Nitrogen and energy loss in the marine teleost Lithognathus mormyrus (Linnaeus)

Nitrogen excretion and assimilation efficiencies in Lithognathus mormyrus (Linnaeus), a marine teleost present in high-energy surf zones in Algoa Bay, South Africa, were determined under controlled laboratory conditions at 15, 20 and 25 °C. Ammonia was the major form of nonfaecal nitrogen excreted by starved and fed L. mormyrus. Urea and amino acids were secondary excretory products. Ammonia excretion rates were temperature independent and the excretion rates of fed fish were significantly higher than starved fish at 20 and 25 °C but not at 15 °C. The mass component (b) of the mass/ammonia excretion equation was temperature independent and ranged from 0.590 to 0.669 and from 0.670 to 0.767 for starved and fed fish, respectively. The mean percentage of food energy lost via the dissolved nonfaecal excretory products (exogenous plus endogenous) was 4.12%. Assimilation efficiencies ranged from 71.89 to 98.78% for dry matter and from 96.89 to 99.88% on an energy basis. The combined nonfaecal and faecal energy loss was calculated at 10.11% of the ingested energy. The omnivorous ichthyofauna present in the surf zone ecosystem recycle 33 g N · m strip · yr⁻¹. This constitutes < 1 % of total phytoplankton nitrogen requirements.     

NITROGEN EXCRETION IN THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL, 1908)

Excretion of ammonia, urea and primary amines (assayed as fluorescamine-positivesubstances, FPS) was measured in the Antarctic limpet Nacellaconcinna. The mean contributions to overall excretion rate were89% ammonia, 8% urea and 3% FPS, although in some individualsurea formed almost 40% total excreted nitrogen and in othersprimary amines formed over 30%. Ammonia and urea excretion rateswere not correlated, suggesting the ureagenesis has a specificphysiological role and is not simply an alternative end-pointto ammonia. In starved limpets urea excretion at first increasedby at least x2, and then declined to low levels after 44 days.Ammonia excretion also increased, but only after 20 days, andthen stayed high until at least day 44. These different patternsconfirm the independent roles of ammonia and urea productionin Nacella. (Received 10 June 1993; accepted 25 August 1993)     

The Nitrogen Content of Plants and the Self-thinning Rule of Plant Ecology: A Test of the Core-skin Hypothesis

The ‘core-skin’ hypothesis postulates that secondarilythickened plants behave energetically as an inert ‘core’covered by an active ‘skin’, the ‘skin’being two-imensional, the ‘core’ three-dimensional.This would explain the ‘self-thinning ‘or‘–3/2’ rule of plant ecology, that is, the tendencyfor log (dry weight per plant) and log (number of plants perunit area) to progress along a straight line relationship, withslope = – 3/2’. The hypothesis was tested as follows. Plant nitrogen contentwas used as an estimate of the mass of ‘skin’ perplant, and dry weight as an estimate of the mass of the ‘core’.As plants mature the slope of the relationship between y = log(mass of nitrogen per plant) and x = log (mass of dry matterper plant) is expected to decline from an initial value of 1.0towards a final value of 0.66. The intercept of the relationshipis expected to reflect the intrinsic content of ‘skin’per unit of ‘core’. Genotypic variation in thisparameter should cause genotypic differences in the maximumattainable yield of biomass per unit area. The expectations were investigated by fitting the function y= p+qx+r exp – x to 30 sets of data on plant nitrogencontent, plant weight and time in 18 different vegetables. Simplelinear regressions of y on x were fitted to more limited setsof data on weights and nitrogen contents of mature trees. Theexpectations were, with some minor exceptions, confirmed. Nitrogen, yield, plant competition, self-thinning     

Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions

The feeding rate and behaviour of whelks (Buccinum undatum)offered cockles (Cerastoderma edule) in laboratory experimentswere examined. When presented with cockles in a range of sizes(10–40 mm), 14 B. undatum (34.6–88.3 mm),held individually in aquaria, consumed a wide size range ofcockles. Small whelks (<40 mm) consumed cockles (<23 mm),whereas large whelks, (>60 mm) ate a greater numberof larger cockles (>30 mm) and a wider size range ofcockles (12–40 mm) than smaller whelks. The majority(90%) of the shells of the predated cockles were undamaged andthe few (<10%) that were damaged showed only slight abrasionsto the anterior and posterior shell margin. Filmed observationsof B. undatum feeding on C. edule showed a method of attackthat has not previously been reported and involved the use ofthe whelk's foot to asphyxiate the cockle or to pull the shellvalves apart. No filmed evidence was found for the previouslyreported shell ‘wedging’ technique for prising openthe closed shell valves of C. edule, although 10% of the shellsof consumed cockles in feeding experiments had damaged shellmargins. (Received 4 April 2007; accepted 30 June 2007)     

PATTERNS OF REPRODUCTION IN THREE SANDY BEACH WHELKS OF THE GENUS BULLIA GRIFFITH

The breeding cycles of two species of sandy beach whelk (Bulliadigitalis and B. pura) are presented and compared with a thirdspecies (B. rhodostoma). In all three species, egg maturationand copulation occur in spring while summer marks the depositionand spawning of egg capsules. B. digitalis and B. pura migrateoffshore to lay their eggs, the juveniles of both species restrictingthemselves to beyond the breaker zone. Newly hatched snailsof B. rhodostoma appear in the intertidal towards late summer.The discovery of a penis-like structure on females of B. rhodostomais investigated. The pseudopenis was also found on B. pura butnever on B. digitalis. The possibility of a sex-change was eliminatedon the histological investigation of the gonads of a range ofsnails and the examination of sex-ratios over a period of fivemonths. General trends in reproductive behaviour are also discussed. (Received 18 March 1984;     

Homeostasis in Nitrogenous Uptake/Assimilation by the Green Alga Platymonas (Tetraselmis) striata (Prasinophyceae)

When nitrate, ammonium, or urea were the sole nitrogen sourcesfor the growth of Platymonas striata there was a short initiallag period, after which uptake/assimilation occurred at a constantrate. Glycine ‘uptake’ was however non-linear withtime. Addition of ammonium or urea markedly inhibited nitrate‘uptake’ whereas although glycine was initiallytotally inhibitory, nitrate ‘uptake’ recommencedabout 1 h after addition, but at a greatly reduced rate. Ammoniumtotally inhibited urea ‘uptake’, but did not inhibitglycine ‘uptake’. When ammonium, urea, or glycinewere present at the same time as nitrate the total rate of nitrogen'uptake/assimilation was within 40% (or closer) of that of nitratenitrogen ‘uptake’ alone. In the first two casesthis reflected a total switching off of nitrate ‘uptake’whilst the new substrate was assimilated at a rate similar tothe initial nitrate rate, whereas in the case of glycine, bothsubstrates were used simultaneously. Once the concentrationof any of the inhibitory nitrogen sources had been reduced toa low level the ‘uptake’/assimilation of nitraterecommenced. It is suggested that the ability of P. striatato maintain a more or less constant rate total nitrogen ‘uptake’/assimilationirrespective of the mixture of utilizable nitrogen sources presentedto it, is not due to controls at the level of the entry of substrateinto the cell, but to intracellular actions at the enzyme level.The relative constancy of, and high rate of ‘uptake’,irrespective of nitrogen source and over a wide range of extracellularconcentrations, is tentatively considered to be due to saturationof the assimilatory mechanisms under the conditions employed;all the sources lead, either directly or indirectly, to theproduction of amino groupings for entry into nitrogenous metabolism.This homeostasis of nitrogen ‘uptake’/assimilationwould clearly be of considerable benefit to the alga in nature,enabling it to maximize growth in changing environmental conditions. Platymonas striata, nitrogen update, nitrogen assimilation     

Metabolism and elemental composition of aggregate and solitary forms of Salpa thompsoni (Tunicata: Thaliacea) in waters off the Antarctic Peninsula during austral summer 1999

