Plant Physiology

Beyer, Elmo M.

doi: 10.1104/pp.52.1.1pmid: 16658489

Abstract Three types of whole plant experiments are presented to substantiate the concept that an important function of ethylene in abscission is to reduce the transport of auxin from the leaf to the abscission zone. (a) The inhibitory effect of ethylene on auxin transport, like ethylene-stimulated abscission, persists only as long as the gas is continuously present. Cotton (Gossypium hirsutum L. cv. Stoneville 213) and bean (Phaseolus vulgaris L. cv. Resistant Black Valentine) plants placed in 14 μl/l of ethylene for 24 or 48 hours showed an increase in leaf abscission and a reduced capacity to transport auxin; but when returned to air, auxin transport gradually increased and abscission ceased. (b) Ethylene-induced abscission and auxin transport inhibition show similar sensitivities to temperature. A 24-hour exposure of cotton plants to 14 μl/l of ethylene at 8 C resulted in no abscission and no significant inhibition of auxin transport. Increasing the temperature during ethylene treatment resulted in a progressively greater reduction in auxin transport with abscission occurring at [unk]27 C where auxin transport was inhibited over 70%. (c) Auxin pretreatment reduced both ethylene-induced abscission and auxin transport inhibition. No abscission occurred, and auxin transport was inhibited only 18% in cotton plants which were pretreated with 250 mg/l of naphthalene acetic acid and then placed in 14 μl/l of ethylene for 24 hours. In contrast, over 30% abscission occurred, and auxin transport was inhibited 58% in the corresponding control plants. Collectively, the results presented here and elsewhere indicate that ethylene regulates the sensitivity of the cells in the abscission zone to the more direct actions of the gas (e.g., enzyme induction, secretion) by reducing auxin transport. 1 Central Research Department Contribution No. 2009. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Leonard, R. T.; Hodges, T. K.

doi: 10.1104/pp.52.1.6pmid: 16658500

Abstract ATPase activity of plasma membranes isolated from oat (Avena sativa L. cv. Goodfield) roots was activated by divalent cations (Mg2+ = Mn2+ > Zn2+ > Fe2+ > Ca2+) and further stimulated by KCl and a variety of monovalent salts, both inorganic and organic. The enzyme exhibited greater specificity for cations than anions. The presence of Mg2+ was necessary for KCl stimulation. Ca2+ was ineffective in replacing Mg2+ for activation of plasma membrane ATPase, but it did activate other membrane-bound ATPases. The pH optima for Mg2+ activation and KCl stimulation of the plasma membrane ATPase were 7.5 and 6.5, respectively. The plasma membrane ATPase showed little synergistic effects of K+ and Na+, and it was only slightly sensitive to ouabain. Oligomycin did not inhibit the ATPase, while N,N′-dicyclohexylcarbodiimide was a potent inhibitor of the enzyme. The apparent Km for Mg2+ activation (0.84 mm) of the ATPase was about twice that of the apparent Km for ATP (0.38 mm). The effect of KCl in stimulating the enzyme was not on the apparent Km values for ATP and Mg2+ but rather on maximum velocity. The kinetics of KCl stimulation of the plasma membrane ATPase were similar to the kinetics of 42K+ influx into oat roots and neither followed the Michaelis-Menten equation but rather were best described by a single activity curve with continually changing kinetic parameters. These results support the concept that cation transport at the plasma membrane of root cells is coupled to a cation-activated ATPase which is functional from low (0.01 mm) to high (50.0 mm) concentrations of KCl. 2 Present address: Department of Plant Sciences, University of California, Riverside, Calif. 92502. 1 This research was supported by a grant from the National Science Foundation (GB-31052X). Journal paper No. 5001 of the Purdue University Agricultural Experiment Station. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Manahan, Charles O.; App, Alva A.

doi: 10.1104/pp.52.1.13pmid: 16658490

Abstract Embryos from rice (Oryza sativa L. var. Bluebonnet) and wheat (Triticum aestivum L.) contain an aminoacyl-tRNA protein transferase which transfers arginine from arginyl-tRNA to the N terminus of a protein acceptor. The activity was measured in vitro in a reaction mixture containing embryo supernatant fraction, buffer, sulfhydryl reagent, and arginyl-tRNA. It was not dependent on the usual cofactors for ribosomal protein synthesis, nor was it sensitive to cycloheximide or puromycin. However, the activity was inhibited by ribonuclease. The enzyme was purified 33-fold from a crude homogenate of rice embryos. An apparent endogenous substrate from rice embryos was prepared free of transferase activity; however, the transferase was not purified sufficiently to show absolute dependence on the presence of this endogenous substrate. 1 This research was supported in part by Grant GB 19914 from the National Science Foundation. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Rehfeld, D. W.; Jensen, R. G.

