Carbon Economy and Translocation of 14C in Leaflets of the Seventh Leaf of Tomato During Leaf Expansion

The growth pattern (leaf expansion, carbon metabolite accumulation)and the assimilation and translocation of leaf assimilate inthe leaflets of the seventh leaf of tomato were examined onsix occasions during a period of 35 days beginning 10 days afterthe leaf was first visible. Leaf expansion progressed basipetally within the leaf. The primarypartitioning of the currently-fixed ¹⁴C and the 24 h incorporationof both self-fixed and imported ¹⁴C were closely related tothe degree of leaf expansion. Therefore, leaflets of up to halffinal size within the same leaf, were markedly different inphysiological function. Maximum import of ¹⁴C-leaf assimilate from the six basal leavesinto the seventh leaf was recorded at 15 per cent expansion.The terminal and top-pair of leaflets reached one quarter fullsize first and exported ¹⁴C leaf assimilate to the basal-pairof leaflets and to the rest of the plant when the seventh leaf,as a whole, was only one tenth expanded. The transition fromimport to export in a given leaflet was gradual and overlapping. During the early part of leaflet expansion, more imported ¹⁴C-leafassimilate was used for protein synthesis than for the synthesisof sugars and starch. Meanwhile, the capacity for sucrose synthesisfrom the self-fixed carbon increased significantly precedingthe onset of export. Each leaflet resembles a whole leaf in functional development.     

Changes in Photosynthesis, Carbon Budget and Mineral Content during the Growth of the First Leaf of Cucumber

The relationships between photosynthesis, dry matter accumulationand translocation have been studied during the development ofthe first true leaf of cucumber. The leaf was grown in an irradianceof 50W m^–2 photosynthetically active radiation for 10h^–1 at 20 C and 2 g m^–3 CO₂. The maximum rate of net photosynthesis, on a leaf area basis,occured at full expansion. Photochemical efficiency, based onincident radiation, also increased up to this stage and wasrelated to the concentration of chlorophyll in the leaf. Darkrespiration and the light compensation point fell over the wholeperiod of leaf expansion. A carbon budget analysis showed that the rate of carbon accumulationin the leaf reached a peak at 70 percent expansion. The leafchanged from a net importer to a net exporter of carbon whenit was about 30 percent expanded. The rate of export increasedwith leaf expansion (and with net photosynthesis) and was twiceas high in the day an in the night at full expansion. At fullleaf expansion there was a reduction in the amount of starchlost overnight, and the carbon exported amounted to 80 per centof the daily net carbon fixed. Cucumber, Cumic satinu L., leaf development, photosynthesis, translocation, carbon budget, mineral content     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

Relationship between Leaf Structure and Gas Exchange in Wheat Leaves at Different Insertion Levels

Net photosynthesis rate (P_n), stomatal conductance to CO₂ andresidual conductance to CO₂ were measured in the last six leaves(the sixth or flag leaf and the preceding five leaves) of Triticumaestivum L. cv. Kolibri plants grown in Mediterranean conditions.Recently fully expanded leaves of well-watered plants were alwaysused. Measurements were made at saturating photosynthetic photonflux density, and at ambient CO₂ and O₂ levels. The specificleaf area, total organic nitrogen content, some anatomical characteristics,and other parameters, were measured on the same leaves usedfor gas exchange experiments. A progressive xeromorphic adaptation in the leaf structure wasobserved with increasing leaf insertion levels. Furthermore,mesophyll cell volume per unit leaf area (V_mes/A) decreasedby 52·6% from the first leaf to the flag leaf. Mesophyllcell area per unit leaf area also decreased, but only by 24·5%.However, nitrogen content per unit mesophyll cell volume increasedby 50·6% from the first leaf to the flag leaf. This increasecould be associated to an observed higher number of chloroplastcross-sections per mm² of mesophyll cell cross-sectional areain the flag leaf: values of 23000 in the first leaf and 48000in the flag leaf were obtained. P_n per unit leaf area remainedfairly constant at the different insertion levels: values of33·83±0·93 mg dm^–2 h^–1 and32·32±1·61 mg dm^–2 h^–1 wereobtained for the first leaf and the flag leaf, respectively.Residual conductance, however, decreased by 18·2% fromthe first leaf to the flag leaf. Stomatal conductance increasedby 41·7%. The steadiness in P_n per unit leaf area across the leaf insertionlevels could be mainly accounted for by an opposing effect betweena decrease in V_mes/A and a more closely packed arrangement ofphotosynthetic apparatus. Adaptative significance of structuralchanges with increasing leaf insertion levels and the steadinessin P_n per unit leaf area was studied. Key words: Photosynthesis, structure, wheat     