Oxygen consumption, ammonia excretion and phosphate excretionrates were measured on the aggregate form (aggregated sexualblastozooid generation) and solitary form (solitary asexualoozooid generation) of Salpa thompsoni sampled from waters offthe Antarctic Peninsula from December 1999 to February 2000,in conjunction with body composition analysis (water, ash, carbon,nitrogen and phosphorus). The specific metabolic rates of S.thompsoni were weight-independent. No significant differencesbetween the aggregate and solitary forms were observed for theweight-specific rates with the exception of the oxygen consumptionrate on phosphorus weight. Metabolic loss estimated for theaggregate and solitary forms was 3.0 and 3.5% day^–1 forbody carbon, 1.6 and 1.8% for body nitrogen, 3.9 and 10.6% forbody phosphorus, respectively. Contents of carbon (6.0% of dryweight for the aggregate form and 5.1% for the solitary form),nitrogen (1.5 and 1.3%) and phosphorus (0.15 and 0.11%) tendedto decrease with the increase of dry weight. All mean valuesof each body constituent (water, ash, C, N and P) for the aggregateand solitary forms were not significantly different in the samedry weight ranges.     

THE OLFACTORY-GUSTATORY BASIS OF FOOD PREFERENCE IN THE HERBIVOROUS PROSOBRANCH, LITTORINA LITTOREA (LINNAEUS)

Studies of food preference often measure the rate of consumptionof prey items by a predator; this confounds the factors determiningattractiveness and edibility, ignoring the fact that preferencesare probably resolved at the pre-ingestive stage of a consumer'sfeeding behaviour. In this paper, a novel technique has beendeveloped to measure the importance of chemical stimuli to feed,perceived by olfactory and gustatory means, as determinantsof the subsequent feeding behaviour of the generalist intertidalherbivore,Littorina littorea (L.). Cell-free extracts of a rangeof algae were presented simultaneously, impregnated in artificialcellulose-based substrates. Subsequent ranking of feeding preferencesreveals hierarchies which correspond with those establishedby other workers, using intact algae to feed L. littorea. Extractsof ephemeral early successional species (e.g. Ulva lactuca,Porphyra umbilicalis) generally provoke a more positive feedingresponse than perennial late successional species (e.g. Fucusvesiculosus, Asco-phyllum nodosum). Animals fed a preferredalga (Ulva lactuca) prior to preference trials displayed a reductionin the strength of preference relative to starved animals. Therewas no evidence of ‘switching’ of preference rankingsdue to satiation, however. These findings confirm the importanceof olfactory-and gustatory-mediated feeding behaviour as theprimary determinant of food preference in L. littorea. Theyare consistent with the hypothesis that the factors which determinethe attractiveness of a food type, such as chemical cues, arethe criteria by which consumers predict the value of that food.     

Relative Sensitivity and Tolerance of some Gladiolus Cultivars to Sulphur Dioxide

Five Gladiolus cultivars, namely ‘Aldebaran’, ‘BrightEye’, ‘Illusion’, ‘Manisha’ and‘Manmohan’, were exposed to 1 and 2 µg l^–1sulphur dioxide to test their relative-sensitivity toleranceto the pollutant Plants were fumigated experimentally for 2h daily Foliar injury symptoms were observed first in ‘Manisha’followed by ‘Aldebaran’ and ‘Illusion’at the higher dose Photosynthetic pigments and leaf extractpH were significantly decreased, particularly in ‘Manisha’and ‘Illusion’ Overall disturbances in the plantmetabolism due to SO₂ treatment led to retarded growth of plants,as evident from decreased shoot length and phytomass valuesThe order of sensitivity of the five Gladiolus cultivars toSO₂ was as follows, with the greatest first Manisha, Illusion,Aldebaran, Bright Eye, Manmohan Cultivars, Gladiolus, sensitivity, sulphur dioxide, tolerance     

The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay

Ammonia excreted by mixed zooplankton populations over an annual(1972–1973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH₃-N dry wt^–1 day^–1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH³-N mg dry wt^–1 day^–1. Grossphytoplankton production integrated over the year (1972–1973)averaged 151 mg C m^–3 day^–1 for an 8 m water column;peaks of 332 and 905 mg C m^–3 day^–1 occurred duringthe winter-spring and summer blooms, respectively. Excretedammonia, integrated seasonally and annually, contributed only0.2% and 4.9% of the nitrogen required for observed gross productionduring the winter-spring and summer blooms, respectively, and4.4% annually. However, excreted ammonia may be an importantsource of the nitrogen required by Skeletonema costatum, thedominant diatom in Narragansett Bay, during the post-bloom periodwhen 186% of the nitrogen required for its net production wasmet by ammonia excretion. A combination of zooplankton ammoniaexcretion and benthic ammonia flux contributed 22% of the nitrogenrequired for the annual gross production (440 g C m^–2)while 51% of the nitrogen required for the net production ofSkeletonema was accounted for by regenerated nitrogen. ¹This research was supported by NSF grant GA 31319X awardedto Dr.T.J.Smayda.     

