Plant Physiology

Jacobs, William P.

doi: 10.1104/pp.61.3.307pmid: 16660280

Abstract To test the hypothesis that photoinduction acts by changing the ability of the plant to transport hormones, rather than by changing the ability of organs to synthesize them, the transport of carboxy-labeled indole-3-acetic acid was measured in the short day plant Xanthium pensylvanicum. Plants grown under noninductive conditions were matched for developmental stage, then assigned by a mathematically random method to either short day or noninductive conditions of “short day + light break.” After the plants had been subjected to one to seven cycles, the movement of auxin was followed through sections cut from the middle of petioles of various ages. Photoinduction, even with as many as seven cycles, had no effect on auxin movement in either the basipetal or acropetal direction. Auxin movement in vegetative Xanthium was similar to that in Coleus and Phaseolus: strongly polar in a basipetal direction through younger petioles, but with polarity declining with increasing petiole age and concomitant decreasing elongation. 1 This research was aided by facilities made available to the Department of Biology by the Whitehall and John A. Hartford Foundations. This content is only available as a PDF. © 1978 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)

Roberts, Stephen W.; Knoerr, Kenneth R.

doi: 10.1104/pp.61.3.311pmid: 16660281

Abstract Xylem pressure potentials and stomatal diffusion resistances were measured in the field in Ilex opaca Ait. during days which differed in temperature and vapor pressure deficit. Water flux into leaves was calculated by combining the field data with laboratory determinations of the relation between tissue water deficit and water potential. Estimates of apparent plant resistance were then calculated from fluxes and differences between soil water potential and xylem tension. The resistance depended strongly on water flux, dropping by a factor of over 7 from low to high water flow rates. This extends the generality of variable plant resistances measured in controlled environment studies to I. opaca as it occurs naturally in the field. The relation of apparent plant resistance to water flux as estimated in this study can be useful in simulation models which calculate water uptake to leaves as a flux driven by a difference in soil and leaf water potentials across a resistance between the bulk soil and the leaf. 1 This work was supported in part by Duke University Research Award 468-8301 to S. W. R. This content is only available as a PDF. © 1978 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)

Yoshikawa, Masaaki; Yamauchi, Kazuma; Masago, Hajime

doi: 10.1104/pp.61.3.314pmid: 16660282

Abstract Actinomycin D inhibited the synthesis of poly(A)-containing messenger RNA in healthy soybean (Glycine max [L.] Merr. cv. Harosoy 63) hypocotyls and in hypocotyls inoculated with the pathogenic fungus Phytophthora megasperma var. sojae A. A. Hildb., but had little effect on protein synthesis within 6 hours. Blasticidin S, conversely, inhibited protein synthesis in the hypocotyls without exhibiting significant effects on messenger RNA synthesis. The normal cultivar-specific resistance of the Harosoy 63 soybean hypocotyls to the fungus was completely diminished by actinomycin D or blasticidin S. The fungus grew as well in hypocotyls treated with either inhibitor as it did in the near isogenic susceptible cultivar Harosoy, and production of the phytoalexin glyceollin was concomitantly reduced. The effects of actinomcyin D and blasticidin S were pronounced when the treatments were made at the time of fungus inoculation or within 2 to 4 hours after inoculation, but not after longer times. These results indicated that the normal expression of resistance to the fungus and production of glyceollin both required de novo messenger RNA and protein synthesis early after infection. Furthermore, actinomycin D and blasticidin S also were effective in suppressing resistance expression and glyceollin production in soybean hypocotyls when inoculated with various Phytophthora species that were normally nonpathogenic to the plants. This indicated that the mechanism of general resistance to these normally nonpathogenic fungi also involves de novo messenger RNA and protein synthesis and production of glyceollin. 1 This research was supported in part by Grant 256040 from the Ministry of Education of Japan to M.Y. This content is only available as a PDF. © 1978 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)

