Changes in the non-structural carbohydrate content of cotton (Gossypium spp.) fibres at different stages of development

The neutral sugars (glucose, fructose, and sucrose) and the sugar phosphates (glucose 6-phosphate, glucose 1-phosphate and fructose 6-phosphate) soluble in hot aqueous 80% methanol from the fibres of cotton — Gossypium arboreum L., G. barbadense L., and G. hirsutum L. — were determined at various stages of fibre development. In addition, the (13)--D-glucan content was measured and in the case of G. arboreum the rate of (13)--D-glucan and cellulose synthesis was determined with [¹⁴C]sucrose as the precursor. For each of the species a similar chronology was obtained for the changes in content of the various non-structural carbohydrates. At the early stages of secondary wall formation, glucose and fructose exhibited a maximum which was closely followed by a maximum in the (13)--D-glucan content and in the sugar phosphates. On the other hand, the sucrose content increased regularly until fibre maturity. The rates of synthesis of (13)--D-glucan and of cellulose were highest following the maximum in the (13)--D-glucan content, when the latter was being depleted.Abbreviations DMSO dimethyl-sulphoxide - DPA days post anthesis - UDP-glucose uridinediphosphoglucose     

Molecular mapping of a new gene Rrs4 CI 11549 for resistance to barley scald (Rhynchosporium secalis)

Doubled haploid (DH) progeny from a cross between the scald susceptible barley (Hordeum vulgare L.) cultivar Ingrid and the resistant accession CI 11549 (Nigrinudum) was evaluated for resistance in the pathogen Rhynchosporium secalis (Oudem) J.J. Davis. Two linked and incompletely dominant loci confer resistance CI 11549 against isolate 4004. One is an allele at the complex Rrs1 locus on chromosome 3H close to the centromere; the other is located 22 cM distally on the long arm. The latter locus is designated Rrs4. In BC₃-lines into Ingrid from CI 2222 (another Nigrinudum) resistance seems governed by one locus close to the telomeric region of chromosome 7H, probably allelic to Rrs2. In neither case did we find any trace of the recessive gene rh8 reported to be present in Nigrinudum. Various resistance donors of Ethiopian origin designated as Nigrinudum, Jet or Abyssinian were identical to a great extent with respect to markers, but differed in resistance to different isolates of scald or in barley yellow dwarf virus (BYDV) resistance. The implications for their use as differentials in scald tests and screening of germplasm collections are discussed.     

Sugar Uptake and Utilisation during Adventitious Bud Differentiation on in Vitro Leaf Explants of ‘Wegierka Zwykła’ Plum (Prunus Domestica)

Leaf explants of plum Wegierka Zwyka were cultured on modified MS medium supplemented with 7.5 µM TDZ (thidiazuron) and 0.9 µM 2,4-D (2,4-dichlorophenoxyacetic acid), with the addition of either sucrose or glucose at a concentration of 2%, 3%, 4%, 5% or 6% (w/v). Regeneration was carried out in two steps: the first in darkness, the second in photoperiod conditions after subculture onto fresh medium. The study assessed the influence of the kind of sugar used and its concentration in the medium on organogenesis efficiency, and on sugar uptake from the medium. The results suggest that sucrose is a better carbon source than glucose for organogenesis of Wegierka Zwyka, even though at lower concentrations the efficiency of the sugars was comparable. With increasing concentration of sugars, the efficiency of organogenesis decreased, a relation more evident for media with glucose. In the first (dark) step of regeneration, the explants utilised less carbohydrates from the media than in the second step, when the main increase of explant weight took place. In the second phase, at 2–5% concentrations glucose uptake was higher than sucrose uptake.     

