Cultivars of Hexaploid Wheat of Contrasting Stature and Chlorophyll Retention Differ in Cytokinin Content and Responsiveness

The work reported here compared cytokinin content and sensitivityin a selection of hexaploid wheat (Triticum aestivum L.) cultivarsusing the following measurements: leaf cytokinins at three timepoints during light-growth and at four 24 h intervals afterlight-grown plants were transferred to darkness; sensitivityof root growth to direct applications of isopentenyl adenosine([9R]iP); and, sensitivity of germination and subsequent rootand shoot growth to 18 h imbibition of seeds in benzyladenine(BA). Accumulation of zeatin riboside-type cultivars was greatestduring light-growth in Tibet Dwarf, a wheat with an extremedwarf phenotype, intermediate in Omar standard and dwarf cultivars,and lowest in the standard and dwarf versions of Itana. Cytokininlevels were otherwise not directly correlated to plant staturein these wheats. There were no cultivar-associated qualitativedifferences in the types of cytokinins detected in this study.During the 16 h light period, the content of zeatin riboside-typecytokinins increased up to tenfold and then declined to basallevels during dark growth. Chlorophyll retention during dark-growthwas correlated with leaf cytokinin content. Data collected ata restricted number of sampling points during dark-growth suggesteda cyclic accumulation of [9R]iP-type cytokinins and the apparentcycle in Tibet Dwarf was offset by 24 h. Tibet Dwarf showedthe greatest root growth inhibition after exposure of seedlingroots to [9R]iP or imbibition of seeds in BA. Neither of thesetreatments affected shoot growth in any of the cultivars. Wheat; Triticum aestivum ; cytokinin; zeatin riboside; benzyladenine; root inhibition     

Postanthesis temperatures influence cytokinin accumulation and wheat kernel weight

High temperatures during reproductive development alter kernel development and reduce yield and quality in wheat ( Triticum aestivum L.). Understanding how temperature alters kernel formation will help the development of genetic approaches to enhance heat tolerance in this cereal. A relationship between kernel development and postanthesis cytokinin accumulation is well documented, but the effect of temperature on this relationship is not known. This study quantified the effects of a postanthesis temperature treatment (7 d at 35/25 °C day/night) on kernel development and cytokinin accumulation in a soft white winter wheat (c.v. Stephens). Kernels from control plants maintained at 25/15 °C accumulated zeatin, dihydrozeatin and their corresponding 9-ribosides from 1 to 4 d postanthesis. Postanthesis kernel cytokinin accumulation was reduced by 50–80% by the temperature treatment. Kernel cytokinin content in control plants declined to baseline by 5 d postanthesis and remained at that level. Kernels from treated plants had a secondary peak of cytokinin accumulation 6–8 d after anthesis. This treatment significantly reduced kernel weight. The magnitude of the effect on kernel number was smaller than on kernel weight, but was statistically significant. Reduced kernel weight was accompanied by reduced cytokinin accumulation. Exogenous cytokinins did not mitigate the temperature effects on kernel weight, but at the highest concentrations, did reduce the effect on kernel number.     

The Effect of Heat Stress on Wheat Leaf and Ear Photosynthesis

The effect of heat-hardening on carbon exchange rate per unitarea (CER) of flag leaves, whole ears, and ears with the awnsremoved, was measured in hexaploid (Triticum aestivum L.) andtetraploid (T. turgidum L. and T. dicoccoides) wheat varieties.The CER for awns was calculated by the difference. For the non-hardened hexaploid cv. ‘H-895’ the CERfor the leaves and glumes had an optimum temperature of 25°C.By contrast, the CER for the awns increased from 25°C to32°C, indicating an optimum at 32°C or more. Heat-hardeningdecreased the CER of leaves and glumes at the optimum temperature,but increased the CER especially in leaves at supra-optimaltemperatures. Thus, leaf CER in hardened plants became essentiallyindependent of temperatures between 25°C and 32°C. AwnCER was little affected by heat-hardening. For all 12 varieties, leaf and ear CER was smaller in hardenedplants at 30°C than in non-hardened plants at 22°C.Leaf and ear CER measured at 30°C differed significantlybetween varieties within a species. Whole ear CER at 30°Cwas negative in most varieties although the calculated valuefor the awns was positive. Thus, the high temperature optimumfor CER of the awns was a major factor in the variation amongwheat varieties in tolerance of ear CER to heat. The biochemicalattributes of the photosynthetic mechanism in awns responsiblefor the high temperature optimum were already present in wildtetraploid wheat. There was a positive correlation across allvarieties between ear CER at 30°C and the percentage ofawns in total ear area (r = 0930, P = 0 This together with previousresults (Blum, 1985a), suggests that a large amount of awnsin the ear is a sensible selection index in wheat for improvedproduction in hot, dry environments. Key words: Carbon exchange rate, photosynthesis, awns, heat, stress, wheat, breeding     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Photosynthetic Responses of Different Varieties of Wheat to High Temperature: I. EFFECT OF GROWTH TEMPERATURE ON DEVELOPMENT AND PHOTOSYNTHETIC PERFORMANCE

