Temperature Sensitivity of the Latent Phase in Ethylene-induced Elongation

The temperature sensitivity is reported for the latent period preceding ethylene-induced elongation in the adaxial half of the leaf petiole of Helianthus annuus. When intact plants were exposed to 10 μl of ethylene/l of air over the temperature range 18 to 35 C, the minimum latent time was 62 minutes at 28 C and the maximum was 132 minutes at 18 C. The temperature coefficient, Q₁₀, changed from 2.1 below 28 C, to 0.7 above. In 100 μl of ethylene/l of air, the latent time was reduced by 14% at 18 C, but was significantly increased at 28 and 38 C. These results show that the latent period in the elongation response of the petiole to ethylene cannot be reduced below about 60 minutes by raising either the leaf temperature or the atmospheric ethylene concentration.     

Free Methionine Levels in rin and Normal Isogenic Tomato Fruits Ripened in the Field or in Storage

Free methionine levels in rin and normal tomato fruits were determined microbiologically. Similar levels (1750 μg/100 g fresh weight) for mature green fruits of both rin and a normal isogenic line suggest that the lack of ripening of rin fruits is not due to low methionine levels. Methionine levels of mature green rin and normal fruits were 1750 μg/ 100 g fresh weight. Normal fruits ripened either on or off the vine were 2860 and 2500 μg/100 g fresh weight, respectively. The rin fruits which were left on the plant or held in air at 20 C until soft and yellow were significantly lower in methionine than C₂H₄-treated rin fruits or any normal fruits. Harvested rin and normal fruits held at 20 C in continuously applied ethylene (10 μl/l) had higher methionine levels than comparable air controls; levels in treated rin fruits were significantly higher than those in normal fruits.     

Water Permeability during Tomato Fruit Development in Normal and rin Nonripening Mutant

This work tested one aspect of the relations between membrane permeability and fruit ripening. Membrane permeability was measured as [³H]water efflux rate from preloaded fruit pericarp disks. Different stages of fruit development were compared between two tomato (Lycopersicon esculentum Mill) strains: the normal Rutgers and the isogenic nonripening rin strain. The first significant increase in permeability was measured in Rutgers tissue at 110% of development, after fruit ripening had already begun as indicated by ethylene and CO₂ evolution and lycopene synthesis. The rin did not show any increase in tissue permeability during fruit development or maturation.     

Comparison of Propylene-induced Responses of Immature Fruit of Normal and rin Mutant Tomatoes

Continuous application of propylene to 40 to 80% mature fruits of normal tomato strains (Lycopersicon esculentum Mill.) advanced ripening in fruits of all ages by at least 50%. Although preclimacteric respiration was stimulated by propylene treatment, there was no concomitant increase in ethylene production. Once ripening commenced, the rates of endogenous ethylene production were similar in both propylene-treated and untreated fruits. Continuous exposure to propylene also stimulated respiration in immature fruits of rin, a nonripening mutant. Although respiration reached rates similar to those during the climacteric of comparable normal fruits there was no change in endogenous ethylene production which remained at a low level. Internal ethylene concentrations in attached 45 to 75% mature fruits of rin and a normal strain were similar. It is suggested that the onset of ripening in normal tomato fruit is not controlled by endogenous ethylene, although increased ethylene production is probably an integral part of the ripening processes.     

Ethylene, a regulator of young fruit abscission

In an earlier study we reported that detached cotton flowers produced sufficient ethylene before the period of natural abscission to suggest that ethylene might be a natural regulator of young fruit abscission. The present report explores this probability further. Intact cotton (Gossypium hirsutum L.) fruits produced ethylene at rates as high as 36 μl ethylene/kg fresh wt·hr during the 2 days before they abscised. Direct measurements of ethylene in gas samples withdrawn from fruits indicated that production of 1 μl ethylene/kg fresh wt·hr is equivalent to an internal concentration of approximately 0.1 μl/l. Fumigation of fruiting cotton plants with only 0.5 μl/l caused 100% abscission of young fruits and floral buds within 2 days. This correlated with the estimated endogenous levels of ethylene. Reduced pressure, which reduced the internal levels of ethylene, delayed abscission of young fruits and leaves, a result which supports our conclusion from this study— that ethylene is one of the regulators of young fruit abscission in cotton.     