Murai, Norimoto; Armstrong, Donald J.; Taller, Barbara J.; Skoog, Folke

doi: 10.1104/pp.61.3.318pmid: 16660283

Abstract The distribution of incorporated synthetic cytokinins (N6-[8-14C]benzyladenine ([8-14C]bzl6Ade) and N6[8-14C]furfuryladenine ([8-14C]fr6Ade) in ribosomal RNA prepared from tobacco callus (Nicotiana tabacum L. var. Wis. No. 38) grown in the presence of one of these for 25 or 26 days has been studied. The rRNA of tissue supplied with [8-14C]bzl6Ade or [8-14C]fr6Ade was fractionated by methylated albumin-Kieselguhr column chromatography and preparative gel electrophoresis, respectively. In each case about 80% of the incorporated cytokinin was recovered as the ribonucleoside [8-14C]bzl6A or [8-14C]fr6A in the rRNA peak after the fractionations. [8-14C]fr6A was found associated with both the 18S and 25S rRNA components in quantities roughly proportional to their 260 nm absorbance. This pattern of apparently nonspecific association was not affected by prior denaturation of the RNA with formamide. The distribution of [8-14C]fr6A moieties in mono- and oligonucleotides derived from combined treatment of [8-14C]fr6Ade-labeled rRNA with ribonuclease T1 and pancreatic ribonuclease A was measured by fractionating the digest on a DEAE-cellulose column in the presence of 7 m urea and determining the [8-14C]fr6A content in each fraction. The [8-14C]fr6A content in the oligonucleotides varied from 46 to 210 μmol/mol of adenosine (A). The mol ratio of [8-14C]fr6A to A was three to four times greater for oligonucleotides containing uridine or cytidine ([A]nUp or [A]nCp) than for those containing quanosine ([A]nGp). 2 Present address: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331. 1 This work was supported in part by National Science Foundation Research Grant BMS72-02226A02 to F. S. This content is only available as a PDF. © 1978 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)

Frost, William B.; Blevins, Dale G.; Barnett, Neal M.

doi: 10.1104/pp.61.3.323pmid: 16660284

Abstract Week-old wheat seedlings absorbed at least 40% NO3− from NaNO3 when preloaded with K+ than when preloaded with Na+ or Ca2+. Cultures of Triticum vulgare L. cv. Arthur were grown for 5 days on 0.2 mm CaSO4, pretreated for 48 hours with either 1 mm CaSO4, K2SO4, or Na2SO4, and then transferred to 1 mm NaNO3. All solutions contained 0.2 mm CaSO4. Shoots of K+-preloaded plants accumulated three times more NO3− than shoots of the other two treatments. Initially, the K+-preloaded plants contained 10-fold more malate than either Na+- or Ca2+-preloaded seedlings. During the 48-hour treatment with NaNO3, malate in both roots and shoots of the K+-preloaded seedlings decreased. Seedlings preloaded with K+ reduced 25% more NO3− than those preloaded with either Na+ or Ca2+. These experiments indicate that K+ enhanced NO3− uptake and reduction even though the absorption of K+ and NO3− were separated in time. Xylem exudate of K+-pretreated plants contained roughly equivalent concentrations of K+ and NO3−, but exudate from Na+ and Ca2+-pretreated plants contained two to four times more NO3− than K+. Therefore K+ is not an obligatory counterion for NO3− transport in xylem. 2 Present address: Department of Agronomy, Curtis Hall, University of Missouri, Columbia, Missouri 65201. 1 This research was supported by Project No. K-014 from the Maryland Agricultural Experiment Station. Scientific article No. A2319, Contribution No. 5325 of the University of Maryland Agricultural Experiment Station. This content is only available as a PDF. © 1978 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)

Hanscom, Zac; Ting, Irwin P.

doi: 10.1104/pp.61.3.327pmid: 16660285

Abstract Experiments were performed to test the hypothesis that succulents “shift” their method of photosynthetic metabolism in response to environmental change. Our data showed that there were at least three different responses of succulents to plant water status. When plant water status of Portulacaria afra (L.) Jacq. was lowered either by withholding water or by irrigating with 2% NaCl, a change from C3-photosynthesis to Crassulacean acid metabolism (CAM) occurred. Fluctuation of titratable acidity and nocturnal CO2 uptake was induced in the stressed plants. Stressed Peperomia obtusifolia A. Dietr. plants showed a change from C3-photosynthesis to internal cycling of CO2. Acid fluctuation commenced in response to stress but exogenous CO2 uptake did not occur. Zygocactus truncatus Haworth plants showed a pattern of acid fluctuation and nocturnal CO2 uptake typical of CAM even when well irrigated. The cacti converted from CAM to an internal CO2 cycle similar to Peperomia when plants were water-stressed. Reverse phase gas exchange in succulents results in low water loss to carbon gain. Water is conserved and low levels of metabolic activity are maintained during drought periods by complete stomatal closure and continual fluctuation of organic acids. 2 Department of Biology, San Diego State University, San Diego, California 92182. 1 Supported in part by National Science Foundation Grant OIP 74-15673. This content is only available as a PDF. © 1978 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)

Shive, John B.; Brown, Kirk W.