Acclimation in Seedlings of a Tropical Tree, Bischofia javanica, Following a Stepwise Reduction in Light

Acclimation of fully developed leaves of Bischofia javanicaBlume to shadelight was examined. Seedlings were grown undersimulated daylight (1000 µmol m^–2 s^–1), thentransferred to a simulated shadelight (40 µmol m^–2s^–1). When a high-light leaf was transferred to low light, large negativenet photosynthetic rates (P_m) were recorded. This decrease wasrapid, but within 7 d the rate increased and became equal tothe low-light control leaf. These changes in photosynthesisdid not follow the pattern of changes in stomatal conductance(g_s). Transfer to the low light resulted in a dramatic decreasein leaf weight per unit area (L_w), and most of the decreasesin L_w occurred within 3 d of transfer when the P_m of the transferredleaf was well below that of the low-light control leaf. There was a significant decrease in chlorophyll a in the transferredleaf without an appreciable change in chlorophyll b resultingin a large decrease in the chlorophyll a to chlorophyll b ratio.Leaf chlorophylls per unit area were higher in the transferredleaf than the low-light control leaf. Maximum photosyntheticrate in the transferred leaf was decreased by 40% compared tothat for the high-control leaf, but was almost at the same extenthigher than the low-light control leaf The results are discussedin the context of carbon gain capacity of its seedlings underlight-limiting forest understorey habitats. Bischofia, chlorophylls, light, photosynthesis, shade acclimation, tree seedlings, tropical tree     

Validation of a Photosynthesis Model through the Use of the CO2Balance of a Greenhouse Tomato Canopy

Several leaf photosynthesis models were developed from wellcontrolled experiments in growth chambers. However, only a fewhave been validated under greenhouse conditions for their quantitativeand qualitative adequacy. In this paper, rates of net photosynthesisfor a tomato crop (Lycopersicon esculentum Mill) were measuredin a semi-commercial greenhouse (615 m³) for a significant timeperiod. Concomitant measurements of climatic conditions andLAI were used for simulation of net photosynthesis using theTOMGRO model which integrates Acock's model for photosynthesiscalculations. From simulations and from sensitivity analysis,the prediction of net photosynthesis appeared to be very sensitiveto the quantum use efficiency. The Acock model with originalparameters underestimated the net photosynthesis rate, but anincrease in the quantum use efficiency by 10% gave a good fit.In an effort to generalize the validity of the model, a residualanalysis was performed and showed a systematic bias relatedto light intensity intercepted by the canopy. The Marquardtalgorithm was used to adjust our data to the model but did noteliminate residual heterogeneity of variance with new parametervalues. On the basis of collected data, the criteria of goodnessof fit used showed that the photosynthesis model is inadequatein describing the CO₂-balance of the greenhouse agrosystem.However, it was determined that it could be used as a submodelwithin a more complex model for predicting growth and development.Copyright 1999 Annals of Botany Company Greenhouse, CO₂-balance, photosynthesis, TOMGRO model, Acock's model, residuals, tomato Lycopersicon esculentum Mill.     

