Carbon Partitioning in Mature Leaves of Pepper: Effects of Daylength

Grange, R. 1. 1985. Carbon partitioning in mature leaves ofpepper: effects of daylength.—J. exp. Bot. 36: 1749–1759. The partitioning of recently fixed carbon has been examinedin mature pepper leaves grown in 6, 10 or 14 h photoperiodsat different irradiances chosen to give similar radiation integralsand in a 6 h photoperiod at the lowest of these irradiances.The partitioning of carbon into export, starch, sugars and respirationwas followed over the photopenod and the subsequent night ina mature leaf. The maximum export rate during the day (approximately 18 µgC cm^–2 leaf h^–1) was not significantly differentamong the treatments. Net photosynthesis rate was directly relatedto irradiance; the proportion of net photosynthesis exportedduring the day was 33% in 6-h days and 57% in 14-h days. Leafstarch accumulation (as a proportion of net photosynthesis rate)increased slightly when plants were grown in 6-h days. The remobilization of starch and sugars at night allowed exportrates to remain similar over 24 h when plants were grown in10-h or 14-h photoperiods. Leaves grown in 6-h days showed nosignificant changes in export rate during the first few hoursof night but exhausted their starch reserves during the nightand export rates declined. Sucrose and hexose levels decreased at the onset of darkness,but did not fall below 40 µg cm^–2 in plants grownin 10-h or 14-h photoperiods; when this level was reached after3–4 h of darkness, starch breakdown began. In leaves grownin both 6-h treatments, sucrose levels fell below 40 µgcm^–2 when starch reserves were depleted during the nightand the export rate decreased concurrently. The results are discussed in relation to the control of exportand starch metabolism in the leaf. Key words: Pepper, partitioning, daylength     

The Extent of Starch Turnover in Mature Pepper Leaves in the Light

The extent of starch turnover in pepper leaves in the lighthas been estimated. After leaves were labelled with ¹⁴CO₂ atconstant specific activity for 4–7 h, the irradiance wasreduced to a level which caused no net change in the starchcontent of the leaf, and the supply of ¹⁴CO₂ was removed. Therewas no significant change in specific activity of starch overthe following 6–10 h, thus there was no exchange of ¹⁴C-starchwith ¹²C-assimilates entering the chloroplasts. Starch, turnover, ¹⁴C-labelling, pepper, Capsicum annuum L.     

Carbon Partitioning and Export in Mature Leaves of Pepper (Capsicum annuum)

The partitioning of recently fixed carbon by mature pepper leaveshas been examined over a 10 h photoperiod using a constant specificradioactivity ¹⁴CO₂ labelling technique. Changes in the ratesof carbon partitioning into export, starch, sucrose and hexoseswere examined following changes in irradiance during the photoperiod.Leaves grown under 80 W m^–2 PAR were exposed to this irradiancefor the first 4 h of the photoperiod then the iiradiance wasdecreased. Leaves accumulated sufficient reserves in the first4 h to maintain export at the initial rate (approximately 20µg carbon cm^–2 leaf h^–1) over the following6 h of the photoperiod when the net photosynthesis rate (Pn)was decreased to 10% of the initial rate by the decreased irradiance.Export was initially maintained by the depletion of sucroseand hexose and then by carbon from the degradation of starchin the light. If leaves were exposed to low irradiance at the beginning ofthe photoperiod, then the export rate was linearly related tothe Pn during that period. When Pn exceeded that required tomaintain an export rate of approximately 20 µg carboncm^–2 h^–1, then more carbon was partitioned intostarch. At low initial irradiance, a greater proportion of photosynthatewas partitioned into export rather than starch and at high initialirradiancc the reverse occurred. There was a linear relationship between starch accumulationrate and Pn for all leaves but the relationship between Pn andexport rate was only significant for leaves with low levelsof reserve carbon. The results show that mature pepper leaves subjected to differentirradiances maintain constant export rates through alterationsof carbon partitioning. Export at low Pn is maintained at theexpense of sugar and starch reserves, with partitioning in highirradiance being predominantly to starch. Key words: Carbon partitioning, Starch, Export, Pepper (Capsicum annuum L.)     

