Ethylene Evolution Rate Research Articles

Comparisons in Agronomic and Physiological Traits of Rice Genotypes Differing in Cadmium-Tolerance

Cadmium (Cd) is one of major contaminants in agricultural soil, threatening agricultural production and human health. To understand agronomic and physiological characteristics of rice genotypes differing in Cd-tolerance would have great signifi-cance in selecting or breeding a Cd-tolerant cultivar. In this study, two Cd-tolerant rice genotypes of Shanyou 63 (indica hybrid) and Yangjing 9538 (japonica) and two Cd-susceptible genotypes of Yangdao 6 (indica) and Wuyunjing 7 (japonica) were pot-grown at a farm of Yangzhou University, Yangzhou, Jiangsu Province in 2004 and 2005. 150 mg kg-1 Cd was added into pot soil before seedling transplanting (Cd treatment), and no Cd addition was taken as control (CK). Under the Cd treatment, the grain yield was reduced by 6.2–8.9% for the Cd-tolerant genotypes and by 38.3–47.1% for the Cd-susceptible ones when compared with their respective CKs. The reduction in grain yield was mainly attributed to the reductions of panicles per pot and spikelets per panicle. The differences in seed-setting rate and 1 000-grain weight were not significant between the Cd treatment and CK. The Cd treatment markedly inhibited the tillering of the Cd-susceptible genotypes, resulting in the reduction in dry matter accumula-tion during the whole growth period. Cd little affected the translocation of non-structural carbohydrate from culms and sheaths and harvest index. For Cd-susceptible genotypes, the Cd treatment significantly reduced root oxidation activity and photosynthetic rate, activities of superoxide dismutase and catalase of leaves, and obviously increased contents of superoxidate radical and hy-drogen peroxide and ethylene evolution rate of leaves, and the concentration of 1-aminocylopropane-1-carboxylic acid in root bleedings from the tillering to jointing stages, while the Cd treatment much less affected the above physiological traits for the Cd-tolerant genotypes. The differences in the above traits at heading and afterwards and abscisic acid content in leaves during the whole growth period were not significant between the Cd treatment and CK. The results indicate that the effects of Cd on ricegrowth and development are mainly during the early growth period (from tillering to jointing), and more tillers, stronger root ac-tivity and antioxidative defense system, and less ethylene synthesis in the plants during this period would be considered as agro-nomic and physiological traits of Cd-tolerant genotypes of rice.

Responses of ethylene and ACC in rice grains to soil moisture and their relations to grain filling

The objectives of this study were to investigate ethylene and 1-aminocylopropane-1-carboxylic acid (ACC) in rice grains and root bleeding sap during the grain filling period and their relationship to the grain filling rate. Two high lodging-resistant rice (Oryza sativa L.) cultivars were grown in pots or tanks. Three treatments, including well watered (WW), moderate soil-drying (MD) and severe soil-drying (SD), were conducted from 9 days of post-anthesis until maturity. The effects of chemical regulators on the concentrations of ethylene and ACC in the grains were also studied. The results show that MD significantly increased the grainfilling rate and grain weight, whereas SD significantly reduced the grain-filling rate and grain weight. Concentrations of ethylene and ACC in the grains were very high at the early grain filling stage and then sharply decreased during the linear period of grain growth. MD reduced the ACC concentrations and ethylene evolution rate, whereas SD remarkably increased the ACC concentrations and ethylene evolution rate. Both the ethylene evolution rate in rice grains and the ACC concentrations in the root-bleeding sap were significantly and positively correlated with the ACC concentrations in rice grains. The ethylene evolution rate was significantly and negatively correlated with the grain-filling rate. The application of amino-ethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, at 9–13 days of postanthesis significantly reduced the ACC concentrations and ethylene evolution rate of grains, but significantly enhanced the activities of sucrose synthase, ADP glucose pyrophosphorylase and soluble starch synthase. The results were reversed when ethephon, an ethylenereleasing agent, was applied. The results suggest that moderate soil drying during the grain-filling period in rice could inhibit the production of ethylene and ACC and therefore accelerate grain filling and increase grain weight.

