Distribution of Assimilates in Gladiolus grandiflorus as Affected by Water Deficit

The distribution patterns of photosynthesis products derivedfrom ¹⁴CO₂ and of applied ¹⁴C-sucrose were studied in floweringgladiolus plants (Gladiolus grandiflorus cv. Eurovision) irrigatednormally or water stressed. Even small stresses led to a decreasein the mobilizing ability of the inflorescence and an increasein that of the corm. The stress caused a great reduction in¹⁴CO₂ fixation, and, to a lesser degree, a delay in assimilatetranslocation out of the source leaves. In all cases, well irrigatedor stressed, the corms had the highest water potential (leastnegative), followed by the inflorescences and the leaves. Thegreater the stress, the greater were the differences betweenthose organs. It is proposed that under water deficit the waterpotential of the main sink (inflorescence) decreases and itsturgor dependent growth is slowed down, so reducing its mobilizingability, and causing delayed translocation out of the leaves.The water potential of the corm — the competitive sink— remains high enabling its growth to continue and assimilatesare attracted to it. ¹⁴C-distribution, corm, flower, Gladiolus grandiflorus, water deficit, water potential     

Patterns of Assimilate Distribution and Source--sink Relationships in the Young Reproductive Tomato Plant (Lycopersicon esculentum Mill.)

Patterns of distribution of ¹⁴C were determined in 47-day-oldtomato plants (Lycopersicon esculentum Mill.) 24 h after theapplication of [¹⁴C]sucrose to individual source leaves fromleaves 1–10 (leaf 1 being the first leaf produced abovethe cotyledons). The first inflorescence of these plants wasbetween the ‘buds visible’ and the ‘firstanthesis’ stages of development. The predominant sink organs in these plants were the root system,the stem, the developing first inflorescence and the shoot ‘apex’(all tissues above node 10). The contribution made by individualsource leaves to the assimilate reaching these organs dependedupon the vertical position of the leaf on the main-stem axisand upon its position with respect to the phyllotactic arrangementof the leaves about this axis. The root system received assimilateprincipally from leaf 5 and higher leaves, and the stem apexfrom the four lowest leaves. The developing first inflorescencereceived assimilates mainly from leaves in the two orthostichiesadjacent to the radial position of the inflorescence on thevertical axis of the plant; these included leaves which weremajor contributors of ¹⁴C to the root system (leaves 6 and 8)and to the shoot apex (leaves 1 and 3). This pattern of distributionof assimilate may explain why root-restriction treatments andremoval of young leaves at the shoot apex can reduce the extentof flower bud abortion in the first inflorescence under conditionsof reduced photoassimilate availability. Lycopersicon esculentum Mill, tomato, assimilate distribution, source-sink relationships     

The Photosynthetic Net Carbon Dioxide Exchange Potential in Conventional and 'Leafless' Phenotypes of Pisum sativum L. in Relation to Foliage Area, Dry Matter Production and Seed Yield

The effect of the ‘leafless’ mutation (in whichtendrils replace leaflets and the stipules are reduced to avestigial form) upon foliage area, photosynthetic net CO₂ uptakepotential, dry matter production and seed yield in Pisum sativumwas studied by comparing two near-isogenic lines of genotypeafafstst and ++++. The mutation is of potential agronomic valuein that it offers improved lodging resistance, crop drying andharvester throughput. In the conventional phenotype the total foliage area of themain axis attained a plateau (456 cm²) at day 56 from seedlingemergence, whereas corresponding values for the ‘leafless’mutant showed a total area of 208 cm² at day 68 with no indicationof a plateau. The agronomic consequence of this is discussed.During the vegetative phase of the plant the maximum CO₂ uptakepotential in the fully expanded conventional leaf was 8·5mg CO₂ leaf^–1 h^–1 and in the ‘leafless’mutant this value was 7·0 mg CO₂ leaf^–1 h^–1.For most ‘leaves’ of the latter phenotype this valuewas between 30 and 60 per cent less than for their conventionalcounterpart. There was a consistently higher photosyntheticpotential per unit area in tendrils of the ‘leafless’mutant than in leaflets of the conventional phenotype. The respectivemean specific values for the two phenotypes were 53 and 37 mgCO₂ dm^–2 h^–1. The problem of obtaining a meaningfulsurface area value for tendrils is discussed and the cylindricalnature of tendrils is taken into account. The ‘leafless’ mutant consistently accumulated 50per cent less dry matter than did conventional plants in theperiod from seedling emergence to anthesis and yield of maturedry seed per plant showed a reduction of 50 per cent both inseed number and total seed weight. The implications for future breeding and selection programmesaimed at haulm reduction are discussed in relation to evaluatingthe ability of the background genotype to produce adequate tendrilsin the presence of afafstst. Triticum aestivum, wheat, callus culture, organogenesis     