Mitochondria in fine afferent nerve fibres of the knee joint in the cat: a quantitative electron-microscopical examination

The distribution of mitochondria, their content and concentration (expressed as the ratio of the mean volume of mitochondria and the surface of the sensory axon) were determined in group-III and-IV nerve fibres innervating the knee joint capsule in the cat. Mitochondria mainly accumulated in axonal swellings (beads) and end bulbs of the terminal branches. Between single nerve fibres, marked differences in the content and the concentration of mitochondria were obtained in proximal portions (inside of the perineurium) and in distal portions (unmyelinated sensory endings). In group-III nerve fibres, the mitochondrial concentration ranged from 0.005 to 0.030 m³/m² (proximal portion) and from 0.016 to 0.080 m³/m² (distal portion). In unmyelinated group-IV nerve fibres, the values also showed a broad variation ranging from 0.001 to 0.011 m³/m² (proximal portion) and from 0.003 to 0.019 m³/m² (distal portion). The wide range of mitochondrial concentrations may reflect different energy consumption during receptive processes: nerve fibres with a low mechanical threshold and a high probability of excitatory events may be rich in mitochondria, whereas fibres with a high mechanical threshold and a low probability of excitatory events may be poor in mitochondria.     

Nuclear Overhauser effect investigation on GM1 ganglioside containingN-glycolyl-neuraminic acid (II3Neu5GcGgOse4Cer)

The conformational properties of the oligosaccharide chain of GM1 ganglioside containingN-glycolyl-neuraminic acid, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer, were studied through NMR nuclear Overhauser effect investigations on the monomeric ganglioside in dimethylsulfoxide, and on mixed micelles of ganglioside and dodecylphosphocholine in water. Several interresidual contacts for the trisaccharide core--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-were found to fix the relative orientitation of the three saccharides, while the glycosidic linkage of the terminal -Gal-was found to be quite mobile as the -Gal-(1-3)--GalNAc-disaccharide exists in different conformations. These results are similar to those found for two GM1 gangliosides containingN-acetyl-neuraminic acid and neuraminic acid [1].Abbreviations Ganglioside nomenclature is in accordance with Svennerholm [23] and the IUPAC-IUB Recommendations [24] GM3(Neu5Ac) II³Neu5AcLacCer, -Neu5Ac-(2-3)--Gal-(1-4)--Glc-(1-1)-Cer - GM3(Neu5Gc) II³Neu5GcLacCer, -Neu5Gc-(2-3)--Gal-(1-4)--Glc-(1-1)-Cer - GM1(Neu5Ac) II³Neu5AcGgOse₄Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - GM1(Neu5Gc) II³Neu5GcGgOse₄Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - GM1(Neu) II³NeuGgOse₄Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu-(2-3)]--Glc-(1-1)-Cer - GD1a IV³Neu5AcII³Neu5AcGgOse₄Cer, -Neu5Ac-(2-3)--Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - GalNAc-GD1a IV⁴GalNAcIV³Neu5AcII³Neu5AcGgOse₄Cer, -GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - Neu neuraminic acid - Neu5Ac N-acetyl-neuraminic acid - Neu5Gc N-glycolyl-neuraminic acid - Cer ceramide     

Primary structure of the marmoset (Saguinus fuscicollis) hemoglobin. I. Use of tryptic maleylated peptides in the solubilization and sequence elucidation of the α- and β-chains

The primary structure of adult marmoset hemoglobin has been determined. The - and -chains of HbA were separated on a CM23 column in 8 M urea using a sodium phosphate gradient. Tryptic digests of the - and -chains were fractionated on a Dowex 50W-X2 column using a pH and pyridine acetate gradient. Large peptide fragments were obtained by the cyanogen bromide cleavage of the - and -chains, as well as by tryptic digestion of the maleylated - and -chains. The sequence was derived from the amino acid compositions and sequences of the individual tryptic peptide, automated sequence determination of intact - and -chains, as well as automated sequence determination of cyanogen bromide fragments and tryptic maleylated peptides derived from the - and -chains. The complete structure of marmoset adult hemoglobin is closely homologous to that of other primate hemoglobins. The sequence of the marmoset -chain differs from the -chain of human HbA at positions 8, 19, 23, 68, and 116. The -chain from marmoset HbA differs from the -chain of human HbA at positions 5, 13, 21, 50, 87, and 125.This work was supported in part by funds from a Physicians' Medical Education and Research Foundation Grant of the University of Tennessee Memorial Research Hospital and by NIH General Research Support Grant FR-5541 to the institution.     

