Details

Autor(en) / Beteiligte

• SAMARAKOON, ANANDA BANDARA

Titel

ETHYLENE-PROMOTED ELONGATION GROWTH IN RANUNCULUS SCELERATUS L

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1981

Link zum Volltext

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The physiology of submergence-induced growth (accommodation growth) of petioles of the celery-leaved buttercup, Ranunculus sceleratus L. was investigated. This growth allows the blades of submerged leaves to reach the water/air interface within a short time. Experiments indicate that changes in ethylene physiology regulate the elongation growth of petioles. Treatment of leaves in air with ethylene (1 to 10 (mu)l l('-1)) induces growth comparable to that occurring on submergence. Submerged leaves accumulate up to 6 (mu)l l('-1) ethylene in 24 h while leaves maintained in air have internal ethylene levels of 0.05 to 0.1 (mu)l l('-1). Treatment of leaves with Co('2+) (an inhibitor of ethylene biosynthesis) inhibits accommodation growth, although the tissue remains responsive to added ethylene. In contrast, treatment with Ag('+) (an inhibitor of ethylene action) prevents both accommodation growth and the effect of added ethylene. High concentrations of IAA (10('-4) to 10('-3) M) produce growth promotions similar to those due to submergence or ethylene. Treatment with Ag('+) which largely eliminates the responsiveness to ethylene allows growth in response to IAA. The blade tissue has a natural ethylene evolution rate of 2 to 3 nl gm fr wt('-1) h('-1), but no ethylene release is detectable from the petioles. However, when treated with 5 x 10('-4) M ACC (1-aminocyclopropane-1-carboxylic acid), the immediate precursor of ethylene, both tissues release ethylene at high rates (10 to 15 nl gm fr wt('-1) h('-1)). ACC accumulates in leaves, along with ethylene, during submergence. The blade is amphistomatous and the petiole has a highly lacunate structure. These features may allow rapid release of ethylene when the blade is in air but accumulation and diffusion of ethylene into the petiole when the leaf is submerged. Growth promotion by ethylene is strictly dependent on the presence of auxin. Ethylene-promoted growth is lost when the blade is removed. Treatment of leaves with anti-auxin compounds such as NPA (1-N-naphthylphthalamic acid) and morphactins inhibit the growth promoted by ethylene but not that due to 10('-4) M IAA. Petiole sections (without blades) grow in high levels of auxin (10('-4) to 10('-3) M) but not in ethylene or low levels of auxin (10('-7) to 10('-5) M). However, treatment with ethylene and low auxin together produces a highly synergistic growth approaching that found in submerged bladed petioles. CO(,2) alone has no effect on petiole growth but high CO(,2) (10%) is antagonistic to the ethylene-promoted growth. R. sceleratus flowers under 18 h photoperiods (LD) but remains vegetative under 8 h photoperiods (SD). A minimum of 20-30 LD cycles are required for flower bud initiation which occurs prior to the elongation of flower stalk. The effect of LD on flowering and subsequent growth of the flower stalk can be mimicked by treatment with GA(,3) under SD. When plants that have been induced to flower by exposure to 28 LD cycles are submerged, there is a rapid elongation of the flower stalk. This effect of submergence can be mimicked by treatment with ethylene but not by spraying the plants with GA(,3) or IAA. It is concluded that the petiole growth in submerged R. sceleratus is regulated by changing levels of ethylene in the tissue either due to reduced diffusivity or altered biosynthetic rates. This ethylene-induced growth only occurs in tissues with a low auxin concentration. The stem of this LD flowering plant becomes sensitive to ethylene after flower initiation allowing flower stalks also to demonstrate accommodation growth. The significance of such ethylene induced growth is discussed in relation to the effects of ethylene on cell growth throughout the plant kingdom.