Plant Physiology

Boyer, J. S.; Potter, J. R.

doi: 10.1104/pp.51.6.989pmid: 16658486

Abstract The effect of decreases in turgor on chloroplast activity was studied by measuring the photochemical activity of intact sunflower (Helianthus annuus L. cv. Russian Mammoth) leaves having low water potentials. Leaf turgor, calculated from leaf water potential and osmotic potential, was found to be affected by the dilution of cell contents by water in the cell walls, when osmotic potentials were measured with a thermocouple psychrometer. After the correction of measurements of leaf osmotic potential, both the thermocouple psychrometer and a pressure chamber indicated that turgor became zero in sunflower leaves at leaf water potentials of −10 bars. Since most of the loss in photochemical activity occurred at water potentials below −10 bars, it was concluded that turgor had little effect on the photochemical activity of the leaves. 2 Present address: Southern Weed Science Laboratory, Plant Science Research Division, Agricultural Research Service, United States Department of Agriculture, Stoneville, Miss. 38776. 1 This work was supported by Grant B-036-ILL from the Office of Water Resources Research, United States Department of Interior. 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)

Potter, J. R.; Boyer, J. S.

doi: 10.1104/pp.51.6.993pmid: 16658487

Abstract Electron transport in chloroplasts isolated from desiccated sunflower (Helianthus annuus L. cv. Russian Mammoth) leaves was compared with electron transport in sunflower chloroplasts in sorbitol-containing media having various osmotic potentials. In media having low osmotic potentials and dichloroindophenol as electron acceptor, the activity for electron transport was inhibited, but the inhibition was much less than that due to comparable desiccation in vivo. The inhibition at low osmotic potentials was rapidly reversed by returning the chloroplasts to media having high osmotic potentials, but the activity of chloroplasts from desiccated tissue showed no reversal when the chloroplasts were placed in media having high osmotic potentials. Nevertheless, the inhibition of chloroplast activity due to desiccation in vivo was basically reversible, because chloroplasts recovered quickly when they were rehydrated in vivo. The large differences between desiccation in vivo and exposure to low osmotic potential in vivo indicate that osmotic solutions did not reproduce the effects of tissue desiccation. It is concluded that decreases in the Gibbs free energy of water due to decreased osmotic potentials probably have only a small effect on electron transport in chloroplasts from desiccated tissue and do not account for the major effects of leaf desiccation on electron transport. 2 Present Address: Southern Weed Science Laboratory, Plant Science Research Division, Agricultural Research Service, United States Department of Agriculture, Stoneville, Miss. 38776. 1 This work was supported by Grant B-036-ILL from the Office of Water Resources Research, United States Department of Interior. 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)

Tsai, C. M.; Hassid, W. Z.

doi: 10.1104/pp.51.6.998pmid: 16658488

Abstract UDP-d-glucose, at a micromolar level in the presence of MgCl2 and oat (Avena sativa) coleoptile particulate enzyme which contains both β-(1 → 3) and β-(1 → 4) glucan synthetases, produces glucan with mainly β-(1 → 4) glucosyl linkages. An activation of β-(1 → 3) glucan synthetase by UDP-d-glucose and a decrease in the formation of β-(1 → 3) glucan in the presence of MgCl2 have been observed. However, at high substrate concentration (≥ 10−4m), the activation of β-(1 → 3) glucan synthetase is so pronounced that the formation of β-(1 → 3) glucosyl linkage predominates in synthesized glucan regardless of the presence of MgCl2. These observations may explain the striking shift in the composition of glucan of particulate enzyme from a β-(1 → 4) to β-(1 → 3) glucosyl linkage when UDP-d-glucose concentration is raised from a low concentration (≤ 10−5m) to a higher concentration (≥ 10−4m). Besides UDP-d-glucose, CDP-d-glucose can also serve as substrate for the formation of β-(1 → 3) glucan in the presence of β-(1 → 3) synthetase. 2 Present address: Yale University School of Medicine, Department of Pharmacology, 333 Cedar Street, New Haven, Conn. 06510. 1 This investigation was supported in part by Research Grant A-1418 from the National Institutes of Health, United States Public Health Service, and by Research Grant GB 11819 from the National Science Foundation. Support of this work by the Agricultural Experiment Station of the University of California is also acknowledged. 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)

