Effect of Drought on Metabolism and Partitioning of Carbon in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the partitioning of carbonon the third and seventh day from anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. The 9-d drought treatment, imposed just after anthesisduring the period of cell division in the grains, reduced grainyield by 18 per cent in Warigal and 30 per cent in Condor. Netcarbon fixation was up to 60 per cent higher in Warigal thanCondor towards the end of the drought period and this correlatedwith better osmotic adjustment in the flag leaf. Carbon partitioningbetween plant organs responded to water deficit more rapidlythan net carbon fixation. On day 3, carbon allocation to theroots of droughted plants was maintained in Condor and increasedby 14 per cent in Warigal, whereas carbon allocation to theear decreased in both varieties. However the roots did not competewell with the ear when the water deficit became more severe.Warigal accumulated 3 times more stem reserves than Condor underdrought. In the roots, the pattern of carbon allocation betweenrespiration and carbon accumulation changed soon after impositionof drought. Although total root respiration decreased underdrought it became more energy efficient, particularly for Warigal,as less respiration took place via the alternative pathway.On day 3, the larger carbon allocation to the roots and thelower root respiration accounted for the 4-times larger sugaraccumulation in droughted roots of Warigal compared with thoseof Condor. Osmotic adjustment in mature leaves and roots maybe of importance for the maintenance of vital processes andfor recovery after drought. Triticum aestivum L., wheat, drought, carbon, partitioning     

Effect of Post-anthesis Drought on Cell Division and Starch Accumulation in Developing Wheat Grains

Wheat plants (Triticum aestivum L., cv. Warigal) were subjectedto 20 d of water deficit during the period of endosperm celldivision. Drought accentuated the differences in final grainweight between spikelets and between grains within spikelets.The distal grains of top spikelets were most affected by drought.The maximum number of endosperm cells was, respectively, 30and 40 per cent lower in basal grains and distal grains of draughtedplants. In basal grains of middle spikelets, the number of largestarch granules per cell was unaffected but the number of smallstarch granules per cell was 45 per cent lower in grains ofdraughted plants. The initiation of small starch granules wasmore affected than cell division because severe water deficitoccurred earlier during the former process than the latter.Final dry weight appeared to correlate well with the maximumnumber of endosperm cells, but depended also on the number ofstarch granules per cell. Consequently, the amount of dry matterper cell was not constant in both treatments. The concentration of sucrose per endosperm cell was lower onlyin the droughted distal grains of top spikelets. The supplyof sucrose to endosperm cells did not regulate the initiationof small starch granules. Triticum aestivum L., wheat, drought, grain growth, cell division, starch     

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     

Genotypic Differences in the Production and Partitioning of Carbohydrates Between Roots and Shoots of Wheat Grown under Zinc or Manganese Deficiency

The partitioning of soluble carbohydrates and starch betweenroots and shoots was investigated in wheat genotypes differingin Zn or Mn efficiency. The plants were grown for 11 d in achelate-buffered nutrient solution with sufficient or deficientZn and Mn supply. The Zn-efficient cultivar Warigal had a greatershoot fresh weight under sufficient Zn compared with the Zn-inefficientcultivar Durati. When supplied with sufficient Zn, Warigal hada greater concentration and content of soluble carbohydratesin roots and shoots in comparison with Durati. Under deficientZn supply, Durati had a greater concentration and content ofstarch in roots and shoots compared with Warigal. In an experimentwith varying supply of Mn, the Mn-efficient genotype C8MM hada greater shoot fresh weight than the Mn-inefficient cultivarBayonet under sufficient or deficient Mn supply. The concentrationof soluble carbohydrates in roots and shoots was decreased bydeficient Mn supply in C8MM but not in Bayonet. Starch accumulatedin the roots of Bayonet under deficient Mn supply. The resultssuggest that synthesis of carbohydrates is decreased under Zndeficiency, while they are preferentially partitioned to theroots to increase growth and thus the surface area availablefor Zn uptake. In the case of Mn deficiency, carbohydrate productionwas limited, but partitioning between roots and shoots was notaltered.Copyright 1997 Annals of Botany Company Carbohydrate; deficiency; manganese; assimilate partitioning; starch; Triticum aestivum; zinc     