Comparison of Agronomic and Physiological Traits of Rice Genotypes Differing in Cadmium-Tolerance

Cadmium (Cd) is one of major contaminants in agricultural soil, threatening agricultural production and human health. To understand agronomic and physiological characteristics of rice ( Oryza sativa L.), genotypes differing in Cd-tolerance, 2 Cd-tolerant rice genotypes Shanyou 63 ( indica hybrid) and Yangjing 9538 ( japonica)and 2 Cd-susceptible genotypes Yangdao 6 ( indica) and Wuyunjing 7 ( japonica) were pot-grown in 2004 and 2005. In the Cd treatment, 150 mg kg −1 Cd was added into pot soil before seedling transplanting, and no Cd addition was taken as control. Under the Cd treatment, the grain yield was reduced by 6.2–8.9% for the Cd-tolerant genotypes and by 38.3–47.1% for the Cd-susceptible ones compared with their respective controls. The reduction in grain yield was mainly attributed to the reduction of panicles per pot and spikelets per panicle. The differences in seed-setting rate and 1000-grain weight were not significant between the Cd treatment and the control. The Cd treatment markedly inhibited the tillering of the Cd-susceptible genotypes, resulting in the reduction of dry matter accumulation during the whole growth period. Cd slightly affected the translocation of nonstructural carbohydrate from culms and sheaths, as well as harvest index. For Cd-susceptible genotypes from the tillering to the jointing stages, the Cd treatment significantly reduced root oxidation activity and photosynthetic rate, activities of superoxide dismutase, and the catalase in leaves, but obviously increased the content of the superoxidate radical, hydrogen peroxide, and ethylene evolution rate of leaves, as well as the concentration of 1-aminocylopropane-1-carboxylic acid in root bleedings. After the heading stage, the Cd treatment affected the above-mentioned physiological traits of the Cd-tolerant genotypes much less. The differences in the above-mentioned traits at heading and later, as also the abscisic acid content in leaves during the whole growth period were not significant between the Cd treatment and the control. The results indicated that the effects of Cd on rice growth and development were mainly during the early growth period (from tillering to jointing). More tillers, stronger root activity, and antioxidative defense system, and less ethylene synthesis in the plants during this period were considered as the agronomic and physiological traits of Cd-tolerant genotypes of rice.

POSSIBLE INTERACTIONS OF POLYAMINES AND ETHYLENE DURING RIPENING OF GUAVA (PSIDIUM GUAJAVA L.) FRUITS

The rate of ethylene evolution, 1-amino cyclopropane 1-carboxlylic acid (ACC) content, ACC oxidase activity and free polyamines were monitored during fruit ripening of two guava cultivars (Psidium guajava) i.e., L-49 (shelf life 7-8 days) and Hisar Safeda (shelf life 3-4 days). Ethylene evolution and ACC oxidase activity were substantially high at turning (T) stage and low at the later stages of fruit ripening, indicating the climacteric nature of the fruit. Contrary to this, ACC content increased progressively throughout ripening, suggesting that ACC oxidase was the rate-limiting step in the biosynthetic pathway of ethylene. The level of putrescine, spermidine and spermine was minimum at the onset of climacteric, suggesting a competition for a common intermediate, S-adenosylmethionine, which, at T stage, is channeled toward ethylene and at later stages, toward polyamines. Less ethylene and higher level of polyamines in L-49 than in Hisar Safeda may be one of the reasons for the prolonged shelf life of L-49.