Cooper, W. C.; Horanic, George

doi: 10.1104/pp.51.6.1002pmid: 16658453

Abstract The use of hypobaric pressures has increased the precision of abscission research by enabling us to differentiate between abscission action of ethylene and abscisic acid. When cycloheximide is sprayed on fruit attached to trees, enhanced levels of ethylene occur in the fruit and, subsequently, the fruit abscises. When ethylene in the fruit is eliminated by hypobaric pressures, the fruit does not abscise. Thus, ethylene is the effector of fruit abscission that results from cycloheximide treatment. When abscisic acid is applied to the fruit through stem uptake and ethylene is removed by hypobaric pressures, rapid fruit abscission occurs, which is presumably caused by abscisic acid itself. Thus, either ethylene or abscisic acid will induce abscission of citrus. Likewise, the abscission of debladed petioles of Coleus plants appears to be effected either by ethylene or abscisic acid. 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)

Millerd, Adele; Whitfeld, P. R.

doi: 10.1104/pp.51.6.1005pmid: 16658454

Abstract In Vicia faba L., the tissue specific proteins, legumin and vicilin, are synthesized during the cell expansion phase of cotyledon development. During this growth period, RNA and nuclear DNA increase 8- to 10-fold. 3H-Uridine and 3H-adenosine are incorporated into ribosomal RNA, both 25S and 18S, and into transfer RNA. DNA isolated from cotyledons in the cell division phase of growth has been compared with DNA isolated from cotyledons undergoing expansion growth. Results indicate that the DNA increase involves replication of the whole genome (endoreduplication). 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)

Lau, Oi-Lim; Yang, S. F.

doi: 10.1104/pp.51.6.1011pmid: 16658455

Abstract In hypocotyl segments of mung bean (Phaseolus mungo L.) seedlings, exogenously supplied indoleacetic acid was rapidly conjugated mainly into indoleacetylaspartic acid, which was inactive in inducing ethylene production. Kinetin is known to stimulate indoleacetic acid-induced ethylene production. The mechanism of kinetin action on indoleacetic acid-induced ethylene production by hypocotyl segments of mung bean seedlings was studied in relation to indoleacetic acid uptake and indoleacetic acid metabolism. Kinetin enhanced indoleacetic acid uptake during the initial 2-hour incubation and markedly suppressed the conversion of indoleacetic acid to indoleacetic acid conjugates throughout the whole 7-hour incubation. As a result, there was more free indoleacetic acid and less conjugated indoleacetic acid in the segments treated with kinetin than in those receiving no kinetin. A close relationship was demonstrated between the rate of ethylene production and the level of free indoleacetic acid, which was regulated by kinetin. 1 This work was supported in part by National Science Foundation Grant GB-33907x. 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)

Burger, W. C.

doi: 10.1104/pp.51.6.1015pmid: 16658456

Abstract An endopeptidase preparation from germinated barley Hordeum vulgare L., cv. Trophy, purified by affinity chromatography and density-gradient electrofocusing, consisted of three or four components. The preparation was only partly resolved by electrofocusing, with evidence of three possible components (pI 4.15, 4.28, and 4.37). Gel filtration on Sephadex G-75 yielded an asymmetrical peak, the major part of which corresponded to a molecular weight of 14,100, with evidence of one larger and two smaller components. The activity of the preparation was sulfhydryl-dependent; cysteine was the most effective of several sulfhydryl compounds tested. The preparation was sensitive to O2 in the absence of metal chelating agents and was inhibited by sulfhydryl reagents. It showed very narrow concentration tolerances for both cysteine and a substrate, N,N-dimethylhemoglobin. The Km value on N,N-dimethylhemoglobin at pH 3.8 was 0.064 to 0.067% (w/v) substrate; Vmax was 0.80 to 0.83 A340 per hour. Normal enzyme activity and molecular-size distribution were observed when the endopeptidases were extracted in the inhibited state and subsequently reactivated, thus ruling out the possibility that the enzymes might be autolytic artifacts that arose during extraction and purification. 1 Cooperative investigation, Agricultural Research Service, United States Department of Agriculture and the College of Agricultural and Life Sciences, University of Wisconsin, Madison. The Barley and Malt Laboratory is supported in part by a grant from the Malting Barley Improvement Association. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the United States Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable. 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)

