Wheat Cultivars Respond Differently to a Drying Top Soil and a Possible Non-Hydraulic Root Signal

Research has shown that when plant roots are exposed to a dryingsoil a non-hydraulic (chemical) signal is produced in the rootand transported to the shoot, causing stomatal closure and growthretardation. This study was designed to reveal genetic diversityin wheat response to soil conditions which elicit a root signal,as the first step in the investigation of the genetic controlof the production of and the response to the root signal. Five spring wheat (Triticum aestivum L.) cultivars were establishedin the growth chamber in soil-filled polyvinyl chloride tubes,120 cm long and of an internal diameter of 10·2 cm. Soilwas well fertilized and wet to field capacity at emergence whentwo treatments were imposed: (1) tubes were watered from thetop as needed to eliminate stress (control); and (2) tubes hada constant water table at a soil depth of 100 to 120 cm, withno applied water. Measurements were performed on five dateson leaf water status and stomatal diffusive resistance. Above-groundbiomass and grain yield per plant were determined at maturity. The water table treatment resulted in dry and hard top soilconditions which were previously indicated to elicit a possibleroot signal. Under these experimental conditions, cultivarsdiffered in their leaf water status, stomatal diffusive resistance(R_s) and plant production. In the control treatment, R_s of cultivarsincreased with reductions in their relative water content (RWC)and leaf water potential (LWP), indicating the expected controlof R_s by leaf water status. Under conditions of a drying topsoil, relative water content (RWC) and leaf water potential(LWP) increased in cultivars that had a higher R_s, indicatingthat stomatal activity was controlling leaf water status. Itwas therefore suggested that the drying top soil elicited aroot signal which caused stomatal closure and reduced plantproduction. Under such conditions, two cultivars (Bethlehemand V748) consistently maintained relatively low R_s and highplant production, despite their relatively lower RWC and LWP,as compared with cvs C97, V747 and V652. Limited observationssuggest that in these two cultivars relatively fewer roots mayhave been exposed to the drying top soil, as compared with theother three cultivars. Key words: Triticum aestivum, cultivars, soil moistrue, drought stress, root, root signal, stomata, relative water content, leaf water potential, biomass, yield     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

Growth Habits of Water-stressed Wheat Seedlings as Selection Criteria for Drought Resistance

A technique is described to induce slowly increasing water deficitsin wheat (Triticum aestivum L.) seedlings by rooting them indamp vermiculite and growing them in a humid atmosphere. Aftereight weeks, drought-resistant genotypes can be identified eitherby drought avoidance or by drought tolerance responses. Genotypeswith lesser drought resistance become dormant or produce sterilespikes. The test roughly predicts the relative yield performanceof cultivars in dry field conditions. Triticum aestivum, wheat, matric water deficits, drought resistance, yield selection     

Mixed Nitrogen Nutrition and Productivity of Wheat Grown in Hydroponics

The objective of this study was to study the effects of nitrogen(N) supplied as either mixtures of NO₃ and NH₄ or as all NO₃on the final yield of spring wheat. Two separate greenhouseexperiments evaluated the durum spring wheat (Triticum durumL.) cultivar ‘Inbar’ in 1986, and the hard red springwheat (Triticum aestmum L.) cultivar ‘Len’ in 1987.Nitrogen treatments consisted of all NO, or mixtures (75/25or 50/50) of NO₃ and NH₄. At maturity, plants were harvested,separated into leaves, stems, roots, and grain, and each partanalysed for dry matter and chemical composition Compared to plants receiving only NO₃ as the source of N, mixedN nutrition resulted in greater accumulation of whole plantreduced-N (49 to 108% more), phosphorus (38 to 69% more), andpotassium (25% more) for both cultivars. In all cases, plantsproduced higher grain yields (28% for Len to 78% for Inbar)when grown with mixed N nutrition than with only NO₃. The yieldincrease was not associated with heavier grains or more grainsper ear, but rather with an increase in the number of ear-bearingtillers per plant. For both cultivars, the higher yields withmixed N resulted from the production of more total biomass (36to 76%) as the partitioning of dry matter between plant partswas not altered by N treatment. Under the hydroponic conditionsof this experiment, the utilization of both NO₃ and NH₄ resultedin greater growth, nutrient absorption, and yield than NO₃ alone,which was primarily associated with an enhancement in tillerdevelopment Triticum aestivum L., Triticum durum L., spring wheat, hydroponics, ammonium nutrition, nitrate nutrition, tillering, yield components, partitioning     

