots. However, T stems were significantly taller than the WT stems under low R/FR ratio. Leaflet areas were significantly larger for T, than WT seedlings under both R/FR ratios. Low R/FR ratio did not decrease endogenous levels of GA1 and GA20 in T shoots, but did increase GA8 levels, which were higher than in WT shoots. These results, and hormone/inhibitor application studies, showed that in tomato shoots subjected to low R/FR ratio, GAs play a growth-promotive role in stem elongation, whereas ethylene is growth-inhibitory. Further, these results may imply that decreasing ethylene production under low R/FR ratio causes increases in stem elongation and GA levels.

Partial phenotypic reversion of ABA-deficient flacca tomato (Solanum lycopersicum) scions by a wild-type rootstock: normalizing shoot ethylene relations promotes leaf area but does not diminish whole plant transpiration rate.

To evaluate the role of root-synthesized ABA in regulating growth and stomatal behaviour under well-watered conditions, isogenic wild-type (WT) and ABA-deficient flacca (flc) tomato (Solanum lycopersicum) were reciprocally and self-grafted just below the cotyledonary node. Since flc scions had lower leaf water potentials due to higher transpiration rates, a subset of all graft combinations was grown under a shoot misting treatment to minimize differences in shoot water status. Misting did not alter the relative effects of the different graft combinations on leaf area. WT scions had the greatest leaf area and lowest whole plant transpiration rate irrespective of the rootstock, implying that shoot ABA biosynthesis was sufficient to account for a WT shoot phenotype. In WT scions, the rootstock had no effect on detached leaf ethylene evolution or xylem concentrations of ABA or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). In flc scions, although the WT rootstock suppressed stomatal conductance of individual leaves, there was no detectable effect on whole plant transpiration rate. However, leaf area of flc/WT (scion/rootstock) plants increased 1.6-fold compared to flc self-grafts. WT rootstocks increased xylem ABA concentration in flc scions (relative to flc self-grafts) up to 3-fold, and resulted in xylem ACC concentrations and detached leaf ethylene evolution similar to WT scions. Since the WT rootstock normalized shoot ethylene relations but only partially restored the leaf area of flc scions (relative to that of WT scions), shoot ABA biosynthesis can directly promote leaf area via an unknown, ethylene-independent, mechanism.

Responses of ethylene biosynthesis to saline stress in seedlings of eight plant species

The effect of salinity (100 mM NaCl) on ethylene metabolism in the early phase of vegetative development of several plant species has been investigated. The effects of saline treatment on shoot and root growth, ranged in sensitivity with respect to species: pepper (Capsicum annum L. cv Pairal) > tomato (Lycopersicon esculentum Mill. cv Malpica) > broccoli (Brassica oleraceae L. var. Italica Plenk. cv Marathon F1) ≅ lettuce (Lactuca sativa var. longifolia Lam. cv Inverna) ≅ melon (Cucumis melo L. cv Ruano F1, Roche type) > bean (Phaseolus vulgaris L. cv. Gator Green 15) ≅ spinach (Spinacia oleracea L. cv Boeing) > beetroot (Beta vulgaris L. var. crassa (Alef.) J. Helm. cv Detroit). After saline treatment, ethylene production increased 4.2-fold in pepper shoots. Significant increases were also found in shoots of tomato, broccoli and bean. In contrast, salinity decreased shoot ethylene production rate in melon, spinach, and beetroot. In roots, the general effect of salinity was a decrease in ethylene production, especially in broccoli and bean, except in tomato root, in which a sharp increase in ethylene production occurred. In general, saline treatment increased total ACC concentration in both shoot and root in most of the plant species examined, which was related to plant sensitivity to salinity. For example, pepper shoot was the most sensitive to saline treatment, showing the highest fresh weight inhibition and the highest increase in total ACC concentration (8.5-fold), while, beetroot was less affected by salinity and showed no effect on total ACC concentration in response to saline treatment.

Cytokinin accumulation and an altered ethylene response mediate the pleiotropic phenotype of the pea nodulation mutant R50 (sym16)

R50 (sym16), a pleiotropic mutant of Pisum sativum L., is short, has thickened internodes and roots, and has a reduced number of lateral roots and nodules. Its low nodule phenotype can be restored with the application of ethylene inhibitors; furthermore, it can be mimicked by applying cytokinins (CKs) to the roots of the parent line ‘Sparkle’. Here, we report on the etiolation phenotypes of R50 and ‘Sparkle’, and on the interactive roles of ethylene and CKs in these lines. R50 displayed an altered etiolation phenotype, as it was shorter and thicker, and had more developed leaves than dark-grown ‘Sparkle’. Shoot morphological differences induced by exogenous ethylene or CKs were found to be less severe for R50. Ethylene inhibitor application induced root and shoot elongation and encouraged apical hook opening in both etiolated lines. Liquid chromatography - tandem mass spectrometry analysis indicated that CK concentrations in R50 were higher than in ‘Sparkle’, particularly in mature shoots where the levels were maintained at elevated concentrations. These differences indicate a reduction in the CK catabolism of R50. The accumulation of CKs can be directly related to several traits of R50, with the reduced number of nodules and altered shoot ethylene response being likely indirect effects. Key words: cytokinin, de-etiolation, ethylene, etiolation, pea, nodulation mutant.