Partitioning of 14C Labelled Assimilates in Arctium tomentosum

Plants of the biennial Arctium tomentosum were grown from seedto seed-set in an open field under three different treatments:control plants receiving full light intensity, plants with aleaf area reduced by 45 per cent, and shaded plants receivingonly 20 per cent of natural illumination. At various stagesof development the youngest fully expanded leaf of one plantin each treatment was exposed to ¹⁴CO₂ for half an hour. Subsequentdistribution of labelled assimilates in various plant partswas determined after eight hours. In the first year, the mostdominant sink was the tap root irrespective of variation inassimilate supply. During the production of new vegetative growthin the second season, a larger amount of radioactive photosynthatewas recovered from above ground parts, especially during formationof lateral branches. Seed filling consumed 80–90 per centof labelled carbon exported from the exposed leaf. In the secondyear, the most pronounced difference between treatments wasin the degree of apical dominance, being highest in shaded plantsand lowest in the plants with cut leaves. Results from ¹⁴C experimentsagreed fairly well with a ‘partitioning coefficient’derived from a growth analysis of plants grown independentlyunder the same experimental conditions. Reasons for discrepanciesbetween the ¹⁴C results and the partitioning coefficient arediscussed. Arctium tomentosum, burdock, variation in assimilate supply, assimilate distribution, ¹⁴CO₂, labelling, growth analysis     

Influence of Abscisic Acid and Ethylene on Assimilate Distribution in Gladiolus grandiflorus

Water deficit in gladioli, even to the slightest degree, haspreviously been found to decrease assimilate mobilizing abilityof the inflorescence, increase that of the corm and delay translocationout of leaves. The possible involvement of abscisic acid (ABA) and ethylene(ethene) in these modifications was studied. External applicationsof ethrel caused modifications of assimilate distribution andgrowth similar to those caused by water stress but no connexionwas found between the water status of the plants and ethyleneproduction. External applications of ABA caused no change inassimilate distribution of well watered plants. A diurnal patternof inflorescence elongation and water potential () in fieldgrown plants was observed. A significant reduction in the rate of inflorescence elongationand without any change in ABA level was demonstrated in plantstransferred from 92 to 70 per cent relative humidity for 4 h.It is proposed that under water deficit the of the inflorescencedecreases and its turgor-dependent growth is slowed down. Consequentlyits mobilizing ability decreases, followed by delayed translocationof assimilates out of the leaves. The of the corm (the competitivesink) remains high, enabling its growth and assimilate attraction.ABA or ethylene do not seem to be directly involved in thisprocess. abscisic acid, ¹⁴C-assimilate distribution, competitive sink, ethylene, Gladiolus grandiflorus, water deficit     

Leaf Abscission and Stem Lesions (Intumescences) on Poplar Clones after SO2 and O3 Fumigation: A Link with Ethylene Release?

