The thermal response of leaf extension rate in genotypes of the C4-grassMiscanthus: an important factor in determining the potential productivity of different genotypes

Thermal responses of plant extension rate are reported for 32genotypes of the C₄ grass Miscanthus. Displacement transducerswere used to measure plant extension rate as temperatures werestepped between 20C and 5C. Leaf extension accounted for 83%of the plant extension. The Q₁₀ between 10C and 20C for thegenotypes varied from 3.0 to 4.7. The relationship between temperature(5-20 C) and plant extension rate was found to be describedadequately by fitting a third order polynomial. An estimateof the effect of differences in the thermal response of plantextension rate on the potential yield of the genotypes was calculatedfor Irish climatic conditions using a simple growth model. Potentialyield varied between 3 and 23 t ha^–1 year^–1. Thisdemonstrates the critical role which differences in leaf expansionrate can play in the selection of more productive genotypes.The significance of vapour pressure deficit on the estimatesof thermal response of plant extension rate are discussed. Key words: Leaf growth, Miscanthus, temperature, radiation-use efficiency, vapour pressure deficit, C₄ plants     

Response to Temperature in a Stand of Pearl Millet: VI. LIGHT INTERCEPTION AND DRY MATTER PRODUCTION

Stands of pearl millet were grown in glasshouses in which meanair temperature was controlled to 19, 22, 25, 28 and 31 ?C withan amplitude of ?5 ?C. During the main growth period, leaf areaindex increased at a constant rate which was proportional tomean temperature above a base of 10 ?C. The warmest stand, therefore,intercepted more radiation before anthesis but the transmissioncoefficient was independent of temperature (K 0.3). Based ondry weight at final harvest, the efficiency of conversion forintercepted radiation ranged from about 2.1–2.4 g MJ^–1consistent with field experience. Combining this informationwith figures for the duration of growth in relation to temperaturesuggests that growth rate should be maximal at 25–27 ?Cand total dry weight at 20–22 ?C. Key words: Temperature, Pearl millet, Growth rate, Light     

Characteristics of Starch Grains Isolated from Mature Pepper Leaves Grown under Different Irradiances and Daylengths

The size, shape and number of starch grains have been determinedin mature pepper leaves taken from plants grown under definedconditions of daylength and irradiance. Starch grains were 0.2–7.0 µm diameter and 02–1.5µm in thickness. Grain diameter was positively relatedto daylength and the number of grains per unit leaf area inverselyrelated to daylength. Mean grain diameter was also positivelyrelated to leaf area. Analysis of starch grains from leaves having a wide range ofstarch contents showed that grain diameter was linearly relatedto leaf starch content. However, mean diameter only doubledwith a 10-fold increase in starch content. The number of grainsincreased from approximately 5 ? 10¹⁰ m^–2 of leaf to over200 ? 10¹⁰ m^–2 with increasing starch content. The totalsurface area of grains increased from less than 1.0 m² m^–2leaf to over 20 m² m^–2 leaf. Leaf starch grain shape and size are compatible with both efficientstorage as disc-shaped chloroplasts and the maintenance of hightotal grain surface area by increasing grain number more thandiameter. Possible mechanisms for the control of grain initiation,growth and degradation are suggested. Key words: Starch grains, size, shape, pepper leaves     

Some Effects of Temperature and Irradiance on Growth of the First Four Leaves of Wheat, Triticum aestivum

Plants of Heron wheat were grown at 20 and 15 °C and inquantum flux densities of 400 and 200 µmol m^–2 s^–1.At completion of expansion of the first or second leaf, plantswere transferred between temperatures and quantum flux densities.Final size and cell number were measured for each of the firstfour main-stem leaves. Leaf area was affected only slightlyby treatment and effects on leaf length and width were alsosmall. It was concluded that leaf extension rate, which waslower at the lower temperature and in the lower light regime,is inversely related to the duration of leaf expansion. Leafdry wt was higher for plants grown in high light and for plantsgrown at 15 °C; transfer treatments led to readjustmentswhereby dry wts of leaves expanded after transfer resembledthose of leaves on plants kept throughout in the post-transferconditions. Leaf cell number was not affected by treatment but mean drywt per cell was significantly greater in high light, and forthe first two leaves, at 15 °C. There was a major and highlysignificant effect of treatment on the ratio of dry: fresh wtper cell, this being larger for leaves in high light. Transfertreatments between light regimes led to rapid changes in expandingleaves as was found for leaf dry wt. It was concluded that theexpanding grass leaf is much less dependent on older leavesto provide the necessary materials for cell division and expansionthan is the dicotyledon leaf. It is suggested that the increasein cell dry wt in high light is associated with an increasein cell wall material which is under photomorphogenic control. Triticum aestivum, wheat, leaf growth, cell division, cell expansion, cell size     