Evolution of a protein superfamily: Relationships between vertebrate lens crystallins and microorganism dormancy proteins

Summary A search of sequence databases shows that spherulin 3a, an encystment-specific protein ofPhysarum polycephalum, is probably structurally related to the - and -crystallins, vertebrate ocular lens proteins, and to Protein S, a sporulation-specific protein ofMyxococcus xanthus. The - and -crystallins have two similar domains thought to have arisen by two successive gene duplication and fusion events. Molecular modeling confirms that spherulin 3a has all the characteristics required to adopt the tertiary structure of a single -crystallin domain. The structure of spherulin 3a thus illustrates an earlier stage in the evolution of this protein superfamily. The relationship of - and -crystallins to spherulin 3a and Protein S suggests that the lens proteins were derived from an ancestor with a role in stressresponse, perhaps a response to osmotic stress.     

Myosatellite cells associated with different muscle fibre types in the Atlantic hagfish (Myxine glutinosa,L.)

Summary The incidence of myosatellite cells associated with white and red muscle fibres of the parietal muscle and red fibres of the craniovelar muscle was estimated by quantitative electron microscopy in the Atlantic hagfish (Myxine glutinosa, L.). Myosatellite cell nuclei constitute 3, 11 and 23 % of the total number of nuclei inside the basal lamina of the three types of muscle fibres, respectively. However, the total number of nuclei is highest in white fibres, most of the nuclei belonging to striated muscle cells. Myosatellite cell profiles in transverse sections constitute 23, 41 and 61 % of the number of muscle fibre profiles of the three types, respectively. The intervals between adjacent myosatellite cells are 135 m in white fibres, 55 m in red parietal fibres, and only 25 m in craniovelar fibres. Since craniovelar fibres are also comparatively thin, myosatellite cells constitute a significant fraction of the volume inside the basal lamina in these fibres. The myosatellite cells are 30–50 m long and up to 5 m thick. Some myosatellite cells possess few organelles, whereas others appear to contain many free ribosomes, granular endoplasmic reticulum, prominent Golgi apparatus and lysosome-like bodies.This investigation was supported by the Norwegian Research Council for Science and the Humanities (NAVF grant No. C20.30–37). The authors are indebted to Jorunn Line Vaaland and Berit Branil for technical assistance, and to Dr. Finn Walvig, Biological Station, University of Oslo, Drøbak, for supplying the hagfish     

Different effects of inorganic and triethyl lead on growth and ultrastructure of lily pollen tubes

Summary Pollen tubes ofLilium longiflorum growingin vitro were treated for 1 h with inorganic lead (Pb) and with triethyl lead (TriEL) and studied by light and electron microscopy. Pb was considerably more toxic in relation to inhibition of pollen tube growth (EC₅₀=6 M Pb) than was TriEL (EC₅₀=60 M TriEL). On the other hand, at almost the entire concentration range tested (25-500 M) TriEL caused aberrant tubes and tube swellings. Pb did not cause tube swellings, even at highly growth-impairing concentrations. Pb (60 M) predominantly affected the ultrastructure of the growing cell walls without impairing the distribution of the cell organelles in the tube tips. In contrast, 50 and 100 M TriEL did not visibly influence cell wall ultrastructure but it severely damaged dictyosomes; 100 M TriEL also disturbed the original order of cell organelles in the tube tips. Cortical microtubules were selectively and completely destructed by TriEL at concentrations (50 M) where no effect on polar organization of the tube tips occurred but they remained unimpaired by 60 M Pb, indicating selective and effective interaction of TriEL with these cell organelles.Abbreviations EC⁵⁰ effective lead concentration causing 50% inhibition of pollen tube growth - MTs microtubules - Pb inorganic lead - TriAL trialkyl lead - TriEL triethyl lead     