The Relationship between Sucrose and Starch during 'Dark' Export from Leaves of Uniculm Barley

Uniculm barley plants were grown in 8 h photoperiods at a quantumflux density of 655 µE m^–2 s^–1. Groups ofplants were transferred to four different light environmentsfor one 8 h photoperiod (106, 270, 665, and 975 µE m^–2s^–1) and harvested at intervals throughout the succeedingdark period for subsequent carbohydrate analysis of the youngestmature leaf. Sucrose was the predominant carbohydrate in the leaves (attaininga level of c. 100 mg dm^–2 after 8 h at 975 µE m^–2s^–1) but starch was also of significance (20 mg dm^–2after 8 h at 975 µE m^–2 s^–1). During the dark period, following a photoperiod at the threehighest light levels (270, 665, and 975 µE m^–2 s^–1),sucrose was exported first while the starch level remained fairlyconstant. When the-sucrose level fell to 15–20 mg dm^–2starch degradation began. This critical sucrose level was reachedearlier in those plants subjected to lower quantum flux densitiesduring the preceding photoperiod. The delay in the remobilizationof starch suggests an important regulatory mechanism which maybe dependent upon the sucrose level. At 106 µE m^–2s^–1 the sucrose level rose to only 10 mg dm^–2. Herethere was no discernible delay in the depletion of sucrose orstarch.     

The Effect of Shade During Leaf Expansion on Photosynthesis by White Clover Leaves

In three experiments measurements of photosynthesis were madeon single leaves of white clover (Trifolium repens L.) on threecultivars grown in a controlled environment. Plants which had grown under an irradiance of 30 J m^–2s^–1, or in shade within a simulated mixed sward, producedleaves with photosynthetic capacities some 30 per cent lowerthan did plants grown at 120 J m^–2 s^–1 without shade.There were no differences between treatments either in photosynthesismeasured at 30 J m^–2 s^–1, or in respiration ratesper unit leaf dry weight. Respiration per unit leaf area washigher in the plants grown at 120 J m^–2 s^–1, reflectingthe lower specific leaf area of these leaves. There were nodifferences between the three cultivars examined. Leaves which were removed from the shade of a simulated swardshortly after becoming half expanded achieved photosyntheticcapacities as high as those which were in full light throughouttheir development. It is suggested that it is this characteristicwhich enables clover plants growing in an increasingly densemixed sward to produce a succession of leaves of high photosyntheticcapacity, even though each lamina only reaches the top of thesward at a relatively late stage in its development. Trifolium repens L., white clover, photosynthesis, leaf expansion, shade, specific leaf area, stomatal conductance     

Growth Analysis of Sweet Pepper (Capsicum annuum L.): 2. Interacting Effects of Irradiance, Temperature and Plant Age in Controlled Conditions

A growth analysis was carried out with sweet pepper plants grownin a phytotron. Irradiance conditions were: 0.84 or 3.25 MJm^–2 in 8 h, 1.67 MJ m^–2 in 16 h and 2.51 MJ m^–2in 24 h. Temperatures applied were 25 or 21 °C during thephotoperiod in combination with 25, 21 and 17 or 21, 17 and13 °C respectively during the nyctoperiod. Highest values for leaf area and total dry weight were foundwhen applying 1.67 MJ m^–2 in 16 h, followed by 3.25 MJm^–2 in 8 h, irrespective of the temperature regime. Continuousirradiance ultimately resulted in leaf drop. A reduction inthe day temperature decreased leaf area and total dry weight.At a day temperature of 25 °C the dry weight increased withdecreasing night temperature when applying 3.25 MJ m^–2in 8 h. At a day temperature of 21 °C leaf area and dryweight were reduced when 17 or 13 °C were applied duringa 16 h nyctoperiod. Values for relative growth rate, net assimilation rate, leafarea ratio and leaf weight ratio strongly decreased with advancingplant age. The effects of irradiance treatment on RGR and NARwere analogous to those on total dry weight while the reversepattern was observed for the LAR. A decrease in day temperaturedecreased the RGR. The effects of night temperature exhibitedstrong interactions with day temperature and photoperiod. Theinfluence of temperature on RGR was largely mediated throughchanges in the LAR. The latter parameter was highly correlatedwith the specific leaf weight. Capsicum annuum L., sweet pepper, growth analysis, irradiance, temperature, plant age     

