Plant Physiology

Skokut, Thomas A.; Manchester, Jill; Schaefer, Jacob

doi: 10.1104/pp.79.3.579pmid: 16664455

Abstract The production of somatic embryos in alfalfa (Medicago sativa L., cv Regen S) is increased 5- to 10-fold by alanine and proline. However, utilization of nitrogen for synthesis of protein from alanine, proline, glutamate, and glycine is not qualitatively different, even though the latter two amino acids do not increase somatic embryo formation. These determinations were made by 15N labeling with detection by nuclear magnetic resonance. Overall metabolism of the nitrogen of proline, alanine, glutamate, and glycine is also similar in two regenerating and nonregenerating genotypes with similar germplasm, except that the levels of free amino acids are consistently higher in the nonregenerating line. In addition, when regeneration is suppressed in either of the two regenerating lines, the level of intracellular free amino acids increases. This increased level of metabolites is the only direct evidence provided by analysis of nitrogen metabolism of differences between the regenerating and nonregenerating states in alfalfa. This content is only available as a PDF. © 1985 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)

Schaefer, Jacob

doi: 10.1104/pp.79.3.584pmid: 16664456

Abstract The composition of phosphorus-containing compounds of intact lyophilized alfalfa tissue has been determined, in part, by solid-state 31P nuclear magnetic resonance. The tissue (Medicago sativa L., cv Regen S; and some of its crosses) was grown in culture under both nonregenerating and regenerating conditions, the latter enhanced by the addition of specific amino acids. Analysis of the 31P nuclear magnetic resonance spectra shows that regeneration is favored when metabolism occurs without the production of a low average intracellular pH. This content is only available as a PDF. © 1985 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)

Stitt, Mark; Herzog, Bernd; Heldt, Hans W.

doi: 10.1104/pp.79.3.590pmid: 16664457

Abstract How fructose 2,6-bisphosphate and metabolic intermediates interact to regulate the activity of the cytosolic fructose 1,6-bisphosphatase in vitro has been investigated. Mg2+ is required as an activator. There is a wide pH optimum, especially at high Mg2+. The substrate dependence is not markedly pH dependent. High concentrations of Mg2+ and fructose 1,6-bisphosphate are inhibitory, especially at higher pH. Fructose 2,6-bisphosphate inhibits over a wide range of pH values. It acts by lowering the maximal activity and lowering the affinity for fructose 1,6-bisphosphate, for which sigmoidal saturation kinetics are induced, but the Mg2+ dependence is not markedly altered. On its own, adenosine monophosphate inhibits competitively to Mg2+ and noncompetitively to fructose 1,6-bisphosphate. In the presence of fructose 2,6-bisphosphate, adenosine monophosphate inhibits in a fructose 1,6-bisphosphate-dependent manner. In the presence of adenosine monophosphate, fructose 2,6-bisphosphate inhibits in Mg2+-dependent manner. Fructose 6-phosphate and phosphate both inhibit competitively to fructose 1,6-bisphosphate. Fructose 2,6-bisphosphate does not affect the inhibition by phosphate, but weakens inhibition by fructose 6-phosphate. Dihydroxyacetone phosphate and hydroxypyruvate inhibit noncompetitively to fructose 1,6-bisphosphate and to Mg2+, but both act as activators in the presence of fructose 2,6-bisphosphate by decreasing the S0.5 for fructose 1,6-bisphosphate. A model is proposed to account for the interaction between these effectors. 1 Supported by the Deutsche Forschungsgemeinschaft. This content is only available as a PDF. © 1985 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)

Stitt, Mark; Heldt, Hans W.

doi: 10.1104/pp.79.3.599pmid: 16664458

Abstract In this article, we propose a model describing how the spinach leaf cytosolic fructose 1,6-bisphosphatase is regulated in vivo by an interaction between fructose 2,6-bisphosphate and metabolic intermediates during photosynthesis. Previously published results are reanalyzed to provide a description of the way in which fluxes and metabolites vary in spinach leaves, depending on the relation between the supply of photosynthate and the demand for sucrose. The activity of the spinach leaf cytosolic fructose 1,6-bisphosphatase has been assayed in conditions simulating those expected in leaves as the rate of sucrose synthesis increases in response to rising rates of photosynthesis, and as sucrose synthesis declines in response to accumulation of sucrose in the leaf so that more starch is synthesized. The results show that regulation of the cytosolic fructose 1,6-bisphosphatase by alterations of fructose 2,6-bisphosphate, dihydroxyacetone phosphate, adenosine monophosphate, and phosphate can account for the alterations of flux found in vivo. The properties of a regulatory network, which allows the distribution of triose P between the Calvin cycle, sucrose synthesis, and starch synthesis to be balanced and adjusted, are described. 1 Supported by the Deutsche Forschungsgemeinschaft. This content is only available as a PDF. © 1985 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)