The notal organ of the scorpionfly (Panorpa vulgaris): an adaptation to coerce mating duration

The notal organ in P. vulgaris (Insecta: Mecoptera) is a clamplikestructure on the dorsum of the middle of the male’s abdomenthat holds one of the female’s forewings throughout mating.Males often provide salivary masses as food to their mates duringmating, and a male’s ability to produce saliva dependsupon whether he has fed adequately before mating. To test thehypothesis that the evolutionary function of the notal organis to coerce longer matings than are in the interests of females,the notal organ and the amount of food males and females receivebefore mating were experimentally manipulated. In support ofthe hypothesis, copulation was reduced when the notal organwas made inoperative under the following four conditions: (1)female fed and male starved before mating, no saliva duringmating; (2) same as in condition 1 but with one salivary massduring mating; (3) both sexes starved before mating, no salivarymass during mating; and (4) both sexes fed before mating. However,when females were starved before mating and males were fed,resulting in multiple masses being provided during mating, thenotal organ had no effect on length of copulation, and thusthere was no sexual conflict over mating duration. In addition,the larger the female relative to her mate, the briefer thecopulation when the notal organ was operative, which suggeststhat a physical struggle between the male and female may occurduring sexual conflict about mating duration. This is one ofonly a few studies that provide evidence of adaptation to thedomain of sexual coercion. [Behav Ecol 1991;2:156–164]     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. I. Influence of Pretreatment, Culture Medium and Culture Incubation Conditions on Callus Production and Differentiation

This study was conducted with Lolium temulentum, Festuca pratensis,and the two hybrids L. multiflorum x F. pratensis ‘Elmet’and L. perenne x F. pratensis ‘Prior’. In a comparisonof various durations (7–42 d) of pretreatment at 4 or7 °C the highest yield of microspore-derived callus of L.temulentum was obtained after pretreatment of spikes at 7 °Cfor 28 d, conditions which also proved optimal for panicle pretreatmentwith F. pratensis. For ‘Elmet’, durations of 21–42d were optimal, and for ‘Prior’ the responses tendedto decline with increasing duration. In L. temulentum addition of charcoal (1–2 g l^–1)to medium containing 2, 4-D and KN wa     

Pyrimidine Nucleotide Biosynthesis in Vinca rosea Cells: Changes in the Activity of the de novo and Salvage Pathways during Growth in a Suspension Culture

Marked changes in the activity of the ‘de novo’and ‘salvage’ pathways of pyrimidine biosynthesisduring growth of Vinca rosea cells in a batch suspension culturewere observed. The activity of these pathways was investigated by determiningthe contribution of ¹⁴C of [2-¹⁴Cluracil, 12-¹⁴Cluridine. and[6-¹⁴Clorotate to the cell constituents and by measuring theactivity of the several enzymes of these pathways. During the lag phase of the culture, ‘uracil-’ and‘uridine-salvage’ pathways made the predominantcontribution to nucleotide biosynthesis, but, following theinitiation of cell division, the ‘de novo’ pathwayfor nucleotide biosynthesis operated appreciably. These results suggest that nucleotide synthesis during cellgrowth in a suspension culture can be divided into two stages:a ‘turnover stage’, during the lag phase of cellgrowth, and a ‘true biosynthetic stage’, which isinitiated in the cell division phase.     

