Integrated Analysis of Growth and Light Interception in Winter Lettuce II. Differences between Cultivars

‘Integrated growth analysis’ (emphasizing aspectsof crop and plant structure) and ‘light conversion analysis’(stressing the efficiency of interception and photosyntheticconversion of light) have been used to investigate the wintergrowth of different cultivars of butterhead and crisphead typesof glasshouse lettuce. Measurements from ‘Ambassador’ (large-framed butterhead),‘Renate’ (medium-sized butterhead) and ‘Cristallo’(crisphead) were made, statistical progressions were fittedto the primary data and hence estimates of all the analyticalcomponents were derived. Curves for crop growth rate, like those for most other components,followed a generally similar pattern for all three cultivars.In integrated growth analysis, the biomass curve for Ambassadorlay above the curves for the other cultivars. The weight advantagewas initially 60 per cent and it persisted with only a smallreduction (to 40 per cent) until the final harvest. Relativegrowth rate varied little between cultivars because differencesobserved in leaf area ratio were complementary to those seenin net assimilation rate. In light conversion analysis, differences in light interceptingefficiency between cultivars were not statistically significant,though Ambassador attained full interception 4 days earlierthan Renate and 6 days earlier than Cristallo. Differences inlight utilizing efficiency were small and non-significant exceptduring the post-rosette stage when the value for Renate waslower than that of either Ambassador or Cristallo. Deviationsaround the fitted curves were correlated with fluctuations inthe light regime. An assessment is made of the utility and limitations of thetwo procedures. It is concluded that both approaches can assistin analyzing the rate of dry matter production in crops or plantstands. Integrated growth analysis is advantageous when theneed arises to treat individual and population-based attributessimultaneously, while light conversion analysis provides a meansof explicitly incorporating the primary environmental variableinfluencing growth. Lactuca sativa L., lettuce cultivars, growth analysis, crop growth rate, relative growth rate, light interception, light utilization     

The Importance of Light Intensity for Pollen Tube Growth and Embryo Survival in Wheat x Maize Crosses

The success of Triticum aestivumxZea mays crosses, used to producewheat doubled haploids, is influenced by light intensity. Toexamine the basis for this response, pollen tube growth, embryosurvival and indicators of photosynthetic rate were measuredin two wheat cultivars (‘Karamu’ and ‘Kotuku’)crossed with maize at two irradiance levels (250 or 750 µmolm^-2s^-1, PAR). Pollen tube growth was significantly affectedby light intensity in ‘Karamu’ plants but not in‘Kotuku’ plants, despite both cultivars being pollinatedby the same maize source. The percentage of pollen tubes reachingthe cavity between the ovarian wall and integuments, or in themicropyle of ‘Karamu’ plants at high light intensity(65%) was nearly three-times greater than that at low lightintensity (22%). Thus, either low light intensity can affectthe maternal wheat plant in a way that inhibits pollen tubegrowth and/or high light intensity may promote pollen tube growthin ‘Karamu’ plants. Significant differences in ratesof electron transport in plants grown at the two light intensitiesindicated that the rate of photosynthesis may also have an effecton pollen tube growth. These results have importance for improvingthe efficiency of wheat x maize crosses and other wide cerealcrosses. Copyright 2001 Annals of Botany Company Intergeneric hybridization, light intensity, pollen tube growth, embryo survival, Triticum aestivum, wheat,Zea mays , maize     

Philosophical Aspects of Measurements, Equations and Inferences in Plant Growth Studies

Growth analysis is based on equations that are ‘identities’because they are algebraically self-evident, whereas the moredeterministic models of plant growth are based on ‘conditionalequations’ that represent quantitative hypotheses. Growthanalytical studies consequently focus on the values of the componentsand not on the validity of the equations, whereas ‘validation’is a prime concern for other growth models. Implications ofmeasurement theory, of dependent and independent variables andof compensating components arise in the use of both types ofequation for quantifying growth. There is now available a rangeof approaches, from traditional growth analysis, through variousdevelopments of growth analysis including light conversion analysis,to complex mechanistic models of growth. Growth analysis, yield component analysis, light conversion analysis, mathematical models, measurement theory, derived quantities, independent variables, equations of growth     

Cultivar Differences in the Performance of Bean Seedlings at Suboptimal Temperatures

