Roger F. Horton

The effect of ethylene and other regulators on coleoptile growth of rice under anoxia

Abstract Caryopses of rice ( Oryza sativa L. cultivar ‘Mercury’) were imbibed for 2 days in water or 10 μM solutions of indoleacetic acid (IAA), kinetin, gibberellic acid or abscisic acid in the presence of a gas stream of air or nitrogen. Fully-imbibed caryopses were placed on agar in vertically-maintained Petri dishes in chambers in the dark at 29°C. Subsequent growth of roots and coleoptiles in air or nitrogen, with the later addition of 10 μ1.1 −1 ethylene, was determined. Rice seedlings grown in total anoxia in a nitrogen stream did not develop roots, but could do so if air or 0.5% oxygen was introduced after 3 or 4 days of anoxia. Coeloptile elongation in nitrogen proceeded at a rate comparable to that in air over the 5-day experimental period. Treatment of seedlings in air, during imbibition or during subsequent growth, with indoleacetic acid, gibberellic acid or ethylene promoted coleoptile elongation. The growth of coleoptiles in nitrogen was not enhanced in the presence of these growth promoters, and was inhibited by treatment with abscisic acid or kinetin. The role of endogenous regulators in cellular elongation under anoxia is discussed.

Abscisic acid inhibition of potassium influx into stomatal guard cells

Summary Abscisic acid, which inhibits stomatal opening, prevents the influx of K + ions into the guard cells in epidermal strips from leaves of Vicia jaba .

Petiole growth in the celery-leaved crowfoot (Ranunculus sceleratus L.): Effects of auxin-transport inhibitors

Abstract Leaves of the semi-aquatic celery-leaved crowfoot ( Ranunculus sceleratus L.) exhibited petiole growth through cell elongation in response to submergence or when treated with ethylene or auxin. The auxin-transport inhibitors, naptalam (1- N -naphthylphthalamic acid) and the morphactins IT 3456 (2-chlorofluorenol methyl ester) and IT 3233 (9-hydroxyfluorenolcarboxylic acid-9-n-butyl ester) had no effect on the response to 10 −4 M indole acetic acid (IAA), but inhibited the growth response to 1 μl 1 −1 ethylene. Isolated petiole segments were more sensitive to auxin than to ethylene.

Submergence-promoted growth of petioles of Ranunculus pygmaeus Wahl.

Abstract Petioles of mature, fully expanded leaves of the dwarf buttercup, Ranunculus pygmaeus Wahl. elongate after the intact plant is submerged. This ‘depth accommodation’ growth can be mimicked by treatment of the plant with 10 μl l −1 ethylene in air. Younger petioles (particularly those whose very early expansion occurs under water) also elongate considerably during submergence, but, unlike petioles of mature leaves, this growth is strongly dependent on cell division as well as cell elongation. The submergence-induced growth of young petioles cannot be fully mimicked by ethylene treatment, and the isolation of young leaves from the intact plant reduces their capacity to respond to submergence. Submergence-promoted growth of petioles, at all stages of development, does not appear to be dependent on tension arising from the buoyancy of leaf blade under water.

Carbon Dioxide Assimilation in Pulvini of Phaseolus vulgaris L.

Summary Pulvini of Phaseolus vulgaris have no stomates on their epidermis. Although their tissues contain high levels of chlorophyll, these structures are unable to reduce the amount of carbon dioxide when maintained in the light in closed vessels (i.e. they exhibit no carbon dioxide compensation point). Blade and petiole tissues, which are contiguous with the distal pulvinus, exhibit compensation points which are typical for C3 plants. Pulvini cannot fix large amounts of 14 CO 2 from the atmosphere and extracts contain activities of carboxylating enzymes different from those of other leaf tissues.

Ethylene-Induced Growth in Amphibious Plants

Aquatic plants have long been of interest to physiologists. Many species are major weeds in many parts of the world, and others are commercially important crop plants. Furthermore, aquatic plants have provided us with a number of valuable systems for continuing studies of photosynthesis and ionic relations which are the basis of our understanding of these processes in the entire plant kingdom.