Leaf Extension in Zea mays: III. FIELD MEASUREMENTS OF LEAF EXTENSION IN RESPONSE TO TEMPERATURE AND LEAF WATER POTENTIAL

Leaf extension rates of young maize plants were measured inthe field. Large diurnal fluctuations of air temperature fromabout 5—35°C caused extension rates to vary from 0·4mm h^–1– 3·6 mm h^–1. When the temperatureof the shoot apical meristem was kept at 30–34°C,extension rates remained constant, despite diurnal fluctuationsof air temperature. Leaf water potentials () above –8 or –9 bars hadlittle apparent effect on extension rate. It was concluded that gradients within leaves could account for this.     

Effects of CO2 Enrichment on Four Poplar Clones. I. Growth and Leaf Anatomy

The poplar clones Columbia River, Beaupre, Robusta and Raspaljehave been investigated under the present (350 µmol mol^–1)and double the present (700 µmol mol^–1) atmosphericCO₂ concentration. Cuttings were planted in pots and were grownin open-top chambers inside a glasshouse for 92 d. The number of leaves, total length of stem, total leaf area,overall growth rate, total leaf, stem and root d. wt respondedpositively to increased CO₂ but the leaf size and biomass allocationshowed no change with CO₂ enrichment. Beaupre and Robusta showeda larger growth response than either Columbia River or Raspalje. The effects of CO₂ enrichment were restricted to the early phaseof growth at the beginning of the growth season. Leaf cell numbers in all the clones were not affected by CO₂enrichment. Leaf thickness was affected; this was mainly theresult of larger mesophyll cells and more extensive intercellularspaces. Poplar clones, CO₂ enrichment, growth, leaf anatomy, leaf cell number     

In-Phase Cycling of Photosynthesis and Conductance at Saturating Carbon Dioxide Pressure Induced by Increases in Water Vapour Pressure Deficit

Bunce, J. A. 1987. In-phase cycling of photosynthesis and conductanceat saturating carbon dioxide pressure induced by increases inwater vapour pressure deficit.—J. exp. Bot. 38: 1413–1420. The leaf to air water vapour deficit was increased suddenlyfrom about 1·0 to 2·5 IcPa for single leaves ofsoybean (Glycine max L. Merr.) plants held at 30 °C, 2·0mmol m ^–2 s^–1 photosynthetic photon flux density(PPFD) and carbon dioxide pressures saturating to photosynthesis.After a lag of about 10 min, photosynthetic rate and stomatalconductance to water vapour began to decrease, and then cycledin phase with each other. The period of the cydes was about20 min. During these cycles the substomatal carbon dioxide pressurewas constant in the majority of leaves examined, and was alwaysabove saturation for photosynthesis. Epidermal impressions showedthat most stomata changed in aperture during the cycles, andthat very few were ever fully closed. Water potential measuredon excised discs changed by at most 0·1 MPa from theminima to the maxima in transpiration rate. In contrast, forleaves of sunflower (Helianthus animus L.) grown at low PPFD,the increase in VPD led to leaf wilting and decreased photosynthesis,followed by recovery of turgor and photosynthesis as stomatalconductance began to decrease. In these leaves photosynthesisand conductance then cycled approximately 180° out of phase.It is suggested that in soybeans decreased leaf conductanceinduced by high VPD provided a signal which decreased the rateof photosynthesis at carbon dioxide saturation by a mechanismthat was not related to a water deficit in the mesophyll. Key words: Photosynthesis, stomatal conductance, cycling, vapour pressure deficit     

Ion Concentration and Carbohydrate Status of the Elongating Leaf Tissue 4Hordeum vulgare Growing at High External NaCl: II. CAUSE OF THE GROWTH REDUCTION