Thermal and Water Relations of Roots of Desert Succulents

Two succulent perennials from the Sonoran Desert, Agave desertiEngelm. and Ferocactus acanthodes (Lem.) Britton and Rose, loselittle water through their roots during drought, yet respondrapidly to light rainfall. Their roots tend to be shallow, althoughabsent from the upper 20 mm or so of the soil. During 12–15d after a rainfall, new root production increased total rootlength by 47 per cent to 740 m for A. deserti and by 27 percent to 230 m for F. acanthodes; root dry weight then averagedonly 15 per cent of shoot dry weight. The annual carbon allocatedto dry weight of new roots required 11 per cent of shoot carbondioxide uptake for A. deserti and 19 per cent for F. acanthodes.Elongation of new roots was greatest near a soil temperatureof 30°C, and lethal temperature extremes (causing a 50 percent decrease in root parenchyma cells taking up stain) were56°C and -7°C. Soil temperatures annually exceeded themeasured tolerance to high temperature at depths less than 20mm, probably explaining the lack of roots in this zone. Attached roots immersed in solutions with osmotic potentialsabove -2·6 MPa could produce new lateral roots, with50 per cent of maximum elongation occurring near -1·4MPa for both species. Non-droughted roots lost water when immersedin solutions with osmotic potentials below -0·8 MPa,and root hydraulic conductance decreased markedly below about-1·2 MPa. Pressure-volume curves indicated that, fora given change in water potential, non-droughted roots lostthree to five times more water than droughted roots, non-droughtedleaves, or non-droughted stems. Hence, such roots, which couldbe produced in response to a rainfall, will lose the most tissuewater with the onset of drought, the resulting shrinkage beingaccompanied by reduced root hydraulic conductance, less contactwith drying soil, and less water loss from the plant to thesoil. Agave deserti, Ferocactus acanthodes, roots, soil, temperature, water stress, drought, Crassulacean acid metabolism, succulents     

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     

Transport of Recently Assimilated15N Nitrogen to Individual Spikelets in Spring Wheat Grown in Culture Solution

Two cultivars of spring wheat ( Triticum aestivum L.), Sport(high protein) and WL4 (low protein), were grown to maturityin culture solution. Nitrogen in the form of nitrate was addedin daily doses at stepwise-decreasing relative rates to ensurenormal development, and both cultivars received the same totalamount of N during development. At weekly intervals from anthesisto maturity the daily nitrate dose was, for selected groupsof plants, labelled with¹⁵N. After the labelling period theselected plants were harvested and analysed. The cultivar WL4produced more biomass than Sport, as well as more spikeletsand more grains per ear, with a higher mean grain weight, suchthat grain yield of WL4 was 57% greater than Sport. The earsof both cultivars were heterogenous: mean grain weight was highestin middle spikelets, which also contained more grains; the Ncontent followed the pattern of dry weight with more N in themiddle spikelets; but the N concentration was practically thesame in all spikelets (2.15% of d. wt in WL4 and 3.33% in Sport).The distribution of¹⁵N showed that the main stem ear maturedmuch earlier than tiller ears. The results of this nitrogen-labellingexperiment show that, late in development, substantial amountsof recently-absorbed N were immediately assimilated and transportedto the ears. Transport of¹⁵N decreased earlier to the top spikeletsthan to the bottom spikelets. As both cultivars were grown underidentical conditions and both received the same amount of Nit was concluded that the difference in grain N concentrationwas not caused by differences in the capacity of N assimilationand translocation but rather by different rates of accumulationof non-nitrogenous dry matter in the grains. Ear; grain; nitrate; nitrogen transport; Triticum aestivum L.; yield     

Nitrogen Redistribution during Grain Growth in Wheat (Triticum aestivum L.) : IV. Development of a Quantitative Model of the Translocation of Nitrogen to the Grain

Translocation of nitrogen was measured in wheat (Triticum aestivium L. cv SUN 9E) plants grown without an exogenous supply of nitrogen from the time that the flagleaf began to emerge, and a model of nitrogen translocation was constructed to describe translocation on one day during the linear period of grain growth. Nitrogen for grain development was derived entirely by the redistribution of nitrogen from vegetative organs. Leaves contributed 40%, glumes 23%, stem 23%, and roots 16% of the nitrogen incorporated by the grains on the fifteenth day after anthesis. Less than 50% of the nitrogen exported from leaves was translocated directly to the grain via the phloem, the rest was translocated to the roots and was cycled in the roots and exported to the shoot in the transpiration stream. Nitrogen imported by leaves and glumes via the xylem was not accumulated in these organs but was transferred to the phloem for reexport from the organs. A large proportion (60%) of the nitrogen in the transpiration stream was cycled in the glumes. The glumes were also a major source of nitrogen for grain development. It was considered likely that this organ always plays an important role in nitrogen metabolism in wheat.     