Effects of Nitrogen Fertilizer on Growth and Yield of Spring Wheat

Nine amounts of nitrogen fertilizer, ranging from 0 to 200 kgN ha^–1, were applied to spring wheat cv. Kleiber in the3 years 1972-1974. In 1972 grain dry weight with 125 kg N ha^–1or more was 100 g m^–2 (23 per cent) greater than withoutnitrogen. Grain yield was unaffected by nitrogen in the otheryears. Leaf area at and after anthesis was increased throughoutthe range of nitrogen tested, most in 1972 and least in 1973.Consequently, the addition of 200 kg N ha^–1 decreasedthe amount of grain produced per unit of leaf area by approximately25 per cent in all years. The dry weight of leaves and stems at anthesis and maturitywas increased by nitrogen in all years, similarly to leaf area.However, the change in stem dry weight between anthesis andmaturity was not affected by nitrogen; stems increased in dryweight for about 20 days after anthesis and then decreased tovalues similar to those at anthesis. The uptake of CO₂ per unit area of flag leaf or second leaf(leaf below the flag leaf) was slightly decreased by nitrogenwhen the increase in leaf area caused by nitrogen appreciablydecreased the light intensity at the surface of these leaves.In spite of such decreases the CO₂ absorbed by flag and secondleaves per unit area of land was always increased by nitrogen,and relatively more than was grain yield. It is suggested that increases in respiratory loss of CO₂ withincreasing nitrogen fertilizer may explain why nitrogen increasedvegetative growth and leaf area relatively more than grain yield.     

The Fate of the Dry Matter, Carbohydrates and 14C Lost from the Leaves and Stems of Wheat during Grain Filling

In a field study with six winter wheat genotypes losses of drymatter from the stems between 30 June and maturity averaged172 g m^–2 (range 82–236), there being significantdifferences in loss between genotypes. Respiration from thestems during the same period was estimated to amount to 106g m^–2 (range 104–225). The amount of dry mattermobilized from the stems, calculated by difference, was estimatedas 66 g m^–2. The loss of ethanol- and water-soluble carbohydratefrom the stems (170 g m^–2; range 124–215) was verysimilar to the dry weight loss. Carbon-14 labelling was used to trace the time course and theamount of the movement of assimilates from the vegetative organsto the grain. Only 14•3 per cent (range 10•3–21•0)of the products of photosynthesis over the period 21 May-20June were relocated to the grains. This relocation amountedto an average of 7 per cent (range 5•7–11•4)of the final grain weight. It was estimated that during the18 days following anthesis on 20 June photosynthesis contributed48 per cent (range 39–55) of the final grain dry weight.Of this, about half was translocated to the grain within 10days of initial assimilation. The remainder appeared to be storedtemporarily in the stems and leaves and translocated to thegrains during the period 17–29 July. In general, relocationof dry matter from the vegetative organs to the grains, assessedby carbon-14 labelling, was greatest in those genotypes (Hobbitand Sportsman) which lost most dry weight from the stems andleaves.     

The Water Relations of Young Olive Trees in a Mediterranean Winter: Measurements of Evaporation from Leaves and Water Conduction in Wood

We report measurements of evaporation rate, leaf resistanceto evaporation and water conduction in the stems of young olivetrees (Olea europea L.) growing in Messina, Italy, during thewinter and early spring. We have measured what Zimmermann calls‘leaf specific conductivity’ (LSC) of stem segmentsexcised from olive trees. The LSC is a measure of the specifichydraulic conductivity of stem segments normalized per unitarea of leaves supplied by the stem segment rather than perunit area of sapwood cross-sectional area. We find that theLSC's of primary stems were the largest followed in magnitudeby the LSC's of secondary stems and tertiary stems. Under winterand early spring conditions the maximum evaporative flux fromCoratina and Nocellara varieties of olive trees is about 2.6x 10^–5 kg 8^–1 m^–2. From this and the LSC measurementswe calculate that the pressure gradients needed to maintainthis rate of evaporation in the steady state is 65 kPa m^–1in primary stems, 170 kPa m^–1 in secondary stems and 560kPa m^–1 in tertiary stems. Olive, Olea europea L, evaporation, leaf specific conductivity, hydraulic conductivity, leaf resistance     

Temporal and Spatial Development of the Cells of the Expanding First Leaf of Arabidopsis thaliana (L.) Heynh