The cause for the growth reduction of a salt-tolerant varietyof barley (cv. ‘Beecher’) was investigated in plantsgrowth for 5 d at 120 mM and 180 mM NaCl. The NaCl treatmentsincreased the concentrations of soluble carbohydrate in theelongating tissues of the growing leaf, while starch did notchange. This shows that photosynthesis was not limiting growth,and indicates that the cause for the growth reduction was locatedin the growing leaves, specifically in the elongating tissue. Leaf elongation increased rapidly after transfer of plants from120 to 60 mM NaCl. The rate elongation during the first hourafter transfer was already equal to that of plants grown at60 mM NaCl, despite the persistence of high Cl^– and (Na⁺+ K⁺) concentrations in elongating as well as fully elongatedtissues. This indicates that the growing tissues suffered fromwater deficit rather than from adverse effects of ions on metabolism.     

Saturation Deficit, Canopy Formation and Function in Sorghum bicolor (L.)

Hamdi, Q. A., Harris, D. and Clark, J. A. 1987. Saturation deficit,canopy formation and function in Sorghum bicolor (L.).—J.exp. Bot. 38: 1272–1283. Stands of two sorghum genotypes, SPV 354 and MK. 35-1, weregrown in controlled-environment glasshouses at three levelsof saturation vapour pressure deficit (SD), at the same temperatureand with unrestricted soil moisture. Vegetative growth was monitoredby growth analysis and non-destructive measurements were madeof leaf appearance, leaf extension and final size, and fractionallight interception. Rates of leaf appearance were reduced athigh SD in both genotypes, although this may have been an artefactof the method of measurement, and MK 35-1 produced leaves moreslowly than SPV 354. Leaf extension was also slowed as SD increasedand, since the duration of extension for individual leaves ofa given age remained constant, resulted in smaller leaf areaindices (L) in dry air than in humid air. The cumulative interceptionof radiation and the dry matter/radiation quotient (e) bothdecreased as SD increased. Key words: Sorghum, saturation deficit, canopy formation     

Carbon Dioxide Exchange of Spring-wheat in Relation to Age and Photon-flux Density at Different Growth Temperatures

CO₂-exchange rates (CER) of the sixth and the flag leaves oftwo spring-wheat varieties, Kolibri and Famos, were comparedusing an open-circuit infrared gas analysing system. Measurementswere repeated every two weeks starting when leaf blades werefully expanded. Single plants were grown in a controlled environmenthaving a photopuiod of 15 h and a day/night temperature of 24/19°C(H), 18/13 °C (M), and 12/7 °C (L) respectively untilapprox. 2 weeks after anthesis and at 18/13 °C until maturity.The photosynthetic photon-flux density (PPFD) at the top ofthe plants was 500 µE m^–2 sec^–1. During themeasurements PPFD was gradually reduced from 2000 to 0 µEm^–2 sec^–1 whereas the temperature was maintainedat the respctive growth-temperatures during the light period.The CER of the sixth leaf declined fairly similarly for bothvarieties, except for Kolibri where a faster decline was observedduring the first two weeks after full leaf expansion. The CERof the flag leaf declined more slowly than that of the sixthleaf. With the flag leaf of Famos, the decline was nearly linear,whereas with Kolibri it was very slow during the first few weeksbut rapid as the leaves further senesced. This pattern becamemore pronounced as the growth temperature decreased. The declinein relation to leaf age was much smaller at low PPFD than athigh PPFD during the same period. At full leaf expansion Kolibrireached higher maximum CER than Famos except at H. As the PPFDwas reduced the difference became smaller and at very low PPFDsuch as 50 µE m^–2 sec^–1 was reversed for thesixth leaf. Under optimum growth conditions maximum values ofCER were greater than 50mg CO₂ dm^–2h^–1 and PPFDfor light saturation was close to 2000 µE m^–2 sec^–1.A comparison between the actual CER and a fitted curve widelyused, PN=(a+b/l)^–1–DR, showed that the goodnessof fit strongly depends on cultivar, treatment and leaf ageas well as on the number and the level of PPFD from which datafor calculations are taken. Triticum aestivum, L., wheat, photosynthesis, photon-flux density, light response, carbon, dioxide exchange     