Long-term effects of a doubled atmospheric CO2 concentration on the CAM species Agave deserti

To examine the effects of a doubled atmospheric CO₂ concentrationand other aspects of global climate change on a common CAM speciesnative to the Sonoran Desert, Agave deserti was grown under370 and 750 µmol CO₂ mol^–1 air and gas exchangewas measured under various environmental conditions. Doublingthe CO₂ concentration increased daily net CO₂ uptake by 49%throughout the 17 months and decreased daily transpiration by24%, leading to a 110% increase in water-use efficiency. Underthe doubled CO₂ concentration, the activity of ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco) was 11% lower, phosphoenolpyruvatecarboxylase was 34% lower, and the activated:total ratio forRubisco was 25% greater than under the current CO₂ concentration.Less leaf epicuticular wax occurred on plants under the doubledCO₂ concentration, which decreased the reflectance of photosyntheticphoton flux (PPF); the chlorophyll content per unit leaf areawas also less. The enhancement of daily net CO₂ uptake by doublingthe CO₂ concentration increased when the PPF was decreased below25 mol m^–2 d^–1 when water was withheld, and whenday/night temperatures were below 17/12 C. More leaves, eachwith a greater surface area, were produced per plant under thedoubled CO₂ concentration. The combination of increased totalleaf surface area and increased daily net CO₂ uptake led toan 88% stimulation of dry mass accumulation under the doubledCO₂ concentration. A rising atmospheric CO₂ concentration, togetherwith accompanying changes in temperature, precipitation, andPPF, should increase growth and productivity of native populationsof A. deserti. Key words: Crassulacean acid metabolism, gas exchange, global climate change, Sonoran Desert     

Photosynthesis by developing embryos of oilseed rape (Brassica napus L.)

The aim of this study was to assess the photosynthetic potentialof developing seeds of oilseed rape (Brassica napus L.) andto compare photosynthetic properties of embryo plastids withthose of leaf chloroplasts from the same species. Measurementsof CO₂-dependent O₂ evolution show that developing seeds ofB. napus are photosynthetically active in vitro. Essentially,all of the photosynthetic activity of the developing seed isaccounted for by the embryo. The rate of photosynthesis by developingembryos increased until the onset of desiccation, after whichit declined, so that by maturity embryos were no longer photosyntheticallyactive. Photosynthetic activity was positively correlated withchlorophyll content throughout development. Comparison of thephotosynthetic characteristics of leaf and embryo chloroplastsrevealed that rates of uncoupled electron transport were 2.5-foldgreater in those from the embryo. Light-saturated rates of CO₂-dependentO₂ evolution, per unit chlorophyll, and CO₂ saturation pointswere similar for chloroplasts from both tissues. However, light-saturationpoints and chlorophyll a/b ratios were lower for embryo thanfor leaf choroplasts. Embryos and embryo chloroplasts also containedconsiderably less ribulose 1,5-bisphosphate carboxylase/oxygenaseprotein per unit total protein, than leaves. Although excisedembryos were capable of high rates of CO₂-dependent O₂ evolution(90–100 mol mg^–1 chlorophyll h^–1) under asaturating photosynthetic photon flux density (PPFD), low transmittanceof light through the silique wall (30%), together with the highPPFD required to achieve light compensation points in developingseeds (500 mol m^–2 s^–1), suggests that photosynthesisin vivo is unlikely to make a net contribution to carbon economyunder normal environmental conditions. Key words: Embryo, development, photosynthesis, chloroplast, Brassica napus L.     

Growth and Physiology of One-year old Poplar (Populus) Under Elevated Atmospheric CO2 Levels