In vitro propagation of Rauwolfia micrantha, a rare medicinal plant

Shoot tip and single node explants from young shoots of 1-year old flowering plants of Rauwolfia micrantha Hook. f. were cultured on Murashige & Skoog (MS) medium variously supplemented with 6-benzyladenine (BA) and -naphthaleneacetic acid (NAA). A combination of 13.2 M BA and 2.68 M NAA induced high frequency (77%) formation of up to 3 shoots from each node in 8 weeks. The regeneration of shoot tips from the field-grown plants and in vitro shoots placed horizontally differed. Repeated subculturing of the shoot tips and single nodes at 6-week intervals for over a year in combination of 4.4 M BA and 0.27 M NAA enabled mass multiplication of shoots without any evidence of decline. Rooting of the excised shoots on medium containing 2.6 M NAA was preceded by callus formation. The rooted plants were removed off the callus, hardened off and 80% established in pots. Micropropagated plants displayed uniform morphological, growth, flowering, fruiting and seed germination characteristics.Abbreviations BA 6-benzyladenie - IAA indole-3-acetic acid - IBA indole-3-butyrie acid - 2-ip 2-isopentenyladenine - MS Murashige & Skoog (1962) - NAA -naphthaleneacetic acid     

The innervation of the myometrium of the cynomolgus monkey (Macaca fascicularis)

Summary The autonomic innervation of the myometrium of Macaca fascicularis consists of bundles of unmyelinated nerve fibres running between the smooth muscle cells, and is therefore considered to be of the fascicular (= unitary) type. Close contacts between nerve fibres and smooth muscle fibres were not found. Modification of the chromaffin method according to Tranzer and Richards made it possible to visualize the heterogeneity of the nerve fibres in a single bundle. The following fibre types were found to coexist: (1) noradrenergic fibres containing synaptic vesicles with a dense granule, (2) cholinergic fibres containing empty synaptic vesicles, and (3) non-adrenergic noncholinergic (NANC) fibres containing only or predominantly large dense-cored vesicles, which do not react with this method. Noradrenergic fibres are the most numerous (around 60%), followed by NANC fibres (30%) and cholinergic elements (around 10%). The distribution of these three types is similar in the cervix, the isthmus and the body of the uterus in pregnant and non-pregnant females.     

Hexagonally ordered “rosettes” of particles in the plasma membrane ofMicrasterias denticulata Bréb. and their significance for microfibril formation and orientation

Summary Cells ofMicrasterias denticulata Bréb. at the stage of secondary wall formation have been studied by freeze-etching. It was found that the plasma membrane exhibits oval areas in which arrays of membrane particles occur. These particles form rosettes which are arranged in a hexagonally ordered lattice with a center to center spacing of 25 nm. Nearly the same periodicities can be found between microfibrils. It is concluded that the rosettes probably together with the thickened area of the plasma membrane below them represent the apparatus for the production and orientation of microfibrils. The hypothesis suggesting the incorporation of membrane templates functional in microfibril formation, originally advanced byKiermayer andDobberstein (1973) has received further support.     

Induction,polarity and spatial control of cytokinesis in some abnormal subsidiary cell mother cells ofZea mays