Morphological, Anatomical and Physiological Responses Related to Differential Shoot vs. Root Growth Inhibition at Low Temperature in Spring and Winter Wheat

Several morphological, anatomical and physiological changesand their relationship with differential root vs. shoot growthinhibition at low temperature (5°C) were studied in springand winter wheat cultivars. Root:shoot ratios, expressed eitheras a function of root and shoot fresh weight or as a functionof root and leaf areas, increased at low temperature and thisincrement was more pronounced in spring cultivars than in winterones. Although winter cultivars developed relatively smallerroot systems at 5°C, this characteristic was counterbalancedby a lower stomatal frequency and increased thickness of epidermalcell walls in leaves unfolded at this temperature, relativeto spring cultivars. Likewise, at 5°C a decrease in theosmotic potential of shoots and roots was observed in parallelwith sugar accumulation; this decrease was more marked in wintercultivars. These results indicate a differential morpho-anatomicaland physiological plasticity of winter and spring cultivarsduring development at low temperature. The possible associationbetween these changes and plant water economy at low temperaturesis discussed. Copyright 2001 Annals of Botany Company Spring wheat, winter wheat, Triticum aestivum, low temperature, root:shoot ratio, root surface area, stomatal frequency, osmotic potential     

The effect of elevated atmospheric CO2 and drought onstomatal frequency in groundnut (Arachis hypogaea (L.))

The effects of elevated atmospheric CO₂, alone or in combinationwith water stress, on stomatal frequency in groundnut (Arachishypogaea (L.) cv. Kadiri-3) were investigated. CO₂ exerted significanteffects on stomatal frequency only in irrigated plants. Theeffects of drought on leaf development out weighed the smallereffects of CO₂ concentration, although reductions in stomatalfrequency induced by elevated atmo-spheric CO₂ were still observed.When stands of groundnut were grown under irrigated conditionswith unrestricted root systems, an increase in atmospheric CO₂from 375 to 700 ppmv decreased stomatal frequency on both leafsurfaces by up to 16% in droughted plants, stomatal frequencywas reduced by 8% on the adaxial leaf surface only. Elevatedatmospheric CO₂ promoted larger reductions in leaf conductancethan the changes in stomatal frequency, indicating partial stomatalclosure. As a result, the groundnut stands grown at elevatedCO₂ utilized the available soil moisture more slowly than thosegrown under ambient CO₂, there by extending the growing period.Despite the large variations in cell frequencies induced bydrought, there was no treatment effect on either stomatal indexor the adaxial/abaxial stomatalfrequency ratio. The data suggestthat the effects of future increases in atmospheric CO₂ concentrationon stomatal frequency in groundnut are likely to be small, especiallyunder conditions of water stress, but that the combination ofassociated reductions in leaf con-ductance and enhanced assimilationat elevated CO₂ will be important in semi-arid regions Key words: Arachis hypogaea L, Leguminosae, groundnu, stomatal frequency, CO₂, drought     

Soil water deficits decrease the internal conductance to CO2 transfer but atmospheric water deficits do not

