Late Maturation of Large Metaxylem Vessels in Soybean Roots: Significance for Water and Nutrient Supply to the Shoot

The large, late metaxylem (LMX) in the roots of soybean beginsdevelopment in the centre of the stele after lignification ofthe early metaxylem poles. Subsequent maturation of the firstappearing LMX elements is gradual. They were never mature inthe 8-d-old seedlings examined. In 10 to 15-d-old plants thefirst LMX matured to open vessels at a mean of 17 cm proximalto the root tip. Additional LMX vessels developed in more proximalregions of the roots and these also matured gradually. Based on calculations from relative vessel diameters, the potentialflow of xylem sap in a single central LMX vessel is 50 timesthat in the total of all the early metaxylem (EMX) vessels ofa typical primary root of soybean. There was a marked dependence of relative leaf area on the lengthof primary root with open LMX vessels. This may result fromthe predicted increased water and nutrient flow to the shoot,facilitated by the opening of the large vessels. It is suggestedthat, as in maize, the living LMX elements may function in ionaccumulation. Dicotyledonous roots, soybean, Glycine max, xylem vessels, xylem maturation, water conduction     

The Effect of Soil Compaction on Differentiation of Late Metaxylem in Common Bean (Phaseolus vulgaris L.)

Recent studies among several plant species have shown that maturationof the largest vessels in primary xylem of roots occurs muchlater than is commonly assumed. These results have importantimplications for studies of water and nutrient uptake sincethe condition of the vessels, termed late metaxylem (LMX), mighthave a large effect on the potential conductivity of the xylem.To determine whether this phenomenon occurred in common bean(Phaseolus vulgaris L.), patterns of root xylem differentiationwere studied in young bean plants. Soil bulk density was variedin one trial to determine whether differentiation of LMX wassensitive to the growing medium. Vessels of LMX lost cell contentsand-became functional conduits between 100 and 150 mm from theroot apex. Increasing soil bulk density caused the zone of maturationof LMX to shift toward the root apex, but this zone was nevercloser than 67 mm. In the region where the primary root increasedin diameter as it merged with the hypocotyl, a zone was foundwhere vessels increased in number, had a reduced diameter, andwere arranged in a ring, the normal tetrarch arrangement ofthe xylem being lost. Potential conductivity in this zone wasconsiderably less than in zones with conventional large LMXvessels, so the zone appears to present an important restrictionto water transport from the root to the shoot. Thus, while thephenomenon of late maturation of LMX occurs in common bean,its significance in transport of water from roots to shootsis unclear Phaseolus vulgaris L., common bean, metaxylem, soil compaction, roots, anatomy     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis I. Anatomy and Respiration in Triticum aestivum L.

Anatomical changes in roots of wheat seedlings (Triticum aestivumL. cv. Hatri) following oxygen deficiency in the rooting mediumwere investigated. The response of the plant to stress was testedat a very early developmental stage when the first adventitiousroots had just emerged. In order to analyze the adaptation ofdifferent roots, respiration rates of the roots 1–3 and4–n were compared with the respiration rates of the totalroot system. Oxygen deficiency was induced either by flushingnutrient solution with nitrogen or flooding of sand. In contrast to plants grown in well aerated media, both stressvariants led to a significant increase of the intercellularspace of the root cortex in seminal and first adventitious roots.Radial cell enlargement of cortical cells near the root tip,cell wall thickenings in flooded sand cultures and an increasein phloroglucinol-stainable substances were found to be furtherindicators of low oxygen supply. The roots 4–n which were promoted in growth under hypoxiashowed higher respiration rates; hence the total root respirationwas not restricted. Triticum aestivum L. cv. Hatri, wheat, roots, anatomy, anaerobiosis, stress, root respiration, intercellular space     

Hydraulic propagation of pressure along immature and mature xylem vessels of roots of Zea mays measured by pressure-probe techniques