Similarities between the Actions of Ethylene and Cyanide in Initiating the Climacteric and Ripening of Avocados

A continuous exposure of intact avocados (Persea americana) to 400 μl/l of cyanide results in a rapid increase in the rate of respiration, followed by a rise in ethylene production, and eventual ripening. The pattern of changes in the glycolytic intermediates glucose 6-phosphate, fructose diphosphate, 3-phosphoglyceric acid, and phosphoenolpyruvate during the rapid rise in respiration in both ethylene and cyanide-treated fruits is similar to that found in fruits made anaerobic where a 2.3- to 3-fold increase in the rate of glycolysis is observed. It is suggested that both during the climacteric and in response to cyanide, glycolysis is enhanced. It is proposed that cyanide implements the diversion of electrons to the cyanide-resistant electron path through structural alterations which are independent of the simultaneous inhibition of cytochrome oxidase.     

Relationship between Ethylene and the Growth of Ficus sycomorus

The relationship between ethylene and growth was investigated in Ficus sycomorus L. A marked increase in ethylene emanation preceeded all the phases of rapid growth and ripening of the syconium.     

Starch Synthetase, Phosphorylase, ADPglucose Pyrophosphorylase, and UDPglucose Pyrophosphorylase in Developing Maize Kernels

Three types of whole plant experiments are presented to substantiate the concept that an important function of ethylene in abscission is to reduce the transport of auxin from the leaf to the abscission zone. (a) The inhibitory effect of ethylene on auxin transport, like ethylene-stimulated abscission, persists only as long as the gas is continuously present. Cotton (Gossypium hirsutum L. cv. Stoneville 213) and bean (Phaseolus vulgaris L. cv. Resistant Black Valentine) plants placed in 14 μl/l of ethylene for 24 or 48 hours showed an increase in leaf abscission and a reduced capacity to transport auxin; but when returned to air, auxin transport gradually increased and abscission ceased. (b) Ethylene-induced abscission and auxin transport inhibition show similar sensitivities to temperature. A 24-hour exposure of cotton plants to 14 μl/l of ethylene at 8 C resulted in no abscission and no significant inhibition of auxin transport. Increasing the temperature during ethylene treatment resulted in a progressively greater reduction in auxin transport with abscission occurring at [unk]27 C where auxin transport was inhibited over 70%. (c) Auxin pretreatment reduced both ethylene-induced abscission and auxin transport inhibition. No abscission occurred, and auxin transport was inhibited only 18% in cotton plants which were pretreated with 250 mg/l of naphthalene acetic acid and then placed in 14 μl/l of ethylene for 24 hours. In contrast, over 30% abscission occurred, and auxin transport was inhibited 58% in the corresponding control plants.     

Upsurge in respiration and peroxide formation in potato tubers as influenced by ethylene, propylene, and cyanide

A continuous application of ethylene (10 μl/l) and propylene (500 μl/l) to potato tubers (Solanum tuberosum L.) resulted in an upsurge of respiration and a concomitant rise in peroxides. When applied in 100% O₂, the effect of ethylene and propylene on respiration and peroxide formation was augmented. Hydrogen cyanide (500 μl/l) mimicked the action of ethylene and propylene inducing a respiratory rise and a corresponding increase in peroxides. As with ethylene, the effect of HCN was augmented in high O₂ tensions. The results support the suggestion that ethylene activates the cyanide-insensitive respiratory pathway.     

Ethylene-Enhanced 1-Aminocyclopropane-1-carboxylic Acid Synthase Activity in Ripening Apples

Apples (Malus sylvestris Mill, cv Golden Delicious) were treated before harvest with aminoethoxyvinylglycine (AVG). AVG is presumed to reversibly inhibit 1-aminocyclopropane-1-carboxylic acid (ACC) activity, but not the formation of ACC synthase. AVG treatment effectively blocked initiation of autocatalytic ethylene production and ripening of harvested apples. Exogenous ethylene induced extractable ACC synthase activity and ripening in AVG-treated apples. Removal of exogenous ethylene caused a rapid decline in ACC synthase activity and in CO₂ production. The results with ripened, AVG-treated apples indicate (a) a dose-response relationship between ethylene and enhancement of ACC synthase activity with a half-maximal response at approximately 0.8 μl/l ethylene; (b) reversal of ethylene-enhanced ACC synthase activity by CO₂; (c) enhancement of ACC synthase activity by the ethylene-activity analog propylene.

Induction of ACC synthase activity, autocatalytic ethylene production, and ripening of preclimacteric apples not treated with AVG were delayed by 6 and 10% CO₂, but not by 1.25% CO₂. However, each of these CO₂ concentrations reduced the rate of increase of ACC synthase activity.