The internal conductance to CO₂ supply from substomatal cavitiesto sites of carboxylation poses a large limitation to photosynthesis.It is known that internal conductance is decreased by soil waterdeficits, but it is not known if it is affected by atmosphericwater deficits (i.e. leaf to air vapour pressure deficit, VPD).The aim of this paper was to examine the responses of internalconductance to atmospheric and soil water deficits in seedlingsof the evergreen perennial Eucalyptus regnans F. Muell and theherbaceous plants Solanum lycopersicum (formerly Lycopersiconesculentum) Mill. and Phaseolus vulgaris L. Internal conductancewas estimated with the variable J method from concurrent measurementsof gas exchange and fluorescence. In all three species steady-statestomatal conductance decreased by 30% as VPD increased from1 kPa to 2 kPa. In no species was internal conductance affectedby VPD despite large effects on stomatal conductance. In contrast,soil water deficits decreased stomatal conductance and internalconductance of all three species. Decreases in stomatal andinternal conductance under water deficit were proportional,but this proportionality differed among species, and thus therelationship between stomatal and internal conductance differedamong species. These findings indicate that soil water deficitsaffect internal conductance while atmospheric water deficitsdo not. The reasons for this distinction are unknown but areconsistent with soil and atmospheric water deficits having differingeffects on leaf physiology and/or root–shoot communication. Key words: Carbon dioxide, drought, internal conductance, mesophyll conductance, photosynthesis, stomatal conductance, transfer conductance, vapour pressure deficit, water deficit Received 11 October 2007; Revised 9 November 2007 Accepted 15 November 2007     

A combination of stomata deregulation and a distinctive modulation of amino acid metabolism are associated with enhanced tolerance of wheat varieties to transient drought

Introduction

Mediterranean winter crops are commonly and increasingly exposed to irregular rainfall and high temperatures, which lead to transient drought events of different degrees, adversely affecting growth and yield. Hence, exploring the diverse degrees of tolerance to drought existing in the crop and the molecular strategies behind it is pivotal for the development of ad hoc breeding programs.

Objective

We investigated the physiological and metabolic response of six commercial wheat cultivars to transient water stress at the tillering and grain-filling stages.

Methods

Drought experiments in lysimeters were set up at two developmental stages including six wheat cultivars. Newly expanded youngest leaves and flag leaves were sampled during the drought and following recovery. Metabolite profiles were generated using a GC–MS based protocol. Data on transpiration were continually acquired by measuring the weight variation of pots using electronic temperature compensated load cells.

Results

The tillering stage in wheat is more sensitive to droughts than the grain filling stage. The former stage was characterized by pronounced metabolic alterations also during recovery from the drought, and plants exhibited reduced transpiration. Notably, cultivars varied considerably in their susceptibility to drought. Exceptionally only in cv Zahir was transpiration not reduced at tillering. During recovery, the transpiration rate of Yuval and Zahir was not significantly affected, while except Ruta the other varieties maintained lower values. At grain-filling, a moderate decrease in transpiration in response to drought was evident in Bar-Nir, Yuval and Zahir varieties as compared with the stronger response of Gedera, Galil and Ruta. The transpiration trend during recovery remained lower than the control plants, particularly in Gedera and Zahir, while it reached higher values than control plants in Yuval and Ruta varieties. Metabolite profiling of leaves across cultivars showed varietal specific trends of response. Particularly during tillering, amino acid metabolism was differentially regulated across cultivars. For instance, Ruta and Zahir exhibited major changes in central carbon nitrogen metabolism during stress response, accumulating large amounts of proline and threonine during tillering, while in Bar-Nir a general decrease in relative amino acid content was noted. Changes in stress related GABA were common to Galil, Ruta, Yuval and Zahir. Desiccation related raffinose family oligosaccharides were mostly associated with a later stage of grain-filling and recovery stages of response.

Conclusion

The results indicate the occurrence of stage-dependent metabolic diversification along with a physiological response during transient droughts among wheat cultivars. It can be concluded that the most tolerant cultivar was Zahir, where a combination of stomatal closure deregulation and a significant accumulation rate of stress-related metabolites were evident.

