Growth and Dry-weight Distribution in Callistephus chinensis as Influenced by Lighting Treatment

Plants of two cultivars of Callistephus chinensis (Queen ofthe Market and Johannistag) were grown in 8 h of daylight perday with one of the following treatments given during the 16h dark period: (a) darkness—‘uninterrupted night’,(b) I h of light in the middle of the dark period—a ‘nightbreak’, (c) I min of light in every hour of the dark period—‘cycliclighting’, (d) light throughout—‘continuouslight’. The plants receiving uninterrupted dark periods remained compactand rosetted in habit with small leaves, while leaf expansion,stem extension, and flower initiation were promoted in all threeillumination treatments (b, c, d). Although these three treatmentsproduced similar increases in leaf area, continuous light wasthe most effective for the promotion of both stem growth andflower initiation while cyclic lighting was generally more effectivethan a I-h night break. Continuous light also caused more dry matter to be divertedto stems at any given vegetative dry weight and it was shownthat the stem weight ratio of both varieties was correlatedwith stem length.     

Leaf Growth in Dactylis glomerate following Defoliation

Defoliation to a height of 2.5 cm considerably reduced the increasein leaf area in young Dactylis glomerata (cocksfoot) plantscompared with that of intact plants, the reduction in the rateof appearance of new leaves being relatively greater than thereduction in expansion of existing leaves. The growth of thoseexpanding leaves which were cut during defoliation accountedfor 94 per cent of the total increase in leaf area during thefirst four days after defoliation. In such a leaf, expandingcells were confined to a basal section which was well belowthe ligule of the enclosing fully expanded leaf. There was a positive relationship between rate of leaf expansionand total soluble carbohydrate content of the stubble when thecarbohydrate content was varied by placing the plants in thedark, but not when it was varied by defoliation and subsequentgrowth. These and other results suggest that the concentrationof soluble carbohydrate in the bases of expanding leaves wasa factor controlling leaf expansion following defoliation, andthat the concentration in any one leaf depended on the photosyntheticcontribution from its exposed portion. When the external nutrient supply was high, removal of the laminaeof fully expanded leaves, which comprised about two-thirds ofthe total leaf area, did not reduce leaf expansion. When thenutrient status was low, these leaves were of primary importance,presumably because of their role as a source of labile nutrients.     

Studies on the Expansion of the Leaf Surface: IV. THE CARBON AND PHOSPHORUS ECONOMY OF A LEAF

The fixation, utilization, and translocation of carbon and thenet import and export of phosphorus by three leaves of Cucumissativus over the course of their lives were measured in a controlledenvironment. The rate of photosynthesis of a leaf followed a regular dailypattern, rising to a maximum during the first 2 hrs. of thelight period and subsequently falling. Dark respiration wasusually highest at the beginning of the dark period and fellthroughout it. The daily rate of photosynthesis per unit areaof a leaf fell during its later life partly as a result of shadingby upper leaves and also because of an independent age factor.The rate of dark respiration per unit area was high in veryyoung leaves but fell rapidly with age. The amount of phosphorus in each leaf reached a maximum beforethe leaf had reached its maximum dry weight. There was thensubstantial net loss of phosphorus from the leaf. The changing function of each leaf as a sink or source of carbohydrateand mineral nutrients was determined. Four stages were recognized:(1) early development from inception until some time after unfolding,when the leaf was dependent upon imported carbohydate; (2) aperiod of rapid expansion, associated with a high rate of uptakeor mineral nutrients, during which translocation of assimilatedcarbon from the leaf was most rapid; (3) a time of decliningrates of growth, photosynthesis and export of carbon, associatedwith substantial loss of phosphorus; (4) finally, a short sensescentphase with net loss of CO₂, terminating in the death of theleaf.     