Anatomy of the Root-Shoot Junction in Wheat Seedlings with Respect to Internal Oxygen Transport and Root Growth Retardation by External Oxygen Shortage

Anatomical alterations in the root-shoot junction followinghypoxic conditions were studied in young wheat plants (Triticumaestivum L. cv. Hatri) grown in nutrient solution flushed withair or nitrogen gas. The root-shoot junction was characterizedby densely packed tissues with only small intercellular spaces.Seven days of hypoxia did not alter the anatomy of this region,suggesting that it does not constitute an important pathwayfor oxygen diffusion from aerial shoot to the aerenchymatousroots. A likely alternative path for oxygen movement is thegas-filled interspace between coleoptile and shoot base. Rootsemerging from more apical parts of the stem elongated more quicklyin hypoxic conditions than those from more basal parts. Thiswas related to the path length from the main point of entryof atmospheric oxygen into the plant. Additionally, oxygen shortagein the ambient root medium decreased the number of mitoses perroot tip, as determined by the Feulgen method. This effect wasmost severe in the basally inserted roots, that are presumedto be the most oxygen deficient. Triticum aestivum L. cv. Hatri, wheat, hypoxia, root-shoot junction, anatomy, internal oxygen transport, root tip, mitosis     

The effect of nitrogen and growth regulators on stem and root characteristics associated with lodging in two cultivars of winter wheat

The effects of nitrogen and plant growth regulators (stem shorteners)on root and shoot characteristics associated with lodging resistancewere investigated in two winter wheat (Triticum aestivum L.)cultivars of contrasting lodging resistance: the susceptibleGalahad and the resistant Hereward. The morphology and mechanicalstrength of the stems and anchorage systems grown at two levelsof nitrogen and with or without growth regulators were measuredand related to the incidence of lodging recorded in a fieldtrial. In both cultivars high levels of nitrogen increased theheight of the stem, thereby increasing the ‘self-weight’moment transmitted into the ground and weakened both the stemsand the anchorage coronal roots. As a result, the anchoragestrength was also reduced, plants failing in the root systemin simulated lodging tests. Growth regulators, in contrast,had little effect on the bending strength of the shoots androot systems, but reduced plant height so that the over turningmoments generated by the weight of the shoot were less. Therewere also differences between cultivars: Galahad plants hadweaker anchorage due to the smaller number and lower strengthof the coronal roots. The morphological and mechanical measureswere used to calculate a safety factor against both stem androot lodging. Five factors were found to influence the safetyfactors, these were: cultivar type, the type of lodging, therate of nitrogen and growth regulator application, and time,being lowest in Galahad plants at high levels of nitrogen andwithout growth regulators and at grain filling when the earswere heaviest. This was consistent with the observed patternof lodging: root lodging occurred at grain filling and onlyin Galahad which had been treated with high nitrogen rates,most strongly in plants without growth regulators. Key words: Lodging, safety factors, anchorage, ‘self-weight’ moment     

Uptake of zinc from chelate-buffered nutrient solutions by wheat genotypes differing in zinc efficiency

Zinc-efficient Triticum aestivum (cv. Warigal) and Zn-inefficientTriticum turgidum conv. durum (cv. Durati) were grown in chelate-buffered,complete nutrient solutions providing either deficient or sufficientZn supply. When transferred to fresh chelatebuffered nutrientsolutions containing a wide range of Zn supplies (0–1.28µmol m^–3 Zn²⁺ activity) for 24–48 h, bothgenotypes increased net Zn uptake linearly with an increasein solution Zn²⁺ activities. Zincefficient Warigal accumulatedZn at a greater rate than Zn-inefficient Durati. The greaterrate of net Zn uptake was observed by plants of both genotypeswhen pretreated at deficient Zn supply. Net loss of Zn to thesolution was higher in plants pretreated with sufficient Znand was inversely related to Zn²⁺ activity in the external solution.When continuously supplied with 40 nmol m^–3 Zn²⁺, netZn uptake by Zn-efficient Warigal was significantly greaterthan that of Zn-inefficient Durati, but the difference diminishedwith plant age. Shoot concentrations of Fe, Mn and Cu were higherwhen plants were grown at deficient than at sufficient Zn supply.The Zn-efficient genotype transported less Zn and Fe to shootsand had higher Fe concentrations in roots than the Zn-inefficientgenotype, supporting the hypothesis that Zn efficiency may beconnected with inefficient transport of Fe from roots to shootsand thus initiation of the Fe-deficiency response resultingin increased release of Zn- and Fe-binding phytosiderophores.It is concluded that differential Zn efficiency of wheat genotypesis at least partly due to a greater ability of efficient genotypesto accumulate Zn. Key words: Chelate-buffering, genotypes, micronutrients, Triticum spp., uptake, zinc efficiency     