Toxoglossan gastropods of the subfamily Crassispirinae (Turridae) lacking a radula, and a discussion of the status of the subfamily Zemaciinae

Two new species of Horaiclavus, lacking radula, venom glandand proboscis, are described. The genus is placed in the subfamilyCrassispirinae (Turridae). Both species possess a peculiar foregutstructure, the muscular rhynchodaeal outgrowth situated in therhynchocoel. The possible function of the rhynchodaeal outgrowthis discussed. Other studied species of Horaiclavus possess aradula of a typical ‘crassispirine’ type but lackthe outgrowth. The anatomy of the foregut of the new speciesis superficially similar to that of Zemacies excelsa (Turridae:Zemaciinae), which also possesses an additional structure ofthe rhynchocoel, namely the ‘pyriform gland’. Conchologically,there is no resemblance between Zemacies and Horaiclavus andit is concluded that similar foregut arrangement appeared independentlyin both lineages. A new monotypic subfamily Zemaciinae was erectedmostly on the basis of the unique foregut arrangement of Zemaciesexcelsa. We express doubts concerning the importance of thesecharacters in establishing a new taxon of subfamilial rank andtherefore the validity of the subfamily Zemaciinae. (Received 16 May 2007; accepted 1 October 2007)     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM     

CORRIGENDUM

p.40, 1. 20. For ‘does develop.’ ‘read’‘does not develop.‘     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

The Influence of the Plant Growth-regulator, 2-Methyl-4-Chlorophenoxyacetic Acid, on the Metabolism of Carbohydrate, Nitrogen and Minerals in Solanum lycopersicum (Tomato)

The effects of the foliar application of phytocidal concentrationsof 2-methyl-4-chlorophenoxyacetic acid (MCPA) on change in totaldry weight, and in ‘available carbohydrate’ (starch,‘total’ and ‘reducing’ sugars), totalnitrogen, phosphorus, potassium, calcium, and magnesium of ‘tops’and roots of tomato plants have been followed over a periodof 14 days following spraying. There were two main treatments—‘nutrient’(nutrient supply to roots continued after spraying) and ‘water’(distilled water only supplied to roots after spraying) and‘water’ (distilled water only supplied to rootsafter spraying)—the sub-treatments consisting of ‘MCPA’versus ‘no-MCPA’ for each of the main treatments.Twelve different times of sampling were used. In analysing the present data, the quantity ‘residualdry weight’ (total dry weight less ‘available carbohydrate’),which was originally introduced by Mason and Maskell as a basisof reference for analyses of plant organs in short-period experimentsnot involving appreciable growth, has been used as an estimateof the permanent structure of plant growth. This new use ofthe ‘residual dry weight’ basis has brought outimportant features which were obscured when the data were leftin their primary form (as percentages of total dry weight oramounts per plant). Growth, as measured by increase in ‘residual dry weight’,was greatly inhibited by 2-methyl-4-chlorophenoxyacetic acidshortly after spraying, in both the presence and the absenceof nutrient. In the presence of 2-methyl-4-chlorophenoxyacetic acid, netassimilation rate (estimated as rate of increase in total dryweight per gram ‘residual dry weight’ of the ‘tops’)was greatly diminished while uptake of total nitrogen and ofP₂O₅ (estimated as increase in total nitrogen or of P₂O₅ ofthe whole plant per day per 1 g. ‘residual dry weight’of the roots) appeared to undergo a similar but much smallerdiminution. It seemed probable, however, that in the presenceof MCPA a larger proportion of the carbohydrate actually formedwas utilized for synthesis of aminoacids and protein. In the plant as a whole there was no evidence of actual depletionof ‘available carbohydrate’ as a result of MCPAtreatment, this fraction showing a steady increase in all treatmentsthroughout the experiment. The rate of increase was, however,much reduced by MCPA treatment. The ‘tops’ presentedmuch the same picture as the whole plant, but for the rootsthe situation was quite different. While the roots of the ‘no-MCPA’plants and also of the ‘MCPA-water’ plants showeda steady increase in available carbohydrate, those of the ‘MCPA-nutrient’plants rose only very slightly (from the initial value of 8mg. per plant to about 10 mg.) during the first 2 days, andthen in the next 2 days declined to a value (about 6 mg.) belowthe initial and remained at this low level for the rest of theexperiment. It is suggested that the phytocidal effect of 2-methyl-4-chlorophenoxyaceticacid in the presence of nutrient may be due to depletion ofthe ‘available carbohydrate’ supplies in the roots,which is shown to be brought about, in part, by reduced transportfrom the tops, and partly by the relatively greater utilizationof the carbohydrate present. These results offer an explanationfor the facts that plants showing vigorous growth are more easilykilled by MCPA and that perennial plants, particularly thosewith storage tissues in their roots, are more resistant. Further,they suggest the useful practical application that MCPA treatmentshould be given when the carbohydrate reserves of the rootsare at a minimum. For perennial plants, conditions might beexpected to be optimal for the application of MCPA in late spring,at a time when the first ‘flush’ of growth is slowingdown and before any appreciable new reserves of carbohydratehave been accumulated. It was also shown that 2-methyl-4-chlorophenoxyacetic acid preventedthe net synthesis of starch, but still permitted an appreciablenet formation of sucrose. 2-methyl-4-chlorophenoxyacetic acid appeared to have no effecton the uptake of potassium, calcium, or of magnesium. The lackof effect on potassium is contrasted with the previous observationby Rhodes, Templeman, and Thruston (1950) that sub-lethal concentrationsof MCPA, applied over a relatively long period to the rootsof tomato plants, specifically depressed the uptake of potassium.     

