Ethylene-induced Pea Internode Swelling

Abstract

Exposure of etiolated pea (Pisum sativum L. var. Alaska) subapical sections to ethylene disrupts normal polar cell expansion, but fresh weight increase is little affected and the tissue expands radially, swelling. Ethylene has no effect on gross ribonucleic acid metabolism before or during the period when swelling occurs, but incorporation of "4C-proline and leucine into wall-associated protein is markedly inhibited after an initial 3-hour lag period which precedes swelling. Ethylene affects the composition of this protein, altering the prolinehydroxyproline ratio. The gas also alters the optical birefringence pattern of the cell wall, indicating that the cellulose microfibrillar orientation has been changed.The normal growth pattern of excised subapical sections from the third internode of etiolated pea seedlings is a highly polar expansion. When ethylene is applied, linear expansion is markedly inhibited, but fresh weight increase is hardly affected and the tissue expands radially. Since no cell divisions occur in this internodal tissue of either intact seedlings or excised sections in the presence or absence of ethylene, the ethyleneinduced shift to nonpolar, radial expansion is due solely to cellular swelling (2). Ethylene induces subapical swelling in excised sections by a process resembling that which occurs in intact seedlings; for example, the same concentrations of ethylene are effective (6, 7). In vivo, however, ethylene reduces the rate, but greatly prolongs the duration of cellular expansion (3, 5), whereas excised sections are not so affected and invariably stop growing in 12 to 18 hr. When excised sections swell in response to ethylene, their total dry weight, weight of wall material, respiration, content of various sugars, and permeability are not altered (6, 7). Slight stimulation of RNA synthesis in response to ethylene has been noted in certain intact vegetative tissues (14, 16), but does not occur in isolated soybean hypocotyl (15) and has not previously been studied in pea internodal sections. During ethylene-induced swelling the optical birefringence pattern of the cell wall is altered (7) MATERIALS AND METHODSSeeds of Pisum sativum L. (var. Alaska) were soaked in tap water for 6 hr, planted in vermiculite, and grown in darkness at 25 C. After 7 days, 1-cm sections were cut from the third internode of the epicotyl immediately below the hook and lots of 10 or 15 were incubated with or without 10 ,d/liter of ethylene in sealed 125-ml flasks with 10 ml of medium containing 5 mM potassium phosphate buffer (pH 6.8), 2% sucrose, S M cobalt chloride, and varying amounts of IAA and 'H-or "4C-labeled substrates (6). Following isotope incubations, tissue was rinsed with distilled water and floated in ice water for 15 min to clear residual isotope from the free space. Under these conditions, sections exposed to "4C-proline (0.05 ,uc/ ml) for about 1 sec retained less than twice background count.Effects of Ethylene on Uptake. Short term uptake of "4C-proline by pea internode tissue was studied ...

The Site of Cellulose Synthesis

“…2) seems to be related to concurrent changes in the direction in which cellulose microfibrils are laid down in lateral cell-walls. When elongation ceases, there is a shift from mainly transversely-oriented microfibrils to microfibrils which are oriented primarily in a longitudinal direction (4,6,16,19). It is possible that ER-bound cellulose synthetase becomes established at the cell surface in such a way as to function in the synthesis of longitudinal microfibrils, which limit the rate of cell elongation but not necessarily lateral expansion.…”

Soluble Cell Wall Polysaccharides Released from Pea Stems by Centrifugation

“…Although ethylene has been shown to alter the orientation of cellulose microfibrils, little is known of changes which occur in the noncellulosic polymers of the radially expanding pea stem cell wall. The effects of ethylene on growth contrast with those of auxin since auxin stimulates elongation of intact or excised pea internodes (6,7,10). In auxin-treated tissue, cell elongation is correlated with an increase in cell wall plasticity (9) and with the enhanced metabolism of a water-soluble xyloglucan fragment (12,13,22,23) and a pectic polymer (23) in the cell wall.…”

“…Although ethylene inhibits elongation of intact or excised pea internodes, it does not inhibit growth as defmed as an irreversible change in tissue volume, as ethylene-treated internodes expand radially (3,10). It to do so by altering the orientation of the cellulose microfibrils in the cell wall (2,6,7,17).…”

“…In some experiments, the ethanolinsoluble fraction was separated into acidic and neutral components (4) by passing the material through a 1.5 x 9 cm Dowex-lacetate column. The neutral polymers were eluted with 12 ml H20, and acidic materials were removed with 6 ml of 6 N acetic acid followed by 10 Uronic acids and hydroxyproline were determined colorimetrically using the methods of Blumenkrantz and Asboe-Hansen (5) and Kivirikko and Liesmaa (11), respectively.…”

Transient Exposure to Ethylene Stimulates Cell Division and Alters the Fate and Polarity of Hypocotyl Epidermal Cells

“…As seedling growth accompanies cell division in the apical meristem, suppression of seedling growth by ethylene implies that the gaseous hormone inhibits both cell elongation and division. Inhibition of DNA synthesis by ethylene was reported in meristems of shoots and roots of pea (Pisum sativum; Burg and Burg, 1968;Apelbaum and Burg, 1972;Eisinger and Burg, 1972) and in wounded tissue of potato (Solanum tuberosum; Sato et al, 1976). Because ethylene's formative effects should include changes in cell division control, we are especially interested in the effects of ethylene on those cells that remain competent for cell division, such as the progenitors of trichomes and stomata.…”