Causes of Poor Grain Plumpness of Two-Line Hybrids and Their Relationships to the Contents of Hormones in the Rice Grain

Abstract This study was designed to elucidate the grain filling characteristics and the causes of poor grain plumpness of some two-line hybrid rice combinations and their hormonal mechanism. Six varieties, including three two-line hybrid rice combinations, that show differences in seed-setting and grain filling, were used. And the contents of starch, sucrose, zeatin (Z) + zeatin riboside (ZR), indole-3-acetic acid (IAA), and abscisic acid (ABA), the ethylene evolution rate, activities of sucrose synthase (SuSase) and starch synthase (StSase) in grains, the seed-setting and grain filling rate were investigated. The correlations amongst these were analyzed. The results showed that the poor grain filling of two-line hybrids was mainly attributed to the higher unfilled grain rate and the lower filling degree of inferior grains. During the early and mid grain filling periods, the sucrose content in inferior grains was greater than that in superior grains for the combinations with poor grain filling, indicating that the substrate concentration was not the principal factor for their slow grain filling and poor grain plumpness of the inferior grains of two-line hybrids. Z + ZR, IAA, and ABA in superior grains were obviously greater than those in inferior grains at early grain filling stage. The maximum and mean contents of Z + ZR, IAA, and ABA were positively very significantly correlated with the maximum and mean grain-filling rate, filling degree, and grain weight. The evolution rate of ethylene was greater in inferior grains than in superior grains and greater for the combinations with poor grain plumpness than those with good grain plumpness at the early or mid filling stages. The evolution rate of ethylene was negatively and significantly correlated with the grain filling rate, the grain filling degree, and the grain weight. Spraying ethephon (ethylene-releasing agent) at the early grain filling stage increased the evolution rate of ethylene, reduced the ABA content and activities of SuSase and StSase, and decreased the grain filling degree and the grain weight. The results were reversed when cobatous nitrate (an inhibitor of ethylene synthesis) was applied. The results suggested that the hormones and their balance play a role in the regulation of grain filling and enzymatic activities, and the poor grain filling is attributed to the low contents of Z + ZR, IAA, and ABA, and the high evolution rate of ethylene in the inferior grains of some two-line hybrid rice combinations. The results suggested that hormones play important roles in the grain filling of some two-line hybrid rice combinations, and their filling degree can be improved by regulating the hormonal contents.

Relationships of Ethylene Evolution Rate and 1-Aminocylopropane -1-Carboxylic Acid Concentration in Grains during Filling Period with Appearance Quality of Rice

To elucidate the relationship between ethylene evolution from the grains and the appearance quality of rice, ten different rice genotypes were used to determine the ethylene evolution rate, 1-aminocylopropane-1-carboxylic acid (ACC) concentration in grains during grain filling and the appearance quality of rice, and the effects of chemical regulators on concentrations of ethylene and ACC in the grains during grain filling were also investigated to verify the roles of ethylene in the rice quality formation. The ethylene evolution rates and ACC concentrations in grains during the mid and late grain filling stages were very significantly and positively correlated with chalky kernel percentage and chalkiness. The cultivars with a low ACC concentration in grains exhibited a close amyloplast arrangement and small space between starch granules, whereas those with a high ACC concentration in grains showed a loose arrangement and wide space between the granules. Application of 1 μmol/L ACC to panicles at mid and late grain filling stages significantly loosened amyloplast arrangement and increased chalky kernel percentage, chalky area and chalkiness, and the results were reversed when 1 μmol/L amino-ethoxyvinylglycine, an inhibitor of ACC synthesis enzyme, was applied to panicles. A practice of moderate dry-wet alternate irrigation reduced ethylene evolution and ACC concentration in grains and thereby reduced chalkiness. The results suggested that ethylene and ACC in grains play an important role in the endosperm structure and appearance quality of rice, and the appearance quality would be improved by reducing ethylene evolution and ACC in grains through either variety breeding and selection, or chemical regulations or cultivation techniques.