Effects of Nitrogen on the Development and Growth of the Potato Plant. 1. Leaf Appearance, Expansion Growth, Life Spans of Leaves and Stem Branching

Potatoes (Solanum tuberosum L) were planted in pots in a temperature-controlledglasshouse to collect data on the rate of leaf apearance, leafexpansion, apical lateral branching and active life spans ofleaves The treatments consisted of three rates of nitrogen supply,i e the NI treatment with 2 5 g N per pot and the N2 and N3treatments with 8 and 16 g N per pot, respectively The rate of leaf appearance was 0·53 leaves d^–1(one leaf per 28 °C d) and was negligibly affected by nitrogensupply The rate of leaf expansion was related to leaf numberand nitrogen supply The areas of mature leaves increased withleaf number on the main stem to reach a maximum for leaf numbers12–14, and declined for higher leaf numbers Leaves onapical lateral branches declined in mature area with increasein leaf number The expansion rate of leaves was the dominantfactor that determined the mature leaf area, irrespective ofleaf number and nitrogen treatment The smallest leaves wereobserved at the lowest rate of nitrogen supply Nitrogen promotedapical branching and hence the total number of leaves that appearedon a plant The proportion of total leaf area contributed byleaves on apical branches increased with time and nitrogen supply Active life span, i e the period of time between leaf appearanceand yellowing of the leaf, showed a similar relation to leafnumber as mature leaf area, at least in qualitative terms Leavesof the N3 treatment showed systematically longer life spansthan leaves of the NI and N2 treatment in the order of 3 weeksThe number of main stem leaves was not affected by nitrogensupply Potato, Solanum tuberosum L, leaf development, leaf extension, plant structure, nitrogen nutrition     

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.     

Abscisic acid mimics effects of dehydration on area expansion and photosynthetic partitioning in young soybean leaves

Abstract. Leaf area expansion, photosynthetic carbon dioxide uptake and leaf dry mass accumulation were compared for expanding leaves of well-watered soybean ( Glycine max [L.] Merr.) plants, mildly dehydrated plants and well-watered plants treated with abscisic acid (ABA). Both ABA treatment and dehydration reduced area expansion in the light and over a 24 h period without decreasing the photosynthetic rates of expanding leaves. Dry mass accumulation during the light was less in ABA-treated and water-stressed leaves than in control leaves, with no differences among treatments in leaf mass per unit of area. ABA treatment and water stress both increased export of carbon from expanding leaves in the light. ABA applied near the end of the light period also increased export of carbon during the following dark period. However, it is unlikely that decreased availability of photosynthate caused slow expansion in the ABA and dehydration treatments, because expansion rates were not slowed in plants kept in dim light, even though photosynthetic rates and dry mass accumulation rates were greatly reduced. The data suggest that ABA may mediate the effects of mild dehydration on leaf area expansion and partitioning of photosynthate.     

Studies in the Nutrition of Apple Rootstocks: II. Effects of Concentration of Iron in the Nutrient Solution on Growth and Chlorophyll Content

Rooted one-year shoots were grown for one season by sprayingtheir roots with nutrient solution. Iron supplied as Fe-EDTAat four concentrations resulted in plants which were respectively(a) severely chlorotic, (b) mildly chlorotic, (c) dark greenand healthy (controls), and (d) dark green but with slight reductionin growth. Severely deficient plants showed 40–70 per cent reductionsin growth as measured by fresh weight, shoot length, diameterincrease, leaf area, net assimilation and relative growth-rates.Dry weights were reduced 70–80 per cent and of the totaldry-weight increment a greater proportion remained in the leaves,which had a lower dry weight and higher water content per unitarea. However, because the initial old stem formed a greaterproportion of the total dry weight, the leaf area ratio remainedabout 11 per cent lower than in the controls. Severely deficientplants had, per unit of chlorophyll, a higher dry-weight increaseand net assimilation rate than the controls. Mild deficiency caused 10–20 per cent reductions in growthand net assimilation rate; the leaf area ratio was normal. Possible mechanisms of the effects of low iron supply are discussed,while the small growth reduction at the highest Fe-EDTA concentrationis attributed to chelate toxicity     

Chloroplast Protein Synthesis During Barley Leaf Growth and Senescence: Effect of Leaf Excision