The three-dimensional quantitative leaf anatomy in developingyoung (9–22 d) first leaves of wild type Arabidopsis thalianacv. Landsberg erecta from mitosis through cell and leaf expansionto the cessation of lamina growth has been studied. The domainsof cell division, the relative proportion of the cell typespresent during development and the production of intercellularspace in the developing leaf have been determined by image analysisof entire leaves sectioned in three planes. Mitotic activityoccurs throughout the youngest leaves prior to unfolding andcell expansion is initiated firstly at the leaf tip with a persistentzone of mitotic cells at the leaf base resulting in a gradientof development along the leaf axis, which persists in the olderleaves. Major anatomical changes which occur during the developmentare, a rapid increase in mesophyll volume, an increase in thevein network, and expansion of the intercellular spaces. Thepattern of cell expansion results in a 10-fold variation inmesophyll cell size in mature leaves. In the youngest leavesthe plan area of mesophyll cells varies between 100 µm²and 400 µm² whereas in mature leaves mesophyll cells rangein plan area from 800 µm² to 9500 µm². The volumesof mesophyll tissue and airspace under unit leaf area increase3-fold and 35-fold, respectively, during leaf expansion. Thevolume proportions of tissue types mesophyll:airspace:epiderrnal:vascularin the mature leaf are 61:26:12:1, respectively. This studyprovides comparative information for future identification andanalysis of leaf development mutants of Arabidopsis thaliana. Key words: Arabidopsis, quantitative leaf anatomy, leaf expansion, image analysis     

Carbon Partitioning in Mature Leaves of Pepper: Effects of Transfer to High or Low Irradiance

Grange, R. I. 1987. Carbon partitioning in mature leaves ofpepper: Effects of transfer to high or low irradiance.—J.exp. Bot. 38: 77–83. Pepper plants were grown at an irradiance of either 55 W m^–2or 90 W m^–2 PAR. Changes in net photosynthesis, carbonexport, starch and sugar contents in a single mature leaf weremeasured at intervals for 8 d following transfer of plants betweenthe two irradiances. On transfer from low to high irradiance,the net photosynthesis rate increased immediately but exportrate increased only slowly, to a maximum after 3 d. While assimilationexceeded export more starch and sucrose accumulated in the dayand remained in the leaf at the end of each night. Hexose contentsat the end of night remained low and constant, but the daytimemaximum rose during the first 2 d from transfer, thereafterreturning to pre-transfer contents. Following transfer of leaves from high to low irradiance starchpresent in the leaf provided sufficient reserves to maintainthe rate of export for one day. Subsequently, the sucrose contentfell and the export rate declined to near that in leaves grownin low irradiance. Sucrose and hexose accumulation following transfer from lowto high irradiance suggests a limitation to export ‘downstream’from sucrose synthesis, probably in the loading step from mesophyllto phloem. Key words: Pepper, export, starch, loading     

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     

The Effect of Current Photosynthesis on the Origin of Translocates in Old Tomato Leaves

The rate of carbon transport from an old tomato leaf (54 days),grown at 80 W m^–2, was measured under light flux densitiesbetween 7 and 90 W m^–2. Under low light, the rate of carbontransport over a 6 h period was about 1 mg C dm^–2 h^–1,well in excess of the concurrent photosynthetic rate. The lossfrom these leaves of ¹⁴C-leaf assimilate which was fixed beforethe experimental period amounted to 62 per cent of the totalinitial uptake and was higher than that from leaves with higherconcurrent photosynthetic rates. The higher loss of ¹⁴C fromleaves with low photosynthetic rates was due to a greater contributionof ¹⁴C from the starch and residue fractions. The rate of transportappeared to be determined by the concentration of the labilesucrose, not the total sucrose concentration. In comparisonwith young fully-expanded tomato leaves (Ho, 1976) the sizeof the labile sucrose pool appeared to decrease with age. Thephotosynthesistranslocation coefficient was low (k₁k₂=0•21)for an old tomato leaf. Based on these results a scheme of carbonpartitioning in relation to translocation is proposed. Criteriafor assessing the efficiency of translocation in leaves arediscussed.     

The Control of the Light Acclimation of Photosynthesis in Glycine max: Dependence on Import as Modified by Intraplant Shading