Both fast and slow chlorophyll fluorescence kinetics were usedto assess the differential heat sensitivity of ten wheat (Triticumaestivum L.) varieties commonly grown in northern, temperateor (sub-) tropical climate zones. No consistent differencesbetween the groups were found. Studies on the role of growthtemperature in modulating the response of photosynthesis toheat stress were carried out on two of the varieties, APU (Finnish)and K65 (Indian), the former being more sensitive to heat stress.Growth and development of these varieties were similar underboth cool (13 °C day, 10 °C night) and warm (30 °Cday, 25 °C night), regimes. The cool-grown plants exhibitedhigher rates of net CO₂ exchange than the warm-grown plantswhen expressed on a chlorophyll basis and, in both regimes,photosynthesis declined with age prior to reduction in chlorophyllcontent. Net CO₂ exchange in leaves of K65 showed greater sensitivityto short-term heat stress than APU when plants were grown underthe cool regime. Plants grown under the warm regime exhibitedan upward shift in the optimum temperature for net CO₂ exchangein both varieties, with K65 showing somewhat superior performanceat high temperature compared with APU. Stomatal aperture wasessentially unaffected by assay temperature during these measurements. Key words: CO₂ exchange, growth temperature, Triticum aestivum     

Nitrogen Uptake and Accumulation in Grains of Three Winter Wheat Varieties with Altered Source--Sink Ratios

In two pot experiments, removal of the top halves of ears (halving)of three winter wheat (Triticum aestivum L.) varieties at varioustimes after anthesis increased the nitrogen content in the grainsof the lower half of the ear. The increase was greater withearly (anthesis and 5 d later) than late (15 and 25 d post-anthesis)removal in the Splendeur and Hobbit varieties, but there wereno significant differences among halving times in Maris Huntsman.Halving also increased nitrogen as a percentage of dry weightof grain. The percentage of nitrogen in the grain decreasedas the time of halving was delayed in Splendeur (expt. 1) andHobbit, but was unaffected by the time of halving in Splendeur(expt. 2) and Maris Huntsman. Nitrogen uptake of shoots afteranthesis decreased with halving. Early halving decreased nitrogenuptake to a lesser extent than did late halving in Splendeurin expt. 1 and in Hobbit, while it decreased nitrogen uptakemore than late halving in Splendeur in expt. 2 and in Mans Huntsman. Key words: Grain nitrogen, nitrogen uptake, source-sink, wheat, variety     

Effects of Temperature and Growth Regulators on Formation of Anlagen, Tendrils and Inflorescences in Vitis vinifera L.

The effects of single, combined and sequential application ofgibberellic acid (GA), chlormequat and cytokinins on the formationof anlagen, tendrils and inflorescences were studied in grapevines(cv. Muscat of Alexandria) grown with natural illumination athigh temperature (30 °C day to 25 °C night) and at lowtemperature (21 °C day to 16°C night or 18 °C dayto 13 °C night). GA promoted the formation of anlagen andgrowth of tendrils regardless of temperature, but inhibitedinflorescence production. Chlormequat had the opposite effecton anlagen formation and tendril growth and promoted inflorescenceformation from pre-formed anlagen or from tendril initials.While low temperature is normally unfavourable for inflorescenceformation, this was induced by chlormequat even at low temperature,but only with summer light conditions. Cytokinin application to plants pre-treated with chiormequatcaused tendrils to grow into inflorescences regardless of temperatureregimes. Moreover, shoot primordia were also formed in place⁸oftendrils in cytokinin treated plants even without chlormequatpre-treatment. Vitis vinifera L., grapevine, gibberellic acid, chlormequat, cytokinins, benzyladenine, inflorescence, tendrils     