Turgor pressure was measured in cortical cells and in xylem elements of excised roots and roots of intact plants of Zea mays L. by means of a cell pressure probe. Turgor of living and hence not fully differentiated late metaxylem (range 0.6–0.8 MPa) was consistently higher than turgor of cortical cells (range 0.4–0.6 MPa) at positions between 40 and 180 mm behind the root tip. Closer to the tip, no turgor difference between the cortex and the stele was measured. The turgor difference indicated that late-metaxylem elements may function as nutrient-storage compartments within the stele. Excised roots were attached to the root pressure probe to precisely manipulate the xylem water potential. Root excision did not affect turgor of cortical cells for at least 8 h. Using the cell pressure probe, the propagation of a hydrostatic pressure change effected by the root pressure probe was recorded in mature and immature xylem elements at various positions along the root. Within seconds, the pressure change propagated along both early and late metaxylems. The half-times of the kinetics, however, were about five times smaller for the early metaxylem, indicating they are likely the major pathway of longitudinal water flow. The hydraulic signal dissipated from the source of the pressure application (cut end of the root) to the tip of the root, presumably because of radial water movement along the root axis. The results demonstrate that the water status of the growth zone and other positions apical to 20 mm is mainly uncoupled from changes of the xylem water potential in the rest of the plant.Abbreviations and Symbols CPP cell pressure probe - EMX early metaxylem - LMX Late metaxylem - P_c cell turgor - P_r root pressure - RPP root pressure probe - t_1/2,c half-time of water exchange across a single cell - t_1/2 half-time of water exchange across multiple cells We thank Antony Matista for his expert assistance in the construction and modification of instruments. The work was supported by grant DCB8802033 from the National Science Foundation and grant 91-37100-6671 from USDA, and by the award of a Feodor Lynen-Fellowship from the Alexander von Humboldt-Foundation (Germany) to J.F.     

The Direction of Growth of Seminal Roots of Triticum aestivum L. and Experimental Modification Thereof

The seminal root system of wheat (Triticum aestivum L.) consistsof a primary seminal root and the first and second pair of seminalroots, counting upwards. These roots are plagiotropic. The directionof growth was estimated as the angle from the vertical for eachof the three types of seminal roots that protruded from a hemispherical,soil-filled basket buried in the field. The angle of growthvaried with cultivar. It was smallest in the primary seminalroot and largest in the second pair of roots in all 12 cultivarsgrown in the field. Attempts to modify the angle of growth weremade under controlled environmental conditions. When the grainwas sown with its embryo face down, the angle of growth of thefirst pair of roots became smaller in the cultivars with inherentlylarger angles. The excision of the primary seminal root affectedthe first pair of roots and the excision of the first pair affectedthe second pair. These effects comprised a decrease in the angleof growth and an increase in root diameter. These changes inthe angle of growth caused by root excision is interpreted asa kind of compensatory growth. The direction of root growthand its impact on shaping wheat root system is discussed.Copyright1994, 1999 Academic Press Compensatory growth, direction of growth, gravitropism, liminal angle, plagiotropism, seminal roots, Triticum aestivum L., wheat     

Effect of moderate salinity on patterns of potassium, sodium and chloride accumulation in cells near the root tip of barley: Role of differentiating metaxylem vessels

X-Ray microanalysis of fully hydrated, bulk-frozen samples was used to measure concentrations of potassium, sodium and chloride in various cell types along seminal roots of barley ( Hordeum vulgare L. cv. California Mariout) seedlings (1 to 150 mm from the tip). In the cytoplasm of all meristematic cells 1 mm from the root tip, the average concentrations of potassium and chloride were ca 200 and 15 m M , respectively. The potassium level was also high in the vacuoles of incipient xylem elements and did not drop to significantly lower values until 10 mm from the tip in protoxylem, 50 mm in early metaxylem and 150 mm in late metaxylem (LMX). Light microscopy observations (Nomarski optics) of hand-cut sections showed the presence of cytoplasmic strands and also the presence of intact cross walls in LMX up to a distance of 100 mm. Both quantitative analysis of ion contents and structural observations suggested that LMX elements act as a large transitional sink of accumulated ions and therefore may not function as a main pathway of transport until perforation of the end wall takes place 100–150 mm from the root tip. Treatment with 50 m M NaCl resulted in higher concentrations of sodium and chloride in LMX elements than in the surrounding cells, suggesting that living xylem elements, which develop a large central vacuole at an early stage of root differentiation, may assist in alleviating salinity stress in the meristematic region of barley root tips. Further, it is proposed that reabsorption of sodium and chloride from the LMX, especially before the disappearance of the cross walls, may provide a means of salinity tolerance.     