doi: 10.1104/pp.52.1.17pmid: 16658491

Abstract Separated mesophyll cells from cotton (Gossypium hirsutum var. Stoneville 1613 Glandless) were isolated with pectinase and mechanical agitation. The separated cells had rates of light-dependent CO2 fixation between 50 to 100 μmoles CO2 per mg chlorophyll per hour. The presence of Ca2+ in the incubation medium did not significantly affect the type of photosynthetic products formed, but 2 mm Ca2+ did cause a 50% decrease in the appearance of photosynthetic products in the incubation medium. The movement of all types of products (sugars, organic, and amino acids) out of the cells was reduced similarly by the Ca2+. Light had no affect on the movement of products out of the cells, whereas 1 mm ethylenediaminetetra-acetate greatly increased the movement. The addition of 1.6 mm NH4Cl to the cell suspensions caused a large increase in the amount of fixed 14C appearing in the amino acid fraction and a decrease in the sugar fraction. These metabolic changes in the cells were reflected in the movement of products out of the cells so that the incubation medium also contained a larger amount of label in amino acids and a smaller amount in sucrose. Although the cell plasma membrane restricted the movement of soluble products, it did not discriminate significantly between the types of products moved. 2 Present address: Department of Biochemistry and Nutrition, The University of Nebraska, Lincoln, Neb. 68503. 3 To whom correspondence should be addressed. 1 This research was supported by Grant 12-14-100-9947(34) from the United States Department of Agriculture, Agricultural Research Service. Initial support came from Grant GB-27453 from the National Science Foundation. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Taylorson, R. B.; Hendricks, S. B.

doi: 10.1104/pp.52.1.23pmid: 16658492

Abstract Potassium cyanide at 3 μm to 10 mm promotes germination of Amaranthus albus, Lactuca sativa, and Lepidium virginicum seeds. l-Cysteine hydrogen sulfide lyase, which catalyzes the reaction of HCN with l-cysteine to form β-l cyanoalanine, is active in the seeds. β-l-Cyanoalanine is the most effective of the 23 α-amino acids tested for promoting germination of A. albus seeds. Aspartate, which is produced by enzymatic hydrolysis of asparagine formed by hydrolysis from β-cyanoalanine, is the second most effective of the 23 amino acids. Uptake of aspartate-4-14C is much lower than of cyanide. Radioactive tracer in K14CN shows uptake of about 1.5 μmoles of HCN per gram of A. albus and L. sativa seeds after 20 hours of imbibition. Extracts of the seeds gave high 14C activity in β-cyanoalanine, asparagine, and aspartate. The acid-hydrolyzed protein extract gave high activity only in aspartate. Tests were negative for free cyanide in the seed. Respiration of the seed is inhibited more than 75% by KCN and by KN3 at 10 mm. Azide at greater than 1.0 mm inhibits the promotion of germination by cyanides. Neither 0.1 mm KCN nor KN3 inhibit O2 consumption, whereas lower concentrations promote germination. It is concluded that the high rate of utilization of cyanide in the reaction to form β-l-cyanoalanine and the subsequent incorporation into protein limit any inhibition of oxygen consumption. The promotion of seed germination is substrate-limited by asparagine-aspartate, which is required for protein synthesis. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Plaut, Z.; Bravdo, B.

doi: 10.1104/pp.52.1.28pmid: 16658493

Abstract Application of water stress to isolated spinach (Spinacia oleracea) chloroplasts by redutcion of the osmotic potentials of CO2 fixation media below −6 to −8 bars resulted in decreased rates of fixation regardless of solute composition. A decrease in CO2 fixation rate of isolated chloroplasts was also found when leaves were dehydrated in air prior to chloroplast isolation. An inverse response of CO2 fixation to osmotic potential of the fixation medium was found with chloroplasts isolated from dehydrated leaves—namely, fixation rate was inhibited at −8 bars, compared with −16 or −24 bars. Low leaf water potentials were found to inhibit CO2 fixation of intact leaf discs to almost the same degree as they did CO2 fixation by chloroplasts isolated from those leaves. CO2 fixation by intact leaves was decreased by 50 and 80% when water potentials were reduced from −7.1 to −9.6 and from −7.1 to −17.6 bars, respectively. Transpiration was decreased by only 40 and 60%, under the same conditions. However, correction for the increase in leaf temperature indicated transpiration decreases of 57 and 80%, similar to the relative decreases in CO2 fixation. Despite the 4-fold increase in leaf resistance to CO2 diffusion in the gas phase when the water potential of leaves was reduced from −6.5 to −14.0 bars, an additional increase of about 50% in mesophyll resistance was obtained. CO2 concentration at compensation also increased when leaf water potential was reduced. 1 This work is a contribution from The Volcani Center, Agricultural Research Organization, Bet Dagan, Israel. 1972 Series No. 2282-E. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Zelitch, Israel; Day, P. R.