Abnormal Sporogenesis in Wheat (Triticum aestivum L.) Induced by Short Periods of High Temperature

Plants of Triticum aestivum L. cv. Gabo, grown at 20 °C,were exposed to 30 °C for short periods during the timebetween the beginning of meiosis in the pollen mother cellsand anthesis. Plant water deficit at this temperature was avoidedby maintaining a high atmospheric relative humidity and tissuewater potential did not change. This temperature treatment appliedfor 3 days, at the time of reduction division and tetrad breakup in the male tissue, lowered grain yield through a drasticreduction in grain set, but was without effect at other stagesof development. Grain set was also reduced by exposing plantsto 30 °C for 1 day only or to a 30 °C day, 20 °Cnight (16 h photoperiod) regime for 3 days during the sensitiveperiod. A reduction in grain set did not result in a compensatoryincrease in the weight of remaining grains. The female fertility of previously heat-stressed plants wasassessed by pollinating with pollen from plants grown at a lowertemperature (20 °C). Grain set in such plants was less thanthat in plants grown at the lower temperature and hand pollinatedwith similar pollen, indicating that female fertility was reducedby high temperature. This was not the sole reason for reducedgrain set, however, as some anthers on heat-stressed plantswere small and neither extruded nor dehisced normally. Suchanthers contained pollen grains that were mostly shrivelled,had abnormal cytoplasm and showed no reaction to 2, 3, 5-triphenyltetrazolium chloride. Similar effects were also noted in pollenfrom apparently normal anthers on heat-stressed plants. Triticum aestivum, wheat, heat stress, pollen, sporogenesis, grain set, male sterility, female sterility     

Photosynthetic Responses of Different Varieties of Wheat to High Temperature: II. EFFECT OF HEAT STRESS ON PHOTOSYNTHETIC ELECTRON TRANSPORT

The effect of heat stress on photosynthetic electron transportwas investigated in thylakoids isolated from the wheat (Triticumaestivum L.) varieties APU (Finland) and K65 (India) grown underboth cool (13 °C day, 10 °C night) and warm (30 °Cday, 25 °C night) regimes which gave rise to varietal differencesin photosynthetic temperature acclimation. The responses ofthe uncoupled activities of both whole-chain electron transportand photosystem II to heat stress were similar. Both activitiesexhibited higher rates in thylakoids isolated from warm-grownplants and were more resistant to high temperature pretreatmentthan in those isolated from cool-grown plants, but varietaldifferences were not observed. Uncoupled photosystem I activity driven by either reduced 2,6-dichlorophenol indophenol (DCPIPH₂) or N,N,N',N'-tetramethyl-p-phenylenediamine (TMPDH₂) showed a stimulation following high temperaturepretreatment which was more marked in thylakoids isolated fromwarm-grown plants, followed by inhibition at extreme high temperatures.This stimulation was due largely to an increase in V_max butdid not occur when reduced diaminodurene, which is highly lipophilic,was used as the electron donor. It appears that stimulationof PS I activity may involve increased accessibility of someartificial electron donors to the native acceptor sites withinthe thylakoid membrane in a process which is influenced by growthtemperature. Key words: Photosynthetic electron transport, heat stress, Triticum aestivum     

Effects of Low Temperature on the Development and Morphology of Rye (Secale cereale) and Wheat (Triticum aestivum)

