Acclimation of Photosynthate Partitioning and Photosynthetic Rates to Changes in Length of the Daily Photosynthetic Period

Pangola, soya bean and spinach plants were grown in long andshort day photosynthetic periods. Reciprocal shifts betweenlong and short day grown plants were made to study acclimationin the rate of leaf starch synthesis with change in daylength.The rate of leaf starch accumulation is a function of the lengthof the daily photosynthetic period. Acclimation, that is a changein partitioning with a change in length of the photosyntheticperiod, occurs in a variety of species. Acclimation in the rateof starch accumulation occurs rapidly in pangola and is apparentlycomplete the day after a change in length of the daily photosyntheticperiod. Soya bean and spinach leaves require a few days in thenew environment for an acclimation to occur. Digitaria decumbens Stent., Glycine max (L.) Merr., Spinacia oleracea L., pangola, soya bean, spinach, specific leaf weight, starch, photosynthesis     

Changes of Anatomical Features, Photosynthesis and Ribulose Bisphosphate Carboxylase-Oxygenase Content of Mango Leaves

Changes in anatomical and physiological features, includingchanges in amount per unit area of anthocyanin and chlorophyll,in leaves of seedling mango (Mangifera indica L. cv. Irwin)trees were determined to understand what controls the rate ofphotosynthesis (Pn) at various stages of development. The youngleaves of seedling trees contained high concentrations of anthocyanin.During enlargement of leaves, the disappearance of anthocyaninand the accumulation of chlorophyll occurred concomitantly;the anthocyanin content began to decrease markedly once theleaf area had reached a maximum. During the early period ofleaf development, the thickness of mesophyll tissue decreasedtemporarily, but when the length of the leaf reached half thatof a mature leaf, the mesophyll began to thicken again. Smallstarch grains appeared in the chloroplasts of the young leavesand chloroplast nucleoids (ct-nuclei) were distributed throughoutthe chloroplasts. When leaves matured, ct-nuclei were displacedto the periphery of chloroplasts because of the accumulationof large starch grains. Compared with young leaves, green andmature leaves contained greater concentrations of ribulose bisphosphatecarboxylase-oxygenase (RuBisCO) protein. The results of immunocytochemicalexamination of RuBisCO under the light microscope reflectedthe results of electrophoresis measurements of RuBisCO. Pn waslow during the chocolate-coloured stage of early leaf development.In green and mature leaves Pn was higher; the average Pn was7·6 mg CO₂ dm^-2 h^-1 under light at intensities above500 µmol m^-2 s^-1.Copyright 1995, 1999 Academic Press Mangifera indica L., mango leaf, chloroplast nucleoids, chloroplast ultrastructure, starch accumulation, anthocyanin, chlorophyll, DAPI staining, SDS-PAGE, immunocytochemical technique     

Variation in Net Photosynthesis, Rubisco Activity and Chloroplast Ultrastructure among Somatic Hybrids of Solanum tuberosum and S. brevidens

The effect of ploidy, parental chloroplast type and parentalnuclear genome dosage on net photosynthesis, Rubisco activityand chloroplast ultrastructure was studied among somatic hybridsof diploid S. brevidens and dihaploid S. tuberosum. An increasein nuclear ploidy resulted in an increase in net photosynthesisand specific leaf weight. There were no significant differencesin net photosynthesis or Rubisco activity between the hybridshaving different parental chloroplast type. Examination of thehexaploid hybrids indicated that Rubisco activity was affectedby nuclear-organelle genome incompatibility, the most affectedcombination being tuberosum chloroplast type with brevidensnuclear genome. Examination of chloroplast ultrastructure revealedwide variation in the size of chloroplasts, starch granules,plastoglobuli and in grana stacking among the hybrids and betweenfusion parents. Key words: Somatic hybrids, Solanum, net photosynthesis, Rubisco, chloroplast ultrastructure     

Intra-Leaf and Intracellular Gradients in Chloroplast Ultrastructure of Dorsiventral Leaves Illuminated from the Adaxial or Abaxial Side during their Development