The effects of elevated atmospheric CO₂ concentrations on theecophysiological responses (gas exchange, chlorophyll a fluorescence,Rubisco activity, leaf area development) as well as on the growthand biomass production of two poplar clones (i.e. Populus trichocarpax P. deltoides clone Beaupré and P. x euramericana cloneRobusta) were examined under open top chamber conditions. Theelevated CO₂ treatment (ambient + 350 µmol mol^-1) stimulatedabove-ground biomass of clones Robusta and Beaupré afterthe first growing season by 55 and 38%, respectively. This increasedbiomass production under elevated CO₂ was associated with asignificant increase in plant height, the latter being the resultof enhanced internode elongation rather than an increased productionof leaves or internodes. Both an increased leaf area index (LAI)and a stimulated net photosynthesis per unit leaf contributedto a significantly higher stem biomass per unit leaf area, andthus to the increased above-ground biomass production underthe elevated CO₂ concentrations in both clones. The larger LAIwas caused by a larger individual leaf size and leaf growthrate; the number of leaves was not altered by the elevated CO₂treatment. The higher net leaf photosynthesis was the resultof an increase in the photochemical (maximal chlorophyll fluorescenceFm and photochemical efficiency Fv/Fm) as well as in the biochemical(increased Rubisco activity) process capacities. No significantdifferences were found in dark respiration rate, neither betweenclones nor between treatments, but specific leaf area significantlydecreased under elevated CO₂ conditions.Copyright 1995, 1999Academic Press Biomass, chlorophyll a fluorescence, elevated CO₂, growth, Populus, poplar, photosynthesis, respiration, Rubisco     

A Comparison of the Growth, Photosynthesis, Stomatal Conductance and Water Use Efficiency of Moricandia and Brassica Species

When grown in pots and well-watered, the relative growth ratesof the above ground parts of two species of Moricandia (M. arvensis,an intermediate C₃–C₄ species, and M. moricandioides,a C₃ species) were inferior to those of two cultivated Brassicaspecies (B. campestris and B. napus). The Moricandia specieshad thicker leaves (greater d.wt per unit leaf area) with morechlorophyll than the Brassica species and had slightly greaterrates of photosynthesis per unit leaf area at an irradiance(400–700 nm) of 2000 µmol quanta m^–2 s ^–1.Leaves of M. arvensis, known to have a CO₂ compensation pointbetween that of C₃ and C₄ species, had a lower ratio of theintercellular to atmospheric partial pressure of CO₂ (C₁/C_a)and a greater instantaneous water use efficiency (WUE) thanthose of M. moricandioides and the Brassica species. Carbon isotope discrimination (     

Changing Patterns of Distribution of the Products of Photosynthesis in the Tomato Plant with Respect to Time and to the Age of a Leaf

Two series of experiments were conducted with tomato plantsgrown in a glasshouse. In the first series the second leaf ofa young plant was exposed to ¹⁴CO₂ for periods up to a maximumof 4 h and the distribution of the ¹⁴C-products was determinedeither at intervals of 10 and 30 min, 1, 2, 3, 4, 5, 6, 12,and 24 h, or 1, 2, 3, 5, 7, 11, and 15 days after the ¹⁴CO₂was initially supplied. Seventeen per cent of the containedradioactive carbon was exported during the first day and a further23 per cent during the following week. At the death of the leaf44 per cent of the carbon originally fixed was present in thedead structure. There is evidence that the roots re-export alarge proportion of the carbon products originally imported. In the second series the tenth leaf of a plant was suppliedwith ¹⁴CO₂, and 24 h later the relative amounts of radioactivitywere determined for every leaf, internode, and fruit truss andfor the roots and shoot apex. The plants were selected so thatleaf 10 was always immediately below truss 1. The experimentwas performed seven times, each time at a different stage bothin the life-cycle of the leaf and the development of the plant.There were differences in the total amounts of radioactivityfound at the end of each experiment but these differences werenot random. The pattern of distribution of the ¹⁴C exportedby leaf 10 changed as the plant developed. The percentage ofthe ¹⁴C initially fixed which was exported by leaf 10 rose toa peak early in its life and then fell sharply but the distributionof ¹⁴C exported followed a different pattern. For a long periodthere was a heavy accumulation of ¹⁴C in the internode immediatelybelow leaf 10 but later in development this was less evidentand the proportions reaching the roots increased. The internodeabove leaf 10 never showed the same degree of accumulation.Truss I dominated the distribution patterns during the phaseof its active growth. These results are discussed and a hypothesisto account for the changing patterns of distribution is presented.     