doi: 10.1104/pp.61.3.331pmid: 16660286

Abstract Cottonwood (Populus deltoides, Marsh.) leaves are amphistomatous and have an adaptation in their petiole which allows them to oscillate in wind. A possible function of these oscillations in enhancing gas exchange was studied. Cottonwood leaves were found to oscillate in the presence of wind velocities frequently encountered in nature. A pressure differential across the leaf was shown to result in bulk flow of air through that leaf. Oscillating a cottonwood leaf at frequencies found to occur in nature was found to increase the rate of O2 flux through the leaf. The measured changes in boundary layer resistances during oscillations were found to be insufficient to account for the increased O2 flux. Thus, the bulk flow of air through an oscillating cottonwood leaf results in a decreased total resistance which is typically 25% less than that of a still leaf. 2 Present address: Department of Biology, Winthrop College, Rockhill, South Carolina 29733. 1 This work was supported by Grant DEB 75-04108 from the National Science Foundation to Texas A&M University Research Foundation. This content is only available as a PDF. © 1978 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)

Malek, Lada; Bewley, J. Derek

doi: 10.1104/pp.61.3.334pmid: 16660287

Abstract The response of the drought-tolerant moss Tortula ruralis ([Hedw.] Gaertn., Meyer, Scherb.) to freezing and thawing at controlled rates has been studied. Slow freezing (at 3 C per hour to −30 C) of hydrated T. ruralis leads to only temporary, reversible changes in metabolism. These changes can be considered to result from desiccation due to extracellular ice formation. In contrast, rapid freezing in liquid N2 and thawing in 20 C water leads to deterioration in all aspects of metabolism studied: ribosome, protein, and ATP levels decrease, and in vivo and in vitro protein synthetic activity is lost rapidly. Such changes probably result from intracellular ice formation. Following freezing and thawing at an intermediate rate (60 C per hour), only ATP levels and in vivo protein synthesis are reduced. The protein-synthesizing apparatus (the polyribosomes) remains intact and active in an in vitro protein-synthesizing system even 24 hours after one 60 C per hour freeze-thaw cycle. These metabolic responses are discussed in terms of the two-factor hypothesis of Mazur et al. (1972 Exp. Cell Res. 71: 345-355). 2 Present address: Institute of Agricultural Science, Tohoku University, Sendai, Japan. 3 Addressee for reprints. 1 Work supported by NRC of Canada Grants A6352 and E2550 and appropriations from the University of Calgary Grants Committee. Completed in partial fulfillment of the M.Sc. degree at the University of Calgary by L. M. This content is only available as a PDF. © 1978 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)

Huang, Anthony H. C.; Moreau, Robert A.; Liu, Kitty D. F.

doi: 10.1104/pp.61.3.339pmid: 16660288

Abstract The activity of a wax ester hydrolase in the cotyledons of jojoba (Simmondsia chinensis) seedlings increased drastically during germination, parallel to the development of the gluconeogenic process. The enzyme at its peak of development was obtained in association with the wax body membrane, and its properties were studied. It had an optimal activity at alkaline pH (8.5-9). The apparent Km value for N-methylindoxylmyristate was 93 μM. It was stable at 40 C for 30 min but was inactivated at higher temperature. Various divalent cations and ethylenediaminetetraacetate had little effect on the activity. p-Chloromercuribenzoate was a strong inhibitor of the enzyme activity, and its effect was reversed by subsequent addition of dithiothreitol. It had a broad substrate specificity with highest activities on monoglycerides, wax esters, and the native substrate (jojoba wax). 2 Recipient of a W. Gordon Belser graduate fellowship. 1 This work was supported by National Science Foundation Grant BMS 75-02320. This content is only available as a PDF. © 1978 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)

Brunold, Christian; Schmidt, Ahlert

doi: 10.1104/pp.61.3.342pmid: 16660289

Abstract When 0.5 mm cysteine is added to cultures of Lemna minor L. growing with sulfate as the sole sulfur source, there is a rapid 80% loss of extractable adenosine 5′-phosphosulfate sulfotransferase. This loss is accompanied by an inhibition of sulfate uptake; however, lack of sulfate is not responsible for the decreasing adenosine 5′-phosphosulfate sulfotransferase activity. Cultivation with cysteine causes an increase in the cyst(e)ine pool of L. minor. This fact taken together with the observed inactivation of adenosine 5′-phosphosulfate sulfotransferase in crude extracts by cysteine suggests that the cysteine pool is involved in the in vivo regulation of the enzyme. The activity of adenosine 5′-phosphosulfate sulfotransferase is restored within 24 hours after transfer to a culture medium without cysteine. This restoration is partially blocked by 6-methyl purine and actinomycin D and completely by cycloheximide. Cycloheximide added to cultures of L. minor L. causes a loss of extractable APSTase comparable to the one obtained with cysteine. This loss may be in part due to cysteine, since cycloheximide causes a pronounced increase in the cysteine pool of L. minor. 1 Supported by Grant 3.610-0.75 from the Swiss National Science Foundation to C. B. and by a grant from the Deutsche Forschungsgemeinschaft to A. S. This content is only available as a PDF. © 1978 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)