摘要:

Proton-ATPases are among the most important primary ion pumps in nature. There are three classes of these enzymes which are distinguished by their structure, function, mechanism of action, and evolution. They function in ATP formation at the expense of a protonmotive force generated by oxidative and photosynthetic electron transports, maintaining a constant pH in the cytoplasm, and forming acidic spaces in special compartments inside and outside the cell. The three classes of proton-ATPases evolved in a way that prevents functional assembly in the wrong compartment. This was achieved by a triple genetic system located in the nucleus, mitochondria and chloroplast, as well as delicate control of the proton pumping activity of the enzymes.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

The effect of ethylene on the growth rate of pollen tubes in styles ofPetunia hybridawas examined. Apart from its strong inhibition of pollination-induced ethylene synthesis, aminoethoxyvinylglycine, placed on the stigma, did not impede tube growth. The inhibitors of the action of ethylene, silver thiosulfate and 2,5-norbornadiene, were similarly ineffective. Application of the ethylene precursor, 1-amino-cyclopropane-1-carboxylic acid, onto the stigma at different intervals prior to pollination evoked synthesis of ethylene, but was without effect on tube growth. However, prepollination (by 24 hours) withNicotiana tabacumpollen, significantly enhanced tube growth ofPetuniapollen. This enhancement was not counteracted by the pretreatment of stigmas with aminoethoxy-vinylglycine. It is concluded that the ethylene associated with pollination is without effect on pollen tube growth in the style, but that other pollination-induced factors may lead to an acceleration of growth.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

Leaves of the tomatoghostmutant show a variegated green/white phenotype due to a somatically unstable genetic block in carotenoid biosynthesis. Colored carotenoids are not synthesized in white leaves; consequently, chlorophyll is destroyed by photooxidation and the plastids formed show little development of internal membrane structures. Carotenoid biosynthesis proceeds to wild type levels in green tissue, thus chlorophyll accumulates and chloroplasts develop normally. The presence of green sectors allows for the production through tissue culture of variegated green/white plants, in which growth is supported by the photosynthetic green tissue. Thus,ghostis the first plant carotenoid mutant that can be grown to maturity. We determined the steady state mRNA levels for two nuclear gene families that code for chloroplast proteins:rbcS, which codes for the small subunit of ribulose-1-5-bisphosphate carboxylase; andcab, which codes for chlorophylla/bbinding protein. Inghostplants grown in light, the steady state mRNA levels for both gene families were low in white leaves but were similar to wild type in green leaves. Light regulation of the transcripts studied was observed in bothghostgreen and white leaves. Transcription experiments conducted on nuclei isolated from green and white leaves indicate that the low levels of cytoplasmic mRNAs observed in the absence of colored carotenoids and/or light are due to reduced rates of transcription. We conclude that maximum transcription ofrbcSandcabgenes in leaves of mature tomato plants requires both light and mature chloroplasts.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

Acetyl-coenzyme A (CoA) carboxylase from maize (Zea maysL.) is inhibited by nanomolar concentrations of both haloxyfop, an aryloxyphenoxypropionate, and tralkoxydim, a cyclohexanedione herbicide. These results suggest that acetyl-CoA carboxylase, which catalyzes the first committed step in fatty acid biosynthesis, may be the target of these herbicides, contrary to an earlier report suggesting that aryloxyphenoxypropionate herbicides do not inhibit acetyl-CoA carboxylase.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

The yields of ethylene from endogenous and exogenous 1-aminocyclo-propane-1-carboxylic acid (ACC) in avocado (Persea AmericanaMill.) fruit pedicel extracts were very low when assayed by the method of Lizada and Yang (1979 Anal Biochem 100: 140-145). Addition of phenolic compounds, which are present in avocado tissues, to the assay mixture significantly reduced the conversion efficiency of ACC to ethylene. A negative correlation was found between the amount of the plant material in the assay mixture and the conversion efficiency of ACC to ethylene. Removal of phenolic compounds from pedicel extracts by polyvinylpolypyrrolidone, Amberlite XAD-7, and Dowex-50 column chromatography or lead acetate precipitation greatly increased the yields of thylene from ACC in these extracts. The use of polyvinylpolypyrrolidone column chromatography also enabled us to obtain more accurate estimations of endogenous ACC levels in carnation (Dianthus caryophyllusL.) petal extracts. The conversion efficiency of ACC to ethylene could be improved by increasing the concentrations of mercuric chloride and NaOCl in the assay mixture.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

Hydrogen-1 nuclear magnetic resonance spectroscopy was used to study water allocation in cell compartments of sun and shade leaves. NMR spectra ofAcer platanoideswere resolved into two peaks that were assigned to chloroplast and nonchloroplast water. Sun leaves contained 1.7 times more water per unit area of surface than shade leaves, and the water was allocated differently. Chloroplasts in sun leaves contained 17% of the total leaf waterversus47% in shade leaves. Comparing equal leaf surface areas, the chloroplasts in shade leaves contained 60% more water than those in sun leaves.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