Physiology and Growth of Wheat Across a Subambient Carbon Dioxide Gradient

Two cultivars of wheat (Triticum aestivum L.), 'Yaqui 54' and'Seri M82', were grown along a gradient of daytime carbon dioxideconcentrations ([CO₂]) from near 350-200 µmol CO₂ mol^-1air in a 38 m long controlled environment chamber. Carbon dioxidefluxes and evapotranspiration were measured for stands (plantsand soil) in five consecutive 7·6-m lengths of the chamberto determined potential effects of the glacial/interglacialincrease in atmospheric [CO₂] on C₃ plants. Growth rates andleaf areas of individual plants and net assimilation per unitleaf area and daily (24-h) net CO₂ accumulation of wheat standsrose with increasing [CO₂]. Daytime net assimilation (P_D, mmolCO₂ m^-2 soil surface area) and water use efficiency of wheatstands increased and the daily total of photosynthetic photonflux density required by stands for positive CO₂ accumulation(light compensation point) declined at higher [CO₂]. Nighttimerespiration (R_N, mmol CO₂ m^-2 soil surface) of wheat, measuredat 369-397 µmol mol^-1 CO₂, apparently was not alteredby growth at different daytime [CO₂], but R_N /P_D of stands declinedlinearly as daytime [CO₂] and P_D increased. The responses ofwheat to [CO₂], if representative of other C₃ species, suggestthat the 75-100% increase in [CO₂] since glaciation and the30% increase since 1800 reduced the minimum light and waterrequirements for growth and increased the productivity of C₃plants.Copyright 1993, 1999 Academic Press Atmospheric carbon dioxide, carbon accumulation, evapotranspiration, light compensation point, net assimilation, respiration, Triticum aestivum, water use efficiency, wheat     

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     

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.     

Effect of CO2 Concentration on Growth, Carbon Distribution and Loss of Carbon from the Roots of Maize

The effects of three ranges of CO₂ concentration on growth,carbon distribution and loss of carbon from the roots of maizegrown for 14 d and 28 d with shoots in constant specific activity¹⁴CO₂ are described. Increasing concentrations of CO₂ led toenhancement of plant growth with the relative growth rate (RGR)of the roots affected more than the RGR of the shoots. Between16% and 21% of total net fixed carbon (defined as ¹⁴C retainedin the plant plus ¹⁴C lost from the root) was lost from theroots at all CO₂ concentrations at all times but the amountsof carbon lost per unit weight of plant decreased with time.Possible mechanisms to account for these observations are discussed. Key words: Growth, Roots, Carbon loss, [CO₂]     

Photosynthesis of Stands of Tomato, Cucumber and Sweet Pepper Measured in Greenhouses under Various CO2-concentrations

The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO₂-concentrations between 200 and 1200 µmolmol^-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO₂ balance, usingnitrous oxide (N₂O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO₂ concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyP_max 5-9 g m^-2 h^-1 CO₂ uptake; ratio P_max/LAI 1·5-3 gm^-2 h^-1; light compensation point 32-86 µmol s^-1 m^-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol^-1 and CO₂ compensation point 18-54 µmolmol^-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO₂, CO₂ balance, CO₂ use efficiency, cucumber, _{Cucumis sativus} L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas     

The Dynamics of Leaf Growth and Photosynthetic Capacity in Capsicum frutescens L.

In Capsicum frutescens L. cv. California Wonder the specificleaf weight (dry weight per unit laminar area) at leaf unfoldingis three times higher in the eighth leaf than in the first leafproduced. Intermediate leaves exhibit a trend between the twoThe change in specific leaf weight during laminar expansionis greatest in leaf 1 and least (sometimes zero) in leaf 8.Large changes in specific leaf weight during laminar expansionare associated with a large degree of palisade cell expansion,while leaves showing smaller rates of change have less palisadecell expansion but cell division is more evident. At leaf unfoldingthe fraction I protein content per unit laminar area is higherin upper than in lower leaves. Ribulose diphosphate carboxylaseactivity per unit laminar area and ¹⁴CO₂ fixation per unit laminararea have a similar pattern of development in all leaves andshow no correlation with the changes in specific leaf weight.The peak of activity in all leaves occurs when the laminar areais 10 cm². These results are compared with previous data onlaminar expansion and are seen as in accord with current ideason leaf growth.     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