Seedlings of Secale cereale cv. Rheidol and Triticum aestivumcv. Mardler were grown at shoot/root temperatures of 20/20 °C,20/8 °C and 8/8 °C. During vegetative growth both cerealsproduced leaves, tillers and roots in a defined pattern, ata species-specific rate which was linearly related to the temperatureof the shoot meristem. Thus, plant development could be standardizedon a temperature x time (°C d) basis despite contrastinggrowth-temperature treatments. When compared at a similar developmentalstage, the cooling of whole plants or of plant roots resultedin an increase in the d. wt: f. wt ratio of both shoot and roottissues, a decrease in the length of both the longest shootand root, and the development of broader and thicker leaves.Although the effects of temperature on developmental characteristicscould be accurately predicted by an empirical relationship,the effects on morphological characteristics could not. Development, phyllochron, rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivum L.)was reinterpreted from a developmental perspective, using currentconcepts of the developmental regulation of wheat morphologyand phenology. At temperatures above 0 °C, the effects ofthe process of vernalization per se in wheat are confoundedby the effects of concurrent vegetative development. These effectsare manifested by differences in the number of leaves initiatedby the shoot apex prior to floral initiation, which in turnaffects the subsequent rate of development to ear emergenceand anthesis. Leaf primordia development during vernalizationand total leaf number at flowering were used to develop criteriato define both the progress and the point of saturation of thevernalization response. These criteria were then used to reinterpretthe results of Chujo ( Proceedings of the Crop Science Societyof Japan 35 : 177–186, 1966), and derive the temperatureresponse of vernalization per se for plants grown under saturatinglong day conditions. The rate of vernalization increased linearlywith temperature between 1 and 11 °C, such that the timetaken to saturate the vernalization response decreased from70 d at 1 °C to 40 d at 11 °C. The rate declined againat temperatures above 11 °C, and 18 °C was apparentlyineffective for vernalization. Total leaf number at saturation,however, increased consistently with temperature, as a resultof the balance between the concurrent processes of leaf primordiuminitiation and vernalization. Total leaf number at saturationincreased from 6 at 1 °C to 13.3 at 15 °C, which inturn influenced the time taken to reach ear emergence. The advantagesof using this developmental interpretation of vernalizationas the basis for a mechanistic model of the vernalization responsein wheat are discussed. Triticum aestivum L.; wheat; vernalization; rate; temperature; primordia; leaf number; flowering     

Critical Concentration of Tissue 9

Solution culture experiments with spring wheat (Triticum aestivumcv. Neepawa) showed that the critical phosphorus concentrationin the shoot (CPC) was lower when root temperatures were optimalfor growth. Root temperatures of 10, 15, 20 and 25°C wereused, the optimal was 25°C. The plants were sampled at definedstages, either at 4·0 g fr. wt. or with 6 mature leavesand the phosphorus (P) status of the plants at the samplingtime was evaluated by observing the responses of other plantsto an additional supply of P. These two precautions were criticalto the interpretation of the data and may explain the discrepancyin the literature about the relationship between plant growthrate and the CPC. Key words: Relative growth rate, Wheat     

Effect of High Temperature Stress at Anthesis on Grain Yield and Biomass of Field-grown Crops of Wheat

Spring wheat (Triticum aestivumL., ‘Chablis’) wasgrown under field conditions from sowing until harvest maturity,except for a 12-d period [70–82 days after sowing (DAS)coinciding with anthesis] during which replicated crop areaswere exposed to a range of temperatures within two pairs ofpolyethylene-covered temperature gradient tunnels. At 82 DAS,an increase in mean temperature from 16 to 25 °C duringthis treatment period had no effect on above-ground biomass,but increased ear dry weight from 223 to 327 g m^-2and, at 83DAS, reduced root biomass from 141 to 63 g m^-2. Mean temperatureover the treatment period had no effect on either above-groundbiomass or grain yield at maturity. However, the number of grainsper ear at maturity declined with increasing maximum temperaturerecorded over the mid-anthesis period (76–79 DAS) and,more significantly, with maximum temperature 1 d after 50% anthesis(78 DAS). Grain yield and harvest index also declined sharplywith maximum temperature at 78 DAS. Grain yield declined by350 g m^-2at harvest maturity with a 10 °C increase in maximumtemperature at 78 DAS and was related to a 40% reduction inthe number of grains per ear. Grain yield was also negativelyrelated to thermal time accumulated above a base temperatureof 31 °C (over 8 d of the treatment from 5 d before to 2d after 50% anthesis). Thus, grain fertilization and grain setwas most sensitive to the maximum temperature at mid-anthesis.These results confirm that wheat yields would be reduced considerablyif, as modellers suggest, high temperature extremes become morefrequent as a result of increased variability in temperatureassociated with climate change.Copyright 1998 Annals of BotanyCompany Triticum aestivum, spring wheat, temperature, grain number, grain yield, root growth.     