Differences in premature leaf abscission and in visible steminjury in genetic lines of poplar followed continuous fumigationswith air pollutant levels of SO₂ (90–100 nl l^–1)and O₃ (70–80 nl l^–1) either separately or together.The clones used were: Populus deltoides var. missiouriensisMarsh., P. nigra cv. ‘italicd’ L., and the hybridsP. nigra cv. ‘italica’ xP. deltoides (He-X/3) andP. nigra cv.‘italica’ x P. nigra cv. ‘Serres’(He-K/7). While most leaf abscission occurred within 20 d fromthe start of fumigation, stem lesions (intumescences), appearedonly after 72 d. Their anatomical characteristics include theformation of lysigenous aerenchyma in the lower parts of theintumescence, the sloughing of superficial cells from the injuredarea, and the development of crystalline formations on the surfaceof the lesions. P. deltoides exhibited the least morphologicalresponse to the gases. Ethylene released from fumigated leaves was determined at thesame gas concentration of SO₂ (100 nl l^–1), O₃ (75 nll^–1) and their mixture. Leaves of P. deltoides consistentlyshowed the lowest ethylene production after the gas treatments.P. ‘italica’ production was higher but was littlealtered by the treatments. The two hybrids He-X/3 and He-K/7showed the greatest increases in ethylene evolution with time.With He-K/7 exposed to the gas mixture the production of ethylenedecreased after the initial sharp rise during days 1–2,and reflected the considerable leaf damage observed after day3. The results suggest that sensitivity to air pollution, (as shownby leaf abscission and the formation of stem intumescences)can be correlated with the level of pollutant-induced ethyleneevolution from leaves. Initially high levels could induce abscission,whilst prolonged production could be responsible for intumescenceinitiation. The discussion proposes a series of events fromSO₂ and/or O₃ entry into the leaf and the physiological reasonsfor the clonal differences. Key words: Sulphur dioxide, ozone, ethylene, poplar, leaf abscission, stem lesions     

Modifications of Translocation Rate in Studies of Apple Leaf Efficiency

M.7 apple rootstocks were used during the peak period of shootextension for comparisons of dry-matter production per unitleaf area between intact plants and others which had been partiallydefoliated. Dry-matter increment per unit leaf area over a 16-dayinterval was some 70 per cent higher in partially defoliatedplants than in controls. ¹⁴CO₂ was supplied to designated leaves of comparable age andposition. Sample discs were taken from the ‘fed’leaves at intervals up to 9 days from supplying ¹⁴CO₂. Translocationrates were estimated by comparison with leaves on a third setof plants whose petioles were steamed to prevent translocationimmediately on removal of the ¹⁴CO₂ feeding chambers. Translocationrates in partially defoliated plants were enhanced some 30 percent compared with controls. It is suggested that features of the plant outside the studiedleaves may have contributed to the overall efficiency of assimilateproduction and utilization. Malus sylvestris L., apple, dry matter production, leaf efficiency, defoliation, translocation, assimilate distribution, sorbitol, sucrose     

Effects of Gibberellic Acid and Naphthaleneacetic Acid on Petiole Senescence and Subtended Peduncle Growth of Cyclamen persicum Mill

Removal of the blade from the leaf subtending the first flowerbud on Cyclamen persicum ‘Swan Lake’ plants causedthe petiole of that leaf to senesce, but had no effect on thegrowth of the flower peduncle in the debladed petiole's axil.A 10 mg NAA l^–1 application generally had no effect onpetiole senescence, peduncle elongation or flowering date whenapplied to the cut end of the petiole after blade removal. A25 mg GA₃ l^–1 application or a combination of 25 mg GA₃l^–1 application or a combination of 25 mg GA₃ l^–1plus 10 mg NAA l^–1 delayed petiole senescence and enhancedpeduncle elongation and subsequent flowering. No treatment significantlyaltered peduncle length at the time of flowering. Cyclamen persicum Mill, ‘Swan Lake’, tissue receptivity, flowering, GA₃, NAA     

A Cytochrome P450 Mediated Naringenin 3'-Hydroxylase from Sweet Orange Cell Cultures

