Modulated Degradation of Ribulose Bisphosphate Carboxylase in Leaves on Top-Pruned Shoots of the Mulberry Tree (Morus alba L.)

Yamashita, T. 1987. Modulated degradation of ribulose ftisphosphatecarboxylase in leaves on top-pruned shoots of the mulberry tree(Morus alba L.).—J. exp. Bot. 38: 1957–1964. The effects of pruning shoot tops on the synthesis and degradationof ribulose 1,5–Wsphosphate carboxylase (RuBPCase) inleaves on remaining shoots were investigated in mulberry trees.Leucine labelled with ¹⁴C was fed to leaf discs from field-grownmulberry trees and ¹⁴C incorporation into RuBPCase was examined.Proportion of ¹⁴C in RuBPCase to leucine–¹⁴C absorbedby leaf discs was remarkably lowered by top-pruning, thoughoccasionally a slight increase was observed soon after pruning.Yet RuBPCase content in leaves on top-pruned shoots became progressivelyhigher than that in leaves on intact shoots. Changes in ¹⁴Cin Ru1BPCase in leaves of mulberry saplings previously fed ¹⁴CO₂were followed. Following ¹⁴CO₂ feeding, the attainment of themaximal level of ₁₄C in RuBPCase was retarded by top-pruning.The highest level of ₁₄C in RuBPCase was maintained in leaveson top-pruned shoots but decreased in leaves on intact shoots.Specific radioactivity in RuBPCase continued to increase inleaves on top-pruned shoots even after attaining a maximum levelin the control leaves. These facts suggest that the increasein RuBPCase by top-pruning results from a cessation of its degradationfor the remobilization of nitrogen for newly developing leaveson shoot tops. Key words: RuBP carboxylase, shoot pruning, mulberry (Morus alba)     

Variation in Concentration of Ribulose-1, 5-bisphosphate Carboxylase in Leaves of Barley, Wheat and Hybrids of Crested Wheatgrasses

Amounts of the enzyme ribulose-1,5-bisphosphate carboxylasewere estimated in seedling leaves of barley (Hordewn vulgareL.) and flag leaves of wheat (Triticum aestitum L.) by radialimmuno diffusion. A fourfold variation among barley varietiesfor amount of RuBPCase at the seedling stage was observed (c.3.5–15mg g^–1 fr. wt). Range in variation for amountof flag leaf RuBPCase among wheat varieties was 6-09-9.39 mgRuBPCase g^–1 fr. wt. F₁ hybrids from interspecific andintergeneric crosses of crested wheatgrasses (Agropyron andElymus spp.) and their amphidiploid analogues were comparedfor amount of RuBPCase in the most recent fully expanded leavesharvested before seed set. Amount of enzyme varied from 3.4to 77.6 mg g^–1 fr. wt among the hybrids. No effect chromosomenumber on enzyme concentration was observed among 13 hybridsand their amphidiploid counterparts. Key words: RuBPCase, wheatgrasses     

Activities of Carbonic Anhydrase and Carboxylating Enzymes in Chlamydomonas segnis Adapted and Adapting to Air Levels of Carbon Dioxide

Activities of carbonic anhydrase (CA), phosphoenolpyruvate carboxylase(PEPCase) and ribulose 1,5-bisphosphate carboxylase (RuBPCase)were compared in air- and 5% CO₂adapted and adapting cells ofChlamydomonas segnis during the cell cycle in continuously illuminatedsynchronous cultures. Air-adapted cells exhibited considerablylower PEPCase activities, but higher RuBPCase and CA activitiesthan 5% CO²-adapted cells. Most (75 to 88%) of the CA activityin air-adapted cells appeared to be located in the periplasmicspace. Transferring 5% CO₂-adapted cells to air scarcely influencedRuBPCase activity, but led to 85% decrease in the activity ofPEPCase and to 400% increase in that of CA. In such air-adaptingcells, more than half (54 to 70%) of the CA activity was intracellular.The proposal that PEPCase and RuBPCase in addition to CA maybe involved in the regulation of inorganic carbon uptake byair-adapted and adapting cells under CO₂-limiting conditionsis discussed. (Received June 11, 1987; Accepted September 5, 1987)     

Photosynthetic Characteristics of Spinach Leaves Grown with Different Nitrogen Treatments