Circadian Ethylene Synthesis in Sorghum bicolor: Expression and Control of the System at the Whole Plant Level

Ethylene production by sorghum is rhythmic and the amplitude of the rhythm is increased both by dim, far-red enriched light and in mutant plants deficient in phytochrome B. The mechanisms involved in controlling ethylene production were examined in detail by measuring the rate of ethylene production among organs and tissues, examining the organ-specific levels of ACC (1-aminocyclopropane-1-carboxylic acid, the ethylene precursor) and investigating the contribution of the roots to shoot ethylene production. The results demonstrate that the expanding leaves were the major source of ethylene under dim, far-red enriched light and in the phytochrome B mutant. Enhanced ethylene production by the expanding leaf appeared to be the result of targeted delivery of ACC to this tissue. Root ACC levels were much higher than those in the shoot but roots converted much less of this endogenous ACC to ethylene. Applying ACC to the roots had only a marginal effect on their ethylene production, but greatly increased that of the shoots. Decapitated shoots continued to produce ethylene in a rhythmic pattern but the amplitude decreased with time compared to intact plants. The results collectively suggest that some, but not all, of the shoot ethylene rhythm depends on the transport of ACC from the roots to the shoots.

Laterally applied Ethrel causes local increases in radial growth and indole-3-acetic acid concentration in Abies balsamea shoots.

The terminal (1-year-old) shoot of quiescent, two-year-old balsam fir (Abies balsamea (L.) Mill.) seedlings was ringed with lanolin containing 0, 1 or 10 mg g(-1) Ethrel, an ethylene-generating compound, and cultured for 6 weeks under environmental conditions favorable for growth. Bud break and the elongation of the current-year terminal shoot were monitored, and the subjacent previous-year terminal shoot that had been treated with Ethrel was harvested to measure stem radial growth by microscopy, shoot ethylene evolution by gas chromatography, and cambial region indole-3-acetic acid (IAA) concentration by combined gas chromatography-mass spectrometry. Compared with the lanolin controls, Ethrel at 1 and 10 mg g(-1) did not affect bud break or longitudinal growth, but stimulated tracheid production and bark increment up to about 2-fold at the application site, though not above or below it. In addition, the 1 and 10 mg g(-1) Ethrel treatments increased the cambial region IAA concentration about 3-fold and the evolution of ethylene at least 40-fold at the application site, compared with unwounded portions of both treated and control shoots. The 10 mg g(-1) Ethrel treatment also stimulated ethylene evolution about 10-fold, both above and below the application site. However, this stimulation was not associated with an elevation in cambial region IAA concentration. Similarly, the lanolin control treatment increased ethylene evolution at the application site about 10-fold, without affecting the cambial region IAA concentration. Our results suggest that the localized stimulation of radial growth in woody shoots ringed with Ethrel is mediated by an increase in IAA concentration, which in turn is induced by a threshold, abnormally high concentration of Ethrel-derived ethylene.

Effect of Cultivar, Strain, and Growth Regulator Treatments on Shoot Development and Ethylene Evolution in Apple Trees1

Abstract ‘Miller Sturdeespur Delicious’ apple (Malus domestica Borkh.) trees made less extension growth than ‘Imperial Red Delicious’ (non-spur) under controlled conditions. No differences in extension growth were measured between ‘MacSpur’ and ‘Imperial McIntosh’ (non-spur) trees. Development of the spur-type morphology was determined by the number of lateral buds which grew into spurs during the second growing season. Application of (2-chloroethyl)phosphonic acid (ethephon) alone, or in combination with butanedioic acid mono-(2, 2-dimethylhydrazide) (daminozide) decreased extension growth and increased shoot ethylene evolution in growth chamber studies, and promoted flowering in the field. Application of daminozide plus ethephon was more effective than ethephon alone. Daminozide alone did not affect shoot ethylene. No change in ethylene evolution or shoot development was detected following applications of gibberellin 4/7 (GA) or 2, 3, 5-triiodo benzoic acid (TIBA) to spur or non-spur type trees. Bark scoring had no effect on shoot ethylene. However, this treatment also promoted flowering of young trees in the field. It is suggested that while some manipulations can increase shoot ethylene evolution and also promote flowering, the ethylene evolved following treatment operates indirectly by retarding growth, rather than by directly stimulating flower bud initiation.

Stress Ethylene Production in Apple Shoots1

Abstract Increases in internal ethylene concentrations occurred after attached and detached apple (Malus domestica, Borkh. cv. Winesap) shoots were placed in a horizontal position. Ethylene was higher in the underside of the shoot, and decreased linearly in a basipetal direction along the axis. Bent and horizontally-oriented detached shoots did not increase in ethylene at 20°C, but increased to identical levels at 30°, suggesting that responses to the 2 types of stress were identical. Although gravitational stress alone increased ethylene levels, an experiment designed to separate bending stress from gravitational stress was inconclusive because rotation decreased shoot ethylene levels.