A microsomal flavonoid 3'-hydroxylase (F3'H) catalyzing themetabolism of naringenin to eriodictyol in Citrus sinensis (L.)Osbeck cv. ‘Hamlin’ cell suspension cultures wasshown to be a cytochrome P450 enzyme. This reaction requiredO₂ and NADPH and was inhibited by CO, with partial reversalof CO-inhibition by light at 450 nm. Cytochrome P450 contentranged from 10–20 pmol (mg microsomal protein)^–1.The F3'H reaction was shown to be linear in regard to proteinconcentration between 2.5 and 25 µg of microsomal protein.The optimum pH for the reaction was 7.4–7.6 and the temperatureoptimum was between 30 and 37°C. The apparent K_m and V_maxfor naringenin were 24 µM±3.2 and 81.4±7.9pmol eriodictyol min^–1 (mg protein)^–1, respectively.The microsomal F3'H was also capable of forming dihydroquercetinfrom dihydrokaempferol (40 pmol min^–1 (mg protein)^–1)and of quercetin from kaempferol (3.25 pmol min^–1 (mgprotein^–1). Cytochrome c and ketoconazole were the bestinhibitors of WH activity followed by piperonyl butoxide anda-naphthoflavone. Light was shown to be an inducer of the F3'Halmost doubling the specific activity and increasing the microsomalcytochrome P450 content by 30% over that of dark grown cells.F3'H activity was also confirmed in microsomal preparationsof young (new flush) leaves from ‘Hamlin’ treesand flavedo of ‘Hamlin’ oranges, ‘Marsh’grapefruit, and ‘Lisbon’ lemon. No activity wasobserved in older, hardened leaves and albedo of all the fruittested. Initiation of embryogenesis in the ‘Hamlin’cell suspension cultures by switching from a sucrose mediumto a glycerol-based medium resulted in the down-regulation ofF3'H. ¹Mention of a trademark, warranty, proprietary product, or vendordoes not constitute a guarantee by the U.S. Department of Agricultureand does not imply its approval to the exclusion of other productsor vendors that may also be suitable.     

Leaf Growth in Cotton (Gossypium hirsutum L.) 1. Growth in Area of Main-stem and Sympodial Leaves

A model is presented for growth of individual and successivemain-stem leaves of cotton, based on a series of indoor experimentsand data sets from the literature. Three variable parametersare used to describe individual leaf growth: relative growthrate of meristematic tissue (R¹), relative rate of approachof final area (R₂) and a ‘position parameter’ (t_0.5)which governs the transition from meristematic to extensiongrowth. Final area of a leaf does not occur in the model asa deterministic quantity but it is a result of the processesduring growth. The model generates successive mainstem leavesand sympodial leaves as an integrated system. Assimilate shortagesoccurring in the plant operate on R₁ leading to the characteristicchange of final leaf area along the mainstem. Gossypium hirsutumL., cotton, leaf growth, relative growth rate, meristematic tissue, extension growth, mathematical model     

Rubisco Activity: Effects of Drought Stress

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activityis modulated in vivo either by reaction with CO₂ and Mg²⁺ tocarbamylate a lysine residue in the catalytic site, or by thebinding of inhibitors within the catalytic site. Binding ofinhibitors blocks either activity or the carbamylation of thelysine residue that is essential for activity. At night, inmany species, 2-carboxyarabinitol-1-phosphate (CA1P) is formedwhich binds tightly to Rubisco, inhibiting catalytic activity.Recent work has shown that tight-binding inhibitors can alsodecrease Rubisco activity in the light and contribute to theregulation of Rubisco activity. Here we determine the influencethat such inhibitors of Rubisco exert on catalytic activityduring drought stress. In tobacco plants, ‘total Rubiscoactivity’, i.e. the activity following pre-incubationwith CO₂ and Mg²⁺, was positively correlated with leaf relativewater content. However, ‘total Rubisco activity’in extracts from leaves with low water potential increased markedlywhen tightly bound inhibitors were removed, thus increasingthe number of catalytic sites available. This suggests thatin tobacco the decrease of Rubisco activity under drought stressis not primarily the result of changes in activation by CO₂and Mg²⁺ but due rather to the presence of tight-binding inhibitors.The amounts of inhibitor present in leaves of droughted tobaccobased on the decrease in Rubisco activity per mg soluble proteinwere usually much greater than the amounts of the known inhibitors(CA1P and ‘daytime inhibitor’) that can be recoveredin acid extracts. Alternative explanations for the differencebetween maximal and total activities are discussed.     