PROLONGING THE LONGEVITY OF CYMBIDIUM FLOWERS THROUGH GENETIC TRANSFORMATION

A substantial portion of commercially produced cymbidiums is sold as cut flowers that often require shipment to distant markets. Like many other species, ethylene released following harvest causes short flower longevity. The loss of flowers might be minimized by genetically transforming plants for reduced sensitivity to ethylene. A Cymbidium hybrid that produces large, dark pink-reddish flowers was selected for transformation. Shoot tips were excised and cultured in vitro, and protocorms were bombarded with a plasmid construct containing the boers gene, a mutant of the ethylene receptor gene, ERS, isolated from Brassica oleracea var. botrytis L. The mutant confers reduced sensitivity to ethylene. The ubiquitin promoter together with the hygromycin resistance gene was included in the construct. Bombardment was performed with the BioRad Biolistic PDS-1000/He gun. After 80 days of culture on hygromycin containing medium, putative transformants were isolated as regenerating protocorms. Protocorms also gave rise to plant differentiation subsequently in hygromycin containing culture medium. Transformants were preliminarily confirmed by PCR and RT-PCR for HPH and boers genes, and ultimately verified by genomic Southern hybridization. GC analysis of volatiles collected from leaves of transformed and nontransformed plantlets showed different rates of ethylene evolution. However, exposure of the leaves to exogenous ethylene caused rapid browning of leaves of nontransformed plants, but not of those from transformed plants. At this writing, the transgenic cymbidium plants are continuing to grow vigorously in the greenhouse, but have not yet matured for studying the ethylene sensitivity of their excised or intact flowers.

Possible roles for ethylene and gibberellin in the phenotypic plasticity of an alpine population of Stellaria longipes

Four phenotypically different genotypes from an alpine population of Stellaria longipes Goldie s.l. (Caryophyllaceae) were collected from neighbouring sites at the top of the Plateau Mountain in southeastern Alberta, Canada, to examine a possible hormonal basis for their differences in stem length, leaf size, and flowering characteristics. All four genotypes had a dwarf shoot phenotype, compared with the low-elevation ecotype. Among the four genotypes, PMI-D was the tallest and had the largest leaves and flowers as well as more flowers per plant. PMI-D also maintained the flowering state, upon repropagation, without low temperature, short-day vernalization. Under controlled long-day warm conditions, the PMI-D genotype had a higher rate of ethylene evolution, but contained levels of endogenous gibberellin A1 that were similar to the other three (smaller) alpine genotypes. PMI-D was more sensitive to exogenously applied ethylene and growth-active gibberellins than other alpine genotypes. In contrast, the other three genotypes were smaller, had fewer (and smaller) flowers, and exhibited low ethylene evolution and a reduced sensitivity to applied ethylene and growth-active gibberellins. Speculatively, this behaviour may indicate an adaptation within this unique population of “dwarf” phenotypes that involves enhanced sensitivity to endogenous ethylene and gibberellins.

Effect of 1-methylcyclopropene and/or chitosan coating treatments on storage life and quality maintenance of Indian jujube fruit

Indian jujube ( Ziziphphus mauritina, cv. ‘Cuimi’) fruits were harvested at stage of mature-green and then treated with 1-methylcyclopropene (1-MCP) at two doses (0 and 600 nl l −1) for 12 h at room temperature. Half of the fruits were coated with 1.5 g/100 ml of chitosan (CTS) solution after 1-MCP treatment and subsequently stored at room temperature and 80–90% relative humidity (RH). Results indicated that 600 nl l −1 of 1-MCP, 1.5 g/100 ml of CTS or their combination were effective in terms of senescence inhibition during storage and compared to control, the storage life was extended by 7, 5 and 8 d, respectively. Fruits treated with the combination of 1-MCP and CTS coating showed better retention of chlorophyll content, total soluble solids, ascorbic acid and fruit firmness, delayed climacteric ethylene evolution and respiration rate, reduced stem-end rots incidence, decreased PG and LOX activities than those with other treatments. Coating alone reduced weight loss and stem-end rots incidence. It delayed the declining firmness and the onset of climacteric ethylene production and respiration rate, but did not influence the peak levels of ethylene and respiration rates. The treatment with only 1-MCP delayed the degreening process and suppressed PG and LOX activities through 10 d at room temperature. The results showed that the treatment with the combination of 1-MCP and CTS coating improved greatly the storage life extension and quality maintenance of Indian jujube fruit at room temperature storage.