     

Effect of seed on ripening control components during avocado fruit development

Seedless avocado fruit are produced alongside seeded fruit in the cultivar Arad, and both reach maturity at the same time. Using this system, it was possible to show that avocado seed inhibits the ripening process: seedless fruits exhibited higher response to exogenous ethylene already at the fruitlet stage, and also at the immature and mature fruit stages. They produced higher CO₂ levels, and the ethylene peak was apparent at the fruitlet stage of seedless fruit, but not of seeded ones. The expression levels of PaETR, PaERS1 and PaCTR1 on the day of harvest at all developmental stages were very similar between seeded and seedless fruit, except that PaCTR1 was higher in seedless fruit only at very early stages. This expression pattern suggests that the seed does not have an effect on components of the ethylene response pathway when fruits are just picked. The expression of MADS-box genes, PaAG1 and PaAGL9, preceded the increase in ethylene production of mature seeded fruit, but not at earlier stages. However, only PaAGL9 was induced in seedless fruit at early stages of development. Taken together, these data suggest that these genes are perhaps involved in climacteric response in seeded fruit, and the seed is responsible for their induction at normal fruit ripening.     

Regulation of Tomato Fruit Polygalacturonase mRNA Accumulation by Ethylene: A Re-Examination

Polygalacturonase (PG) is the major enzyme responsible for pectin disassembly in ripening fruit. Despite extensive research on the factors regulating PG gene expression in fruit, there is conflicting evidence regarding the role of ethylene in mediating its expression. Transgenic tomato (Lycopersicon esculentum) fruits in which endogenous ethylene production was suppressed by the expression of an antisense 1-aminocyclopropane-1-carboxylic acid (ACC) synthase gene were used to re-examine the role of ethylene in regulating the accumulation of PG mRNA, enzyme activity, and protein during fruit ripening. Treatment of transgenic antisense ACC synthase mature green fruit with ethylene at concentrations as low as 0.1 to 1 μL/L for 24 h induced PG mRNA accumulation, and this accumulation was higher at concentrations of ethylene up to 100 μL/L. Neither PG enzyme activity nor PG protein accumulated during this 24-h period of ethylene treatment, indicating that translation lags at least 24 h behind the accumulation of PG mRNA, even at high ethylene concentrations. When examined at concentrations of 10 μL/L, PG mRNA accumulated within 6 h of ethylene treatment, indicating that the PG gene responds rapidly to ethylene. Treatment of transgenic tomato fruit with a low level of ethylene (0.1 μL/L) for up to 6 d induced levels of PG mRNA, enzyme activity, and protein after 6 d, which were comparable to levels observed in ripening wild-type fruit. A similar level of internal ethylene (0.15 μL/L) was measured in transgenic antisense ACC synthase fruit that were held for 28 d after harvest. In these fruit PG mRNA, enzyme activity, and protein were detected. Collectively, these results suggest that PG mRNA accumulation is ethylene regulated, and that the low threshold levels of ethylene required to promote PG mRNA accumulation may be exceeded, even in transgenic antisense ACC synthase tomato fruit.     

Abscission: the role of ethylene modification of auxin transport

The role of ethylene-mediated reduction of auxin transport in natural and ethylene-induced leaf abscission was studied in the cotton (Gossypium hirsutum L., cv. Stoneville 213) cotyledonary leaf system. The threshold level of ethylene required to cause abscission of intact leaves was between 0.08 and 1 μl/l with abscission generally occurring 12 to 24 hours following ethylene fumigation. The threshold level of ethylene required to reduce the auxin transport capacity in the cotyle-donary petiole paralleled that required for stimulation of abscission. In plants where cotyledons are allowed to senesce naturally there is a decline in auxin transport capacity of petioles and increase in ethylene synthesis of cotyledons. The visible senescence process which precedes abscission requires up to 11 days, and increases in ethylene production rates and internal levels were detected well before abscission. Ethylene production rates for entire cotyledons rose to 2.5 mμ1 g⁻¹ hr⁻¹ and internal levels of 0.7 μl/l were observed. These levels appear to be high enough to cause the observed decline in auxin transport capacity. These findings, along with those of others, indicate that ethylene has several roles in abscission control (e.g., transport modification, enzyme induction, enzyme secretion). The data indicate that ethylene modification of auxin transport participates in both natural abscission and abscission hastened by exogenous ethylene.     