The Relationship between Sugar and Amino Acid Export to the Phloem in Young Wheat Plants

The relationship between amino acid and sugar export to thephloem was studied in young wheat plants (Triticum aestivumL. ‘Pro-INTA, Isla Verde’) using the EDTA-phloemcollection technique. Plants grown with a 16 h photoperiod showeda rapid decrease in the concentration of sugars and amino acidsin the phloem exudate from the beginning of the dark period.When plants grown with a 16 h photoperiod were kept in the darkfor longer than 8 h the free amino acid content in leaves andexudate (on a dry weight basis) increased continually throughoutthe 72 h of darkness. During the first 24 h of darkness thesugars in the phloem exudate decreased to 30% of the initialvalue, and returned to the control level when plants were returnedto light. When plants grown under low light intensity for 10d were transferred to high light intensity, they showed an increasein leaf sugar content (dry weight basis) after 3 d but therewere no differences in leaf free amino acid content (dry weightbasis) compared to low-light plants. The sugar concentrationin the phloem exudate was increased by higher light intensities,but there was no difference in the amino acid concentrationof the phloem exudate, and thus the amino acid:sugar ratio inthe phloem decreased in the high-light plants. The present resultssuggest that amino acids can be exported to the phloem independentlyof the export of sugars. Copyright 1999 Annals of Botany Company Sugar exudation, amino acid transport, nitrogen, phloem, transport, wheat, Triticum aestivum L.     

Expression of Vernalization Genes in Near-isogenic Wheat Lines: Effects of Night Temperature

Four near-isogenic lines of wheat (Triticum aestivum L.em Thell)were used to compare selected night temperatures for their effectivenessas vernalizing temperatures. All treatments (conducted withina phytotron) had a common day temperature of 20 °C for 12h and night temperatures were 4, 7, 10, 13 and 20 °C. Interpretationof results for reproductive development was confounded by threeinteracting factors, their relative importance varying withgenotype. Firstly, development rate was generally slower atlower night temperatures. Secondly, in contrast, there was atendency for lower night temperatures to hasten developmentrate if vernalization requirements were satisfied. Thirdly,the lower night temperatures provided a more favourable environmentfor leaf production such that for some genotypes, vernalizedplants had higher final leaf numbers than unvernalized plants.Only for the genotype with the strongest vernalization response(vrn1 vrn2) did hastening of development due to vernalizationoverride any delaying effects. For this genotype, 4, 7 and 10°C were vernalizing temperatures. For the other three genotypes,any hastening of development due to vernalization was outweighedby delaying effects of lower night temperatures. Spikelet numberand days to anthesis were positively correlated in three ofthe four genotypes. It appeared that differences in spikeletnumber were a direct result of night temperature influencingthe duration of the spikelet phase and/or rate of spikelet initiation.Plant size at flowering was determined by the differential effectsof night temperature on growth and development rates. Triticum aestivum L., wheat, vernalization, night temperature, isogenic lines     

Differential Inhibition of Shootvs.Root Growth at Low Temperature and its Relationship with Carbohydrate Accumulation in Different Wheat Cultivars

Shoot and root growth rate, carbohydrate accumulation (includingfructan), reducing sugar content and dry matter percentage weremeasured in six wheat cultivars, ranging from winter to springtypes, grown at either 5 or 25 °C. At 5 °C (comparedwith 25 °C), the relative growth rate (RGR) of shoots wassimilarly reduced in all cultivars, but the RGR of shoots wasmore affected in winter wheats. This difference resulted insmaller root:shoot ratios than in spring wheats, which alsodeveloped more first-order lateral roots. A direct relationshipbetween carbohydrate accumulation at low temperatures and reductionin root growth was established. These results suggest that differentialshootvs.root growth inhibition at low temperature may play akey role in carbohydrate accumulation at chilling temperatures.This differential response might lead to improvements in survivalat temperatures below 0 °C, regrowth during spring, andwater and nutrient absorption at low temperatures.Copyright1997 Annals of Botany Company Wheat; Triticum aestivum; low temperatures; root growth; root: shoot ratio; sugar accumulation     

The Growth and Development of the Wheat Apex: The Effects of Photoperiod on Spikelet Production and Sucrose Concentration in the Apex