doi: 10.1104/pp.52.1.33pmid: 16658494

Abstract A normal appearing plant with a low rate of photorespiration (ratio of 14CO2 released light/dark = 1.6) was found in an unselected tobacco (Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net CO2 assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of 14CO2 released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of CO2 dm−2 hr−1) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25%) than did selfing inefficient plants (about 6%), but this proportion did not increase in successive generations. Wide variations in photorespiration and photosynthesis were observed within populations of normal appearing plants grown in the same greenhouse environment. Several plants had photosynthetic rates as great as 25 mg of CO2 dm−2 hr−1 coupled with light/dark ratios below 2.0. The characteristics of two representative contrasting plants were studied more extensively and were fairly constant, irrespective of leaf position on the stalk, leaf size, or time of sampling within approximately a 2-week period. One plant with a mean light/dark ratio of 1.7 showed a mean net photosynthesis of 23.4 mg of CO2 dm−2 hr−1, while an inefficient plant with a light/dark ratio of 3.7 had an average photosynthetic rate of only 17.0 mg CO2 dm−2 hr−1. The dark respiration was similar in these plants. Thus decreasing the photorespiratory rate by about one-half increased net photosynthesis by 38%. The results suggest that diminishing photorespiration, in an otherwise suitable genetic background, will result in large increases in net photosynthesis and plant productivity. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Herner, R. C.; Sink, K. C.

doi: 10.1104/pp.52.1.38pmid: 16658495

Abstract Little or no change in ethylene or CO2 production occurred in rin tomato mutant fruits monitored for up to 120 days after harvest. Of the abnormally ripening tomatoes investigated, including “Never ripe” (Nr Y a h, Nr c l2 r), “Evergreen” (gf r) and “Green Flesh” (gf), only rin did not show a typical climacteric and ethylene rise. Fruits from F1 plants resulting from reciprocal crosses between rin and normal plants apeared to ripen normally, but when compared to normal fruit, their ripening was delayed as measured by ethylene and CO2 production and color change. These fruits produced only one-third to one-half as much ethylene at the peak of production compared to normal fruits. Exogenous ethylene or propylene treatment did not stimulate ethylene production by rin fruits but did stimulate CO2 production. The CO2 stimulation persisted only in the presence of the exogenous olefins. Stimulation of CO2 production could be repeated several times in the same fruit. Wounding stress stimulated both ethylene and CO2 production in rin fruits. It was concluded that rin tomato fruits behave like nonclimacteric fruits. 1 Michigan Agricultural Experiment Station Journal Article No. 6242. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Birecka, H.; Briber, K. A.; Catalfamo, J. L.

doi: 10.1104/pp.52.1.43pmid: 16658496

Abstract Sweet potato (Ipomoea batatas) root parenchyma and tobacco (Nicotiana tabacum) stem pith, both known to increase peroxidase activity after excision, differed from each other in their isoperoxidase patterns and in the isoperoxidase responses to injury and exogenous ethylene. In potato root sections, the injury-dependent peroxidase increase was due to an induction of two isoenzymes, as well as to a promotion of some constitutive ones. In tobacco pith, this increase was entirely due to seven isoperoxidases not detectable, or detectable only in traces, immediately after excision. Actinomycin D did not inhibit the development of any isoperoxidases in the potato root sections and strongly repressed the development of all injury-induced isoenzymes in tobacco pith. Cycloheximide totally inhibited the development of all isoperoxidases in both species, with the exception of two injury-enhanced isoenzymes in root parenchyma. In root sections, indoleacetic acid had a weak inhibitory effect on one injury-induced isoperoxidase only, whereas in tobacco pith it inhibited the development of the injury-induced, as well as the constitutive, isoperoxidases. Exogenous ethylene did not induce, enhance, or significantly suppress any of the tobacco pith isoenzymes, whereas in potato root sections, it suppressed slightly the development of the injury-induced, had no effect on some of the injury-enhanced, and greatly promoted some of the injury-unaffected or-enhanced isoperoxidases. Removal of ethylene stopped the ethylene-dependent peroxidase increase without affecting the injury-induced increase. When applied to intact potato roots, ethylene did not induce any new isoperoxidases and promoted the same constitutive isoenzymes as it did in root sections. Thus, the tissue peroxidase response to ethylene seems independent of its response to injury. Differences between tissue species in their response to ethylene may depend on the presence or absence of isoperoxidases sensitive to ethylene. The inhibition of injury-dependent peroxidase development by indoleacetic acid cannot be explained by an ethylene-induced inhibition. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Moore, T. S.; Lord, J. M.; Kagawa, T.; Beevers, Harry

doi: 10.1104/pp.52.1.50pmid: 16658497

Abstract The intracellular location of several enzymes concerned with phospholipid metabolism was investigated by examining their distribution in organelles separated on sucrose gradients from total homogenates of castor bean (Ricinus communis var. Hale) endosperm. The enzymes phosphatidic acid phosphatase, CDP-diglyceride-inositol transferase, and phosphatidyletha-nolamine-l-serine phosphatidyl transferase were all primarily or exclusively confined to membranes of the endoplasmic reticulum. These results and those reported previously on lecithin synthesis establish a major role of the endoplasmic reticulum in phospholipid and membrane synthesis in plant tissues. 2 Present address: Department of Biochemistry, The University, Leicester, England. 3 Present address: C.S.I.R.O., Division of Plant Industry, Canberra, Australia. 1 This work was supported by the Atomic Energy Commission Contract AT-1 04/3, National Science Foundation Grant GB-24961, and United States Public Health Services Postdoctoral Fellowship 1-F2-AM-51, 665-01 to T.M. This content is only available as a PDF. © 1973 American Society of Plant Biologists This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)