Spinach plants (Spinacia oleracea L.) were grown hydroponicallywith different concentrations of nitrate nitrogen, ranging from0.5 to 12 mM, in a glasshouse under full sunlight. Using anopen gas exchange system, the rate of CO₂ assimilation, A, wasdetermined as a function of intercellular partial pressure ofCO₂, P_i, with a constant amount of absorbed light per unit Chl.When expressed on a leaf area basis, A measured at high irradianceand at p_i=500 µbar, was proportional to the in vitro rateof uncoupled whole-chain electron transport as well as to Chlcontent. There was a curvilinear relationship between the mesophyllconductance (the slope of the A : P_i curve near the CO₂ compensationpoint) and the in vitro RuBP carboxylase activity. The curvaturedid not appear to be due to enzyme inactivation in vivo in leaveswith high nitrogen contents. The curvature suggested the presenceof a CO₂ transfer resistance between the intercellular spacesand the site of carboxylation of 2.2 m² s bar mol^–1 CO₂,which is similar to that previously observed in wheat. Thisimplied that, while nitrogen deficiency increased the ratioof in vitro activity of electron transport to that of RuBP carboxylase,the two activities remained balanced in vivo. Irradiance response curves were determined by both net CO₂ andO₂ exchange. The two methods gave reasonable agreement at lightsaturation. The quantum yield measured by O₂ evolution was 0.090?0.003mol O₂ mol^–1 absorbed quanta, whereas after correctingfor p_i = 500µbar, the quantum yield for CO₂ assimilationwas only 82% of that measured by oxygen evolution. ²Present address: Plant Environmental Biology Group, ResearchSchool of Biological Sciences, The Australian National University,G.P.O. Box 475, Canberra, A.C.T. 2601, Australia. (Received July 29, 1987; Accepted November 2, 1987)     

Ammonium release by nitrogen sufficient diatoms in response to rapid increases in irradiance

It has been hypothesized that nitrogen-replete diatoms, butnot flagellates, may release NO₂^–, NH₄⁺ or dissolved organicnitrogen (DON) following rapid increases in irradiance (andconsequently an increase in cellular electron energy), as mightbe expected to occur in a vertically well mixed estuarine system.Just as the increase in irradiance leads to an increase in cellularenergy, so too would a decrease in temperature, due to the temperaturedependency of biosynthetic enzymes. This hypothesis was testedby comparing the response of nitrogen-replete diatoms (Skeletomenacostatum, Thalassiosira weissflogii and Chaetoceros sp.) andflagellates (Dunaliella tertiolecta, Pavlova lutheri and Prorocentrumminimum) to rapid increases in irradiance and decreases in temperature.Short-term (<3 h) changes in extracellular NO₂^– andNH₄⁺ concentrations were measured in cultures following theseexperimental shifts, as well as in cultures retained at thegrowth irradiance. Net rates of NO₂^– and NH₄⁺ releasewere calculated from the time course of extracellular nitrogenconcentrations. As a fraction of NO₃^– uptake, NO₂^–release rates under the increased irradiance increased marginallyrelative to NO₂^– release rates under the growth irradiance.Release rates of NH₄⁺ under the increased irradiance increasednearly fivefold over release rates at the growth irradiance,and accounted for 84% of the NO₃^– uptake rate. In directcontrast to the diatom species, the flagellate species releasedNO₂^– under the higher experimental irradiance at ratesone half those of the release rates under the growth irradiance,and continued to take up NH₄⁺ under both irradiance conditions.Within the experimental boundaries, these findings have importantphysiological and ecological implications. The magnitude ofthe observed nitrogen release represents a significant physiologicalsink for electrons and, in fact, calculations suggest that upto 62% of the total electrons harvested could be consumed. Froman ecological perspective, these findings add to the body ofliterature which suggests that a significant fraction of thenitrogen that is taken up is ultimately released in dissolvedform. More importantly, these data suggest that DON is not theonly compound that phytoplankton may release in the aquaticenvironment.     