Summary Cytokinesis in the subsidiary cell mother cells (SMCs) ofZea mays leaves grown in the presence of 5 mM of caffeine solution is usually partially inhibited. A continuous wall strip, resembling a portion of the subsidiary cell (SC) wall, is laid down in the preprophase microtubule band (PMB) cortical zone. Sometimes, the incomplete SC (SC) wall grows centripetally in the absence of a phragmoplast and the gap becomes smaller or closes. The SC nucleus escapes through the SC wall gap into the larger SMC compartment and may fuse with the other nucleus.The aberrant SMCs (a-SMCs) pass through another division cycle, reattempting to produce a SC. A typical PMB is found in the SC space, in the site of the previous PMB. Moreover, in some preprophase SMCs, the cytoplasm adjacent to the SC wall is traversed by a small number of microtubules. The preprophase nuclei are partly or totally separated from the PMB by the perforated SC wall and may lie far from the latter.Usually, one mitotic spindle is assembled. The cycling paired polarized nuclei appear to synchronize and their chromosomes line up together on a single metaphase plate. Although the mitotic spindle axis is diversely oriented, one of its poles tends to be stabilized in the proximity of the SC wall gap. These divisions separate abnormal cells. Most or all the cell plate edges fuse with wall regions far from the PMB cortical zone. However, when some of them approach the SC wall strips, they are attracted and intersect their rims. In rare occasions the cell plate, invading the SC space is guided by the PMB cortical zone to create a SC-like curved wall portion, in absence of a daughter nucleus.Observations show that the cell plate arrangement in redividing aberrant SMCs is not subjected to a strict spatial control. The disorder of polarization sequence generated by the SC wall ring and especially the perturbation of the spatial (and functional?) relationship between PMB-PMB cortical zone and the nucleus—mitotic spindle is a causal factor of the variable cell plate arrangements.     

Vitreous state in vitro culture: ethylene versus cytokinin

The occurrence of a developmental anomaly i in vitro culture, named vitreous plant, has been shown to be a deficiency in lignification. Several causes have been proposed, most recently the physical state of the culture medium and ethylene. Experiments, conducted to verify these suggestions, led toresults that did not confirm either the physical state or ethylene as causal agents. It rather appeared that cytokinins did induce the anomaly, probably by excessively promoting cell-divisions at the expense of cell-differentiation.     

Hormonal regulation of gene expression in the “slender” mutant of barley (Hordeum vulgare L.)

The slender mutant of barley resembles a normal barley plant treated with high doses of gibberellic acid (GA₃). Expression of GA₃-regulated and abscisic acid (ABA)-regulated mRNAs was studied in the endosperm and roots of mutant and wild-type (WT) plants.Production of -amylase (EC 3.2.1.1) by WT embryoless half-grains was dependent on the presence of GA₃, and was prevented by ABA. In contrast, -amylase was produced by half-grains of the slender mutant in the absence of added GA₃, although it was still reduced by ABA. The spectrum of -amylase mRNAs in slender embryoless half-grains incubated in the absence of added GA₃ was the same as in WT endosperm half-grains incubated in the presence of GA₃. These results indicate that the endosperm of the slender mutant exhibits similar properties to WT endosperm treated with GA₃.In roots the expression of an ABA-inducible mRNA was similar in slender and WT seedlings either treated with exogenous ABA or exposed to dehydration. This result, and the effect of ABA on -amylase production by the endosperm, indicate that the slender plants retain sensitivity to ABA.Abbreviations ABA abscisic acid - AMV avian myeloblastosis virus - GA gibberellin - GA₁ gibberellin A₁ - GA₃ gibberellic acid - WT wild-type     

In vitro growth reduction of tomato and carnation microplants

Shoots which proliferated from shoot tip explants of Colorado White Simm carnation and Fantastic tomato on MS medium containing 5 mgl^-1 benzyladenine were rooted and grown in vitro as microplants. Tomato microplants grown in medium with 5 gl^-1 sucrose had less overall shoot and root growth than those with 10,20, or 30 gl^-1 sucrose regardless of NAA level. Carnation shoot growth was reduced by 5 g l^-1 sucrose but root growth was not affected except when no sucrose was supplied. Microplant height and rooting of carnation were maximal when grown in 20 gl^-1 sucrose whereas tomato microplant growth was greatest with 30 gl^-1 sucrose. Microplants of both species had reduced height and root growth when the MS nutrient salts were lowered to 25%, 50%, or 75% compared to full strength when sucrose was supplied at 5 gl^-1.     