Post-anthesis development of inferior and superior spikelets in rice in relation to abscisic acid and ethylene

The purpose of this study was to test the hypothesis that the interaction between abscisic acid (ABA) and ethylene may be involved in mediating the post-anthesis development of spikelets in rice (Oryza sativa L.). Two rice genotypes were field-grown, and the changes of ABA, ethylene, and 1-aminocylopropane-1-carboxylic acid (ACC) levels in spikelets during grain filling and their relationships with endosperm-division and grain-filling rates were investigated. The results showed that earlier-flowering superior spikelets exerted dominance over later-flowering inferior spikelets in endosperm cell-division and grain-filling rates. The two genotypes behaved the same. Later-flowering spikelets had higher levels of ethylene and ACC than earlier-flowering spikelets. The ethylene evolution rate was significantly and negatively correlated with the cell division and grain filling rates. By contrast to ethylene, later-flowering spikelets contained a lower ABA content/concentration and showed a low content ratio of ABA to ACC than earlier-flowering ones. The cell-division and grain-filling rates were significantly and positively correlated with both ABA contents and the ratio of ABA to ACC. Application of cobalt ion (inhibitor of ethylene synthesis) or ABA at an early grain-filling stage significantly increased endosperm cell division rate and cell number, grain-filling rate, and grain weight of inferior spikelets. Application of ethephon (an ethylene-releasing agent) or fluridone (an inhibitor of carotenoid synthesis) had the opposite effect. The results suggest that antagonistic interactions between ABA and ethylene mediate endosperm cell-division and grain-filling in rice. A higher ratio of ABA to ethylene in rice spikelets is required to maintain a faster grain-filling rate.

POSTHARVEST USE OF 1-MCP TO EXTEND STORAGE LIFE OF MELON IN BRAZIL - CURRENT RESEARCH STATUS

Efficiency of 1-MCP on postharvest life of whole and fresh-cut cantaloupe melons was evaluated. Melons were treated with doses varying from 0 to 900 nl.L -1 in order to define the best concentration of 1-MCP. Flesh softening was the main characteristic affected in all experiments and softening delay was according to the dose, although differences between doses above 300 nl.L -1 were not significant. Respiration and ethylene evolution rates were reduced and both CO 2 and ethylene peaks were delayed in trials with whole melons. 1-MCP doubled postharvest life of cantaloupe melons at ambient temperature (from 1 to 2 weeks). Treated melons were acceptable for 27 days, whereas control fruit could be stored for no longer than 7 days.[...]

Efficacy of 1-Methylcyclopropene (1-MCP) in Prolonging the Shelf-life of 'Rendaiji' Persimmon Fruits Previously Subjected to Astringency Removal Treatment

Fruits of ‘Rendaiji’ persimmon (Diospyros kaki Thunb.), known to be highly susceptible to rapid softening after harvest or astringency removal treatment, were treated with 20 μL · L−1 1-methylcyclopropene (1-MCP) at 20°C for 24 h after treatment with ethanol vapor to remove astringency. The fruit were then stored at 20°C to monitor ripening-related changes, such as physicochemical, physiological, and biochemical parameters at regular intervals. 1-MCP treatment delayed fruit softening brought about by exposure to ethanol vapor and extended shelf-life of the fruits by 8 days. No suppression in ethylene evolution and respiration rate was observed in 1-MCP-treated fruits. Fruits treated with 1-MCP had higher soluble solids content, less weight loss and slower color development and they softened normally. 1-MCP-treatment caused a transient suppression in polygalacturonase (PG) activity; pectin methyl esterase (PME) and β-galactosidase activities were significantly inhibited, but had no deleterious effects on the quality of ‘Rendaiji’ persimmon fruits.

