Relation of Phytochrome-enhanced Geotropic Sensitivity to Ethylene Production

Abstract

Brief exposure of etiolated pea (Pisum sativum cv. Alaska) seedlings to red light enhances subsequent development of geotropic curvature of the stem. Both this response and inhibition of ethylene production by red light become maximal 8 hours after illumination. Very low concentrations of applied ethylene inhibit development of geotropic curvature, whereas hypobaric treatment enhances geotropic sensitivity by removing endogenous ethylene. Increased geotropic sensitivity after illumination is accompanied by increased lateral migration of 'H-indoleacetic acid in response to gravity, and ethylene inhibits this lateral migration. It is suggested, therefore, that red light-enhanced geotropic sensitivity is caused by increased lateral auxin transport resulting from a reduction in ethylene production after illumination.Several instances are known in which ethylene intervenes (6,12, 13, 15,16) MATERIALS AND METHODS Plant Material. Seeds of Pisum sativum cv. Alaska were soaked for 3 hr, germinated in 12.5-cm plastic pots containing wet vermiculite, and grown in darkness at 23 C for 7 days. In most experiments, 1-cm subapical sections from the third internode were used, but in some cases the entire apical part and third internode were excised by cutting the stem about 1 cm below the second node. Plants were handled under dim green light, and in some cases illuminated for 5 min with red light (1250 erg/cm2 sec) from a fluorescent source (13) at various times before the tissue was cut.Geotropic Induction. Geotropic curvature was induced in isolated 1-cm sections by floating 10 of them without shaking 1This work was supported by National Science Foundation Grant GB-27424 to S.P.B. on 20 ml of solution (2% sucrose, 5 /-M CoCl2 and 5 mm potassium phosphate buffer, pH 6.8) contained in a 10-cm Petri dish. Hypobaric experiments were performed with intact apical parts laid horizontally on a Lucite mount having 10 grooves. The basal cut ends were kept moist with wet paper towel, the Lucite mounts placed in 10-liter capacity desiccators, and hypobaric conditions established at 120 mm Hg of water-saturated flowing 02 as described previously (13). Attempts to displace ethylene with a competitive inhibitor, CO2., were abandoned when it was found that 5 to 10% CO2 markedly inhibits stem growth, in contrast to hypobaric treatment (1), which does not affect the growth rate of the subapex. Curvatures were measured with a goniometer from shadowgraphs, and results presented as the average of 10 measurements with standard error.Lateral Transport of 3H-IAA. Ten 1-cm sections were placed horizontally on grooves of a Lucite mount, and a donor agar block (1.5%) containing 0.12 fLM [5-3H] IAA (17 c/mmole) was attached to the apical cut ends of the sections. A receiver agar block (1.5%) was attached to the basal cut surfaces. The Lucite mount was placed in a desiccator containing H20-saturated air, and after 120 min the agar blocks were removed, the apical 1 mm of each section excised, and the remaining part split longitudinally with a r...

Effect of Carbon Dioxide and Light on Ethylene Production in Intact Sunflower Plants

“…It has recently been reported that light inhibits ethylene production in segments of green oat leaves but not in etiolated leaves (7). The experiments dealing with the effect of monochromatic light on plant tissues suggest an inhibitory effect of red light as compared to darkness on the rate of ethylene production (8,11,12,18). However, Janes et al (10) found no effect of red light on the rate of ethylene production in the intact lettuce seedlings.…”

The Effect of Light and Phytochrome on 1-Aminocyclopropane-1-Carboxylic Acid Metabolism in Etiolated Wheat Seedling Leaves

“…Although most reports related that white or red light inhibited ethylene production (5,8,17,19), one report observed that red light promoted ethylene production in the shoot of pea seedling (16). It (2,5,9). Possible involvement of phytochrome in inhibiting ethylene formation in these etiolated hook region by promoting ACC malonylation is currently under investigation.…”

“…However, light did not cause any significant increase in the extractable ACC-malonyltransferase activity. A number of reports have shown that light regulated ethylene production which in turn modified plant growth (4,5,9,18,19 m-2 s-'), red light or far-red light. The red and far-red light sources were from a projector equipped with a 650 nm and 730 nm filter, respectively.…”

“…A number of reports have shown that light regulated ethylene production which in turn modified plant growth (4,5,9,18,19). Depending on the tissues and conditions employed, light promoted (16,18) and inhibited (2)(3)(4)(5)(6)(7)(8)(9)(10)20) ethylene production.…”

“…Depending on the tissues and conditions employed, light promoted (16,18) and inhibited (2)(3)(4)(5)(6)(7)(8)(9)(10)20) ethylene production. Since the plant tissues used in these earlier studies normally contained low level of endogenous ACC,3 the effects of light on the changes in ACC levels in relation to ethylene production were not examined.…”