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     

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     

Ultrastructure of xylem parenchyma cells of barley roots in relation to ion transport to the xylem

Summary The structure of xylem parenchyma cells is examined in relation to transport of ions through the root. Measurement of uptake of ⁸⁶Rb⁺ and its transport through the root at different distances from the apex show that this is a general activity along the length of the root and not confined to a limited region. Thus transport through the root is not stopped by removal of that part of the root tip containing metaxylem vessels with living contents. The structure of xylem parenchyma appears to be suitable for involvement in ion transport from the stele to the xylem. At 1 cm behind the tip, where metaxylem vessels have no living contents but ion uptake and transport are going on at high rates, xylem parenchyma cells are rich in cytoplasm with extensive rough endoplasmic reticulum and well-developed mitochondria. Their cell walls contain numerous plasmodesmata, establishing the possibility of a symplastic pathway across the stele up to the vessels. The results are discussed in relation to regulation of ion transport to the xylem vessels in roots.Dedicated to Professor O. Stocker on the occasion of his 85th birthday.     

Growth of Zea mays L. plants with their seminal roots only. Effects on plant development, xylem transport, mineral nutrition and the flow and distribution of abscisic acid (ABA) as a possible shoot to root signal

Maize (Zea mays L.) was grown in quartz sand culture eitherwith a normal root system (controls) or with seminal roots only(‘single-rooted’). Development of adventitious rootswas prevented by using plants with an etiolated mesocotyl andthe stem base was positioned 5–8 cm above the sand. Eventhough the roots of the single-rooted plants were sufficientlysupplied with water and nutrients, the leaves experienced waterdeficits and showed decreased transpiration as trans plrationalwater flow was restricted by the constant number of xylem vesselspresent in the mesocotyl. As a consequence of this restriction,transpirational water flow velocities in the metaxylem vesselsreached mean values of 270 m h^–1 and phloem transportvelocities of 5.2 m h^–1. Despite limited xylem transportmineral nutrient concentrations in leaf tissues were not decreasedin single-rooted plants, but shoot and particularly stem developmentwas somewhat inhibited. Due to the lack of adventitious rootsthe shoot:root ratio was strongly increased in the single-rootedplants, but the seminal roots showed compensatory growth comparedto those in control plants. Consistent with decreased leaf conductance,ABA concentrations in leaves of single-rooted plants were elevatedup to 10-fold, but xylem sap ABA concentrations in these plantswere lower than in controls, in good agreement with the well-wateredconditions experienced by the seminal roots. Surprisingly, however,ABA concentrations in tissues of the seminal roots of the single-rooted plants were clearly increased compared to the controls,presumably due to increased ABA import via phloem from the water-stressedleaves. The results are discussed in relation to the role ofABA as a shoot to root signal. Key words: Zea mays, seminal roots, plant development, xylem transport, mineral nutrition, ABA, shoot-to-root signal     

Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis II. Morphology and Anatomy of Evolution Forms

Morphological and anatomical parameters which are variable underroot anaerobiosis in Triticum aestivum were checked on fivetaxa of primitive and modern wheats (and the related genus Aegilops).The plants were grown in nutrient solution which was eitheraerated or flushed with nitrogen. When the plants were flushedwith nitrogen a general retardation in longitudinal root growthoccurred in all of them, but only Triticum aestivum showed aclear promotion of growth of later appearing roots enablingit to maintain the same root/shoot ratio even under stress conditions.There was an increase in the volume of intercellular space inthe root cortex of nearly all the plants investigated. The diameterand the lignin content of the roots and the form of their corticalcells also varied. All these changes were expressed in the primitivewheats to a lesser extent than in the advanced Triticum aestivumindicating that there is a clear increase in the adaptive responsein the latter. Triticum species, Aegilops species, wheat, roots, anatomy, anaerobiosis, stress, intercellular space, selection     

The Mechanics of Anchorage in Wheat Triticum aestivum L.: I. THE ANCHORAGE OF WHEAT SEEDLINGS