Photoinhibition under Atmospheric O2, the Activation State of RuBP Carboxylase and the Content of Photosynthetic Intermediates in Soybean and Wheat

Ward, D. A. and Drake, B. G. 1987. Photoinhibition under atmosphericO₂, the activation state of RuBP carboxylase and the contentof photosynthetic intermediates in soybean and wheat.—J.exp. Bot. 38: 1937–1948. Associations between photosynthesis, the activation state ofRuBP carboxylase and the contents of photosynthetic intermediateswere compared in soybean and wheat leaves before and after exposureto photoinhibitory treatments in the presence of atmosphericO₂. Exposing attached leaves to a supra-saturating irradiance(3 800 µmol quanta m^{– 2} s^–1) for 2 h in CO_2-freeair decreased carboxylation efficiency and the light-saturatedphotosynthetic rate in air by approximately 50%. Exposure tothe photoinhibitory treatment for periods in excess of 2 h didnot cause a further decrease of photosynthesis in soybean. Althoughphotosynthesis was reduced, the initial and total (fully-activated)activities of ribulose 1,5-bisphosphate carboxylase (RuBPCase)in leaf extracts were unaltered in each species by the photoinhibitorytreatment. This was true for leaves sampled under both air andat a rate-limiting intercellular CO₂ partial pressure (C_i) of75 µPa Pa^–1. The contents of ribulose l,5-bisphosphate(RuBP) and 3-phosphoglyceric acid (3-PGA) were reduced by thephotoinhibitory treatment in soybean leaves sampled in air andat a rate-limiting C_i, although the RuBP/3-PGA ratio was unaffected.The relative reduction of RuBP content in soybean leaves atrate-limiting C₁ was similar to the corresponding reductionof carboxylation efficiency. For wheat,the relative reductionof RuBP content at rate-limiting C_i (–19%) caused by thephotoinhibitory treatment was considerably less than the correspondingdecrease of carboxylation efficiency (–49%).The RuBP/3-PGAratio of wheat was also increased significantly by the photoinhibitorytreatment The significance of these observations to the regulationof CO₂-limited photosynthesis in leaves experiencing photoinhibitionunder atmospheric oxygen is discussed. Consideration is alsogiven to the previous contention that contemporary measurementsof initial activity in crude extracts may provide a spuriousindication of the amount of the enzyme-CO₂-Mg_{2 +} form of RuBPcarboxylase present in the leaf. Key words: Carboxylation efficiency, RuBP carboxylase, photoinhibition, RuBP, 3-PGA     

Interaction between Nitrogen Deficit of a Plant and Nitrogen Content in the Old Leaves

We examined changes in nitrogen content of the first leavesin relation to growth and nitrogen status of sunflower (Helianthusannuus L.) plants that were raised hydroponically at two irradiancelevels (high and low light, HL and LL) and at two nitrogen concentrations(high and low nitrogen, HN and LN). Initial increases in totaldry mass and total nitrogen of the whole plant were faster inHL-plants than in LL-plants irrespective of nitrogen supply,but in LN-plants the increase in total nitrogen was soon blunted.When plants grown under the same irradiance were compared, nitrogencontent of the first leaves (leaf N) decreased faster in LN-plantsthan in HN-plants, while for the plants grown at the same nitrogenconcentrations, it decreased faster in HL-plants than in LL-plants.Since these changes in leaf N were not explained solely by thechanges in plant dry mass or plant nitrogen, we introduced anindex, ‘nitrogen deficit (ND^*)’, to quantify nitrogendeficit of the whole plant. ND^* was expressed as ND^*(t)=[N_max–N(t)]xDM(t),where N_max and N(t) were nitrogen contents in the young, expandingleaves that had just unfolded to expand, at the initial stagewith sufficient nitrogen and at time t, respectively, and DM(t),plant dry mass at t. The decrease in leaf N was expressed asa liner function of ND^* irrespective of the growth conditions,which indicates validity of this index. Limitation of the useof ND^*, and mechanisms by which leaves sense nitrogen demandare also discussed. (Received June 17, 1996; Accepted August 30, 1996)     

Photosynthesis by Flag Leaves of Wheat in Relation to Protein, Ribulose Bisphosphate Carboxylase Activity and Nitrogen Supply