Chloroplast protein synthesis was measured during the expansion,maturity and senescence of the oldest leaf of barley, Hordeumvulgare L., var. Hassan. A maximum rate of protein synthesisoccurred near the end of the expansion stage 9 d after sowing.Protein synthesis increased again at the beginning of senescenceand reached a new maximum at day 14 after sowing. Detachmentand incubation of leaves in the dark stimulated chioroplastprotein synthesis by fully expanded or by senescent leaves butnot by expanding leaves. If the detached leaves were kept inthe light, chloroplast protein synthesis was stimulated in fullyexpanded but not in senescent leaves. Short treatments (18 h)of leaf segments with growth substances in either light or indarkness, significantly changed the rate of protein synthesisshown by chloroplasts. The relationship between chloroplastprotein synthesis and leaf senescence is discussed. Key words: Hormones, light, maturity     

Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Vegetative crops of chrysanthemum were grown for 5 or 6 weekperiods in daylit assimilation chambers. Crop responses to differentradiation levels and temperatures were analysed into effectson dry matter partitioning, specific leaf area, leaf photosynthesisand canopy light interception. The percentage of newly formed dry matter partitioned to theleaves was almost constant, although with increasing radiationor decreasing temperature, a greater percentage of dry matterwas partitioned to stem tissue at the expense of root tissue.There was a positive correlation between the percentage of drymatter in shoot material and the overall carbon: dry matterratio. Canopy photosynthesis was analysed assuming identical behaviourfor all leaves in the crop. Leaf photochemical efficiency wasonly slightly affected by crop environment. The rate of grossphotosynthesis per unit leaf area at light saturation, P_A (max),increased with increasing radiation integral, but the same parameterexpressed per unit leaf dry matter, P_w (max) was almost unaffectedby growth radiation. In contrast, P_A (max) was hardly affectedby temperature but P_w (max) increased with increasing growthtemperature. This was because specific leaf area decreased withdecreasing temperature and increased with decreasing radiation.There was a positive correlation between canopy respirationintegral and photosynthesis integral, and despite a four-foldchange in crop mass during the experiments, the maintenancecomponent of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variationwith radiation integral but was negatively correlated with temperature.This decrease in the efficiency of the canopy at interceptingradiation exactly cancelled the increase in specific carbonassimilation rate that occurred with increasing growth temperature,giving a growth rate depending solely on the incident lightlevel. Chrysanthemum, dry matter partitioning, photosynthesis, specific leaf area     

The Production and Distribution of Dry Matter in Maize after Flowering

An experiment in which different groups of leaf laminae wereremoved, or ears shaded, shortly after silking showed that mostof the dry-matter increase after flowering was produced by upperleaves. The top five, the middle four, and the bottom six laminaeaccounted, respectively, for 26 per cent, 42 per cent, and 32per cent of the leaf area duration (D) of the laminae afterflowering; the estimated contributions of the three groups todry-matter production by the laminae after flowering were about40 per cent, 35–50 per cent, and 5–25 per cent,respectively. The sheaths provided about one-fifth of the totalleaf area and probably contributed about one-fifth, and laminaefour-fifths, of the total dry matter produced after flowering.The contribution from photosynthesis by the ear was negligible,presumably because its surface area was only 2 per cent of thatof the leaves. Leaf efficiency (dry matter produced per unitarea) decreased greatly from the top to the base of the shoot.When laminae were removed, the grain received a larger fractionof the dry matter accumulated after flowering, less dry matterremained in the stem, and the photosynthetic efficiency of theremaining leaves was apparently increased. When alternate laminae were removed at the time of silking (half-defoliation)D was decreased by 40 per cent, and the subsequent productionof dry matter decreased nearly proportionately, so that netassimilation rate (E) was not affected but grain dry weightwas decreased by only 32 per cent. At the final harvest, thegrain of half-defoliated plants constituted 80 per cent of thedry matter accumulated after flowering, compared with 65 percent for intact plants. Stem weight decreased from two weeksafter flowering in half-defoliated plants, but remained nearlyconstant in intact plants. When pollination was prevented andno grains formed, E during the first month after flowering wasunaffected; the dry matter that would have passed into the grainaccumulated in the stem and husks, not in the leaves. The decrease in stem weight caused by defoliation suggests thatpreviously stored dry matter was moved to the grain. That suchmovement is possible was shown by keeping prematurely harvestedshoots in the dark for two weeks with their cut ends in water;the dry weight of the grain increased and that of the stem,laminae, husks, and core decreased. Nevertheless, dry-matterproduction after flowering was more than sufficient for graingrowth, and previous photosynthesis probably contributed littleto the grain.     