The number of thylakoids per granum, which is smaller in sun-typechloroplasts than in shade-type chloroplasts, was counted forthe chloroplasts at various positions within the single leavesof Spinacia oleracea L. and Glycine max (L.) Merrill. The thylakoidnumber increased with depth from the adaxial surface, but thistrend was not evident within respective cells. Therefore, photosyntheticproperties of chloroplasts should be similar within a cell butdifferent among cell layers. The similarity within a cell maybe due to the nuclear control of the chloroplast developmentand/or to chloroplast movement along the cell walls. Illumination of the leaves of G. max from the abaxial side duringtheir expansion resulted in the complete inversion of the intra-leafgradient in the thylakoid number, indicating that the formationof the intra-leaf gradient in chloroplast properties is influencedby the intra-leaf light environment during the later phase ofleaf development. ¹presennt address: Department of Environmental Biology, ResearchSchool of Biological Sciences, Australian National University,P.O. Box 475, Canberra, A.C.T. 2601, Australia. (Received March 13, 1986; Accepted May 30, 1986)     

Photosynthesis, Photorespiration and Respiration of Chloroplasts From Acetabularia mediterrania

A chloroplast fraction isolated from Acetabularia mediterrania carries on photosynthesis at rates essentially equal to those of whole cells. Electron and phase contrast microscopy reveals that the chloroplasts are intact and well preserved. Preparations contain no identifiable peroxisomes, but some cytoplasmic and mitochondrial contamination is present. Photosynthesis and CO₂ production in light by chloroplast preparations are in many respects similar to that of bean leaves, although the measured rates are somewhat lower. Respiration and photosynthesis of chloroplast preparations and whole cells of Acetabularia is essentially similar except that cells have a strong dark-type respiration which continues in light and is CO₂ dependent, the substrate being mainly recent photosynthate. The data suggest that chloroplasts are the site of photorespiration.     

Cellular Levels of Ribulose 1,5 Bisphosphate Carboxylase and Chloroplast Compartment Size in Wheat Mesophyll Cells

Pyke, K. A. and Leech, R. M. 1987. Cellular levels of ribulose1,5 bisphosphate carboxylase and chloroplast compartment sizein wheat mesophyll cells.—J. exp. Bot. 38: 1949–1956. The amount of the photosynthetic enzyme ribulose 1,5 bisphosphatecarboxylase (RUBISCO),as determined in mesophyll cells in primarywheat leaves was related to the size of the chloroplast compartmentwithin the cell for wheat species of three ploidy levels. Asimilar comparison was made for several genotypes of the hexaploidbreadwheat Triticum aestivum. Estimation of total chloroplastvolume per mesophyll cell was made assuming chloroplasts tobe oblate spheroid in shape. A significant correlation was found between the amount of RUBISCOper cell and the total chloroplast volume per cell for diploid,tetraploid and hexaploid wheat species. A significant correlationbetween cellular RUBISCO level and total chloroplast volumeper cell was also observed for a range of genotypes of the hexaploidT. aestivum but these genotypes of T. aestivutn accumulate agreater amount of RUBISCO per unit chloroplast volume than doany other wheat species. For these genotypes of T. aestivumthe stromal concentration of RUBISCO was estimated at 0·5mol m^–3 with a ribulose Msphosphate binding site concentrationof 4·0 mol m^–3. These results are discussed with respect to a gene dosage hypothesisto explain the accumulation of RUBISCO in leaf mesophyll cells. Key words: Ribulose, bisphosphate carboxylase, wheat chloroplasts, mesophyll cells     

Regulatory aspects of chloroplast growth in leaves ofXanthium pensylvanicum and etiolated red kidney bean seedling leaves