Hunt, E. Raymond; Weber, James A.; Gates, David M.

doi: 10.1104/pp.79.3.609pmid: 16664459

Abstract Physiological effects of different nitrate applications were studied using the C4 plant, Amaranthus powellii Wats. Plants were grown in a controlled environment chamber and watered daily with nutrient solutions containing 45, 10, 5, or 1 millimolar nitrate. Chloride and sulfate were used to keep the cation and phosphate concentrations constant. Total leaf nitrogen concentration, chlorophyll concentration, specific leaf mass, leaf area, relative growth rate, relative leaf growth rate, unit leaf rate (increase of dry mass per unit leaf area per day), net photosynthetic rate, and incident quantum yield decreased with decreasing nitrate concentration. The per cent decrease of unit leaf rate was similar to the decrease of light-saturated net photosynthetic rate; however, the decrease in relative growth rate was less than that of unit leaf rate because leaf area ratio (leaf area per unit dry mass) increased with decreasing nitrate concentration. Essential mineral concentrations per unit leaf area were about equal among all treatments. Leaf expansion, determined by stomatal density, decreased except for the 1 millimolar treatment which showed relatively more cell expansion but less cell division. Decreased nitrate application was correlated with higher osmotic potentials and lower pressure potentials (determined by pressure-volume curves), whereas leaf water potentials were equal among treatments. Even though total leaf area and shoot mass decreased with decreasing applied nitrate, the increase of the leaf area ratio may be related to selection for the highest possible growth rate. 2 Present address: Laboratory of Biomedical and Environmental Sciences, UCLA, 900 Veteran Ave., Los Angeles, CA 90024. 1 Funded in part by Department of Energy contract DE-AC02-76EV02164. This content is only available as a PDF. © 1985 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)

Hunt, E. Raymond; Weber, James A.; Gates, David M.

doi: 10.1104/pp.79.3.614pmid: 16664460

Abstract The hypothesis of optimal stomatal conductance predicts conductance should vary with changes of the vapor pressure difference between leaf and air (VPD) to keep the partial derivative of transpiration rate (E) with respect to assimilation rate (A) constant (∂E/∂A = λ). Stomatal conductance of Amaranthus powellii Wats. decreased strongly with increasing VPD for leaves with high total leaf nitrogen concentrations; whereas, it decreased slightly with increasing VPD for leaves with low leaf nitrogen concentrations. The calculated value of ∂E/∂A was constant for leaves with high leaf nitrogen concentrations but was not constant for leaves with low leaf nitrogen concentrations. However, the predicted values of stomatal conductance, transpiration rate, and assimilation rate for a constant λ = 220 moles H2O/mole CO2 and the measured values fit the y = x line for all nitrate treatments. These data extend the experimental support for the optimal water use efficiency hypothesis for a C4 plant grown under different nitrate concentrations. 2 Present address: Laboratory of Biomedical and Environmental Sciences, UCLA, 900 Veteran Ave., Los Angeles, CA 90024. 1 Funded in part by Department of Energy contract DE-AC02-76EV02164. This content is only available as a PDF. © 1985 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)

Hunt, E. Raymond; Weber, James A.; Gates, David M.

doi: 10.1104/pp.79.3.619pmid: 16664461

Abstract Optimal allocation of leaf nitrogen maximizes daily CO2 assimilation for a given leaf nitrogen concentration. According to the hypothesis of optimization, this condition occurs when the partial derivative of assimilation rate with respect to leaf nitrogen concentration is constant. This hypothesis predicts a linear increase of assimilation rate with leaf nitrogen concentration under constant conditions. Plants of Amaranthus powellii Wats. were grown at 1, 5, 10, or 45 millimolar nitrate to obtain leaves with different nitrogen concentrations. Assimilation rate at 340 microbar CO2/bar, stomatal conductance, CO2- and light-saturated net photosynthetic rate, the initial slope of the CO2 response of photosynthesis, ribulose-1,5′-bisphosphate carboxylase activity, and phosphoenolpyruvate carboxylase activity were linearly related to estimated or actual leaf nitrogen concentration. The data are consistent with the optimal use of leaf nitrogen. This hypothesis and the hypothesis of optimal stomatal conductance were combined to determine the relationship between conductance and leaf nitrogen concentration. The slope of conductance versus leaf nitrogen concentration was not significantly different than the slope predicted by the combination of the two hypotheses. Stomatal conductance was linearly related to leaf nitrogen in the field and the slope decreased with lower xylem pressure potentials in a manner consistent with the hypotheses. Finally, apparent maximum stomatal aperture of isolated abaxial epidermal strips was linearly related to leaf nitrogen suggesting stomatal conductance and assimilation rate are controlled in parallel by leaf nitrogen concentration or some factor correlated with leaf nitrogen. 2 Present Address: Laboratory of Biomedical and Environmental Sciences, UCLA, 900 Veteran Ave., Los Angeles CA 90024. 1 Funded in part by Department of Energy Contract DE AC02-76EV02164. This content is only available as a PDF. © 1985 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)