Growth of Plants in Different Oxygen Concentrations

Dwarf french beans (Phaseolus vulgaris var. Canadian Wonder)were grown in chambers at 25?C with the roots aerated at 20per cent oxygen and tops variously maintained at: T₁ O₂ 0.21;CO₂ 270?10^–6: T₂; O₂ 0.05, CO₂, CO₂ 270?10^–6: T₃;O₂ 0.21; CO₂ 550?10^–6. Experiment 1 (T₁ and T₂) lasted2 weeks: Experiment 2 (T₁ T₂ and T₃) only one week. Hourly estimatesof CO₂ uptake were made by gas analysis and weekly estimatesof fresh weight, dry matter in tops and roots, and leaf area,by sampling. Light intensity was 80 W m^–2 of photosyntheticallyactive radiation. An attempt was made to explain the results in terms of a simplelight absorption model such that where dV/dt is the rate of CO₂ uptake per plant, ßis the photosynthetic efficiency, I₀ is the incident light intensity,f is the fraction of incident light absorbed by unit leaf layerand L is the leaf area index. The analysis showed that ß(T₂)was at least double ß(T₁), whilst f(T₂) was smallerthan f(T₁) at a given leaf area. The results also required thatthroughout the period of the experiment, fL(T₁)=fL(T₂) at anygiven time, i.e. the treatment with the larger leaf area (T₂)has the smaller value of f, and therefore intercepts less lightper unit leaf area. This could be advantageous for plant growth,but requires further experiments. The photosynthetic rates per unit leaf are about 40 per centgreater in T₂ than T₁. Over the relatively short period of the experiment the resultsare adequately described by U=btⁿ, where U is the accumulatedcarbon dioxide uptake, b is related to the photosynthetic efficiency(different for the differing treatments), and n is a constant(similar for all treatments). This relationship with time isbelieved to be a relationship with accumulated radiation, forthe light was constant throughout the experiments. Comparisons of carbon fixed (measured gas uptake) and dry matteraccumulation (sampling) show great scatter with an average valueof 0.43. The first week's results were generally smaller thanthis value and the second week's greater. Energy fixation as a fraction of photosynthetically active radiationon the ground area covered by the plants ranged from 3.5 to10 per cent. The results from treatment T₃ were similar to T₂ suggestingthat increasing CO₂ concentration decreases the growth inhibitionat 21 per cent O₂.     

The Translocation of 14C-Photoassimilate from Normal and Mutant Leaves to the Pods of Pisum sativum L.

In experiments using radioactive carbon dioxide (¹⁴CO₂) a comparisonwas made of the ¹⁴C-photoassimilate translocation potentialsof two normal leaved (genotype AfAfTlTl) and two mutant formsof Pisum sativum (pea). A ¹⁴CO₂ administration method is describedthat permitted ¹⁴C-translocation studies to be conducted underfield conditions. One of the mutants available produced tendrils in place of leaves(afafTlTl). The other mutant studied was without tendrils buthad a much branched petiole with numerous relatively minuteleaflets (afaftltl). These mutants and the normal-leaved cultivarswith which they were compared were not isogenic lines. Lengthybackcrossing would be required before full assessment couldbe made of the possible agronomic value of such mutations. An interim evaluation of these mutants was based on ¹⁴C-distributionassays that were conducted 48 h after feeding ¹⁴CO₂, to specifiedleaves. The indication was that in translocation terms the leafand pod had a well defined respective source and sink relationshipthat was independent of leaf morphology. In each case the podswhich constituted the major ¹⁴C sinks depended on which leafhad been fed ¹⁴CO₂. With regard to sink specific activity asdefined by the quantity of ¹⁴C incorporated per unit dry weightof pod, the mutants were not significantly different from normal. The implication of these findings was that fundamental changesin pea leaf morphology could be made genetically without a markedeffect on the photoassimilate export potential of the leaf.