The effects of nitrate supply on the composition (cell numbers,protein and chlorophyll contents) of flag leaves of winter wheatgrown with two amounts of N fertilizer and of spring wheat grownin the glasshouse under controlled nitrate supply are describedand related to photosynthesis. Nitrogen deficiency decreasedthe size of leaves, mainly by reducing cell number and, to asmaller extent, by decreasing cell volume. Protein content perunit leaf area, per cell and per unit cell volume was largerwith abundant N. Total soluble protein, ribulose bisphosphatecarboxylase-oxygenase (RuBPc-o) protein and chlorophyll changedin proportion irrespective of nitrogen supply and leaf age.Photosynthesis per unit area of flag leaf and carboxylationefficiency in both winter and spring wheat were proportionalto the amount of total soluble protein up to 7.0 g m^–2and to the amount of RuBPc-o protein up to 4.0 g m^–2.However, photosynthesis did not increase in proportion to theamount of total soluble or RuBPc-o protein above these amounts.In young leaves with a high protein content the measured ratesof photosynthesis were lower than expected from the amount andactivity of RuBPc-o. Carboxylation per unit of RuBPc-o protein,measured in vitro, was slightly greater in N-deficient leavesof winter wheat but not of spring wheat. RuBPc-o activity perunit of RuBPc-o protein was similar in winter and spring wheatleaves and remained approximately constant with age, but increasedin leaves showing advanced senescence. RuBPc-o protein fromN-deficient leaves migrated faster on polyacrylamide gels thanprotein from leaves with high N content. Regulation of the rateof photosynthesis in leaves and chloroplasts with a high proteincontent is discussed. The conductance of the cell to the fluxof CO₂ from intercellular spaces to RuBPc-o active sites iscalculated, from cell surface areas and CO₂ fluxes, to decreasethe CO₂ partial pressure at the active site by less than 0.8Pa at an internal CO₂ partial pressure of 34 Pa. Thus the decreasein partial pressure of CO₂ is insufficient to account for theinefficiency of RuBPc-o in vivo at high protein contents. Otherlimitations to the rate of photosynthesis are considered. Key words: Wheat, photosynthesis, nitrogen, ribulose, bisphosphate carboxylase     

Isolation of Native Pyrenoid Core Matrix Having Ribulose 1,5-bisphosphate Caxrboxylase Activity from the Green Alga Bryopsis maxima

The native pyrenoid core matrix of the green alga Bryopsis maximawas isolated by diethyl ether treatment and sucrose densitygradient centrifugation using 1.8 M phosphate buffer. The purityof the pyrenoids was examined by microscopy, polyacrylamidegel electrophoresis and marker materials. The purified pyrenoidscontained the large subunit and the small subunit of ribulose1,5-bisphosphate carboxylase (RuBPCase) and more than 10 minorpolypeptides. They also showed RuBPCase activity when solubilizedon being transferred to a low-concentration buffer. The specificactivity was 0.62 µmol CO₂ fixed (mg protein)^–1min^–1. This isolation method is suitable for obtainingintact pyrenoids not covered by starch sheaths or membraneswithout the need for chloroplast fixation. (Received July 27, 1987; Accepted October 20, 1987)     

Changes in the Rate of Photosynthesis during Grain Filling and the Enzymatic Activities Associated with the Photosynthetic Carbon Metabolism in Rice Panicles

Photosynthesis is known to occur in rice panicles, but littlehas been reported about the photosynthetic or biochemical characteristicsof such panicles. The estimated gross amount of photo-syntheticallyassimilated CO₂ in a panicle is 30% of that in a flag leaf.This result and the good light-intercepting characteristicsof the panicle in the canopy suggest that photosynthesis inthe panicle may contribute significantly to grain filling. Therice panicle is composed of spikelets and of rachis-branchesincluding rachis which have estimated gross rates of photosynthesisduring the 30-day period after anthesis of 130 to 180 and 50to 100 µmol CO₂.(mg Chl)^–1.h^–1, respectively.The corresponding rate for the flag leaf is 180 to 230 µmolCO₂.(mg Chl)^–.h^–. On the basis of Chl, spikeletshave a high photosynthetic capability which is similar to thatof the flag leaf. The activities of ribulose-l,5-bisphosphate carboxylase (RuBPCase),phosphoenolpyruvate carboxylase (PEPCase), and pyruvate.P_i dikinase(PPDK) in spikelets were 129, 220, and 87 µmol.(mg Chl)^–.h^–,respectively. The activities of PEPCase and PPDK in spikeletswere considerably higher than those in the flag leaf or rachis-branches.Oxygen-insensitive photosynthesis was found only in spikelets.The K_m of NaHCO₃ for photosynthesis by slices of spikelets inan aqueous solution (0.6 mM) was considerably lower than thatfor slices of flag leaf (4.2 mM). All these results indicatethat spikelets have different photosynthetic characteristicsfrom those of the flag leaf and rachis-branches. The possibilityof C₃–C₄ intermediate photosynthesis or C₄-like photosynthesisin spikelets is discussed. ⁴Present address: Department of Biochemistry, Faculty of Science,Saitama University, Urawa, 338 Japan (Received February 14, 1990; Accepted June 12, 1990)     