Translocation of nitrogen in a vegetative wheat plant (Triticum aestivum)

The translocation of nitrogen was studied in vegetative wheat plants ( Triticum aestivum L. cv. SUN 9E) grown with a limited supply of nitrogen. The concentration of nitrogen in xylem sap exuding from the excised roots was the same as the nitrogen concentration in the transpiration stream. Translocation of nitrogen to the shoot was, therefore, calculated as the product of the transpiration rate and the concentration of nitrogen in xylem exudates. On the 22nd day from sowing more nitrogen was translo-cated to the shoot than it incorporated, and 56% of the nitrogen translocated to the shoot was retranslocated to the roots. The nitrogen retranslocated to the roots was more than adequate to supply the requirements of the roots for growth, and the balance of the retranslocated nitrogen was reloaded into the xylem stream. Expressed as a proportion of the total increment of nitrogen in the plant on day 22, between 79 and 100% of the nitrogen absorbed by the plant was "cycled' in the plant (root → shoot → root → shoot). It is suggested that the size of this mobile reserve of nitrogen may vary depending on the growth requirement of the plant, its nitrogen-uptake capacity and the contribution of nitrogen from mobilisation of leaf protein during senescence.     

Mechanical Differences Between Free-standing and Supported Wheat Plants, Triticum aestivum L.

The effect of wind sway on the mechanical characteristics ofthe anchorage roots and the stem was investigated in maturewinter wheat (Triticum aestivumL., cv. Hereward). Wheat plantswere field-grown, either supported by a frame, which preventedwind sway, or unsupported (free-standing) and the morphologyand mechanical properties of the stems and the anchorage, ‘coronal’, roots were measured. Wind sway had little influence on either the stem height orear weight of the plants but did affect the mechanical propertiesof the stem. Stems of supported plants were weaker and moreflexible than the stems of free-standing plants. There werealso differences in the anchorage systems between the treatments:supported plants had just under half as many ‘coronal’ anchorage roots as the free-standing plants. This reducedthe anchorage strength of supported plants by a third. These differences in mechanical structure meant that the free-standingplants were more resistant to stem buckling and more resistantto anchorage failure. However, considering the difference inthe need for mechanical strength in plants from the two regimes,these differences were small. This suggests that wheat has inherentmechanical integrity and, as a monocotyledon with no secondarythickening, it differs little structurally between environments. Triticum aestivumL.; thigmomorphogenesis; anchorage; safety factor; mechanical stimulation     

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     

Patterns of 14C-labelled Assimilate Partitioning in Red and White Clover During Vegetative Growth

A quantitative analysis of the ¹⁴C-labelled assimilate suppliedby the expanded leaves on the primary shoot to growing leaves,stem, lateral shoots (branches or stolons) and roots in redand white clover was conducted during vegetative growth. Stem growth of the primary shoot was inhibited in both cloversand utilized no energy resources. The growing leaves at theprimary shoot apex of white clover imported 4 per cent of theshoot's assimilate compared with 10 per cent in red clover.At the basal end of the primary shoot, the tap root of whiteclover imported 16 per cent of the shoot's assimilate comparedwith 22 per cent in red clover. Branches in red clover and stolonsin white clover were by far the largest sinks for primary shootassimilate, importing 39 per cent and 63 per cent of the labelledassimilate, respectively. Analyses of the translocation of assimilate from individualprimary shoot leaves demonstrated that in both clovers olderleaves exported more of their assimilate to branches or stolons,whereas younger leaves exported more of their assimilate toroots, and possibly in white clover, to growing leaves at thetip of the shoot. Of the labelled assimilate exported to branchesor stolons, each primary shoot leaf exported preferentiallyto the branch or stolon in its own axil, but in addition exportedsubstantial quantities of assimilate to all other axillary shoots,particularly those arising from basal axils where the subtendingleaf had died. Trifolium repens, Trifolium pratense, red clover, white clover, assimilate partitioning, perennation     

Abscisic Acid Translocation and Influence of Water Stress on Grain Abscisic Acid Content

The movement of foliar applied [1-¹⁴C]abscisic acid (ABA) inwheat plants (Triticum aestivum L., cv. Kolibri) was investigatedat two stages of grain development (1000 grains, weight 19 and24 g dry matter). [1–¹⁴C]ABA seemed to be readily translocated within 12h into the developing grains as well as in other plant parts.A subsequent rapid metabolism took place leading to a decreasedactivity of the ABA-containing chromatogram fraction in theyounger plants 48 h after application. The metabolism seemodto be less intensive in the older grains, where the activityrunning with the ABA increased over 64 h. Treating the leaves of barley plants (Hordeum vulgare, L., cv.Union) 2 weeks after anthesis with a gentle stream of warm air(36° C) resulted in a significant increase in the ABA contentof all parts of the ear. The results mentioned above indicatethat this may be partially due to translocation from other partsof the plant such as the leaves.     