Glycerol-, inositol-, and reducing end hexose-containing oligosaccharides in human urine

Ten previously unreported oligosaccharides have been purified from the urines of human subjects using a combination of gel filtration, ion exchange, and thin-layer chromatographies. Their structures were determined by direct probe mass spectrometry, methylation analysis, and proton NMR spectroscopy of the permethylated oligosaccharide alditols.On the basis of composition, the oligosaccharides could be divided into three groups. Five oligosaccharides containing glycerol were characterized as glucosyl1-1glycerol; glucosyl1-1glycerol; galactosyl1-1glycerol; glucosyl-1-1(fucosyl-1-2)glycerol and/or fucosyl-1-1(glucosyl-1-2)glycerol; and glucosyl-1-1(galactosyl-1-2)glycerol or galactosyl-1-1(glucosyl-1-2)glycerol. Four inositol-containing oligosaccharides were characterized as galactosyl1 (fucosyl1)inositol,N-acetylgalactosaminyl1 (fucosyl1)inositol, fucosyl1-2galactosyl1 (N-acetylgalactosaminyl1)inositol and fucosyl1-2galactosyl1-4-N-acetylglucosaminyl1(N-acetylgalactosaminyl1)inositol. Finally, galactosyl1-3(fucosyl1-2)galactosyl1-6galactosyl1-4(fucosyl1-3)glucose, an oligosaccharide with glucose at its reducing end, was tentatively identified. The significance and possible origins of the carbohydrate structures are discussed.     

Expression of a chimeric stilbene synthase gene in transgenic wheat lines

A chimeric stilbene synthase (sts)gene was transferred into wheat. Stilbene synthases play a role in the defence against fungal diseases in some plant species (e.g. groundnut or grapevine) by producing stilbenetype phytoalexins like resveratrol. Resveratrol is also claimed to have positive effects to human health. Embryogenic scutellar calli derived from immature embryos of the two commercial German spring wheat cultivars Combi and Hanno were used as target tissue for cotransformation by microprojectile delivery. The selectable marker/reporter gene constructs contained the bargene either driven by the ubiquitinpromoter from maize (pAHC 25, also containing the uidAgene driven by the ubiquitinpromoter), or by the actinpromoter (pDM 302) from rice. The cotransferred plasmid pStil 2 consisted of a grapevine stscoding region driven by the ubiquitin promoter. Eight transgenic Combi and one Hanno T_Oplant were obtained and, except one Combi T_Oplant, found to be cotransformants due to the integration of both the stsgene and the selectable marker or reporter genes. Expression of the stsgene was proven by RTPCR, and, for the first time, by detection of the stilbene synthase product resveratrol by HPLC and mass spectrometry. The stsgene was expressed in four of the seven transgenic Combi T_{_o}plants. Two of the respective T₁progenies segregated in a Mendelian manner were still expressing the gene. Investigations into methylation of the stsgene showed that in three nonexpressing progenies inactivation was paralleled by methylation.     

High irradiance response promotion of a subsequent light induction response in Sinapis alba L.

Relative quantum responsivity curves for inhibition of hypocotyl elongation in Sinapis alba L. seedlings previously grown in white light confirm that a marked end of day inhibition response can be induced by a monochromatic light treatment (30 min) at the end of the light period. In dark grown seedlings, however, no growth inhibition can be induced by a 30 min monochromatic light treatment. A prerequisite for an induction response appears to be a pretreatment with continuous light. Far red light is most effective with blue and red light showing a lesser effectiveness. The light pretreatment also shows a marked fluence rate dependency with respect to its ability to allow an induction response to manifest itself. The pretreatment required shows all the characteristics of a classical HIR response. The appearance of the effect in plants treated with the herbicide SAN 9789 seems to exclude chlorophyll as being the photoreceptor.Abbreviations SAN 9789 4-chloro-5-(methylamino)-2-(, , -trifluoro-m-tolyl)-3(2H)-pyridazinone - RG9 light long wavelength far red light (Schott RG9 colour glass) - FR far red light - WL white light - BL blue light - RL red light - D darkness - P_tot total phytochrome - P_fr far red absorbing form of phytochrome - HSR high irradiance response     