Uptake of 32P by Young Plants of Banksia hookeriana Meissner When Healthy and Infected with Phytophthora cinnamomi Rands

Young plants of Banksia hookeriana were grown in acid-washedsand with adequate phosphate and water supply, and a proportionwere inoculated with Phytophthora cinnamomi. There were no majordifferences in growth between uninoculated and infected plants,but there was a large increase in uptake of ³²P with increasingroot disease. In healthy plants ³²P uptake was greatest in youngleaf tissue, but in diseased plants labelled phosphate was directedmore towards older leaves where the activity was almost twicethat of young leaves. Enhanced uptake with disease was ascribed to possible blockageof the ‘message’ or ‘signal’ of phosphatetranslocation from shoot to root, such that the diseased rootincorrectly treated the shoot as P deficient and increased Puptake. Key words: Banksia hookeriana, Proteaceae, ³²P uptake, Phytophthora cinnamomi     

Interaction between Nitrogen Deficit of a Plant and Nitrogen Content in the Old Leaves

We examined changes in nitrogen content of the first leavesin relation to growth and nitrogen status of sunflower (Helianthusannuus L.) plants that were raised hydroponically at two irradiancelevels (high and low light, HL and LL) and at two nitrogen concentrations(high and low nitrogen, HN and LN). Initial increases in totaldry mass and total nitrogen of the whole plant were faster inHL-plants than in LL-plants irrespective of nitrogen supply,but in LN-plants the increase in total nitrogen was soon blunted.When plants grown under the same irradiance were compared, nitrogencontent of the first leaves (leaf N) decreased faster in LN-plantsthan in HN-plants, while for the plants grown at the same nitrogenconcentrations, it decreased faster in HL-plants than in LL-plants.Since these changes in leaf N were not explained solely by thechanges in plant dry mass or plant nitrogen, we introduced anindex, ‘nitrogen deficit (ND^*)’, to quantify nitrogendeficit of the whole plant. ND^* was expressed as ND^*(t)=[N_max–N(t)]xDM(t),where N_max and N(t) were nitrogen contents in the young, expandingleaves that had just unfolded to expand, at the initial stagewith sufficient nitrogen and at time t, respectively, and DM(t),plant dry mass at t. The decrease in leaf N was expressed asa liner function of ND^* irrespective of the growth conditions,which indicates validity of this index. Limitation of the useof ND^*, and mechanisms by which leaves sense nitrogen demandare also discussed. (Received June 17, 1996; Accepted August 30, 1996)     

ERRATA

Effects of coupled solute and water flow in plant roots withspecial reference to Brouwer's experiment. Edwin L. Fiscus. p. 71 Abstract: Line 3 delete ‘interval’ insert‘internal’. p. 73 Materials and Methods: line 6: delete ‘diversion’ insert ‘division’ line 9 equation should read J_v=L_p P–RT(C⁰–C¹). 74 Last line of figure legend: 10^–1 should read 10^–11. 75 Line 11: delete ‘seems’ insert ‘seem’. le 1 column heading—10⁶ should read 10¹¹. 77 delete ‘...membrane in series of...’ insert ‘membranein series or...’ Delete final paragraph.     

Comparative Effects of Soil Moisture Stress and Restricted Root Zone Volume on Morphogenetic and Physiological Responses of Soybean [Glycine max (L.) Merr.]

Significant differences in response to soil moisture stress(SMS) and restricted root zone volume (RRZV) were found in twocultivars of soybean [Glycine max (L.) Merr.] (‘Forrest’and ‘Williams’) plants grown under controlled-environmentconditions. Leaf water potentials of SMS-treated plants were0·4-0·6 MPa lower than those of controls and stomata1conductances 23-56% lower. In the case of RRZV treatment, however,there were no differences in either parameter. Initiation ofnew leaves as reflected in the plastochron index was stronglyreduced by SMS but was unaffected by RRZV. Photosynthetic rates(CO₂ fixation dm² of leaf) of plants given SMS were reducedby 11-21% while those of RRZV-treated plants were unaffected.SMS caused a strong preferential allocation of dry matter tothe root at the expense of the shoot in both cultivars. RRZV,however, had no effect on assimilate distribution in ‘Forrest’and only slightly favoured root growth in ‘Williams.’Carbohydrate concentrations of both alcohol-soluble and insolublefractions were increased significantly by SMS, especially inthe leaves, but were little affected by RRZV. Nitrogen concentrationin the root fraction was reduced by 22-24% and that in the leafand stem fractions by 7-14% under SMS but was not affected appreciablyby RRZV. Phosphorus concentration in the leaf, stem, and rootfractions was reduced by 45-65% under SMS but was relativelyunaffected by RRZV. These findings suggest that SMS and RRZVare basically different in their mechanism of action and thatthe impairment of growth resulting from these two stresses mayinvolve different physiological processes. Our results alsoindicate that the suppressive effects of small containers onplant growth do not necessarily result from inadvertent SMS. Key words: Drought, Container effects, Glycine max (L.) Merr     