     

Cuticular water permeability and its physiological significance

Cuticles act as solution-diffusion membranes for water transport.Diffusion in pores does not contribute to cuticular transpiration.An extensive literature survey of cuticular permeances (P) andminimum leaf conductances (g_min) to water is presented. Thetwo variables cannot be distinguished with most experimentaltechniques. Results from different experiments are in good agreementwith each other for some species, for example, Fagus sytvaticaL., but not for others, such as Picea abies (L.) Karst. In adata set of 313 values of P or g_min from 200 species, distributionsof results obtained with different techniques were found todiffer significantly. Likely reasons include water loss fromincompletely closed or incompletely sealed stomata, and thedependence of P on moisture content of the cuticle and on storagetime of isolated cuticles. Contrasting evidence for an interactionbetween cuticular transpiration and stomatal sensitivity toair humidity is presented. The occurrence of unusually highg_min in trees growing at the alpine treeline and its physiologicalsignificance are discussed. It is shown that g_min is of littlevalue as a predictor for drought resistance of crops, with thepossible exception of Sorghum bicolor L. Moench. Possible wateruptake from fog or dew across cuticles is considered briefly. Key words: Epidermal conductance, VPD-response, water absorption, waxes, winter desiccation     

Nocturnal Accumulation of Acid in Leaves of Wall Pennywort (Umbilicus rupestris) Following Exposure to Water Stress

Physiological responses to water stress (drought) have beeninvestigated in Umbilicus rupestris (wall pennywort) by comparingcontrol (well-watered) and draughted plants with respect to(i) diurnal fluctuations in the acid content of the leaves,(ii) CO₂ exchange patterns and (iii) stomatal conductance. Controlplants show no diurnal fluctuations in acid content, whereasafter 6 d of drought a clear CAM-type pattern (nocturnal acidificationfollowed by deacidification in the light) is observed. In controlplants, the CO₂ exchange pattern over a 24 h period is of atypical C-3 ‘square-wave’ type, with extensive CO₂uptake in the light and CO₂ output in the dark. In droughtedplants the day-time CO₂ uptake is confined to a morning ‘burst’,whilst night-time CO₂ output is markedly reduced. There is howeverno net noctural uptake of CO₂. In control plants, stomatal conductanceis high during the day (especially in the first half of theday) falling to a low level at the onset of darkness, and thenrising slowly through the remainder of the night. In droughtedplants, stomatal conductance is very low, except that thereis morning ‘burst’ of high conductance and a periodduring the night when conductance is higher than in controlplants. These results are discussed in relation to the response of U.rupestris to drought both in laboratory and in field conditions. Umbilicus rupestris, wall pennywort, CO₂ exchange, Crassulacean acid metabolism, drought, stomatal conductance, water stress     

Effects of CO2 Enrichment at Different Irradiances on Growth and Yield of Wheat: I. EFFECTS OF CULTIVAR AND OF DURATION OF CO2 ENRICHMENT

Wheat, Triticwn aestivum L., the winter cultivars Hobbit andCappelle-Desprez, and the spring cultivars Sicco and KJeiber,were grown in normal air or air enriched with CO₂ either outdoorsin a glass-roofed cage or in controlled environment rooms. Inneither the winter nor the spring wheat was growth increaseddue to enrichment with CO₂ before anthesis. Enrichment of thetwo winter wheat cultivars increased shoot dry weight significantlyat 15 d after anthesis but produced no significant increasein grain yield. With the spring cultivars there was a significantincrease in shoot dry weight by 18 d after anthesis and thegrain yield was also larger due to an increase in grain size.Shoot weight increased because the stems were larger, and therewas a diversion of assimilate from grain growth to late tillerproduction. Root tissue comprised less than 20% of the totaldry matter at anthesis (for all cultivars); effects of CO₂ enrichmenton root growth appeared to be less important than effects onshoot and ear growth. Growth and yield responses to CO₂ enrichmentwere observed (for the spring cultivars) at irradiances of both250 and 635 µE m^–2 s^–1, but the effects weregreater at the lower irradiance. Key words: CO₂ enrichment, Wheat, Cultivar     