Effects of Temperature and Light on the Carbon Budget of Young Cucumber Plants Studied by Steady-State Feeding with 14CO2

Shishido, Y., Challa, H. and Krupa, J. 1987. Effects of temperatureand light on the carbon budget of young cucumber plants studiedby steady-state feeding with ¹⁴CO°₂J. exp. Bot. 38: 1044–1054. The effect of temperature on the fate of ¹⁴C assimilated insteady-state by the expanding third leaf of cucumber seedlingswas studied at irradiances of either 30 or 75 W m^–2 (PAR)with a daylength of 8 h. The irradiance did not affect the relativedistribution of ¹⁴C assimilated by the source leaf between growth,respiration and export. In the range 15–30°C risesin temperature generally increased the proportion of carbonexported. The average rate of carbon exported during the nightwas about half the rate in the day. About 45% of the exportedcarbon was lost by respiration. The distribution pattern ofcarbon exported during the day differed considerably from thatof carbon exported during the night. The intensity of irradiance did not affect the proportion oflabelled carbon recovered from the roots. Thus the decreasedshoot/root ratio generally observed with increased irradianceis not directly controlled by carbohydrate supply. We found that the distribution patterns of exported ¹⁴C do notnecessarily represent the real carbon distribution, due to differencesin specific activity of imported carbon of individual organs.Consequently distribution patterns of ¹⁴C observed in experimentswith one source leaf have to be considered with caution. Key words: Carbon budget, ¹⁴C, ¹⁴C steady-state feeding, translocation, respiration, assimilate distribution, cucumber, temperature     

Physiological and Anatomical Effects of Growth Temperature on Phaseolus vulgaris L. Cultivars

Two Phaseolus vulgaris L. cultivars were grown at 20/15, 25/20,and 30/25 °C day/night temperatures in growth chambers witha 16 h thermoperiod corresponding to the photoperiod. When thefirst trifoliolate leaf was fully expanded rates of CO₂ exchange(CER) were measured at 27 °C and saturating light usinginfrared gas analysis. Stomatal (r_s) and mesophyll resistances,CO₂ compensation points, activities of the enzymes ribulosebisphosphate carboxylase (RuBPCase), glycolate oxidase (GAO),malate dehydrogenase (MDH), and fructose-1, 6 diphosphate (FDP),chlorophyll content, Hill activities, and leaf anatomy at boththe light and electron microscope level were also investigatedin these leaves. Rates of CO₂ exchange in the light, transpiration rate, andchlorophyll content increased with increasing growth temperaturewhile leaf thickness, specific leaf weight, RuBPCase activity,compensation point, and stomatal resistance decreased. Mesophyllresistance also decreased when calculated assuming zero chloroplastCO₂ concentration (rm, o), but not when calculated assuminga chloroplast CO₂ concentration equal to the CO₂ compensationconcentration (rm, g). Average leaf size was maximal in 25/20°C plants while dark respiration, MDH activity, stomataldensity, and starch were minimal. The activities of GAO andFDP and Hill activity were not affected by temperature pretreatment.     

On the causes of interspecific differences in the growth-irradiance relationship for phytoplankton. II. A general review

