Effect of Ethylene on Cell Division and Deoxyribonucleic Acid Synthesis in Pisum sativum

Abstract

Ethylene and supraoptimal levels of 2,4-dichlorophenoxyacetic acid inhibit the growth of the apical hook region of etiolated Pisum sativum (var. Alaska) seedlings by stopping almost all cell divisions. Cells are prevented from entering prophase. The hormones also retard cell division in intact root tips and completely stop the process in lateral buds. The latter inhibition is reversed partially by benzyl adenine. In root tips and the stem plumular and subhook regions, ethylene inhibits DNA synthesis. The magnitude of this inhibition is correlated with the degree of repression of cell division in meristematic tissue, suggesting that the effect on cell division results from a lack of DNA synthesis. Ethylene inhibits cell division withinm a few hours with a dose-response curve similar to that for most other actions of the gas. Experiments with seedlings grown under hypobaric conditions suggest that the gas naturally controls plumular expansion and cell division in the apical region.Growth of etiolated pea seedlings (38) and many other plants is suppressed by ethylene at least in part because the gas slows the rate of cellular expansion and causes roots and shoots to expand isodiametrically rather than longitudinally (4,(8)(9)(10)(11). In pea seedlings several processes dependent upon cell division are also inhibited by ethylene; for example, primary root elongation and lateral root formation (10, 11), lateral bud development (7), and expansion of the plumular leaf (18,19). Therefore, the effect of the gas on cellular division and DNA synthesis was investigated to determine whether these processes also might be involved in ethyleneinduced growth inhibition. Applied ethylene and auxin generally affect the growth of pea seedlings in a similar manner because auxin induces ethylene production (1,4,9,23,24,32 complete darkness at 23 C and 80% relative humidity. Unless otherwise indicated, 7-day-old plants with third internodes, approximately 1.5 cm long, were selected for experiments on plumular, stem, or bud growth, while 3-day-old seedlings with primary roots, 1 to 2 cm long, were used for studies on root growth. Pots of seedlings also were grown under hypobaric conditions by placing them in a 10-liter desiccator which was evacuated continuously at approximately 0.5 standard cubic foot per hr with a vented exhaust oil-seal pump. The pressure within the desiccator was maintained at 120 mm Hg by continuously admitting pure 02 to the desiccator through a Matheson No. 49 regulator (5). The incoming 02 was saturated at the reduced pressure by passing it through water.Growth Measurements. All tissue was handled under dim green light. A 5-mm stem region was demarcated with two ink spots just below the hook; this is referred to as the subhook region, and the region above it as the hook region. Groups of potted plants were either gassed with ethylene in air tight chambers, sprayed with 2,4-D, treated with a combination of the two hormones or irrigated with 2, 4-D solution. The chambers were aerated for several minutes e...

Control by Ethylene of Arginine Decarboxylase Activity in Pea Seedlings and Its Implication for Hormonal Regulation of Plant Growth

“…Ethylene has been shown to inhibit cell division, DNA synthesis, and growth in meristems of roots, shoots, and axillary buds of etiolated pea seedlings (1). In the shoot apex, cell division was almost completely annulled by ethylene and only 60% inhibition was observed in the root apex (1).…”

Reduction in Extractable Deoxyribonucleic Acid Polymerase Activity in Pisum sativum Seedlings by Ethylene

“…Ethylene or supraoptimal auxin concentration suppresses the growth of pea plants by causing almost complete inhibition of cell division in the apical meristems, lateral buds, and the plumular leaf (2). Furthermore, DNA synthesis in the apical tissue is inhibited by ethylene to the same degree as cell division and at similar hormone concentrations (2).…”

“…Loss Recent studies on the effects of ethylene on growth of etiolated pea seedlings have shown (2) that the gas suppresses growth of the root and shoot apex, lateral branching, and leaf expansion predominantly by inhibiting cell division. Furthermore, ethylene inhibits DNA synthesis in the plumular hook and subapex region of etiolated pea seedlings (2). Growth inhibition was therefore attributed to inhibition of DNA synthesis by ethylene.…”

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

“…In the same study, we demonstrate that endoreduplication is stimulated in a subset of epidermal cells during exposure to ethylene. Early studies demonstrated that ethylene suppresses cell division and mitotic DNA synthesis in apical meristems (Apelbaum and Burg, 1972). However, more recent work on light-grown hypocotyls of Arabidopsis demonstrates that ethylene can both promote hypocotyl enlargement (Smalle et al, 1997) and stimulate endoreduplication (Gendreau et al, 1999), although which cells are affected was not determined.…”

“…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.…”