Modulation of Competition between Fruits and Leaves by Flower Pruning and Water Fogging, and Consequences on Tomato Leaf and Fruit Growth

The effects of water fogging and reducing plant fruit load werestudied in a tomato crop grown in a glasshouse under Mediterraneansummer conditions. The objective of these treatments was toreduce competition between leaves and fruits for carbohydratesand water. Flower pruning increased plant leaf area and increasedfruit, stem, lamina and petiole dry mass (DM). This indicatesthat leaf area growth was limited during the summer due to competitionbetween fruits and leaves for assimilates. In contrast, reducingthe air vapour pressure deficit (VPD) by water fogging had noeffect on plant leaf area or aerial plant DM. Interestingly,there was a significant interaction between plant fruit loadand VPD: the higher the leaf[ratio]fruit ratio the greater theresponses to a reduction in VPD (increase in fruit DM, fruitdiameter, fruit and leaf expansion rate). The data suggest thatunder high fruit loads, water and carbohydrates limit growthunder Mediterranean summer conditions. However, reducing VPDwas not always sufficient to enhance fruit and leaf growth.This might be due to the lower leaf area under high fruit load.In contrast, reducing VPD under low fruit load triggered higherrates of leaf and fruit expansion; this is probably linked toa greater availability of water and carbohydrates. Copyright2001 Annals of Botany Company Assimilate competition, assimilate supply, flower pruning, fruit load, fruit growth, generative/vegetative growth, leaf growth, Lycopersicon esculentum, specific leaf weight, tomato, vapour pressure deficit, water stress     

Nitrate Supply and the Biophysics of Leaf Growth in Salix viminalis

The influence of nitrogen on leaf area development and the biophysicsof leaf growth was studied using clonal plants of the shrubwillow, Salix viminalis grown with either optimal (High N) orsub-optimal (Low N) supplies of nitrate. Leaf growth rate andfinal leaf size were reduced in the sub-optimal treatment andthe data suggest that in young rapidly growing leaves, thiswas primarily due to changes in cell wall properties, sincecell wall extensibility (% plasticity) was reduced in the LowN plants. The biophysical regulation of leaf cell expansion also differedwith nitrogen treatment as leaves aged. In the High N leaves,leaf cell turgor pressure (P) increased with age whilst in theLow N leaves P declined with age, again suggesting that foryoung leaves, cell wall plasticity limited expansion in theLow N plants. Measurements of cell wall properties showed thatcell wall elasticity (%E) was not influenced by nitrogen treatmentand remained constant regardless of leaf age. Key words: Salix, cell wall extensibility, nitrogen nutrition, biophysics of leaf growth     

Photosynthesis, Ribulose-1,5-bisphosphate Carboxylase and Leaf Characteristics of Nicotiana tabacum L. Genotypes Selected by Survival at Low CO2 Concentrations

The photosynthetic characteristics (responses to CO₂ and light),ribulose-1,5-bisphosphate carboxylase (Rubisco) properties,and the size and number of cells of the mesophyll of Nicotianatabacum L. leaves of genotypes selected for survival at lowatmospheric CO₂ concentrations are described. When grown inthe greenhouse with nutrient solutions, the total dry matterproduction of the selected genotypes was 23% greater than thatof the parent genotype; this increase was related to a greaternumber of mesophyll cells of smaller size in the selected plantscompared to the parent. However, it was not related to changesin the photosynthetic characteristics nor to Rubisco properties.These results suggest that the increased dry matter accumulationof the selected genotypes is not due to a reduction in photorespirationnor an increase in the CO₂ assimilation rates. Rather, the selectionof haploid tobacco plantlets in low CO₂ has resulted in plantswith greater leaf area (shown in previous work), due to theproduction of more cells of smaller size and to lower respirationrates per unit of leaf dry mass (previous work), thus increasinglight capture, reducing the loss of assimilates and increasingtotal plant dry matter production. Key words: Photosynthesis, ribulose-1,5-bisphosphate carboxylase, leaf anatomy, tobacco, genotypes     

The Dependence of Calcium Transport and Leaf Tipburn in Strawberry on Relative Humidity and Nutrient Solution Concentration