The Sensitivity of Net Photosynthesis in Several Plant Species to Short-term Fumigation with Sulphur Dioxide

The effects of exposure of up to 2 h with sulphur dioxide ona range of plant species was observed by measuring changes inthe rate of net photosynthesis under closely controlled environmentalconditions. Ryegrass, Lolium perenne ‘S23’ was thespecies most sensitive to SO₂; significant inhibition was detectedat 200 nl l^–1. Fumigations at 300 nl l^–1 also inhibitedphotosynthesis in field bean (Vicia faba cv. ‘Three FoldWhite’ and ‘Blaze’) and in barley (Hordeumvulgare cv. ‘Sonja’). No effect was detected inwheat (Triticum aestivum cv. ‘Virtue’) at concentrationsup to 600 nl l^–1 SO₂, or in oil-seed rape (Brassica napuscv. ‘Rafal’) except at 800 nl l^–1 SO₂). Recoverycommenced immediately after the fumigation was terminated andwas complete within 2 h when inhibition had not exceeded 20%during the SO₂ treatment. Key words: Sulphur dioxide, short-term fumigation, photosynthesis     

Developmental and Biochemical Regulation of 'Constitutive' Nitrate Reductase Activity in Leaves of Nodulating Soybean

The developmental profile of ‘constitutive’ nitratereductase activity (cNRA) in leaves of soybean (Glycine max(L.) cv. Bragg) plants at different ages is described. The youngestleaves had most cNRA and the activity dropped off as a newerleaf developed above it. Each leaf had its distinct active periodof in vivo cNRA. This pattern was different in urea-grown andsymbiotically-grown plants (inoculated with Bradyrhizobium japonicumstrain USDA 110), where the latter had no detectable in vivocNRA in older leaves. Urea-grown plants maintained considerablein vivo NRA in such older leaves. When symbiotically-grown plantshad their nodules removed, in vivo cNRA reappeared in olderleaves within 1 d of removal, nearly reaching levels of youngleaves at 3 d after nodule excision. Allantoic acid (ALL), oneof the known transport ureides of soybeans, was implicated asa possible signal molecule from nodules to leaves. Allantoicacid (100 µM) inhibited in vitro c₁ NRA significantly,with 400 µM ALL resulting in complete inhibition. In contrast,allantoin (ALN) had no inhibitive effect on NRA. Inhibitionof c₁NRA by ALL was by a competitive process, judging from Lineweaver-Burkeplots against nitrate. Kinetics showed a constant Vmax of around105 nmol NO₂ mg^–1 protein h^–1 and a K_m for nitrateof 15 mM, which increased to 60 mM in the presence of 200 µMallantoic acid. Non-specific (ionic and pH-related) influenceswere eliminated. Allantoic acid also had a slight stimulatingeffect of in vitro NRA (up about 25% at 400 µM). Thesefindings suggest that c1NRA may be involved in ureide metabolism,rather than in vivo nitrate metabolism. Key words: Root-shoot interaction, nitrogen metabolism, nodulation, symbiosis     

Aspects of the Comparative Physiology of Ranunculus bulbosus L. and Ranunculus repens L.: II. Carbon Dioxide Assimilation and Distribution of Photosynthates