Spring wheat (Triticum aestivum cv. Warimba) plants were grownin a controlled environment (20°C) in two photoperiods (8or 16 h). In the first instance, plants were maintained in eachof the photoperiods from germination onwards at the same irradiance(375 µE m^–2 s^–1). In the second case, allplants were grown in a long photoperiod until 4 days after double-ridgeinitiation when half the plants were transferred to a shortphotoperiod with double the irradiance (16 h photoperiod at225 or 8 h at 475 µE ^–2 s^–1). The rates of growth and development of the apices were promotedby the longer photoperiod in both experiments. Shoot dry weightgain was proportional to the total light energy received perday whereas the dry weight of the shoot apex increased withincreasing photoperiod even when the total daily irradiancewas constant. The principal soluble carbohydrate present in the shoot apexwas sucrose, although low concentrations of glucose and fructosewere found in the apices of long photoperiod plants late indevelopment. Sucrose concentration was invariably greater inthe slow-growing apices of short photoperiod plants, but roseto approach this level in the long photoperiod plants when theterminal spikelet had been initiated. Triticum aestivum, wheat, apex, spikelet initiation, photoperiod, flower initiation     

Low Temperature-induced Accumulation of Protein is Sustained both in Root Meristems and in Callus in Winter Wheat but not in Spring Wheat

Plant growth was assessed and cellular protein per nuclear DNAamount measured in root meristems and in callus derived fromembryos of a spring (‘Katepwa’) and a winter variety(‘Beaver’) of allohexaploid wheat exposed to lowtemperature treatment. The data obtained were used to test whetherthese genetically distinct varieties of wheat responded differentiallyto cold treatment. Seedlings were grown for 14 d at 20°Cand then transferred to 4°C for 14 d before returning themto 20°C, or else were maintained continuously at 20°C.In winter wheat, root growth at 4°C was significantly greaterover the first 7 d following transfer to 4°C compared withplants retained at 20°C, whereas in spring wheat it wasreduced at 4°C. The pattern of accumulation of cellularprotein for both root meristem cells and in callus cells wasalso generally enhanced at 4°C compared with 20°C inwinter wheat but not in spring wheat. Thus, clear inter-varietaldifferences were established both for dry weight accumulationand cellular protein, and the callus data clearly show thatthe low-temperature-induced accumulation of protein is a cellularphenomenon not necessarily linked to development. The extentto which cold-shock proteins are a component of this low temperature-inducedincrease in cellular protein is discussed. Copyright 2000 Annalsof Botany Company Protein, spring wheat, temperature, tissue culture, Triticum aestivum, winter wheat     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

Developmental Regulation of Low-temperature Tolerance in Winter Wheat

Vernalization and photoperiod genes have wide-ranging effectson the timing of gene expression in plants. The objectives ofthis study were to (1) determine if expression of low-temperature(LT) tolerance genes is developmentally regulated and (2) establishthe interrelationships among the developmental stages and LTtolerance gene expression. LT response curves were determinedfor three photoperiod-sensitive LT tolerant winter wheat (Triticumaestivum L. em Thell) genotypes acclimated at 4 °C under8 h short-day (SD) and 20 h long-day (LD) photoperiods from0 to 112 d. Also, three de-acclimation and re-acclimation cycleswere used that bridged the vegetative/reproductive transitionpoint for each LD and SD photoperiod treatment. A vernalizationperiod of 49 d at 4 °C was sufficient for all genotypesto reach vernalization saturation as measured by minimum finalleaf number (FLN) and confirmed by examination of shoot apicesdissected from crowns that had been de-acclimated at 20 °CLD. Before the vegetative/reproductive transition, both theLD- and SD-treated plants were able to re-acclimate to similarLT₅₀(temperature at which 50% of the plants are killed by LTstress) levels following de-acclimation at 20 °C. De-acclimationof LD plants after vernalization saturation resulted in rapidprogression to the reproductive phase and limited ability tore-acclimate. The comparative development of the SD (non-flowering-inductivephotoperiod) de-acclimated plants was greatly delayed relativeto LD plants, and this delay in development was reflected inthe ability of SD plants to re-acclimate to a lower temperature.These observations confirm the hypothesis that the point oftransition to the reproductive stage is pivotal in the expressionof LT tolerance genes, and the level and duration of LT acclimationare related to the stage of phenological development as regulatedby vernalization and photoperiod requirements. Copyright 2001Annals of Botany Company Triticum aestivum L., wheat, low-temperature tolerance, vernalization, photoperiod, phenological development