The dependence of photosynthetic capacity on imported and locally-assimilatedsupplies of carbon during leaf development under different irradianceswas investigated in Glycine max. The potential export of carbonto the developing, mainstem trifoliate leaf (source-potential)was restricted non-destructively by shading all lower, sourceleaves (source-shading), while local photosynthesis was modifiedconcurrently by exposing the young leaf to different light levelsduring development. When source-shading was applied below the2nd mainstem trifoliate leaf at the bud stage of development,photosynthetic capacity was unaffected in leaves which had developedunder moderate and low irradiances (500 and 250 µmol PARm ^–2 s^–1 respectively), but was reduced significantlyin leaves developed under a high irradiance (900 µmolPAR m ^–2 s^–1). If source-shading was applied beneaththe 2nd leaf at unfolding, the reduction of photosynthetic capacityunder the high irradiance was relatively minor. The photosyntheticcapacity attained by the 2nd leaf during development under differentirradiances was influenced by the previous light environmentof the whole plant. In contrast to the 2nd leaf, the photosyntheticcapacities of the 1st and 4th mainstem leaves were relativelyunaffected by source-shading, even under the highest light regime.While photosynthetic capacity showed a widespread insensitivityto the light level of the lower region of the canopy, source-shadingreduced final leaf size irrespective of node position or localirradiance during leaf development. These effects were not relatedto differences in daily photosynthesis by the expanding leaf,and are discussed in terms of the source/sink balance of thedeveloping leaf. Key words: Glycine max, source-shading, photosynthetic capacity     

Changes in Stomatal Conductance in Intact Ageing Wheat Leaves in Response to Abscisic Acid

The characteristics of ABA-induced changes in the fluxes ofCO₂ and water vapour from whole leaves of spring wheat (Triticumaestivum cv. Wembley) were examined. Aqueous solutions of ABAwere supplied via the transpiration stream to intact leavesof different ages mounted within a gas exchange cuvette. ABA caused a reduction in stomatal conductance (g) that wasproportional to the concentration in the solution fed to theleaf. For the maintenance of a reduction in g there was a requirementfor a continual supply of ABA. At concentrations greater than10^–2 mol m^–3 ABA reduced g by at least 50% of thecontrol value, while 1.0 mol m^–3 closed stomata within2 h. Concentrations as low as 10^–3 mol m^–3 produceda 20% reduction in g. As leaves aged they became less responsiveto applied ABA. The possibility that the stomatal response may change aftera leaf has previously experienced a pulse of ABA was exploredby repeating the exposure of a leaf to 10^–2 mol m^–3ABA. The first pulse of ABA produced a greater reduction ing than a subsequent exposure the following day. This declinein response of g to ABA on repeated exposure was maintainedwith leaves of different ages. The characteristics of the stomatal response to ABA are discussedin the context of what is known about the location of receptorsfor the hormone. It seems likely that a failure to respond toABA that has previously accumulated in the guard cells shouldbe viewed by means of maximizing the sensitivity to the currentsupply of ABA. It is suggested that the smaller response ofthe stomata of older leaves to ABA makes them more susceptibleto water stress, so that they can act as sensors for decliningwater potentials to give early protection to younger, metabolicallyactive leaves. Key words: Abscisic acid, leaf age, stomatal conductance, Triticum aestivum     

The Effect of Shading on the Photosynthetic Rate and Longevity of Grass Leaves

The rate at which the net photosynthesis of grass leaves grownin bright light (119 W m^–2) decreased as they aged wasincreased by severe shading (to 21 W m^–2 or less). However,less severe shading (light intensities of 36 W m^–2 ormore) had no effect. The decrease in photosynthesis was unaffectedby whether the whole plant was shaded or only the leaf whosephotosynthesis was measured. In both shaded and unshaded leaves, photosynthesis measuredin bright light fell faster as the leaf aged than did photosynthesisin dim light. Both mesophyll and stomatal diffusion resistancesrose as the leaf aged but the former rose faster. The chlorophyllcontent fell only towards the end of the life of the leaves.     

Nitrate Effects on Growth of the First Four Main Stem Leaves of a Range of Temperate Cereals and Pasture Grasses

The effects of different applied NO₃^– concentrations onextension growth and final length and area of leaves 1–4of five cereals and six pasture grasses of temperate originwere examined. Increased applied NO₃^– in the range 0.1–0.5.0mol m^–3 caused decreased duration of growth but increasedgrowth rate and final length of leaves 2–4 of the cerealsAvena saliva, Hordeum vulgare, Secale cereale, x Triticosecaleand Triticum aestivum. For all cereals, increased NO₃^–resulted in increased area of leaves 1–4. Pasture grasseswere supplied either 0.5 or 50 mol m^–3 NO₃^–. Increasedapplied NO₃^– (0.5–5.0 mol m^–3) resulted indecreased duration of growth and increased growth rate and finalarea of leaves 1–4 of Bromus wiltdenowii, leaves 2–4ofFestuca arundinaceae and leaves 3 and 4 of Lolium muitiflorum.In addition, length of leaves 3 and 4 of B. witidenowii increasedwith increased NO₃^–. Increased NO₃^– resulted inincreased area of leaves 2–4 of Dactylis gtomerata andLolium perenne and leaves 3 and 4 of Phalaris aquaiica but hadno effect on extension growth of all three species. Avena sativa L, oat, Hordeum vulgare L, barley, Secale cereale L, rye, x Triticosecale Wittm, triticale, Triticum aestivum L, wheat, Bromus willdenowii Kunth, prairie grass, Dactylis gtomerata L, cocksfoot, Festuca arundinaceae Shreb, tall fescue, Lolium multijlorum Lam, Italian ryegrass, Lolium perenne L, perennial ryegrass, Phalaris aquatica L, nitrate, leaf extension, leaf expansion     