Summary The average chloroplast size was studied as a function of leaf growth in leaves of cocklebur (Xanthium, pensylvanicum) and the primary leaves of 9-day old seedlings of red kidney bean (Phaseolus vulgaris).Diameters of chloroplasts were measured in crude tissue homogenates with the aid of a fluorescence microscope. Chlorophyll content of the leaves was determined spectrophotometrically in acetone extracts.For cocklebur, data are presented to show the relationship of average chloroplast diameter to morphological age of leaves (Leaf Plastochron Index) and are discussed in relation to the available leaf growth analyses. In bean, the increase in chloroplast diameter in response to illumination of etiolated leaves of various size was studied as a function of the duration of continuous illumination. The size of the etiolated bean leaves was varied experimentally by exposing the seedlings in darkness to low energy red light. Average diameter of the chloroplasts was found to be related to the size of leaf lamina.In both cocklebur and bean, a definite relationship of chloroplast size to leaf area and morphological age was established. The observed patterns of chloroplast size increase are interpreted to be a reflection of the integration of growth at three levels of organization: the leaf, its cells and the chloroplasts.This study was performed during the tenure of a U. S. Public Health Service postdoctoral fellowship by the senior author and was supported in part by research grant number GM-08145, from the National Institutes of Health, Public Health Service.Predoctoral fellow of the National Science Foundation.     

Microfilaments Anchor Chloroplasts along the Outer Periclinal Wall in Vallisneria Epidermal Cells through Cooperation of PFR and Photosynthesis

In the cytoplasmic layer that faces the outer periclinal wallin epidermal cells of leaves of the aquatic angiosperm Vallisneriagigantea Graebner, we examined a possible interrelationshipamong the configuration of microfilaments, chloroplast motility,and anchoring of chloroplasts. In dark-adapted cells, microfilamentsare arranged in a network array. During a 10-min incubationin darkness 10 to 20 min after irradiation with red light (650nm, 0.41 W m^–2) for 5 min, the number of cells containinga network array decreased substantially while the number ofcells containing microfilaments in a honeycomb array increased.Irradiation with red light rapidly produces an increase in chloroplastmotility, but chloroplast motility declined almost to initiallevels during the 10-min incubation in darkness after the irradiation.Simultaneously, the chloroplasts in these cells became extremelyresistant to centrifugal forces. These effects of red lightwere negated either by far-red light or by the presence of DCMU,and were sensitive to cytochalasin B. It appears, therefore,that microfilaments not only drive the movement of chloroplastsbut also play a crucial role in accumulation of the chloroplastsalong the outer periclinal wall through dynamic changes in theconfiguration under cooperative regulation by P_FR and photosynthesis. (Received July 24, 1998; Accepted September 22, 1998)     

Cell size and chloroplast size in relation to chloroplast replication in light-grown wheat leaves

As part of an investigation into the control of chloroplast replication the number and size of chloroplasts in mesophyll cells was examined in relation to the size of the cells. In first leaves of Triticum aestivum L. and T. monococcum L. the number of chloroplasts in fully expanded mesophyll cells is positively correlated with the plan area of the cells. The linear relationship between chloroplast number per cell and cell plan area is also consistent over a fivefold range of cell size in isogenic diploid and tetraploid T. monococcum. In T. aestivum the chloroplast number per unit cell plan area varies among cells in relation to the size of the chloroplasts. Those cells containing chloroplasts with a relatively small face area have a correspondingly higher density of chloroplasts, and consequently, the total chloroplast area per unit cell plan area is very similar in all the cells. The results indicate that the proportion of the cell surface area covered by chloroplasts is precisely regulated, and that this is achieved during cell development by growth and replication of the chloroplasts.     

A Quantitative Study of Daily Variation in the Cellular Ultrastructure of Palisade Chlorenchyma from Sunflower Leaves