The causes of interspecific differences in the µ-l relationshipare examined in the context of a mechanistic model which relatesµ to irradiance in terms of six factors:, k_c photosyntheticquotient (PQ), Chl a:C, respiration and excretion. The effectof cell size on the light saturated growth rate is also considered.It is shown that photosynthetic efficiency and PQ exhibit remarkablylittle interspecific variability, and average 0.024 ±0.005 µg C(µg Chl a)^–1 h^–1 (µEm^–2 s^–1)^–1 and 1.5 ± 0.2 mol 02 molC^–1 (when NO₃^– is the nitrogen source) respectively.Two useful relationships were derived: (i) between growth efficiency,_g and Chl a:C at µ. = 0; (ii) between the compensationintensity, I_c and the Chl a-specific maintenance respirationrate. Both relationships were independent of temperature anddaylength. Species best adapted to growth at low light werefound to exhibit high Chl a:C ratios and low maintenance respirationrates. As a group, diatoms were consistently the best adaptedfor growth at low irradiance. Chiorophytes, haptophytes, chrysophytesand cryptophytes were intermediate in their performance at lowirradiance. Dinoflagellates exhibited extreme diversity, withspecies spanning the spectrum from very good performance atlow irradiance to very poor. A new µ_max-cell carbon relationshipis given based on growth rates normalized to 15°C. Evidenceis presented to show that noise in this relationship can besignificantly reduced by using only carbon-specific growth ratesand using only data for species grown at the same daylength.     

Light Distribution in Discontinuous Canopies: Calculation of Leaf Areas and Canopy Volumes Above Defined 'Irradiance Contours' for use in Productivity Modelling

Plant canopies can be considered as assemblages of leaves, stemsand fruits growing in zones of differing irradiance demarcatedby contours of mean irradiance as measured on a horizontal surface. The following general equations have been derived to calculatethe leaf area (L_I) and the canopy volume (CV_I) in zones externalto any chosen contour of mean irradiance: (1) L_I = ((1nl)/(–K)(I–T_f) or leaf area index (LAI) if this is less (2) CV_I = L_I/(leaf area density m² m^–2), where I is the specified value of irradiance (horizontal surface)expressed as a decimal fraction of that above the canopy, Kis the appropriate extinction coefficient and T_f is the proportionof the total of available radiation which, if the canopy isdiscontinuous, would reach the ground by passing through gapsbetween the discrete canopy units. Where the canopy is continuousT_f is zero so expression (1) simplifies to L₁ = 1n I/–K(or LAI if this is less). For a range of model hedgerow orchards of varying dimensions,spacings and LAIs, it has been shown that the use of these equationsgives very similar results to those obtained by detailed calculationof light penetration. They therefore seem to be of potentialuse in calculating both potential dry-matter production by discontinuouscanopies of any type and, in the case of orchard fruit crops,the potential effect of changes in tree size, leaf area density,spacing etc. on the canopy volume in which irradiation is adequatefor fruit bud initiation and fruit colour development. light distribution, discontinuous canopy, irradiance contours, leaf area index, orchards     

Growth Analysis of Solution Culture-grown Winter Rye, Wheat and Triticale at Different Relative Rates of Nitrogen Supply

At low nitrogen (N) supply, it is well known that rye has ahigher biomass production than wheat. This study investigateswhether these species differences can be explained by differencesin dry matter and nitrogen partitioning, specific leaf area,specific root length and net assimilation rate, which determineboth N acquisition and carbon assimilation during vegetativegrowth. Winter rye (Secale cereale L.), wheat (Triticum aestivumL.) and triticale (X Triticosecale) were grown in solution cultureat relative addition rates (R_N) of nitrate-N supply rangingfrom 0.03–0.18 d^-1and at non-limiting N supply under controlledconditions. The relative growth rate (R_W) was closely equalto R_Nin the range 0.03–0.15 d^-1. The maximalR_W at non-limitingnitrate nutrition was approx. 0.18 d^-1. The biomass allocationto the roots showed a considerable plasticity but did not differbetween species. There were no interspecific differences ineither net assimilation rate or specific leaf area. Higher accumulationof N in the plant, despite the same relative growth rate atnon-limiting N supplies, suggests that rye has a greater abilityto accumulate reserves of nitrogen. Rye had a higher specificroot length over a wide range of sub-optimal N rates than wheat,especially at extreme N deficiency (R_N=0.03–0.06 d^-1).Triticale had a similar specific root length as that of wheatbut had the ability to accumulate N to the same amount as ryeunder conditions of free N access. It is concluded that thebetter adaptation of rye to low N availability compared to wheatis related to higher specific root length in rye. Additionally,the greater ability to accumulate nitrogen under conditionsof free N access for rye and triticale compared to wheat maybe useful for subsequent N utilization during plant growth.In general, species differences are explained by growth componentsresponsible for nitrogen acquisition rather than carbon assimilation.Copyright 1999 Annals of Botany Company Growth analysis, nitrogen, nitrogen productivity, partitioning, specific root length, Secale cereale L.,Triticum aestivum L., X Triticosecale, winter rye, winter wheat, winter triticale.     