Temperature-sensitive coupling and uncoupling of ATPase-mediated,nonradiative energy dissipation: Similarities between chloroplasts and leaves

The effects of temperature on the dark relaxation kinetics of nonradiative energy dissipation in photosystem II were compared in lettuce (Lactuca sativa L.) chloroplasts and leaves of Aegialitis annulata R. Br. After high levels of violaxanthin de-epoxidation in the light, Aegialitis leaves showed a marked delay in the dark relaxation of nonradiative dissipation, measured as non-photochemical quenching (NPQ) of photosystem II chlorophyll a fluorescence. Aegialitis leaves also maintained a moderately high adenylate energy charge at low temperatures during and after high-light exposure, presumably because of their limited carbon-fixation capacity. Similarly, dark-sustained NPQ could be induced in lettuce chloroplasts after de-epoxidizing violaxanthin and light-activating the ATP synthase. The duration and extent of dark-sustained NPQ were strongly enhanced by low temperatures in both chloroplasts and leaves. Further, the NPQ sustained at low temperatures was rapidly reversed upon warming. In lettuce chloroplasts, low temperatures sharply decreased the ATP-hydrolysis rate while increasing the duration and extent of the resultant trans-thylakoid proton gradient that elicits the NPQ. This was consistent with a higher degree of energy-coupling, presumably due to reduced proton diffusion through the thylakoid membrane at the lower temperatures. The chloroplast adenylate pool was in equilibrium with the adenylate kinase and therefore both ATP and ADP contributed to reverse coupling. The low-temperature-enhanced NPQ quenched the yields of the dark level (F_o) and the maximal (F_m) fluorescence proportionally in both chloroplasts and leaves. The extent of NPQ in the dark was inversely related to the efficiency of photosystem II, and very similar linear relationships were obtained over a wide temperature range in both chloroplasts and leaves. Likewise, the dark-sustained absorbance changes, caused by violaxanthin de-epoxidation (A_508nm) and energy-dependent light scattering (A_536nm) were strikingly similar in chloroplasts and leaves. Therefore, we conclude that the dark-sustained, low-temperature-stimulated NPQ in chloroplasts and leaves is apparently directly dependent on lumen acidification and chloroplastic ATP hydrolysis. In leaves, the ATP required for sustained NPQ is evidently provided by oxidative phosphorylation in the mitochondria. The functional significance of this quenching process and implications for measurements of photo-protection versus photodamage in leaves are discussed.Abbreviations and Symbols A antheraxanthin - Chl chlorophyll - DPS de-epoxidation state of the xanthophyll cycle, ([Z+A]/[V+A+Z]) - F, F steady-state fluorescence in the absence, presence of thylakoid energization - F_o, F_o dark fluorescence level in the absence, presence of thylakoid energization - F_m, F_m maximal fluorescence in absence, presence of thylakoid energization - NPQ nonphotochemical quenching (F_m/F_m)–1 - V violaxanthin - Z zeaxanthin - NRD nonradiative dissipation - PFD photon flux density - [2ATP+ADP] - pH trans-thylakoid proton gradient - S pH-dependent light scattering - _PSII (F_m–F)/F_m, photon yield of PSII photochemistry at the actual reduction state in the light or dark - [ATP+ADP+AMP] We thank Connie Shih for skillful assistance in growing plants and for conducting HPLC analyses. Support from an NSF/USDA/DOE postdoctoral training grant to A.G. is gratefully acknowledged. A.G. also wishes to thank Prof. Govindjee for valuable discussions. C.I.W.-D.P.B. Publication No. 1197.