Model of the mechanics of uprooting lead to the identificationof ‘optimal’ anchorage systems which can withstanda given upward force at a minimum construction cost. Such systemshave many downward-pointing fibrous roots which are strengthenedprogressively towards the base. A study of the anchorage systemof 7- and 21-d-old wheat (Triticum aestivum L.) plants showedthat the plants possessed five seminal roots, of which onlythree pointed vertically. Each root was well suited for anchorage,being convered in root hairs and strengthened progressivelytowards the base by lignification of the stele. Strength andstiffiness of roots but not their mass per unit length increasedwith age. There was little interaction between roots when plantswere uprooted; the three vertical roots broke while the twohorizontal ones pulled out, as occurred when roots were pulledout singly, Uprooting forces increased with age and the rootsystem could withstand uprooting forces greater than those requiredto pull out upper leaves, so reducing the chances of the plantbeing uprooted by a herbivore, By 3 weeks a stiff adventitiousroot system, which would later help prevent the wheat lodging,was developing.     

Root growth and nitrate uptake by wheat (Triticum aestivum L.) following wetting of dry surface soil

The nitrate uptake capacity of surface roots of spring wheat(Triticum aestivum L. cv. Kulin) was investigated followingwetting of dry surface soil. Plants were grown to stem elongationstage with adequate watering at depth while the surface soilwas allowed to dry. Eight weeks after sowing, water or a ¹⁵N-nitratesolution was added to the surface soil to simulate rainfall.Root growth and nitrate uptake were measured up to 4 d afterwetting on plants with unconfined nodal root growth and on plantswith the majority of nodal roots confined within small vials.Prior to wetting, plants from both nodal treatments had seminalroots with collapsed cortices along the upper 10 cm and manyshort, viable lateral roots. Nodal roots, where present, wereonly a few cm long and unbranched. Only plants with unconfinednodal roots were able to take up nitrate within the 24 h beforeany new root growth. By 2 d after wetting there was significantgrowth of the seminal lateral roots, and rapid growth and branchingof nodal roots. From 2 d after wetting, plants with confinednodal roots also took up nitrate, presumably due to the growthof the seminal lateral roots. Hence it appears as though thenodal roots in the unconfined treatment could immediately takeup nitrate, but the seminal roots required new lateral rootgrowth to become active in nitrate uptake. The plants with confinednodal roots had a lower nitrate uptake than those with unconfinednodal roots 4 d after wetting, indicating that the seminal rootsystem was not able to compensate for lack of nodal roots. Insufficientnitrate was taken up after 4 d, by plants from either nodalroot treatment, to increase the shoot N concentration significantly. Key words: Triticum aestivum, nitrate uptake, drought, seminal roots, nodal roots     

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     

Root Development and Aerenchyma Formation in Two Wheat Cultivars and One Triticale Cultivar Grown in Stagnant Agar and Aerated Nutrient Solution

Stagnant nutrient solution containing 0.1% agar and with anextremely low oxygen level (‘stagnant agar solution’)was used to simulate the gaseous composition and slow gas diffusionof waterlogged soils. Comparisons were made between the growthof two wheat cultivars(Triticum aestivum,cvs. Gamenya and Kite)and one triticale cultivar(Triticosecale,cv. Muir) grown instagnant relative to aerated solution. For all genotypes tested,immersion of roots in stagnant agar solution resulted in thedeath of the entire seminal root system and led to profuse branchingof the laterals of the nodal roots. In the stagnant agar solutionaerenchyma, as a percentage of the total cross sectional areaof nodal roots, was 18% for Muir, 14% for Kite and 12% for Gamenya;the roots of species with more aerenchyma also attained a longermaximum root length as predicted by the model of Armstrong (in:Woolhouse HW, ed.Advances in botanical research, vol. 7. London:Academic Press, 1979). Muir also had a nodal root/shoot freshweight ratio of 0.5 compared with 0.2–0.3 in Kite andGamenya. The greater number and length of nodal roots of Muirdid not lead to better shoot growth than in the other genotypes;one possible reason for this lack of improvement is a low efficiencyof aerenchymatous roots in wheat.Copyright 1998 Annals of BotanyCompany Root development; aerenchyma; stagnant agar;Triticum aestivumcv. Gamenya;Triticum aestivumcv. Kite;Triticosecalecv. Muir.     