The Relation Between the Nitrogen Concentration and Photosynthetic Capacity of Potato (Solanum tuberosum L.) Leaves

Measurements of the rate of light-saturated photosynthesis (P_max)were made on terminal leaflets of potato plants growing in cropssupplied with 0, 3, 6, 12, 24 and 36 g N m^–2. Measurementswere made between 100 and 154 d after planting. Two types ofleaf were selected—the fourth leaf on the second-levelbranch (L₄, _B1) and the youngest terminal leaflet that was measurable(L_YM). Later, the total nitrogen concentration of each leaflet(N_L) was measured. A linear regression between P_max and N_L,common to both leaf positions, explained 68.5% of the totalvariation. With L₄, _B1 leaves there was a significant improvementin the proportion of variation explained when regressions withseparate intercepts and a common slope were fitted to individualfertilizer treatments. These results suggest that an increasingproportion of leaf nitrogen was not associated with the performanceof the photosynthetic system with increasing nitrogen supply.This separation between nitrogen treatments was not as clearfor L_YM leaves. Stomatal conductance to transfer of water vapourwas neither influenced by leaf position nor directly by nitrogensupply. Rather conductance declined in parallel with the declinein photosynthetic capacity. Solanum tuberosum, potato, nitrogen, photosynthesis, stomatal conductance, leaf     

Effects of elevated CO2 concentrations on three montane grass species: III. Source leaf metabolism and whole plant carbon partitioning

Agrostis capillaris L.⁵, Festuca vivipara L. and Poaalpina L.were grown in outdoor open-top chambers at either ambient (340 3µmol mol^–1) or elevated (6804µmol mol^–1)concentrations of atmospheric carbon dioxide (CO₂) for periodsfrom 79–189 d. Photosynthetic capacity of source leaves of plants grown atboth ambient and elevated CO₂ concentrations was measured atsaturating light and 5% CO₂. Dark respiration of leaves wasmeasured using a liquid phase oxygen electrode with the buffersolution in equilibrium with air (21% O₂, 0.034% CO₂). Photo-syntheticcapacity of P. alpina was reduced by growth at 680 µmolmol^–1 CO₂ by 105 d, and that of F. vivipara was reducedat 65 d and 189 d after CO₂ enrichment began, suggesting down-regulationor acclimation. Dark respiration of successive leaf blades ofall three species was unaltered by growth at 680 relative to340 µmol mol^–1 CO₂. In F. vivipara, leaf respirationrate was markedly lower at 189 d than at either 0 d or 65 d,irrespective of growth CO₂ concentration. There was a significantlylower total non-structural carbohydrate (TNC) concentrationin the leaf blades and leaf sheaths of A. capillaris grown at680µmol mol^–1 CO₂. TNC of roots of A. capillariswas unaltered by CO₂ treatment. TNC concentration was increasedin both leaves and sheaths of P. alpina and F. vivipara after105 d and 65 d growth, respectively. A 4-fold increase in thewater-soluble fraction (fructan) in P. alpina and in all carbohydratefractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosyn-theticcapacity and leaf carbohydrate concentration was such that therewas a strong positive correlation between photosynthetic capacityand total leaf N concentration (expressed on a per unit structuraldry weight basis), and total nitrogen concentration of successivemature leaves reduced with time. Multiple regression of leafphotosynthetic capacity upon leaf nitrogen and carbohydrateconcentrations further confirmed that leaf photosynthetic capacitywas mainly determined by leaf N concentration. In P. alpina,leaf photosynthetic capacity was mainly determined by leaf CHOconcentration. Thus there is evidence for down-regulation ofphotosynthetic capacity in P. alpina resulting from increasedcarbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positivelycorrelated in P. alpina and F. vivipara. Leaf dark respirationand soluble carbohydrate concentration of source leaves werepositively correlated in A. capillaris. Changes in source leafphotosynthetic capacity and carbohydrate concentration of plantsgrown at ambient or elevated CO₂ are discussed in relation toplant growth, nutrient relations and availability of sinks forcarbon. Key words: Elevated CO₂, Climate change, grasses, carbohydrate partitioning, photosynthesis, respiration     