Primary and Secondary Induction Requirements for Flowering of Contrasting European Varieties of Lolium perenne

The flowering requirements of six European varieties of Loliumperenne L. were studied in controlled environments. In experimentson primary induction, flowering was recorded after transferto long days (LD) in a greenhouse at 12–24°C. In experimentson secondary induction, primary induction was first accomplishedat 6°C/10 h daylength for 12 weeks. When evaluated by the50% heading criterion, the requirement for duration of primaryinduction at 6°C/8 h daylength was <3 weeks in Mediterranean,5–6 weeks in Central European and 7–8 weeks in Scandinavianvarieties. While ‘Veyo’ (Italy) flowered profuselyregardless of temperature or daylength during primary induction,critical temperatures for primary induction in SD and LD were15 and 11°C in ‘Baca’ (Czech Republic) and 11and 7°C in ‘Falster’ (Denmark). The criticalphotoperiod for secondary induction at 15°C ranged from12 h in ‘Veyo’ and 14 h in ‘Baca’ to16.5 h in ‘Falster’ and 17.5 in ‘Kleppe’(Norway). The critical number of LD cycles varied correspondingly.While the Central and North European varieties required fewerLD cycles for 50% heading at 18 than at 12°C, ‘Veyo’showed the opposite response. It is concluded that the requirementsfor both primary and secondary induction of Lolium perenne increasewith increasing latitude of origin of the germplasm. In oneexperiment, 39–87% of the inflorescences came from tillersthat were not visible on transfer from primary to secondaryinduction, thus it is also concluded that there is no juvenilestage in tillers of Lolium perenne. Copyright 2000 Annals ofBotany Company Daylength, flowering, juvenility, perennial ryegrass (Lolium perenne L.), primary induction, secondary induction, temperature, varieties, vernalization     

Quality Traits, Carbon Isotope Discrimination and Yield Components in Wild Wheats

Seventy-one wild and primitive diploid accessions of the S-,A- and D-genome species of Aegilops and Triticum, one tetraploidwheat, T. turgidum L. var. durum Desf., ‘Mexicali’,and two hexaploid wheats, T. aestivum L., ‘Anza’and ‘Yecora Rojo’ were evaluated and compared forprotein and lysine contents, carbon isotope discrimination,and various agronomic traits in the 1987–88 season underfield conditions. Significant variability was observed amongthe 71 accessions and among the three genomes for all traits.For most characters, the D-genome species exhibited the mostvariation, followed by the A- and S-genome species. Aegilopssquarrosa, T. urartu, and T. boeoticum showed large variationfor harvest index. Large variation for grain yield was exhibitedby Ae. squarrosa, Ae. sharonensis and Ae. longissima, whichcould be exploited in hybridization and breeding programs withmodern cultivars. The mean protein and lysine values of thediploids were significantly higher than those of the moderncultivars. The S- and A-genome accessions had higher proteinand lysine contents than the D genome. Among genomes, the meanvalues for yield and harvest index were significantly greaterin S- and D-genome accessions than in the A-genome accessions. The correlation pattern between yield and quality traits wasdifferent in the three genomes. Superior accessions with regardto both grain yield and quality traits were identified in eachspecies studied, except Ae. longissima and Ae. sharonensis.The advantages and uses of these accessions in wheat breedingprograms are discussed. Aegilops spp, Triticum spp, protein and lysine contents, yield components, carbon isotope discrimination