The Growth and Development of Simulated Swards of Perennial Ryegrass: I. Leaf Growth and Dry Weight Change as Related to the Ceiling Yield of a Seedling Sward

The leaf growth, tiller production, light interception, anddry weight increase of a simulated sward of S24 perennial ryegrass(Lolium perenne) were followed during the development of thesward from a collection of two-leaved seedlings to a closedcanopy with an LAI of 23, of which 15 consisted of green leaflaminae. The dry weight of live shoots increased exponentiallyat first, but then entered a long linear phase of increase.This was equivalent to a crop growth rate of 200 Kg ha^–1day^–1 and a conversion efficiency of radiant energy (400–700nm) of 7.2 per cent. Towards the end of the growth period therate of increase of live shoots declined rapidly to zero anda ceiling yield was reached equivalent to 10 metric tons ha^–1.Leaf growth continued at a high rate, but was equalled by therate of leaf death, so that the weight of live leaf tissue remainedconstant. By this time the swards had achieved a stable tillerpopulation (about 1 cm^–1), each tiller bore a constantnumber of live leaves (about three), and the length of eachnewly expanded leaf equalled the length of the old leaf it replaced(about 70 cm). The swards were grown in Perlite so that in theabsence of soil fauna dead leaves accumulated at the base ofthe sward where, after 12 weeks, they accounted for 19 per centof the total weight of dry matter produced.     

The Growth Rate of Successive Leaves of Wheat Plants in Relation to Sugar and Protein Concentrations in the Extension Zone

The growing part of a wheat leaf (the extension zone) is loocatedat the leaf base and following from this it was proposed thatthe absolute leaf extension rate (L_er) can be partitioned intotwo components: the length of the extension zone (L_ez) and therelative extension rate of that extension zone (R_ez). R_ez isan appropriate measure of the efficiency of leaf growth forcomparing different leaves. This model of a wheat leaf was thenused to investigate whether differences in growth rates betweensuccessive leaves on wheat plants were due to differences inhexose sugar or protein concentrations within the extensionzone. Measurements were done in an irrigated field crop suppliedwith 0, 3, 10, or 30 kg N ha^–1 per week. The mean values of L_er at 15 °C increased with leaf numberand with nitrogen supply as did values for L_ez. In contrastR_ez at 15 °C declined from 0.9 d^–1 for the first leavesto 0.3 d^–1 for the flag leaf. Nitrogen supply had littleeffect on R_ez. A separate measure of the efficiency of leafgrowth, the responsiveness of L_er to temperature (measured asthe slope of the temperature response curve), also decreasedwith leaf number by the same order as R_ez and was similarlyunaffected by nitrogen supply. The protein concentrations in the extension zones of the firstleaves were around 40 mg g^–1 fr. wt. and this declinedto approximately 20 mg g^–1 fr. wt for leaves emergingafter tillers emerged and remained low thereafter. Protein concentrationswere not correlated with the external supply of nitrogen. Hexosesugar concentrations followed a reverse pattern of increasingin the later order leaves and these also increased as nitrogensupply decreased. Both R_ez and the responsiveness of L_er to temperature were positivelycorrelated with the protein concentration, the relationshipin each case being described by a rectangular hyperbola equation(P < 0.01), and negatively correlated with hexose concentrations.It was concluded that internal competition between growing pointsfor reduced nitrogen caused the observed effects. However, differencesin protein concentrations may not simply reflect differencesin enzyme concentrations; rather these differences may indicatechanges in some other character such as cell numbers.     

Diurnal Extension Rates of Wheat Leaves in Relation to Temperatures and Carbohydrate Concentrations of the Extension Zone