Effects of Calcium and Magnesium Treatments on Growth, Nutrient Contents, Ethylene Production, and Gibberellin Content in Chrysanthemum Plants

Effects of calcium (Ca) and magnesium (Mg) treatments on growth, nutrient contents, ethylene evolution, and gibberellin (GA) content of Dendranthema grandiflora (Ramat.) Kitam. were investigated. Treatments were as follows (per pot): 0.0 g Ca or Mg (Control), 0.2 g Ca, 0.5 g Ca, 0.2 g Ca+0.2 g Mg, 0.5 g Ca+0.2 g Mg, and 0.2 g Mg. Plant height increased significantly in 0.5 g Ca and 0.5 g Ca+0.2 g Mg treatments but not in other treatments. Shoot dry weight increased in all the treatments except in 0.2 g Mg treatment compared with the control. N content decreased in Ca+Mg and Mg treatments, whereas K content increased in all treatments compared with the control. Ca content increased in 0.2 g Ca and 0.5 g Ca treatments but decreased in 0.2 g Mg treatment; Mg content increased in Ca+Mg and Mg treatments. All treatments reduced ethylene evolution rate faster than the control for 10 days. Total GA-like substances increased in plant treated with 0.5 g Ca+0.2 g Mg. GA-like substances were found in the HPLC fractions 3, 7, 8, and 12 in control plants. GA1- and GA3-like substance contents did not change in 0.2 g Ca, 0.5 g Ca or 0.2 g Mg treated plants but decreased in Ca+Mg treated plants compared with the control. Thus, Ca and Mg treatments affect not only the growth of chrysanthemum plants and nutrient contents but also GA activities and ethylene evolution.

Ethylene evolution changes in the stems of Metasequoia glyptostroboides and Aesculus turbinata seedlings in relation to gravity-induced reaction wood formation

Two-year-old Metasequoia glyptostroboides and 3-month-old Aesculus turbinata seedlings were tilted at a 45° angle to induce compression wood formation on the lower side of the former species and tension wood on the upper side of the latter. Two weeks later, the seedlings were tilted in an opposite direction at 45° so that the upper and lower sides changed to each other. This reverse tilting was kept for 7 weeks for M. glyptostroboides and 6 weeks for A. turbinata. The seedlings were sampled and analyzed at intervals throughout each experimental period so that an ethylene evolution kinetic was monitored. Ethylene evolution from the cambial region of the upper and lower sides of tilted stems was measured separately by gas chromatography with a flame ionization detector. Xylem production expressed as wood area during each experimental period was microscopically determined. In both tilting and reverse tilting periods, the rates of ethylene evolution from the lower side of M. glyptostroboides and the upper side of A. turbinata, where xylem production was accelerated and compression or tension wood formation was induced, had increased to high levels, whereas those from the opposite sides had either remained low (in tilting period) or rapidly recovered to low levels (in reverse tilting period). The cambial activity quantified by wood formation, including reaction wood, in both species showed the same tendency as ethylene evolution. The stem side with vigorous ethylene evolution, xylem development and reaction wood formation reversed with the reversal of tilting orientation. The roles of accelerated ethylene evolution in reaction wood formation in the tilted seedlings of gymnosperm and angiosperm trees are compared and discussed.

A modified total oxyradical scavenging capacity assay for antioxidants in plant tissues