Water Use Efficiency and Biomass Partitioning of Three Different Miscanthus Genotypes with Limited and Unlimited Water Supply

Miscanthus species, which are C₄perennial grasses, have a highbiomass potential but yields at many sites in Europe can belimited by insufficient water supply and plant survival is endangeredunder extreme summer drought. A pot experiment was conductedto measure the influence of reduced water supply on the wateruse efficiency (WUE) and biomass partitioning of three Miscanthusgenotypes (M. x giganteus, M. sacchariflorus, and a M. sinensishybrid) in a controlled environment. The experiment consistedof three phases (phase 1 = 0–20 d; phase 2 = 21–39d; phase 3 = 40–54 d) punctuated by destructive harvests.In phase 1, soil moisture was non-limiting. In the second andthird phases, lowered soil moisture contents induced water deficits.Air vapour pressure deficit (VPD) was 0.49 ± 0.05 kPa.Water deficits caused leaf senescence in M. x giganteus andM. sacchariflorus, but not in the M. sinensis hybrid. Greenleaf conductances were lowest in M. sinensis under water deficit,indicating stomatal regulation. Water use efficiency for wholeplants of each genotype ranged from 11.5 to 14.2 g dry matter(DM) kg^-1H₂O but did not differ significantly between genotypesor water treatments under the conditions of this experiment.However, differences in dry matter partitioning to the shoot(the harvestable component) resulted in genotypic differencesin WUE, calculated on a harvestable dry matter basis, whichranged from 4.1 g DM kg^-1H₂O for M. sacchariflorus to 2.2 gDM kg^-1H₂O for M. x giganteus. Copyright 2000 Annals of BotanyCompany Miscanthus sinensis, Miscanthus sacchariflorus, Miscanthus x giganteus, water use efficiency, biomass, C₄plants, drought     

The Influence of Prior Water Stress and Abscisic Acid Foliar Spraying on Stomatal Responses to CO2, IAA, ABA, and Calcium in Leaves of Solanum melongena

The influence of a water stress or foliar ABA spraying pretreatmenton stomatal responses to water loss, exogenous ABA, IAA, Ca²⁺,and CO₂ were studied using excised leaves of Solanum melongena.Both pretreatments increased stomatal sensitivity of water loss,in the presence and absence of CO₂, but decreased stomatal sensitivityto exogenous ABA. CO₂ greatly reduced the effect of exogenouslyapplied ABA. IAA decreased leaf diffusion resistance for controland ABA sprayed leaves, but did not influence the LDR of previouslywater-stressed leaves. CA²⁺ did not influence LDR of any leavesof any treatments. Key words: Water stress, stomatal response, pretreatments     

Photosynthetic Changes in the Inducible CAM Plant Sedum telephium L. Following the Imposition of Water Stress. 1. General Characteristics

The effects of water stress (drought) on the pattern of photosynthesisin Sedum telephium have been determined. Well-watered plantsexhibit a weak-CAM pattern, with substantial CO₂ fixation inthe day, a low level of CO₂ fixation at night, high daytimestomatal conductance with a lower conductance at night, andno diurnal fluctuation in acid content. Imposition of water-stress causes a switch from weak-CAM toa full-CAM mode of photosynthesis, as indicated by cessationof daytime CO₂ fixation, a marked increase in night-time CO₂fixation, very low daytime stomatal conductance, increased night-timeconductance and significant diurnal fluctuations in acid content. Sedum telephium, CAM, CO₂ fixation, drought, malate, photosynthesis, water stress     

Effects of NORIN 10 and Tom Thumb Dwarfing Genes on Morphology, Physiology and Abscisic Acid Production in Wheat

