Simple Method for Continuous Treatment of Plant Material with Metered Traces of Ethylene or Other Gases

Regulation of growth in stem sections of deep-water rice

Submergence in water greatly stimulates internodal elongation in excised stem sections of deep-water rice (Oryza sativa L. cv. "Habiganj Aman II") and inhibits growth of leaf blades and leaf sheaths. The highest rates of internodal growth have been observed in continuous light. Very little growth occurs in submerged sections kept in darkness or incubated under N2 in the light. The effect of submergence on the growth of deep-water rice is, at least in part, mediated by C2H4, which accumulates in the air spaces of submerged sections. This accumulation results from increased C2H4 synthesis in the internodes of submerged sections and reduced diffusion of C2H4 from the tissue into the water. Increased C2H4 levels accelerate internodal elongation and inhibit the growth of leaves. Compounds capable of changing the rate of C2H4 synthesis, namely aminoethoxyvinylglycine, an inhibitor of C2H4 synthesis, and 1-aminocyclopropane-1-carboxylic acid, the immediate, precursor of C2H4, have opposite effects on growth of internodes and leaves. The enhancement of internodal elongation by C2H4 is particularly pronounced in an atmosphere of high CO2 and low O2. The increase in C2H4 synthesis in internodes of submerged sections is primarily triggered by reduced atmospheric concentrations of O2. The rate of C2H4 evolution by internodes isolated from stem sections and incubated in an atmosphere of low O2 is up to four times greater than that of isolated internodes incubated in air. In contrast, C2H4 evolution from the leaves is reduced under hypoxic conditions. The effect of submergence on growth of stem sections of deep-water rice can be mimicked by exposing non-submerged sections to a gas mixture which is similar to the gaseous atmosphere in the internodal lacunae of submerged sections, namely 3% O2, 6% CO2, 91% N2 (by vol.) and 1 μl l(-1) C2H4. Our results indicate that growth responses obtained with isolated rice stem sections are similar to those of intact deep-water rice plants.

Concentration dependencies of some effects of ethylene on etiolated pea, peanut, bean, and cotton seedlings

The effects of a series of concentrations of ethylene (10, 20, 40, to 10,240 nl/l) on elongation, diameter, and geotropism of the stems and roots of etiolated seedlings of Pisum sativum L., Arachis hypogea L., Phaseolus vulgaris L., and Gossypium hirsutum L. were measured or observed. Of the 24 possible responses, 4 were unaffected at the concentrations used, 5 were affected slightly, and the remaining responses exhibited a 14-fold range of apparent half-maximum concentration dependencies (i.e. 95 nl/l for the effect on pea epicotyl geotropism to 1350 nl/l for the promotion of cotton hypocotyl diameter). Six or possibly eight of these responses appear to have the same concentration dependencies while the others fell in pairs or as individual responses. The data, if interpreted in a manner analogous to enzyme kinetics, are indicative of more than one primary mechanism for ethylene action in plants.

Endogenous ethylene and abscisic Acid relative to phytogerontology

Endogenous production of ethylene and endogenous levels of abscisic acid were measured from Hibiscus rosa-sinensis L. abscission zone explants at six stages of development: tight bud, open flower, closed flower, petal abscission, calyx abscission, and peduncle abscission.Explants acropetal and basipetal to the abscission zone produced less ethylene than the abscission zone explants. Ethylene production increased with time both prior to and during abscission, reaching a peak in the later stages of senescence after abscission was complete.Bound abscisic acid was greatest in segments acropetal to the abscission zone at the closed flower stage. Free abscisic acid was double that of bound abscisic acid in the tight bud stage with the basipetal level exceeding that of the acropetal level until flower closure. Acropetal-free abscisic acid began to rise at petal abscission increasing sharply to a peak at calyx abscission. Both free and bound abscisic acid were greatly reduced at peduncle abscission. A relationship of ethylene and abscisic acid to abscission and senescence appears to exist.

The role of ethylene in the induction of apogamous buds in Pteridium gametophytes

The level of induced apogamy in gametophytic colonies of Pteridium aquilinum (L.) Kuhn is altered by varying the number of colonies per culture vessel or by including a constant number of colonies in culture vessels of different volumes. In either case, placing vials of mercuric perchlorate, an absorber of ethylene, within the closed culture vessels reduced the apogamous response to a very low level. Production of ethylene by the gametophytes was demonstrated by gas chromatography. Ethylene supplied in a continuous-flow system promoted the apogamous response above that of an air control.

Abscission: the phytogerontological effects of ethylene

The role of ethylene in the aging of bean (Phaseolus vulgaris L. cv. Red Kidney) petiole abscission zone explants was examined. The data indicate that ethylene does accelerate aging in addition to inducing changes in break strength. Application of ethylene during the aging stage (stage 1) promoted abscission when followed by a second ethylene treatment during the cell separating stage (stage 2). The half-maximal effective concentration of ethylene to induce aging was around 0.3 microliter per liter; 10 microliters per liter was a saturating dose. CO(2) reversal of ethylene action during stage 1 was incomplete and gave ambiguous results. CO(2) (10%) reversed the effect of 10 microliters per liter ethylene but not 1 microliter per liter ethylene. The possibility that ethylene not only accelerated aging but was also a requirement for it was tested, and experimental evidence in favor of this idea was obtained. It was concluded that ethylene plays a dual role in the abscission of bean petiole explants: a phytogerontological effect and a cellulase-inducing effect.

Stimulation of rice coleoptile growth by ethylene

The growth rate of rice coleoptiles is increased by low concentrations of ethylene, especially in oxygen concentrations lower than air; carbon dioxide enhanced this response. C2H4 is produced by rice seedlings, and this production is also enhanced by carbon dioxide. Ethane and propane were produced in trace amounts but were inactive in growth stimulation as were also methane, propylene, and butane.

Respiratory Response, Ethylene Production, and Response to Ethylene of Citrus Fruit during Ontogeny

The initial respiratory rates at 20 centrigrade of detached oranges (Valencia and navel), grapefruit, and lemons decreased during ontogeny. Small attached oranges respired at the same rate as detached fruits of the same weight, and cutting the pedicel produced no shock or injury stimulus to the respiratory rate. Small oranges and grapefruit (average weight about 15 grams) showed pseudoclimacteric respiratory patterns and produced ethylene. The height of the respiratory rise and the amount of ethylene produced decreased as the fruit increased in weight until the September 4th harvest, when the fruit weights were 120, 64, and 87 grams for grapefruit, Valencia, and navel oranges, respectively; at that time no respiratory rise or ethylene production was observed. The pattern for all subsequent harvest revealed no postharvest rise in the respiratory rates. Lemon fruit, in contrast, had a continuously decreasing respiratory rate at all stages of ontogeny. Exposure to 20 microliters of ethylene per liter induced an increase in the respiratory rate of all varieties at every stage of ontogeny; this was true also in young oranges and grapefruit following their respiratory rise and decline.Evidence is presented that citrus fruits are nonclimacteric fruits.

Ethylene and carbon dioxide in the growth and development of cultured radish roots

Ethylene is produced by cultured radish roots in amounts large enough to be physiologically important. When roots were grown in controlled atmospheres, applied ethylene was generally inhibitory to elongation, lateral root initiation, and cambial activity. 1% CO(2) similarly affected roots not given ethylene. In contrast, elongation and lateral root production of ethylene-treated roots were stimulated by 1% CO(2). The results suggest that the often-observed stimulation of root growth by CO(2) is due to an interaction with endogenous ethylene.