Growth and Biomass Allocation, with Varying Nitrogen Availability, of Near-isogenic Pea Lines with Differing Foliage Structure

The single-gene mutation afila in pea (Pisum sativum L.) resultsin the replacement of proximal leaflets with branched tendrils,thereby reducing leaf area. This study investigated whethertheafila line could adjust biomass partitioning when exposedto varying nutrient regimes, to compensate for reduced leafarea, compared with wild-type plants. Wild-type and afila near-isogeniclines were grown in solution culture with nitrate-N added toinitially N-starved seedlings at relative addition rates (R_N)of 0.06, 0.12, 0.15 and 0.50 d^-1. The relative growth rate (R_W)of the whole plants closely matched R_Nat 0.06 and 0.12 d^-1,but higher R_Nresulted in a slightly higher growth rate. At agiven R_N, the wild-type line had lower plant nitrogen statusthan the afila line. R_Wof the roots of the afila line was lessthan R_Wof the roots of the wild-type at the three higher ratesof N supply despite a greater accumulation of N in the rootsof the afila plants. Consequently, plant nitrogen productivity(growth rate per unit nitrogen) was lower for afila. Dry matterallocation was strongly influenced by nitrogen status, but nodifferences in shoot–root dry matter allocation were foundbetween wild-type and afila with the same plant N status. Theseresults imply that decreased leaf area as a result of the single-genemutation afila affects dry matter allocation, but only accordingto its effect on the nitrogen status. Copyright 2000 Annalsof Botany Company Pisum sativum, pea, nitrogen limitation, growth, shoot–root allocation, relative growth rate, nitrogen productivity, isolines     

Nitrogen Use Efficiency in Growth of Polygonum cuspidatum Sieb. et Zucc

The growth of Polygonum cuspidatum in sand culture was analysedunder varying nutrient conditions. Nitrogen availability influencednitrogen uptake of plants through the uptake rate per unit rootweight rather than the amount of root. In turn, the differentamounts of nitrogen taken up affected plant growth through theireffects on the rate of leaf expansion. Net assimilation rate (NAR) increased with nitrogen contentper unit leaf area (C), but further increase in leaf nitrogencaused diminishing returns of NAR Optimal nitrogen content perunit leaf area (C_opt) to maximize dry-matter production of aleaf could be determined by drawing a tangent from the onginto a curvilinear relation between NAR and C. This optimal contentdivides a nitrogen-limiting range (C < C_opt) from a carbon-limitingone (C> C_opt) along the axis of nitrogen content. Under nitrogenlimitation, efficiency of nitrogen use in dry-matter productioncould increase if the plant had a larger carbon sink. This givesa qualitative explanation to reduced shoot-to-root ratio underlimited availability of nitrogen. Polygonum cuspidatum Sieb. et Zucc, Japanese knotweed, carbon sink, growth analysis, leaf nitrogen, net assimilation rate, nitrogen use efficiency     

Carbon and Nitrogen Assimilation by Vicia faba L. at Low Temperature: the Importance of Concentration and Form of Applied-N

Low temperature (6 C) growth was examined in two cultivarsof Vicia faba L. supplied with 4 and 20 mol m^–3 N as nitrateor urea. Both cultivars showed similar growth responses to increasedapplied-N concentration regardless of N-form. Total leaf areaincreased, as did root, stem and leaf dry weight, total carboncontent and total nitrogen content. In contrast to findingsat higher growth temperatures, 20 mol m^–3 urea-N gavesubstantially greater growth (all parameters measured) than20 mol m^–3 nitrate-N. The increased carbon content per plant associated with increasedapplied nitrate or urea concentration, or with urea in comparisonto nitrate, was due to a greater leaf area per plant for CO₂uptake and not an increased CO₂, uptake per unit area, carbon,chlorophyll or dry weight, all of which either remained constantor decreased. Nitrate reductase activity was substantial inplants given nitrate but negligible in plants given urea. Neitherfree nitrate nor free urea contributed greatly to nitrogen levelsin plant tissues. It is concluded that there is no evidence for a restrictionin nitrate reduction at 6 C, and it is likely that urea givesgreater growth than nitrate because of greater rates of uptake. Vicia faba, broad bean, low temperature growth, carbon assimilation, nitrogen assimilation