Lecharny, Alain; Schwall, Michael; Wagner, Edgar

doi: 10.1104/pp.79.3.625pmid: 16664462

Abstract Low temperature pulses have two effects on the circadian rhythm exhibited by stem extension rate of green Chenopodium rubrum plants. First, low temperature pulses have the same effect on the phasing of the rhythm as a dark period interrupting continuous light. Second, low temperature pulses stimulate stem extension rate during the 10 hours immediately following the end of the pulse. A difference in temperature between soil and air increases this effect. In any case, it is the change in temperature which is essential and not a specific temperature. Effects of light and temperature on phasing and amplitude of the rhythm explain why the maximal stem growth is observed under normal photo-thermoperiodic conditions, i.e. a high temperature during the photoperiod and a low temperature during the dark period. 1 Supported by Deutsche Forschungsgemeinschaft (grant Wa 263/15-1). A grant from the Alexander-von-Humboldt Stiftung to A. L. is gratefully acknowledged. This content is only available as a PDF. © 1985 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)

Beggs, Christopher J.; Stolzer-Jehle, Andrea; Wellmann, Eckard

doi: 10.1104/pp.79.3.630pmid: 16664463

Abstract Induction of the isoflavonoid pigment, coumestrol (3,9-dihydroxy-6H-benzofuro-[3,2-c][1] benzopyran-6-one), in primary leaves of beans (Phaseolus vulgaris L. var Saxa) by ultraviolet (UV) radiation was used as a quantifiable marker for UV damage to a plant system. Coumestrol was induced only by wavelengths below 300 nanometers and its formation could be reversed by treatment with white, but not red light after the UV irradiation period. Formation of coumestrol by UV could also be prevented over a period of 14 hours by simultaneous irradiation with blue light provided that the blue fluence rate was high enough. The results suggest that coumestrol formation is mediated via UV-induced pyrimidine dimer formation in the plant DNA and the photorepair properties of blue light are discussed with respect to possible increases in solar UV due to stratospheric ozone depletion. 1 Supported by the Bundesministerium für Forschung und Technologie (grant KBF 55). This content is only available as a PDF. © 1985 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)

Apelbaum, Akiva; Goldlust, Arie; Icekson, Isaac

doi: 10.1104/pp.79.3.635pmid: 16664464

Abstract Activity of arginine decarboxylase in etiolated pea seedlings appears 24 hours after seed imbibition, reaches its highest level on the 4th day, and levels off until the 7th day. This activity was found in the apical and subapical tissue of the roots and shoots where intensive DNA synthesis occurs. Exposure of the seedlings to ethylene greatly reduced the specific activity of this enzyme. The inhibition was observed within 30 min of the hormone application, and maximal effect—90% inhibition—after 18 hours. Ethylene at physiological concentrations affected the enzyme activity; 50% inhibitory rate was recorded at 0.12 microliters per liter ethylene and maximal response at 1.2 microliters per liter. Ethylene provoked a 5-fold increase in the Kmapp of arginine decarboxylase for its substrate and reduced the Vmaxapp by 10-fold. However, the enzyme recovered from the inhibition and regained control activity 7 hours after transferral of the seedlings to ethylene-free atmosphere. Reducing the endogenous level of ethylene in the tissue by hypobaric pressure, or by exposure to light, as well as interfering with ethylene action by treatment with silver thiosulfate or 2,5-norbornadiene, caused a gradual increase in the specific activity of arginine decarboxylase in the apical tissue of the etiolated seedlings. On the basis of these findings, the possible control of arginine decarboxylase activity by endogenous ethylene, and its implication for the hormone effect on plant growth, are discussed. 1 Supported by the United States-Israel Binational Agricultural Research and Development Fund (BARD) grant I-221-80. This paper is contribution 1362-E, 1985 series, from the Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel. This content is only available as a PDF. © 1985 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)