The total oxyradical scavenging capacity (TOSC) assay of Winston et al. [Free Radical Biol. Med. 24 (1998) 480] was modified through the development and incorporation of a standard curve, yielding a relatively simple but reliable method to quantify the total water-soluble antioxidant capacity (TAC) of plant tissues. The basis of the TOSC assay is the oxidation of α-keto-γ-methiolbutyric acid (KMBA) by 2,2′-azobis-amidinopropane (ABAP) with the evolution of ethylene as the quantifiable end product. A standard curve was established by using a serial dilution (0–100 μM) of the antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) which scavenges peroxyl radicals formed from the thermal homolysis of ABAP, thereby reducing the rate of ethylene evolution. Regression analysis of the standard curve yielded a second-degree polynomial (R2=0.9975) that was used to predict the TAC (μMoles Trolox equivalents) of plant tissues. The precision and utility of the method was tested by determining TAC of skin tissue from ‘Delicious’ and ‘Empire’ apples (Malus domestica Borkh.) at various maturities, following cold storage, and after treatment with 1-methylcyclopropene (1-MCP). The TAC of ‘Delicious’ apples was twofold greater than that of ‘Empire’ apples, and remained relatively constant for up to 60 days in cold storage, then significantly decreased thereafter. This decrease during the latter stages of cold storage may be related to the development of superficial scald in this cultivar. ‘Delicious’ and ‘Empire’ fruit treated with 1-MCP had also a significantly higher TAC at various maturities after 120 days of cold storage. This is the first study to show that a treatment with 1-MCP can potentially maintain some intrinsic functional food quality parameters (i.e. antioxidant levels) in stored fruit. The establishment of a standard curve for use, in conjunction with the TOSC assay, resulted in a precise and highly reproducible predictor of TAC in apple fruit, while also permitting a rapid turnover of tissue samples for analysis.

Leaf area development of ABA-deficient and wild-type peas at two levels of nitrogen supply.

The ABA-deficient wilty pea (Pisum sativum L.) and its wild-type (WT) were grown at two levels of nitrogen supply (0.5 and 5.0 mM) for 5-6 weeks from sowing, to determine whether leaf ABA status altered the leaf growth response to N deprivation. Plants were grown at high relative humidity to prevent wilting of the wilty peas. Irrespective of N supply, expanding wilty leaflets had ca 50% less ABA than WT leaflets but similar ethylene evolution rates. Fully expanded wilty leaflets had lower relative water contents (RWC) and were 10-60% smaller in area (according to the node of measurement) than WT leaflets. However, there were no genotypic differences in plant relative leaf expansion rate (RLER). Growth of both genotypes at 0.5 mM N increased the RWC of fully expanded leaflets, but did not alter ethylene evolution or ABA concentration of expanding leaflets. Plants grown at 0.5 mM N showed a 20-30% reduction in RLER, which was similar in magnitude in both wilty and WT peas. Thus,leaf ABA status did not alter the leaf growth response to N deprivation.

Delay of avocado (Persea americana) fruit ripening by 1-methylcyclopropene and wax treatments

Abstract 1-Methylcyclopropene (1-MCP), an inhibitor of ethylene action, has been shown to extend the postharvest storage period of avocado fruit. Waxing is also known to extend the storage life of avocado by reducing water loss and modifying the fruit internal atmosphere. In this study, 1-MCP and waxing were used to investigate their combined effects on ripening characteristics of avocado fruit. Preclimacteric avocado ( Persea americana Mill. cv. ‘Tower II’) fruit were treated with 1-MCP (0.9 μl l −1 ) for 12 h at 20 °C. Half of the fruit were waxed (Sta-Fresh 819F ® , FMC FoodTech) after 1-MCP treatment and subsequently stored at 20 °C in ethylene-free air at 85% relative humidity. In a separate experiment, ‘Booth 7’ avocados were treated as above and stored at 13 °C. As evaluated by fruit firmness, ethylene evolution, and respiration rate, 1-MCP and wax significantly delayed the ripening of ‘Tower II’ avocado stored at 20 °C. Fruit treated with both 1-MCP and wax had better retention of green peel color and fruit firmness, and delayed climacteric ethylene evolution and respiration rates compared with other treatments. Waxing alone reduced weight loss and delayed softening, but did not delay climacteric ethylene evolution and respiration rates. Whereas firmness of control fruit decreased from >100 to 20 N over a 7-d period at 20 °C, fruit treated with both 1-MCP and wax required more than 11 d at 20 °C to soften to 20 N. The firmness of waxed ‘Booth 7’ avocados declined from >170 to 15 N during 19 d storage at 13 °C whereas fruit treated with both 1-MCP and wax required nearly 5 weeks to reach firmness values of 25 N. 1-MCP treatment, which completely suppressed polygalacturonase activity in ‘Tower II’ and ‘Booth 7’ fruit through 9 d at 20 °C and 36 d at 13 °C, respectively, significantly affected the rate but had little influence on the extent of fruit softening.