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     

The Effects of Copper Supply and Shading on Retranslocation of Copper from Mature Wheat Leaves

Plants of Gamenya wheat (Triticum aestivum L.) were grown inpots of a Cu-deficient sand at two levels of Cu (deficient andsufficient), and harvested on days 13, 22, 28 and 38. In 50per cent of the pots in each Cu treatment, the oldest leaf andleaf 2 of the main stem were shaded when they reached full expansion. The Cu content of the oldest leaf of Cu-sufficient, unshadedplants was high at day 13 and declined rapidly to day 38. Thatof Cu-deficient, unshaded plants was initially relatively lowand declined much more slowly, so that at day 38 it resembledthat of Cu-sufficient plants. Shading the oldest leaf acceleratedthe loss of its Cu in both Cu-deficient and Cu-sufficient plants.The effects of shading and of Cu supply on the loss of Cu fromthe oldest leaf paralleled their effects on the loss of N andchlorophyll. The results suggest that most of the Cu in theoldest leaf does not move out until the leaf senesces. In Cu-deficient plants retention of Cu by old green leaves accentuatedCu deficiency. The release of Cu, resulting from shading theold leaves of Cu-deficient plants, stimulated the growth ofnew leaves. In Cu-sufficient plants, shading depressed growth. copper, shading, retranslocation, wheat, Triticum aestivum L.     

Absorption and translocation of sodium in beans and cotton

At the end of a 4 hour absorption period approximately 95% of the sodium absorbed by bean plants was retained in the secondary roots. The sodium translocated to the shoot was retained in the stem.

2,4-Dinitrophenol decreased the amount retained in the secondary roots of bean plants and increased the amount translocated to the shoot. The stem retained most of the translocated sodium.

Bean plants without roots absorbed considerably more sodium than plants with roots and translocated a greater proportion of the sodium to the petioles and blades. 2,4-Dinitrophenol reduced the amount of sodium in the stem and petioles and increased the amount in the blades.

2,4-Dinitrophenol reduced the amount of sodium retained by the secondary roots of cotton plants but did not appreciably affect the amounts translocated to the shoot.

     

A Quantitative Analysis of the Uptake of Carbon and of the Supply of 14C-labelled Assimilates to Areas of Meristematic Growth in Lolium temulentum

A quantitative analysis of the ¹⁴C-labelled assimilate suppliedby leaves on the main shoot to terminal meristem, stem, tillers,and roots was conducted during parallel periods of reproductiveand vegetative development in Lolium temulentum. The initial rate of entry of carbon into the shoot varied withthe area and photosynthetic efficiency of the assimilating leaf.Subsequently, respiratory losses of carbon during translocationand incorporation of assimilate at the site of utilization alsovaried. The combined effect of these differences resulted inthe supply of recently assimilated carbon being twofold greaterin reproductive shoots than in vegetative shoots, while withinshoots the carbon supply of the youngest fully expanded leafranged from four-or five-fold greater than the oldest leaf inyoung shoots, to two-or three-fold greater in older shoots.In both reproductive and vegetative shoots, the two or threeyoungest leaves thus dominated the supply of carbon for meristematicgrowth. Meristematic tissue in expanding leaves and leaf primordia atthe terminal meristem of the vegetative shoot received 18–27per cent of the total shoot carbon. This meristem utilized aboutthe same proportion of shoot carbon when it developed into aninflorescence, indicating no major change in the level of meristematicactivity. The proportion of shoot carbon utilized in stem growthincreased as both reproductive and vegetative shoots aged; thisincreased meristematic activity in stem internodes was accompaniedby reduced export of carbon to roots, which received less than10 per cent of the shoot carbon when the experiments ended.The main shoot translocated 20–30 per cent of its recentlyassimilated carbon to developing and rooted tillers, which assinks for carbon were thus as important as the terminal meristemand stem. This outward flow of carbon continued relatively uncheckedwhen donor and receptor shoots developed inflorescences.