The pleiotropic effects of three genetically related dwarfinggenes were investigated in near-isogenic lines of wheat. TheNORIN 10 semi-dwarfing alleles, Rht 1 and Rht 2, and the TomThumb allele, Rht 3, were assessed for effects on some vegetativemorphological and physiological characters. The Rht allelesaffected leaf size with a resultant decrease in leaf area ofthe whole plant. Rht 3, which had the most marked effects, reducedleaf area in young plants by as much as 30 per cent. Althoughflag leaf dimensions and stomatal distributions of the flagleaf were altered, the gene had no effect on its area, stomatalconductance or net CO₂ exchange rate. Comparisons of Rht andtall plants revealed no differences in the abscisic acid (ABA)levels of either turgid or partially dehydrated leaves. Triticum aestivum L., wheat, dwarfing genes, leaf structure, abscisic acid, stomatal conductance, CO₂, exchange, relative growth rate     

The Diffusive Conductivity of the Stomata of Wheat Leaves

A leaf chamber (described in detail) was used alternately witha resistance porometer to measure resistance to viscous flowof air through the leaf, and with a diffusion porometer to measurethe differential diffusive flow of hydrogen and air (V_H–V_A)through the leaf and the component of hydrogen flow (V'_H) movingstraight across the leaf. The resistance of the mesophyll isneeded for interpretation: estimates by three different methodsfor viscous flow did not agree very well, but two differentmethods for diffusive flow gave good agreement. For wheat leaves,only very large errors are important. Formal analysis is in three appendixes: I. Interpretation ofviscous and diffusive flow in small pores involves some problemsin molecular physics, complicated by the particular geometryof the wheat stoma. With some uncertainty, formal expressionsare derived for the viscous resistance of a single stoma, rv,and for the resistances to diffusion of hydrogen and air, andof water vapour and carbon dioxide, all expressed as r_s persquare centimetre of leaf surface. The analysis for hydrogen/airis the most uncertain; that for water vapour and carbon dioxideis more reliable. II. An indication is given of the flow characteristicsof the leaf-chamber system, from which rv can be derived, andof the basis for estimating mesophyll resistance. III. The methodof converting estimates of r_s into estimates of V_H–V_Aand V'_H is given. The results presented are expressed as nearly as possible interms of the quantities which were measured. For five leavesthe dependence of V_H–V_A on V'_H agrees well with theoreticalpredictions; the dependence of V_H–V_A (and V'_H) on rv,on average, agrees well with prediction, but involves the assumptionthat the stomata get shorter as they close. The agreement isgood enough to suggest that the formal expressions for r_s interms of stomatal dimensions and molecular gas constants arereliable enough to be carried forward into future transpirationand assimilation studies. The minimum value of ra for watervapour (c. 3 sec cm⁺¹) is close to values found elsewhere bydifferent techniques. At very small stomatal openings there was a large deviationfrom predicted behaviour, such as would occur if the imposedexcess air pressure further closed the stomata during viscousflow experiments.     

The Effect of Nitrogen Fertilization and Irrigation Frequency on Photosynthesis of Potatoes (Solanum tuberosum)

Gas exchange parameters for the potato (Solanum tuberosum L.,cv. ‘Desiree’) crop were measured under field conditions.Nitrogen nutrition was found to have a positive effect on photosynthesisthroughout the growing season. The gas exchange data and thechlorophyll content in the leaves indicated that this effectwas essentially in the mesophyll. Stomatal resistance increasedas photosynthetic rate decreased, but substomatal CO₂ concentration(Ci) was not affected by nitrogen treatments. Long term effects of water deficit on photosynthetic capacitywere also mostly mesophyllic in origin. A reduction in photosyntheticrate was observed after a period of moisture stress and alsoafter relief of drought by irrigation, indicating a limitedcapacity for recovery. A short term afternoon increase in stomatalresistance, associated with lower Ci values, occurred afterlong periods without irrigation. Leaf water potential was affectedby irrigation frequency, but less strongly than the gas exchangeparameters. Mesophyll activity and stomatal behaviour were bothaffected by water stress and by nitrogen deficiency, whereasCi values were not affected in most cases. Solanum tuberosum L, photosynthesis, mesophyll, stomata, irrigation frequency, nitrogen deficiency, chlorophyll, leaf water potential     