Ethylene- and submergence-promoted growth in Ranunculus sceleratus L. petioles: the effect of cobalt ions

Abstract Petioles of the celery-leaved buttercup, Ranunculus sceleratus L., elongate when the leaf blades are submerged. This elongation has been correlated with a rise in internal C 2 H 4 levels. Treatment with C 2 H 4 in air will also enhance petiole growth. The submergence-induced growth is inhibited in the presence of CoCl 2 solutions. Cobalt treatment does not inhibit petiole elongation when the leaves are exposed to C 2 H 4 in air or when the tissues are submerged in C 2 H 4 -saturated CoCl 2 solutions. Thus, the physiological effect of CoCl 2 is completely mitigated by treatment with C 2 H 4 . Cobalt can directly inhibit C 2 H 4 production by leaf tissue. There is no evidence of the effect being dependent on changes in CO 2 metabolism.

Gravitropism in rice seedlings: the effects of anoxia and N-l-naphthylphthalamic acid

Abstract Caryopses of rice (Oryza sativa L. cultivar ‘Mercury’) were imbided for 2 days in water in the presence of a stream of nitrogen gas. Fully-imbibed caryopses were placed on plain 2% agar or on agar containing the phytotropin, N-l-naphthylphthalamic acid acid (NPA) at 5 μM in vertically-held Petri dishes in chambers in the dark at 29°C. Subsequent elongation growth of roots and coleoptiles, in air or in nitrogen gas, over a 36-h period, was determined, together with the angle of deviation from vertical of the apical 2 mm segment of each organ. The variances of the deviation from vertical in each treatment population, as an indicator of the degree of disruption of gravitropic mechanisms, were compared. Rice seedlings did not develop roots under anoxia. Coleoptiles grown in nitrogen elongated slightly more than those in air, but did not fully exhibit strict negative gravitropism. When treated with NPA, both coleoptiles and roots of air-grown seedlings showed diminished gravitropic responses. After seedlings were re-oriented through 90° after 18 h, neither roots nor coleoptiles were able to reattain vertical growth during a further 18 h period, and they exhibited enhanced variance in the direction of elongation. When coleoptiles of anoxically-grown seedlings were similarly reoriented, they also demonstrated a diminished capacity to respond gravitropically. In the presence of NPA, anoxically-grown coleoptiles had severely disrupted responses, but negative gravitropism was not completely eliminated.

Carbon dioxide enrichment, transpiration and 1-aminocyclopropane-1-carboxylic acid-dependent ethylene release from oat leaves

Abstract Enrichment of air with carbon dioxide up to 1200 μl ṡ 1 −1 air results in lower transpiration rates from oat ( Avena sativa ) seedling leaves held in the light at 30% relative humidity. Carbon dioxide treatment also enhances the release of ethylene from leaves treated with 1-aminocyclopropane-1-carboxylic acid (ACC). Thus, while the uptake of ACC via the transpiration stream is depressed by 33% by carbon dioxide enrichment, the release of ethylene from a given amount of ACC is increased by 400%. Neither ethylene nor ACC appear to affect the transpiration rate. The enhancement of ACC-dependent ethylene release cannot be simply correlated with stomatal behaviour.

Peroxidase, Ethylene, and Submergence-Promoted Growth of Petioles of Ranunculus sceleratus L.

Summary The distal 20 mm segments of petioles of intact Ranunculus sceleratus L. plants elongate after submergence. This growth is most pronounced in petioles of recently fully-expanded leaves. Initial peroxidase activities were lower in petioles that had a greater capacity to elongate under water, and lower activities were maintained during submergence. For isolated leaves, submergence or treatment with ethylene in air promoted growth of the petioles and the maintenance of low tissue-peroxidase levels. Petioles of isolated leaves, held with their blades in air or floating at the water/air interface, grow to a small extent but have very high levels of extractable peroxidase activity.