Detailed analysis of the interrelationships between sourcesof photosynthate production and sites of utilization in thetaxonomically closely related species Ranunculus bulbosus L.and R. repens L. showed that leaves whether present on rosette,stem, or stolon had similar levels of ¹⁴CO₂-fixation but thepattern of distribution of radiocarbon to the rest of the plantdiffered. Fruits of R. bulbosus had a lower fixation rate thanleaves but were characterized by total retention of the fixedradiocarbon. Rosette leaves of R. bulbosus supplied the youngleaves, developing apices in the rosette, roots, and corms,whereas the labelled assimilates from cauline leaves were evenlydistributed between reproductive and vegetative parts. The cormwas the major sink both at the flowering and fruiting stages.When plants were treated with ¹⁴CO₂ in the field even higherlevels of radiocarbon moved into the corm than in comparableexperiments under greenhouse conditions. The rosette leaf ofR. repens exported mainly to actively growing stolons in plantswith many stolons bearing rooted ramets although growth of astolon was also substantially supported by photosynthates producedby its own ramets. A proportion of the radiocarbon fixed byleaves of mature ramets was exported and moved in a predominantlyacropetal direction into the stolon apex, stolon axis, and youngramets of the same stolon. The stock in R. repens had a muchlower demand for assimilates than the corm in R. bulbosus. The results are consistent with the concept that R. bulbosusoperates a conservative policy involving the replacement ofthe parent in situ by a daughter from the corm, coupled withextensive fruit production. In R. repens the emphasis is onlateral spread and exploitation of substantial areas of groundby vegetative spread and replacement of the parent by daughtersmany of which may occupy sites some distance from the parent.     

Assimilation of 14CO2 by the Inflorescence of Poa annua L. and Lolium perenne L.

The relative assimilatory activity of the inflorescence, itsindividual components, and the leaves of flowering tillers ofPoa annua L. and Lolium perenneL. was determined over the periodfrom inflorescence emergence to seed shedding. The pattern of¹⁴CO₂ fixation was similar for both species and the inflorescencewas by far the most important assimilatory organ of the reproductivetiller, particularly over the latter period of seed developmentas leaf senescence progressed. With the exception of the seedsall parts of the inflorescence showed significant assimilatoryactivity and the lemmas and paleas accounted for 40–50per cent of the total ¹⁴C fixed by the inflorescence in bothspecies. The importance of the grass inflorescence as a photosyntheticstructure is discussed in relation to similar studies on cereals. Poa annua, Lolium perenne, carbon dioxide assimilation, inflorescence     

A Carbon 14 Study of Metabolism in Tall Fescue Seedlings Acclimating to Growth at Low Temperatures

The youngest fully expanded leaves of young plants of tall fescue(Festuca arundinacea Schreb. cv. S 170) were allowed to assimilate¹⁴CO₂ either (a) at the fifth leaf stage immediately beforetransfer from 17/14?C to 7/4?C (non-acclimated), or (b) aftertransfer from 17/14?C to 7/4?C at the fifth leaf stage, andfurther development in 7/4?C of one or two more leaves (acclimationfor one or two plastochrons). Controls were maintained in 17/14?C and allowed to assimilate ¹⁴CO₂ at the corresponding (fifth,sixth, or seventh) leaf stages. Allocation of 14C amongst sinksand biochemical fractions was analysed during a subsequent periodof growth at 7/4 ?C (cold) or 17/14 ?C (control). Allocationof assimilate to growing parts of the shoot was less than controlsin the non-acclimated plants transferred to the cold and morethan controls in plants acclimated for one plastochron. Afterthe imbalance induced initially by transfer from 17/14?C to7/4 ?C, acclimation for one or two plastochrons brought theallocation amongst sinks and amongst biochemical fates closerto the balance existing in controls. The main shoot and sidetillers differed in the time during acclimation when they becamemore like the controls. The percentage of assimilate in thesoluble carbohydrate fraction of non-acclimated plants and ofplants acclimated for one plastochron, was higher than in controls.The percentage of assimilate in the cell wall fraction was lowerin non-acclimated plants than in controls but the differencefrom controls after two plastochrons acclimation again was less.During the first plastochron after transfer to cold, diversionof assimilate to a reserve pool in sinks could be a factor limitingcell wall synthesis and growth and this limitation may be relievedwhen the reserve pool is ‘full’. Low temperaturereduced the percentage of assimilate in the protein fractionof growing parts of the shoot and the difference was found evenafter two plastochrons acclimation. Key words: Low temperature, metabolism, tall fescue (Festuca arundinacea Schreb. cv. S. 170)