Strawberry plants were grown in controlled-environment cabinetswith different day-and-night relative humidities, in nutrientsolutions of different osmotic potential and different calciumconcentrations. Leaf calcium (% d. wt.) depended strongly on leaf age and waslowest and very sensitive to environment when the leaf was emergingfrom the bud. Calcium in the emergent leaf was greatest andtipburn least when plants were grown in humid nights (VPD usually< 100 Pa) and weak nutrient solutions (osmotic potentialabout –25 kPa). Such plants guttated freely. In contrastplants grown in dry nights (VPD, c. 600 Pa) never guttated,had small concentrations of calcium in emergent leaves and sufferedtipburn. The behaviour of plants transferred between humiditytreatments rapidly reflected the new conditions. Increasingthe osmotic potential of the nutrient increased tipburn anddecreased calcium in emergent leaves even though the nutrientcontained more calcium. When the calcium concentration in the emergent leaf exceeded0.07 per cent of d. wt, tipburn was never seen; below 0.05 percent tipburn was usually severe. These results suggest that pre-emerged, and therefore non-transpiring,leaves depend for their calcium on water flow arising from rootpressure at night. After leaf emergence, calcium intake intoleaves was promoted by dry days, indicating that calcium wasthen supplied by transpirational water flow. Humid nights, drydays and weak nutrient solutions minimize the risk of leaf tipburnin strawberry. Fragaria ananassa Duch., strawberry, tipburn, calcium transport, relative humidity, nutrient supply, guttation     

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     

Flag Leaf Anatomy of Triticum and Aegilops Species in Relation to Photosynthetic Rate

Quantitative anatomical and other measurements were made onfully expanded flag leaves of a series of diploid, tetraploidand hexaploid Triticum and Aegilops species, and photosyntheticrates per unit leaf area were measured at light saturation (P_max). Diploids had the highest P_max, hexaploids the lowest with tetraploidsbeing intermediate. The anatomical features of tetraploids andhexaploids were generally similar, but different from the diploids.The diploids had thinner leaves with less dry matter and chlorophyllper unit area. The surface area of the mesophyll cells per unitvolume of mesophyll tissue was similar for all ploidy levels,as was the ratio mesophyil cell surface area per unit leaf area.It is argued that while these anatomical features are unlikelyto account for the observed variation in Pmax, it is possiblethat other structural factors with which they are correlatedmay causally influence P_max. One such feature is the averagediffusion path length from the plasmalemma at the cell surfaceto the sites of carboxylation. Anatomy, photosynthesis, mesophyll, cell size, Triticum, Aegilops, polyploidy     

Effects of Temperature and Leaf Position on Leaf Area Expansion of Kiwifruit (Actinidia deliciosa) Shoots: Development of a Modelling Framework

This paper describes mathematically the effects of temperatureand position on the expansion of leaves along a kiwifruit (Actinidiadeliciosa) shoot, taking into account shoot morphology. Theleaves were grouped into three zones along the shoot: initialcluster leaves (first zone); the rest of the leaves that werepreformed during the previous season (second zone); and leavesthat were initiated during the current season (third zone).After opening of the initial cluster, the leaves appeared atconstant rates for each of the two temperature treatments considered.The expansion of individual leaves was modelled by a growthfunction with the parameters: final area; duration of the growthwindow; centre of the growth window (timing of expansion); andlower asymptote. Within the first two zones, the pattern ofleaf expansion was affected by nodal position, with basal leaveshaving higher initial rates of expansion than distal leaves.The timing of expansion was linear with respect to the nodalposition within each of the zones, with the slope independentof temperature for the first zone. The slopes of the timingof expansion for the second and third zones depended on temperatureand were correlated for each temperature treatment. Final leafarea was a function of leaf position in the first zone and afunction of timing of leaf expansion for distal leaves startingfrom leaf 10. Temperature had no effect on final leaf area inthe first zone. For the rest of the leaves, temperature affectedfinal leaf area indirectly, through the timing of leaf expansion.The effect of temperature on the growth window of individualleaves within the first zone was less than that for the restof the leaves. However, simulated values for the total leafarea of shoots using the average shoot growth window showedgood agreement with experimental values.Copyright 2001 Annalsof Botany Company Actinidia deliciosa‘Hayward’, shoot development, individual leaf area, temperature effect, positional effects, modelling     