A Novel Cascade Classifier for Automatic Microcalcification Detection

In this paper, we present a novel cascaded classification framework for automatic detection of individual and clusters of microcalcifications (μC). Our framework comprises three classification stages: i) a random forest (RF) classifier for simple features capturing the second order local structure of individual μCs, where non-μC pixels in the target mammogram are efficiently eliminated; ii) a more complex discriminative restricted Boltzmann machine (DRBM) classifier for μC candidates determined in the RF stage, which automatically learns the detailed morphology of μC appearances for improved discriminative power; and iii) a detector to detect clusters of μCs from the individual μC detection results, using two different criteria. From the two-stage RF-DRBM classifier, we are able to distinguish μCs using explicitly computed features, as well as learn implicit features that are able to further discriminate between confusing cases. Experimental evaluation is conducted on the original Mammographic Image Analysis Society (MIAS) and mini-MIAS databases, as well as our own Seoul National University Bundang Hospital digital mammographic database. It is shown that the proposed method outperforms comparable methods in terms of receiver operating characteristic (ROC) and precision-recall curves for detection of individual μCs and free-response receiver operating characteristic (FROC) curve for detection of clustered μCs.     

Ethylene-enhanced Ion and Sucrose Efflux in Morning Glory Flower Tissue

Rib tissue segments excised from open flowers or buds of Ipomoea tricolor Cav. and floated on aqueous media responded to ethylene treatment by rolling up after 2 to 3 hours; a simple method for quantitating the rolling up is presented. The rolling up response was temperature- and oxygen-dependent and was critically affected by the pH of the medium. The ethylene concentration giving a half-maximal response was 0.1 μl/l; continuous ethylene treatment was not required for the response as a 1-hour ethylene exposure enhanced rolling up.     

Ochratoxin Production by the Aspergillus ochraceus Group and Aspergillus alliaceus

Ochratoxin A is a toxic and carcinogenic fungal secondary metabolite; its presence in foods is increasingly regulated. Various fungi are known to produce ochratoxins, but it is not known which species produce ochratoxins consistently and which species cause ochratoxin contamination of various crops. We isolated fungi in the Aspergillus ochraceus group (section Circumdati) and Aspergillus alliaceus from tree nut orchards, nuts, and figs in California. A total of 72 isolates were grown in potato dextrose broth and yeast extract-sucrose broth for 10 days at 30°C and tested for production of ochratoxin A in vitro by high-pressure liquid chromatography. Among isolates from California figs, tree nuts, and orchards, A. ochraceus and Aspergillus melleus were the most common species. No field isolates of A. ochraceus or A. melleus produced ochratoxin A above the level of detection (0.01 μg/ml). All A. alliaceus isolates produced ochratoxin A, up to 30 μg/ml. We examined 50,000 figs for fungal infections and measured ochratoxin content in figs with visible fungal colonies. Pooled figs infected with A. alliaceus contained ochratoxin A, figs infected with the A. ochraceus group had little or none, and figs infected with Penicillium had none. These results suggest that the little-known species A. alliaceus is an important ochratoxin-producing fungus in California and that it may be responsible for the ochratoxin contamination occasionally observed in figs.     

Cellulase Activity, Endogenous Abscisic Acid, and Ethylene in Four Citrus Cultivars during Maturation

At maturity, the fruit of two early maturing orange cultivars, Hamlin and Pineapple (Citrus sinensis [L.] Osbeck), contained more ethylene and abscisic acid than the late maturing Valencia and Lamb Summer (C. sinensis [L.] Osbeck) cultivars. Ethylene (up to 95 nl/l in internal atmosphere) and abscisic (50 μg/kg dry weight flavedo) increased most rapidly in Pineapple, leading to increased cellulase activity and loosening of the fruit. Fruit of the two late maturing cultivars contained less than 25 nl/1 ethylene and 40 μg abscisic acid/kg dry weight of flavedo at peak maturity. Cellulase activity and loosening of the fruit of these late maturing cultivars was slight.     

The hormone content of ripening grape berries and the effects of growth substance treatments

Berries on field-grown Vitis vinifera cv. Doradillo were treated at different times during stage II with benzothiazole-2-oxyacetic acid or 2-chloroethylphosphonic acid, and measurements were made of their growth and hormone content. The concentration of ethylene was low during stage II and declined as berries ripened. Both 2-chloroethylphosphonic acid and benzothiazole-2-oxyacetic acid caused increases in ethylene concentration, yet they had varying effects on ripening: the former applied at the start of stage II and the latter applied 1 week before the end of stage II delayed ripening, while 2-chloroethylphosphonic acid applied at the end of stage II hastened ripening.