The duration and rate of grain growth, and harvest index, of wheat (Triticum aestivum L.) in response to temperature and CO2

Winter wheat (Triticum aestivum L. cv. Hereward) was grown inthe field inside polyethylene-covered tunnels at a range oftemperatures at either 380 or 684 µmol mol^–1 CO₂.Serial harvests were taken from anthesis until harvest maturity.Grain yield was reduced by warmer temperatures, but increasedby CO₂ enrichment at all temperatures. During grain-filling,individual grain dry weight was a linear function of time fromanthesis until mass maturity (attainment of maximum grain dryweight) within each plot. The rate of progress to mass maturity(the reciprocal of time to mass maturity) was a positive linearfunction of mean temperature, but was not affected by CO₂ concentration.The rate of increase in grain dry weight per ear was 2.0 mgd^–1 greater per 1 C rise, and was 8.0 mg d^–1 greaterat 684 compared with 380 µmol mol^–1 CO₂ at a giventemperature. The rate of increase in harvest index was 1.0%d^–1 in most plots at 380 µmol mol^–1 CO₂ andin open field plots, compared with 1.18% d^–1 in all plotsat 684 µmol mol^–1 CO₂. Thus, the increased rateof grain growth observed at an elevated CO₂ concentration couldbe attributed partly to a change in the partitioning of assimilatesto the grain. In contrast, the primary effect of warmer temperatureswas to shorten the duration of grain-filling. The rate of graingrowth at a given temperature and the rate of increase in harvestindex were only independent of the number of grains per earabove a critical grain number of 23–24 grains per ear({small tilde}20 000 grains m^–2). Key words: Winter wheat, grain growth, temperature, CO₂, harvest index, critical grain number     

Morphometric Analysis of Chloroplasts of Cotton Leaf and Fruiting Organs

We examined morphological and ultrastructural differences in chloroplasts of cotton leaves and the fruiting organs, bract, and capsule wall to advance our understanding of their commonly observed differences in photosynthetic efficiency. Chloroplasts from leaves were large (7.1 μm long in cross section), lens shaped with a well developed membrane system differentiated into grana and stroma lamellae that occupied the large cross-sectional area (12.3 μm²) of the organelle. A few small plastoglobuli and starch grains were scattered in the stroma region. The bract chloroplasts were correlative of leaf chloroplasts in size (6.8 μm in length) and shape with the exception that the bract chloroplasts exhibited greater thylakoid number per granum (15.8) than the leaf chloroplasts (10.5). In contrast to leaf and bract, the capsule wall chloroplasts were smaller in size (4.3 μm) and cross sectional area (6.8 μm²) than either the leaf or bract. The most intriguing feature of the capsule wall chloroplasts was its domination by large starch granules (5.3 μm²) in the stroma which filled the whole chloroplast coercing the membrane system to move towards the periphery of the organelle. Grana number and thylakoids per granum were lowest in the capsule wall chloroplasts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth and Nitrogen Fixation of Phaseolus vulgaris L. at Two Irradiances 1. Growth

Plants of Phaseolus vulgaris grown at 7 and 28 W m^–2 showedno differences in rate of development of leaves or flowers.At 7 W m-Z plants had longer internodes, more succulent stemsand leaves, higher ratios of shoot:root and greater leaf areasthat those at 28 W m^–2. These differences were establishedprior to detectable differences in photosynthesis and couldpartly be attributed to an increased proportion of far-red light. Although the final d. wt, carbon content, and fruit yield werehigher at 28 W m^–2, plants at 7 W m^–2 apparentlyhad similar relative growth rates and greater photosyntheticefficiency. Dry weight differences are most easily interpretedas resulting from the establishment of an earlier net carbongain at 28 W m^–2 than at 7 W m^–2.