Morphological Changes in Wheat Seedlings (Triticum aestivum L.) following Root Anaerobiosis and Partial Pruning of the Root System

Morphological changes of roots and shoots following oxygen deficiencyin the root medium and after partial pruning of the root systemwere analyzed to obtain easily measurable parameters of theadaptive capacity of the root system against stress. Wheat seedlings(Triticum aestivum L. cv. Hatri) were cultivated on nutrientsolution which was either aerated or flushed with nitrogen,or were cultivated on flooded sand. On the third day after grainswelling in two pruning variants, roots 1–3 or 4–8were excised. Root anaerobiosis retarded longitudinal growth and biomass accumulationof the shoot and the seminal roots, and stimulated the developmentof adventitious roots. Partial removal caused a general compensativegrowth of the remaining roots under aerobic conditions. Root pruning plus anaerobiosis exceeded the compensatory capacityof the seedlings and thus caused a strong delay of elongationand biomass accumulation of both roots and shoots, includingdecrease of the root/shoot ratio. Roots became independent ofendosperm reserves on the seventh day under aerobic conditionsthough caryopses were not completely exhausted at this time.Additionally, oxygen deficiency delayed the reserve exhaustionprocess. Triticum aestivum L. cv Hatri, wheat, roots, growth analysis, morphology, anaerobiosis, strees, root pruning, compensatory capacity, caryopsis     

Influence of Xylem Water Potential on Leaf Elongation and Osmotic Adjustment of Wheat and Lupin

The leaf elongation rate and osmotic pressure at full turgorof wheat (Triticum aestivum L.) and lupin (Lupinus cosentiniiGuss.) were measured in well watered plants, in plants thatwere allowed to dry the soil slowly over 7 d, and in plantsin which the water potential of the leaf xylem was maintainedhigh by applying pressure to the roots during the drying cycle.Maintenance of high xylem water potentials failed to preventa reduction in the rate of leaf elongation as the soil dried,while the osmotic pressure at full turgor and the degree ofosmotic adjustment increased as the soil water content decreased.The rate of leaf elongation was reduced more and the degreeof osmotic adjustment was higher in leaves with high xylem waterpotentials than in those in which leaf xylem potentials wereallowed to decrease as soil water content decreased. Osmoticadjustment was linearly correlated with the reduction in leafelongation rate in both wheat and lupin. Key words: Osmotic adjustment, leaf elongation, turgor regulation     

Site, Scale and Time-course for Adjustments in Lateral Root Initiation in Wheat Following Changes in C and N Supply

The pattern of lateral root initiation in seminal roots of wheat(Triticum aestivumL. cv. Alexandria) and the location, scaleand time-course for adjustments in initiation were studied afterchanges in C and N supply. Macroscopically visible primordiaappeared in a non-acropetal sequence with the frequency (numberper unit length) increasing with distance behind the main rootapex to a maximum at 40–50 mm behind the root tip. Pruningthe root system to a single seminal axis increased the primordiafrequency by 23% within 15 h. After longer periods, the effectof root-pruning was greater. The enhanced primordia frequencywas first observed in tissue located 0–10 mm behind theapex at the start of treatment. Feeding glucose (50 mM) alsoincreased primordia frequency within 15 h, but to a greaterextent, and here additional primordia were initiated in tissuelocated 0–10and10–20 mm behind the apex at the startof treatment. Withdrawing NO₃^-from one part of a split-rootsystem, whilst maintaining the supply to the other, reducedprimordia frequency in the non-fed roots and, in some cases,a compensatory increase in the NO₃^--fed roots was observed.The location and scale of the adjustments were similar to thosefound with root-pruning and glucose-feeding, but were slightlyslower to appear. In spite of some differences in detail, therewas a broad similarity in site, scale and time-course for adjustmentsin lateral root initiation with these treatments, which is consistentwith the operation of a common mechanism. Whenever an increasein primordia frequency was observed, it was associated withan increase in the ethanol-soluble sugar content of the tissue.However, the reduction in frequency in NO₃^--deprived roots wasalso accompanied by an increase in sugar content. There wasno consistent relationship between total N content of the tissueand primordia frequency, but there was between primordia frequencyand the rate of net NO₃^-uptake. The possible mechanisms controllinglateral root initiation are discussed. Compensatory growth; correlative growth; glucose; initiation; lateral root; nitrate; primordium; split-root; Triticum aestivum; wheat     

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