Mungbean (Phaseolus aureusRoxb.) seedlings were grown hypobarically to assess the effects of low pressure (21-24 kilopascals) on growth and mitochondrial respiration. Control seedlings grown at ambient pressure (101 kilopascals) were provided amounts of O2equivalent to those provided experimental seedlings at reduced pressure to factor out responses to O2concentration and to total pressure. Respiration was assayed using washed mitochondria, and was found to respond only to O2concentration. Regardless of total pressure, seedlings grown at 2 millimoles O2per liter had higher state 3 respiration rates and decreased percentages of alternative respiration compared to ambient (8.4 millimoles O2per liter) controls. In contrast, seedling growth responded to total pressure but not to O2concentration. Seedlings were significantly larger when grown under low pressure. While low O2(2 millimoles O2per liter) diminished growth at ambient pressure, growth at low pressure in the same oxygen concentration was enhanced. Respiratory development and growth of mungbean seedlings under low pressure is unimpaired whether oxygen or air is used as the chamber gas, and further, low pressure can improve growth under conditions of poor aeration.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

Acetolactate synthase (EC4.1.3.18) activity was examined in maize (Zea maysL.) endosperm and embryos as a function of kernel development. When assayed using unpurified homogenates, embryo acetolactate synthase activity appeared less sensitive to inhibition by leucine + valine and by the imidazolinone herbicide imazapyr than endosperm acetolactate synthase activity. Evidence is presented to show that pyruvate decarboxylase contributes to apparent acetolactate synthase activity in crude embryo extracts and a modification of the acetolactate synthase assay is proposed to correct for the presence of pyruvate decarboxylase in unpurified plant homogenates. Endosperm acetolactate synthase activity increased rapidly during early kernel development, reaching a maximum of 3 micromoles acetoin per hour per endosperm at 25 days after pollination. In contrast, embryo activity was low in young kernels and steadily increased throughout development to a maximum activity of 0.24 micromole per hour per embryo by 45 days after pollination. The sensitivity of both endosperm and embryo acetolactate synthase activities to feedback inhibition by leucine + valine did not change during kernel development. The results are compared to those found for other enzymes of nitrogen metabolism and discussed with respect to the potential roles of the embryo and endosperm in providing amino acids for storage protein synthesis.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

Experiments were conducted with field-grown cotton(Gossypium hirsutumL.) in 1985 and 1986 to determine effects of water deficit on levels of conjugated indole 3-acetic acid (IAA) and abscisic acid (ABA) in young fruits (bolls) and their abscission zones in relation to boll retention. Tissues were harvested three times during an irrigation cycle in 1985. They were harvested twice during an irrigation cycle and once after irrigation in 1986 to determine extent of recoveries of measured parameters. As reported earlier, the free IAA content of abscission zones decreased with moisture stress. Irrigation caused a partial recovery in free IAA content of abscission zones and caused a partial recovery in rate of boll retention. In contrast to free IAA, conjugated IAA increased with water deficit, both in 3-day-old bolls and in their abscission zones. Bolls contained much more ester IAA than their abscission zones. Some, but not all, of the increase in ester IAA in bolls during moisture stress could have come from a conversion of amide-linked IAA. Amide IAA decreased slightly during stress and increased after irrigation, but the concentration was low relative to ester IAA. Free and conjugated ABA both increased during stress and decreased after irrigation. However, the concentration of conjugated ABA remained relatively high in abscission zones. Ester IAA, being more resistant than free IAA to enzymic destruction during stress, may hasten recovery of fruit retention after relief of stress by providing a source of free IAA in abscission zones to inhibit continued abscission.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB

摘要:

The ratio of carbon accumulation to transpiration,W, of wheat (Triticum aestivumL.) seedlings increased with increasing soil strength, measured as soil penetrometer resistance, and this was already apparent at the two leaf stage. The ratio was negatively correlated with carbon isotope discrimination, in accord with theory. This means that decrease in intercellular partial pressure of CO2accounted for an important part of the increase inWwith increasing soil strength. Despite a lower CO2concentration in the leaves at high soil strength, assimilation rate per unit leaf area was enhanced. Greater ribulose 1,5-bisphosphate carboxylase activity confirmed that photosynthetic capacity was actually increased. This pattern of opposite variation of assimilation rate and of stomatal conductance is unusual. The ratio of plant carbon mass to leaf area increased markedly with increasing soil strength, mainly because of a greater investment of carbon into roots than into shoots. A strong negative correlation was found between this ratio and carbon isotope discrimination. For a given increase in discrimination, decrease in carbon mass per leaf area was proportionally larger than decrease in assimilation rate, so that relative growth rate was positively correlated to carbon isotope discrimination.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1988

数据来源: ASPB