Stereology was used to describe cytological changes which occurin palisade cells of fully expanded leaves as part of theirnormal daily activity. These changes were evaluated by describingthe relationship between organelle volume and cell volume asratio values (i.e. percentage volumes, V_v; surface-to-volume,S_v). These ratios describe an average cell in terms of its volumecommitment to each organelle compartment. Cells were also describedin terms of actual volume (µm³) or surface area (µm²)of membrane present in an average cell. ANOVA-LSD and Mann-Whitneystatistics indicate significant changes occur in the ratio valuesof the vacuole, chloroplast, oil, starch and microbody compartmentsover the 24 h period. This indicates a re-allocation of cellspace to these compartments during this period. The S_v ratioof internal membranes of the chloroplast and mitochondria showedno significant change over 24 h indicating that there is a constantrelationship between volume and membrane surface area in theseorganelles. Significant changes occurred in average cell volumeover 24 h with maximum volume during the dark period. Sincechanges in cell volume affected the actual volume expressionof all of the organelle compartments there were diurnal variationin the actual size of these compartments, including the internalmembranes of chloroplasts and mitochondria which more than doubledin surface area. Helianthus annuus L, sunflower, cytology, stereology, quantitative microscopy, diurnal, morphometrics, ultrastructure, chlorenchyma, chloroplast, mitochondria, microbodies     

Changes in the Non-Photochemical Quenching of Chlorophyll Fluorescence During Aging of Wheat Flag Leaves

Ultrastructural changes in chloroplasts of primary leaves of 15-d-old bean plants (Phaseolus vulgaris L. cv. Cheren Starozagorski) in response to a single stress (increasing water deficit, WD) as well as to combined stress (WD plus high temperature, WD+HT) were investigated under the possible protective or reparatory effects of the carbamide cytokinin 4-PU-30 [N-(2-chloro-4-pyridyl)-N-phenylurea] applied before or after the stress. Essential structural changes in chloroplast ultrastructure occurred mainly in plants that had experienced WD+HT: the thylakoids were swollen, the envelope was destroyed, and the spatial orientation of inner membrane system was not typical. Changed starch accumulation was also observed. 4-PU-30 protected chloroplast ultrastructure under WD+HT.     

Chloroplast Structure and Starch Grain Accumulation in Leaves That Received Different Red and Far-Red Levels during Development

An important step in understanding influence of growth environment on carbon metabolism in plants is to gain a better understanding of effects of light quality on the photosynthetic system. Electron microscopy was used to study chloroplast ultrastructure in developing and fully expanded leaves of tobacco (Nicotiana tabacum L. cv Burley 21). Brief exposures to red or far-red light at the end of each day during growth under controlled environments influenced granum size, granum number and starch grain accumulation in chloroplasts, and the concentration of sugars in leaf lamina. Far-red-treated leaves had chloroplasts with more but smaller grana than did red-treated leaves. Red light at the end of the photosynthetic period resulted in more and larger starch grains in the chloroplasts and a lower concentration of sugars in leaves. Chloroplast ultrastructure and starch grain accumulation patterns that were initiated in the expanding leaves were also evident in the fully expanded leaves that received the treatment during development. It appears that the phytochrome system in the developing leaves sensed the light environment and initiated events which influenced chloroplast development and partitioning of photosynthate to adapt the plant for better survival under those environmental conditions.     

RNA Synthesis in Phaseolus Chloroplasts: II. RIBONUCLEIC ACID SYNTHESIS IN CHLOROPLASTS FROM DEVELOPING AND SENESCING LEAVES

The rate of RNA synthesis in chloroplasts from the primary leavesof Phaseolus vulgaris L. cv. Canadian Wonder was measured invitro as plant age increased. The rate per leaf began to fallbefore the leaf was 70% expanded. At full expansion, activityhad fallen by 70%. Chloroplast RNA synthesis per unit chlorophyllwas falling before the leaf was 25% expanded. When all parts of the plant above the mature primary leaveswere removed (detopping) chloroplast RNA synthesis in theseleaves rose within 36 h. The rate increased to a maximum 3–4d after detopping, when it was 5–10 times control values;thereafter it fell again. The chlorophyll content began to increaseabout 4 d after detopping, eventually rising by 100%. Detoppingcaused a 3-fold increase in the Triton X-100-soluble DNA contentof chloroplast preparations, measured after 3.5 d. At that timethe rate of RNA synthesis per unit Triton-soluble DNA was thesame in chloroplasts from the primary leaves of intact and detoppedplants. Detopping also resulted in an increase in the depthof the leaf palisade layer. The effects of detopping on chloroplasts were prevented by darknessand reduced by shading. Increased chloroplast RNA polymerase activity was also inducedin the primary leaves by placing a polythene bag over intactplants, enclosing everything above these leaves. Removal ofthe roots from detopped plants prevented the rise in the rateof chloroplast RNA synthesis.     