Ethylene Evolution from Detached Apple Spurs in Response to Chemical Thinners

Ethylene evolution from detached fruiting apple spurs was measured after application of various bloom and post-bloom thinning agents. Ethylene evolution from fresh detached spurs of `Splendor' apple trees increased one day after application of a bloom thinning spray of ethephon or NAA, and remained higher than rates of ethylene evolution by detached spurs from unsprayed control trees for 6 (NAA) or 10 (ethephon) days. Both ethylene evolution and fruit abscission during the initial drop period were higher on trees treated with ethephon compared to NAA, however final fruit set was similar for these two treatments. Ethylene evolution was significantly higher following NAA application onto `Fuji' trees compared with NAAm, but final fruit set was reduced by a similar amount (≈20%) for both of these materials. Application of BA to `Pacific Rose™' apple trees when the average diameter of spur fruit was either 4 mm (6 days after full bloom) or 7 mm (12 days after full bloom) resulted in a significant increase in the rate of ethylene evolution and also reduced final fruit set. When application of BA was delayed until the average diameter of spur fruit was 14 mm (24 days after full bloom) neither the rate of ethylene evolution or final fruit set was affected. Although an increase in the rate of ethylene evolution was a prerequisite for thinning in the present experiments, the magnitude of this increase was not related to the final thinning efficacy. Chemical names used: benzyladenine (BA); 2-chloroethyl phosphonic acid (ethephon); naphthaleneacetic acid (NAA); naphthalene acetamide (NAAm).

Nitrogenase activity in composting horse bedding and leaves

To date little or no nitrogen fixation has been found in composting materials. However, some materials have high C:N ratios and thus might be expected to support nitrogen fixation. We examined windrows of composting horse bedding and leaves for nitrogenase activity via acetylene reduction and used carbon monoxide controls to differentiate ethylene evolved by nitrogenase from that evolved by endogenous processes. In both piles temperatures were substantially elevated and partial pressures of oxygen greatly reduced thus indicating vigorous microbial activity. In the horse bedding, there were only low rates of ethylene evolution and little of this was due to nitrogen fixation. In contrast, much higher rates of ethylene evolution were measured in the leaf pile and 94% of this was due to nitrogenase activity. We estimate that the leaf pile fixed approximately 0.062 mg N/g leaves during a 5-week period.

Ethylene metabolism in Scots pine (Pinus sylvestris) shoots during the year.

Ethylene evolution, concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC conjugates, activities of ACC synthase and ACC oxidase, and cambial growth as measured by tracheid production were monitored from November to July in 1-year-old shoots, and between July and September in current-year shoots, of Scots pine (Pinus sylvestris L.). Needles, buds and four stem parts (cortex, phloem, cambial region and mature xylem) were surveyed. Ethylene evolution was quantified by gas chromatography. Free ACC and bound ACC (after acidic hydrolysis of ACC conjugates) were quantified by combined gas chromatography-mass spectrometry, with [2H]ACC as an internal standard. Activities of ACC synthase and ACC oxidase were measured in crude protein extracts. We detected high activities of ACC synthase in needles and buds, but not in stem fractions except the phloem. In July, during the period of intensive shoot growth, we found ACC only in buds and needles. In contrast, ACC oxidase activity was high in stem tissues, particularly in the cambial region during the period of rapid tracheid production, but no ACC oxidase activity was detected in needles and buds. Nevertheless, needles evolved large amounts of ethylene. Ethylene was produced by all stem fractions, and the peak rate of ethylene evolution in the cambial region coincided with the period of maximal tracheid production. Conjugated ACC was present in every fraction except mature xylem. The concentration of conjugated ACC decreased when rates of tracheid production and ethylene evolution were high, suggesting that conjugated ACC may serve as a source for ACC in the cambial region. The regulation of ethylene biosynthesis in Scots pine shoots is discussed.