Specific Leaf Weight in Zones of Cell Division, Elongation and Maturation in Tall Fescue Leaf Blades

Patterns of change in specific leaf weight (SLW), water-solublecarbohydrate (WSC) content and leaf width were used to delineatethe region of secondary cell wall accumulation, and determinethe rate of increase in structural material along a developingleaf blade of tall fescue (Festuca arundinacea Schreb.). Structuralspecific leaf weight (SSLW) was determined by subtracting WSCmass from dry weight to emphasize structural material. Becausemeristematic activity, cell elongation, and cellular maturationare arranged successively in the grass leaf, these patternsrepresent a developmental sequence through which each segmentof the leaf blade passes. Patterns were generally similar fortwo genotypes, one selected for high (HYT) and the other forlow (LYT) yield per tiller, for a single genotype grown at 17or 25 C, and for two field-grown populations which differedin leaf area expansion rate (LAER). In all three studies, the elongation zone of the developingleaf had 31 to 39 per cent WSC on a dry weight basis. The LYTgenotype had a higher SLW at all stages of development whengrown at 17 than at 25 C, due to greater WSC accumulation.At 20 C, the HYT genotype had a higher SLW all along the elongatingleaf blade than the LYT genotype. This difference was due toa difference in SSLW, while WSC content was similar. The LERwas 64 per cent higher in the high population than the low,but elongation zones were similar in WSC. In all cases, SSLWwas high in the meristematic region, lowest near the distalend of the cell elongation zone, then increased linearly astissue matured. Rate of increase in SSLW was 8.5 and 5.2 g m^–2d^–1 for the HYT and LYT genotypes, respectively, and 7.6and 6.7 g m^–2 d^–1 for the high and low LAER populations,respectively. Festuca arundinacea Schreb., tall fescue, specific leaf weight, leaf width, water-soluble carbohydrates, leaf elongation rate     

Flag Leaf Photosynthesis of Triticum aestivum and Related Diploid and Tetraploid Species

Rates of net photosynthesis of the flag leaves of 15 genotypesof wheat and related species were measured throughout theirlife, using intact leaves on plants grown in the field. At thestage when rates were maximal, they were in general highestfor the diploid species, intermediate for the tetraploidspeciesand lowest for Triticum aestivum (means of 38, 32 and 28 mgCO₂ dm^–2 h^–1 respectively). Rates were stronglynegatively correlated with leaf area, leaf width and the meanplan area per mesophyll cell and positvely correlated with stomatalfrequency and number of veins per mm of leaf width. The differencesamong species in these attributes were mainly related to ploidylevel. It was not possible to determine the relative importanceof each anatomical feature, though the changes in stomatal frequencyhad only slight effects on stomatal conductance and the observeddifferences in rates of photosynthesis were much greater thanwould be expected from those in stomatal conductance alone. There was genetic variation in rates of light dependent oxygenevolution of isolated protoplasts and intact chloroplasts butno difference attributable to ploidy. The mean rate, 91 µmolO₂ mg^–1 chlorophyll h^–1, equivalent to 3.9 mg CO₂mg^-1chlorophyll h^-1 was considerably less than the rate of photosynthesisin comparable intact leaves, which was 7.2 mg CO₂ mg^–1chlorophyll h^–1. The total above-ground dry matter yields were least for thewild diploids T. urartu and T. thauodar and the wild tetraploidT. dicoccoides, but the other wild diploids produced as muchdry matter as the hexaploids. The prospects of exploiting differences in photosynthetic ratein the breeding of higher yielding varieties are discussed. Triticum aestivum L., wheat, Aegilops spp, photosynthesis, stomatal conductance, stomatal frequency, polyploidy     

Leaf Characteristics and Net Gas Exchange of Diploid and Autotetraploid Citrus

The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) ‘Valencia’ sweet orange (Citrus sinensis (L.)Osb.) and ‘Femminello’ lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 5–15% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO₂assimilation rate (A_CO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerA_CO2than their diploids. There were no significant differencesin A_CO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower A_CO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO₂diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; ‘Valencia’ sweet orange; ‘Femminello’ lemon