Guilfoyle, T. J.; Hanson, J. B.

doi: 10.1104/pp.51.6.1022pmid: 16658457

Abstract Optimal activity of chromatin-bound RNA polymerase from soybeans is obtained with 1 mm Mn2−, but only when high ionic strength or polyamines are included in the medium. Such inclusion does not increase the Mg2+ activation of the polymerase, but it does lower the concentration needed for optimum activity from 10 mm to 1 mm. Mg2− activation is inhibited by added Mn2+, and the inhibition is relieved by high ionic strength or spermidine. The RNA polymerase with either cation is almost entirely polymerase I at low and high ionic strength as evidenced by insensitivity to α-amanitin. Treatment of soybean seedlings with 2,4-dichlorophenoxyacetic acid does not change these characteristics; although the activity rises 3- to 4-fold. It is suggested that chromatin as prepared here may be a selected fraction enriched in polymerase I, which is activated by either Mg2+ or Mn2+, and that the Mn2− inhibition of activity is due to a known reaction of Mn2− with DNA which can be relieved by high ionic strength. 1 This work was supported by a National Defense Education Act predoctoral fellowship to T. J. Guilfoyle and by the United States Atomic Energy Commission AT (11-1)-790. 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)

Montague, Michael J.; Ikuma, Hiroshi; Kaufman, Peter B.

doi: 10.1104/pp.51.6.1026pmid: 16658458

Abstract Gibberellic acid was found to cause elongation in Avena sativa (oat) stem segments whether it was applied continuously or as a short pulse. The shorter the pulse time became, the higher was the gibberellic acid concentration needed to cause elongation; the segmental growth apparently depends upon the amount of gibberellic acid taken up by the segments. Avena segments showed a decreased growth response to gibberellic acid if the treatments were initiated at increasingly later times after excision from the plant. This decreased responsiveness to gibberellic acid was inhibited by low temperature (0-4 C), but accelerated by anaerobiosis. On the other hand, growth stimulation by a gibberellic acid pulse at the start of incubation was not altered by cold treatment but was nullified by a nitrogen atmosphere. Both the readiness of the segments for growth stimulation by gibberellic acid and its action in promoting growth clearly involve temperature-dependent, aerobic metabolism. Segments were able to use glucose, fructose, sucrose, and glycerol but not malate, citrate, pyruvate, glycine, or glutamine as substrate for growth. Since final elongation without exogenous substrate was highly correlated with initial content of total carbohydrate and reducing sugar, carbohydrates seem to be the major endogenous growth substrates. The Avena segments are composed of three distinct morphological units: node, internode, and encircling leaf sheath. Although the node and leaf sheath do not grow, they must be present for maximal growth of the internode. Quantitative assessment of the roles of each part suggests that a substance other than gibberellin or sugar is necessary for maximal internodal growth and that this substance may be channeled from the leaf sheath to the internode through the anastomosing vascular tissue of the node. 1 National Science Foundation Pre-doctoral Fellow. 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)

Chalutz, Edo

doi: 10.1104/pp.51.6.1033pmid: 16658459

Abstract Ethylene enhanced the activity of phenylalanine ammonialyase in carrot (Daucus carota L., var. “Nauty”) root tissue. Slight increase in enzyme activity was exhibited by root discs incubated in ethylene-free air. It was probably due to the ethylene formed within the sliced tissue. Addition of ethylene to the air stream increased phenylalanine ammonia-lyase activity and the total protein content of the discs until maximum activity was reached after 36 to 48 hours of incubation. The continuous presence of ethylene was required to maintain high level of activity. Ethylene, at a concentration of 10 microliter per liter induced higher activity than at lower or higher concentrations. CO2 partially inhibited the ethylene-induced activity. Cycloheximide or actinomycin D effectively inhibited the ethylene-induced activity in discs that had not previously been exposed to ethylene. The results appear to support the hypothesis that the mode of action of ethylene may involve both de novo synthesis of the enzyme protein and protection or regulation of activity of the induced enzyme. 1 This work was supported in part by the Fund for the Encouragement of Research of the Executive Committee of the Israel General Federation of Labor. 2 Contribution from The Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1971 Series, No. 2022-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)