The objective of this experiment was to determine how diurnalvariations in rates of leaf extension of wheat plants in anirrigated field crop were related to temperatures and carbohydrateconcentrations of the extension zone. Leaves 3, 4. 5 of themain shoot were studied as each emerged from the encirclingsheath. The carbohydrates in the extension zone of the emergingleaf were analysed by converting them to glucose-6-phosphateand then measuring the reduction of NADP in the presence ofglucose-6-phosphate dehydrogenase. Average hexose concentrations(glucose and fructose) increased each day from 4 up to 5 mgg^–1 fr. wt. and sucrose from 3 up to 7 mg g^–1 fr.wt. with the maximum in mid-afternoon; there were no differencesamong the three leaves. Concentrations of fructans were constantthroughout the day for leaves 3 and 4 but showed a mid-afternoonrise in leaf 5. The average concentrations of fructans in theextension zones increased from 0 to 5 to 11 mg g^–1 fr.wt. for leaves 3, 4, and 5 respectively and was consistent withthe conclusion that there was an increasing over-supply of carbohydratesfor growth of the shoot as the plant increased in size. Ratesof leaf extension were correlated with temperature but not withhexose concentrations. We concluded that the supply of carbohydratesdid not limit the growth of leaves under field conditions buttheir utilization in leaf growth was limited by temperature.The rates of leaf extension increased exponentially with temperatureand the relationship was described by the Arrhenius equation.The Q10 at 15 °C for leaf extension was 2.7 for leaves 4and 5 and 3.2 for leaf 3.     

Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.). 1. Response of Leaf Extension to Temperature during the Transition from Vegetative to Reproductive Growth

The potential for leaf extension of plants of Lolium perennecv S24 growing in small artificial communities under naturalconditions was measured as the plants progressed from the vegetativeto the reproductive state In two consecutive years, 1975 and 1976, ‘simulated swards’were sown in autumn and overwintered in an open, unheated glasshouseIndividual swards from the batch sown in 1975 were brought into a growth room on two occasions in spring 1976 to measuretheir potential for leaf extension at a range of temperatures(5–20 °C) Individual swards from the batch sown inautumn 1976 were brought in to the growth room on 15 occasionsbetween November 1976 and May 1977 and their potential for leafextension was measured at a single temperature of 15 °CFrequent dissections were made in both years to describe changesin the developing apex. The potential for leaf extension at 15 °C decreased fromc 17 mm day^–1 in November to c 10 mm day^–1 in mid-winter.In January, the potential rapidly increased threefold to reach30mm day^–1 by mid February The increase began coincidentwith the earliest stages of floral initiation and was completedby the time of double-ridge formation Spring-grown vegetativeplants, however, showed potential rates of < 20 mm day^–1at 15 °C The results are discussed in relation to reproductive developmentand to changes in the carbohydrate strategy of the plants inearly spring Lolium perenne L perennial ryegrass, leaf extension, temperature response     

Influence of Endophyte and Water Regime Upon Tall Fescue Accessions. I. Growth Characteristics

Superior growth and persistence has been reported in endophyte-infectedgrasses; however, findings may have been confounded by experimentconditions including plant genotype. A controUed-environmentstudy was designed to address some growth characteristics offour tall fescue (Festuca arundinacea Schreb.) accessions asinfluenced by endophyte (Acremonium coenophiahim Morgan-Joneset Gams) and water regime. Endophyte-infected plants were collected,vegetatively propagated and some treated with propiconazole(11 kg a.i. ha^–1) to develop non-infected isolines ofeach accession. The phenotypically diverse accessions, eachrepresented by infected and non-infected isolines, were grownwith adequate (–0–03 MPa), or a series of deficit(<–1·5 MPa) and recovery water regimes, replicatedthree times. Plant growth characteristics were measured during(leaf elongation and tillering) and upon conclusion (phytomassproduction, tillering, and leaf area) of the study. Leaf elongation,as a function of leaf length, was significantly different amongaccessions, and generally decreased with water deficit althoughsome non-infected isolines were not affected. Water deficitdepressed tiller production in virtually all accessions whileendophyte effects depended upon accession. Leaf blade yieldwas not significantly influenced by endophyte status or interactionof endophyte, with water regime and accession; however, pseudostem(stem base and leaf sheath), root and dead leaf yields wereaffected in some cases. Non-structural carbohydrate concentrationin all plant parts except roots, was decreased by water deficit,whereas root non-structural carbohydrate concentration tendedto increase with water deficit. Non-structural carbohydratesof all plant parts was not influenced by endophyte status. Tallfescue-endophyte association responses vary due to genotype,therefore a simple generalization of endophyte impact upon tallfescue productivity and persistence is not possible based uponthe results of this study Festuca arundinacea Schreb., Acremonium coenophiahim Morgan-Jones et Gams, leaf elongation, phytomass production, tillering, water deficit, non-structural carbohydrate     