Responses of Leaf and Tiller Emergence and Primordium Initiation in Wheat and Barley to Interchanged Photoperiod

The influence of constant (9, 13 and 19 h) and reciprocally-interchangedphotoperiods [at terminal spikelet (TS) or triple mound (TM)]on leaf, tiller and primordium development were examined usingphotoperiod-responsive cultivars of spring wheat, ‘UQ189’ and spring barley, ‘Arapiles’. In bothspecies, constant longer photoperiod reduced the duration fromsowing (S) to double ridge (DR), as expected. However, photoperiodsensitivity was not restricted to this mainly vegetative phase.There was also a marked increase or reduction in the durationof reproductive phases between TS/TM and heading (H) when plantswere transferred to shorter or longer photoperiods respectively,compared with controls. These responses were largely independentof the photoperiod during previous phases although minor effectsof the previous photoperiod were observed. For both species,the time course of leaf emergence was linear, or bi-linear,depending on the final leaf number on the main stem. The rateof leaf emergence was faster for the first six to eight leavesthan for the leaves appearing subsequently. The rate of emergenceof early-formed leaves was independent of photoperiod whereasthe rate of emergence of later leaves varied with photoperiod.Photoperiod also affected the dynamics of tillering. The rateof leaf primordium initiation was little affected by variationin photoperiod, but the rate of spikelet initiation increasedwith increases in photoperiod. The rates of leaf and spikeletprimordium initiation were both substantially higher in barleythan in wheat. The fact that the reproductive phase from TS/TMto H was largely independent of the duration of the previousphase provides evidence that this phase might be geneticallymanipulated to increase the time for floret development andhence grain number. Copyright 2000 Annals of Botany Company Photoperiod, rate of development and leaf emergence, tillering, wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.)     

Elevated CO2and Temperature have Different Effects on Leaf Anatomy of Perennial Ryegrass in Spring and Summer

Mature second leaves of Lolium perenne L. cv. Vigor, were sampledin a spring and summer regrowth period. Effects of CO₂enrichmentand increased air temperature on stomatal density, stomatalindex, guard cell length, epidermal cell density, epidermalcell length and mesophyll cell area were examined for differentpositions on the leaf and seasons of growth. Leaf stomatal density was smaller in spring but greater in summerin elevated CO₂and higher in both seasons in elevated temperatureand in elevated CO₂xtemperature relative to the respective controls.In spring, leaf stomatal index was reduced in elevated CO₂butin summer it varied with position on the leaf. In elevated temperature,stomatal index in both seasons was lower at the tip/middle ofthe leaf but slightly higher at the base. In elevated CO₂xtemperature,stomatal index varied with position on the leaf and betweenseasons. Leaf epidermal cell density was higher in all treatmentsrelative to controls except in elevated CO₂(spring) and elevatedCO₂xtemperature (summer), it was reduced at the leaf base. Inall treatments, stomatal density and epidermal cell densitydeclined from leaf tip to base, whilst guard cell length showedan inverse relationship, increasing towards the base. Leaf epidermalcell length and mesophyll cell area increased in elevated CO₂inspring and decreased in summer. In elevated CO₂xtemperatureleaf epidermal cell length remained unaltered in spring comparedto the control but decreased in summer. Stomatal conductancewas lower in all treatments except in summer in elevated CO₂itwas higher than in the ambient CO₂. These contrasting responses in anatomy to elevated CO₂and temperatureprovide information that might account for differences in seasonalleaf area development observed in L. perenne under the sameconditions. Lolium perenne ; perennial ryegrass; elevated CO₂and temperature; stomatal density; stomatal index; cell size