Phototactic Chloroplast Displacement in the Photosynthetic Mutant, Lemna paucicostata Strain 1073

The photosynthetic mutant, strain 1073, of Lemna paucicostataTorr. (L. perpusilla Hegelm.) which has a block in the electrontransport chain between plastoquinone and cytochrome f is capableof light-induced chloroplast displacement movements. At 8000–14000 lx, chloroplasts of the mutant move from their positionadjacent to the inner periclinal wall of the mesophyll cellsto the anticlinal walls, i.e. along those walls parallel tothe direction of the light. Light does not appear to enhancerespiration of the photosynthetic mutant or of the wild typestrain (6746). These and other results support the idea thatchloroplast displacement in light is not solely the result oflight effects on photosynthesis and respiration. Lemna paucicostata Torr., photosynthetic mutant, phototaxis, chloroplast displacement     

Benzyladenine-Induced Increase in DNA Content per Cell, Chloroplast Size, and Chloroplast Number per Cell in Intact Bean Leaves

Primary leaves of intact bean plants (Phaseolus vulgaris L.)were treated with benzyladenine (BA) at different stages oftheir growth. BA induced a marked increase in DNA content percell in growing leaves where no cell division occurred. BA stimulatedthe chloroplast replication compared with untreated leaves.After the replication period, chloroplast size continued toincrease in BA- treated leaves, but not in untreated controls.     

The role of Pi recycling processes during photosynthesis in phosphate-deficient bean plants

Bean plants (Phaseolus vulgaris L. cv. Zlota Saxa) were grownon complete (control plants) and phosphate-deficient (low-Pplants) culture solutions for 17 d. Phosphate deficiency markedlyreduced leaf growth, but only slightly decreased the photosynthesisrate. The intensity of reactions releasing inorganic ortho-phosphateduring photosynthesis was examined. In the leaves of low-P plantsthe pools of photorespiratory metabolites (glycolate and glycine+serine)were markedly increased. At the same time synthesis of solublesugars from intermediates of glycolic acid cycle was probablyenhanced. In low-P leaves the phosphoenolpyruvate carboxylaseactivity and malate synthesis were increased. Phosphoenolpyruvateand malate were effectively used for amino acid synthesis. Bothaspartate and alanine accumulation was twice higher in low-Pleaves. It was found that no enhancement in starch and sucrosesynthesis rate takes place in phosphate deficient bean leaves.Modifications of photosynthetic metabolism observed under moderatephosphate deficiency facilitate plants acclimation to low-Pconditions by enhancement of P₁ recirculation during glycolicand phosphoenolpyruvate metabolism. Key words: Phosphate deficiency, photosynthesis, photorespiration, phosphoenolpyruvate carboxylase     

A Vertical Gradient of the Chloroplast Abundance among Leaves of Chenopodium album