Analysis of the Nitrogen Response of Leaf Extension in Lolium temulentum Seedlings

Lolium temulentum seedlings were grown on a nutrient mediumcontaining NH₄NO₂ at 0, 0·1, 0·5, 1·0 and4·3 mmoll^–1 as the sole N source. Relative andabsolute extension rates, maximal leaf size, duration of extensiongrowth, rate of leaf appearance and plastochron index were determinedfrom the parameters of Richards functions fitted to lengthsof laminae measured at intervals after sowing. The final lengthof leaf I was relatively insensitive to N whereas mean relativeextension rate was increased and duration of growth decreasedwith increasing NH₄NO₂ concentration. Leaves 2 and 3 enlargedprogressively with N at concentrations up to 1·0 mmoll^–1but were unresponsive thereafter. There was no significant correlationbetween final length and mean relative extension rate for leaves1 to 3. Leaves 4 to 6 continued to show increasing length beyond1·0 mmoll^–1 N and final length was significantlycorrelated with mean relative extension rate. Increasing N increasedthe rate of leaf appearance by decreasing the duration of leafextension and plastochron. These results are discussed in relationto the control of leaf and N turnover. Lolium temulentum, rye grass, leaf extension, nitrogen, Richards function, growth analysis     

A Sensitive Auxanometer for Field Use

The essential characteristics of an auxanometer designed tomeasure the extension rates of grass leaves in the field areoutlined. The construction, using a linear-variable differentialtransformer (LVDT) to measure displacement, is described. Laboratorytests showed a linear relation between output and armature displacement,which was independent of changes in temperature between 1 and24 °C. Field tests on winter wheat leaves showed good agreementbetween auxanometer and rule measurements of leaf extensionmade over time periods of 24, 12, and 2 h. The tests and ananalysis of the errors, including the thermal expansion of theauxanometer stand, show that this auxanometer can reliably andaccurately measure leaf extension rates of between 0·1and 10 mm h^–1 in wind speeds up to 4·5 m s^–1.     

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     

An analysis of relative elemental growth rate, epidermal cell size and xyloglucan endotransglycosylase activity through the growing zone of ageing maize leaves

The effect of development on leaf elongation rate (LER) andthe distribution of relative elemental growth rate (REGR), epidermalcell length, and xyloglucan endotransglycosylase (XET) activitythrough the growing zone of the third leaf of maize was investigated.As the leaf aged and leaf elongation slowed, the length of thegrowing zone (initially 35 mm) and the maximal REGR (initially0.09 mm mm^–1 h^–1) declined. The decline in REGRwas not uniform through the growth profile. Leaf ageing sawa maintenance of REGR towards the base of the leaf. Epidermalcell size was not constant at a given position in the growingzone, but was seen to increase as the leaf aged. There was apeak of XET activity close to the base of the growing zone.The peak of XET activity preceded the zone of maximum REGR.XET activity declined as leaves aged and their elongation rateslowed. When leaf elongation was complete a distinct peak ofXET activity remained close to the base of the leaf. Key words: Leaf elongation rate (LER), relative elemental growth rate (REGR), xyloglucan endotransglycosylase (XET)     

The Effects of Temperature on Leaf Growth in Cyperus longus, a Temperate C4 Species

Plants of the C₄ sedge Cyperus longus L. were grown at 10, 20and 30 °C. An asymptotic growth curve, the Richards function,was fitted to growth data for successive leaves. The mean rateof leaf appearance was a linear function of temperature with0.014 leaves appearing per day for every 1 °C increase intemperature. The instantaneous relative rate of leaf extensionshowed a marked ontogenetic drift which was most rapid at 30°C and slowest at 10 °C. The mean absolute extensionrate for foliage had a temperature coefficient of 0.16 cm d^–1° C^–1 in the range from 10 to 30 °C. The durationof leaf growth was independent of leaf number at 10 and 20 °Cbut increased linearly with leaf number at 30 °C. The smalldifferences in relative growth rate at the three temperaturesresulted in large differences in foliage area produced at theend of a 30 d growth period. The final foliage areas at 20 and10 °C were 51 and 9% respectively of that at 30 °C. Cyperus longus, temperature, leaf growth, Richards function, growth analysis