The abundances of chloroplasts in leaves on the main stems ofChenopodium album at different height levels were investigatedin relation to the photosynthetic capacity and light environmentof the leaves. (1) The number of chloroplasts per mesophyllcell decreased with descending position of leaves, except foryoung developing leaves at the top of plants that had smallerchloroplast numbers per cell than matured leaves beneath them.Contents of chlorophyll and ribulose-1,5-bisphosphate carboxylase/oxygenaseper leaf area that were highest in the topmost young leavesand decreased with decreasing height level indicate that thereis a vertical gradient of chloroplast abundance per leaf areadecreasing from the top of the leaf canopy with depth. (2) Light-saturatingrate of photosynthetic oxygen evolution per leaf area of maturedleaves decreased more steeply with decreasing leaf positionthan the chloroplast number per cell. Gradients of chlorophylland the enzyme protein contents were also steeper than thatof the chloroplast number. Loss of photosynthesis in lower leavesis, therefore, ascribed partly to loss of whole chloroplastsand partly to reduced photosynthetic capacities of the remainingchloroplasts. (3) The chloroplast number per cell in newly expandedsecond leaves was comparable to those in leaves that have developedat later stages of the plant growth but decreased graduallyduring leaf senescence both in the dark and light. The formationof the vertical gradient of chloroplast abundance is, therefore,ascribed to loss of whole chloroplasts during senescence ofleaves. (4) Irradiance a leaf receives decreased sharply fromthe top of the canopy with depth. The physiological or ecophysiologicalsignificance of the vertical distribution of chloroplasts amongleaves was discussed taking light environments of leaves intoconsideration. (Received July 31, 1995; Accepted October 20, 1995)     

Characterisation of Non-Uniform Photosynthesis Induced by Abscisic Acid in Leaves Having Different Mesophyll Anatomies

The effects of abscisic acid (ABA) on photosynthesis in leavesof Helianthus annuus L. were compared with those in leaves ofVicia faba L. After the ABA treatment, the response of photosyntheticCO₂ assimilation rate, A, to calculated intercellular partialpressure of CO₂, P_i, (A(p_i) relationship) was markedly depressedin H. annuus. A less marked depression was also observed inV.faba. However, when the abaxial epidermes were removed fromthese leaves, neither the maximum rate nor the CO₂ responseof photosynthetic oxygen evolution was affected by the applicationof ABA. Starch-iodine tests revealed that photosynthesis was not uniformover the leaves of H. annuus treated with ABA. The starch contentwas diffferent in each bundle sheath extension compartment (thesmallest subdivision of mesophyll by veins with bundle sheathextensions, having an area of ca. 0.25 mm² and ca. 50 stomata).In some compartments, no starch was detected. The distributionof open stomata, examined using the silicone rubber impressiontechniques, was similar to the pattern of starch accumulation.In V.faba leaves, which lack bundle sheath extensions, distributionof starch was more homogeneous. These results indicate that the apparent non-stomatal inhibitionof photosynthesis by ABA deduced from the depression of A(pⁱ)relationship is an artifact which can be attributed to the non-uniformdistribution of transpiration and photosynthesis over the leaf.Intercellular gaseous environment in the ABA-treated leavesis discussed in relation to mesophyll anatomy. ¹ Present address: Department of Botany, Duke University, Durham,NC 27706, U.S.A. (Received September 30, 1987; Accepted January 13, 1988)     

Control of starch granule numbers in Arabidopsis chloroplasts

The aim of this work was to investigate starch granule numbers in Arabidopsis (Arabidopsis thaliana) leaves. Lack of quantitative information on the extent of genetic, temporal, developmental, and environmental variation in granule numbers is an important limitation in understanding control of starch degradation and the mechanism of granule initiation. Two methods were developed for reliable estimation of numbers of granules per chloroplast. First, direct measurements were made on large series of consecutive sections of mesophyll tissue obtained by focused ion beam-scanning electron microscopy. Second, average numbers were calculated from the starch contents of leaves and chloroplasts and estimates of granule mass based on granule dimensions. Examination of wild-type plants and accumulation and regulation of chloroplast (arc) mutants with few, large chloroplasts provided the following new insights. There is wide variation in chloroplast volumes in cells of wild-type leaves. Granule numbers per chloroplast are correlated with chloroplast volume, i.e. large chloroplasts have more granules than small chloroplasts. Mature leaves of wild-type plants and arc mutants have approximately the same number of granules per unit volume of stroma, regardless of the size and number of chloroplasts per cell. Granule numbers per unit volume of stroma are also relatively constant in immature leaves but are greater than in mature leaves. Granule initiation occurs as chloroplasts divide in immature leaves, but relatively little initiation occurs in mature leaves. Changes in leaf starch content over the diurnal cycle are largely brought about by changes in the volume of a fixed number of granules.