Growth analysis of plants raised under controlled environments(10–5, 12, 15, 18 and 20 °C, and 21 h photoperiod)was used to examine whether varietal differences in the minimumgermination temperature of four bean cultivars persist duringgrowth at suboptimal temperatures. A method to estimate theminimum vegetative growth temperature, based on axis relativegrowth rate, was developed. In order to compensate for ontogeneticdrift, the harvests were conducted at the same stage of developmentof the plants. Axis relative growth rates, reduction rates ofthe cotyledons and other growth parameters were calculated inorder to compare the cultivars. Cultivar ‘Marschall’showed better growth potential at 12 °C than the others,‘Pergousa‘ at 15 °C, and ‘Marschall’,‘Olsok’ and ‘Pergousa’ at 18 and 20°C. The effect of temperature on axis RGR was similar for‘Marschall’, ‘Olsok’ and ‘Pergousa’(Q₁₀ = 2·1) and more pronounced than for ‘Processor’(Q₁₀ = 1·3). Although there were significant differencesin the growth parameters among the cultivars within each temperatureused, the differences did not correspond with the differencesduring germination at low temperatures. The minimum vegetativegrowth temperature was close to 10 °C for all the cultivarstested. Phaseolus vulgaris L., beans, suboptimum temperature, growth analysis, minimum germination temperature, minimum vegetative growth temperature     

The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration: 1. Grown as Simulated Swards During a Regrowth Period

Simulated swards of each of two selection lines of Lolium perennecv. S23 with ‘fast’ and ‘slow’ ratesof ‘mature tissue’ respiration were establishedin growth rooms at 20/15 °C day/night temperatures and studiedover four successive regrowth periods of 46, 30, 26 and 53 daysduration. The ‘slow’ line outyielded the ‘fast’,both in harvestable shoot (above a 5 cm cut) and in root andstubble. Its advantage increased over successive regrowth periodsto 23 per cent (total biomass). Gas analysis measurements onthe entire communities (including roots), during the final regrowthperiod, showed that the ‘slow’ line had a 22–34per cent lower rate of dark respiration per unit dry weight.This enabled it to maintain its greater mass of tissue for thesame cost in terms of CO₂ efflux per unit ground area. Halfthe extra dry weight produced by the ‘slow’ line,relative to the ‘fast’, could be attributed to itsmore economic use of carbon. The rest could be traced to a 25per cent greater tiller number which enabled the ‘slow’line to expand leaf area faster (though not at a greater rateper tiller), intercept more light and fix more carbon, earlyin the regrowth period. Lolium perenne L., ryegrass, respiration, maintenance respiration, tiller production, simulated swards, canopy photosynthesis, carbon economy     

Integrated Analysis of Growth and Light Interception in Winter Lettuce I. Analytical Methods and Environmental Influences

Measurements on protected lettuce crops have been used to assesstwo new procedures for analysing the rate of dry-matter productionin crops or plant stands. ‘Integrated growth analysis’brings together two traditionally distinct treatments of growthanalysis by resolving crop growth rate (CGR) into stand biomassand the relative growth rate of individual plants. ‘Lightconversion analysis’ resolves CGR as the product of incidentlight receipt, efficiency of light interception by leaves, andefficiency of utilization of intercepted light in dry-matterproduction. Observations from winter lettuce trials were used to fit statisticalprogressions to the primary data and to obtain instantaneously-derivedestimates of all of the analytical components. Trials in threesuccessive years yielded similar patterns in time for the componentsof each of the analytical procedures, giving confidence in theirvalidity. In light conversion analysis, changes in CGR were due mainlyto incident light, which varied threefold, and to interceptingefficiency, which rose from a low initial value to full interceptionat hearting; the efficiency of utilization of light varied lessdramatically, with the value at hearting being about twice thatat planting. In integrated growth analysis a 30 per cent increasein CGR due to CO₂ enrichment, and a 5 per cent increase dueto lower daily minimum temperature, could each be coherentlyresolved into variations in biomass, leaf area ratio and netassimilation rate. In different ways it is concluded that both of these approachescan assist in analysing growth and in identifying the optionsavailable for improving crop yield. Lactuca sativa L., lettuce, growth analysis, crop growth rate, relative growth rate, light interception, light utilization     

Physiological and Ecological Studies in the Analysis of Plant Environment: VII. An Analysis of the Differential Effects of Light Intensity on the Net Assimilation Rate, Leaf-Area Ratio, and Relative Growth Rate of Different Species

Since relative growth rate is the product of net assimilationrate and leaf-area ratio (leaf area/plant weight), it followsthat if the effects of shading on both net assimilation rateand leaf-area ratio can be expressed mathematically, then therelationship between light intensity and relative growth ratecan be derived from the product of the two mathematical expressions. For all the ten species investigated in field and pot cultureexperiments, it has been found that during the early vegetativephase both the changes in leaf-area ratio and net assimilationrate, over the range of 0·1 to full daylight, are linearlyrelated to the logarithm of the light intensity. In consequence,the relationship between relative growth rate and the logarithmof light intensity—being the product of the two linearregressions—is curvilinear. For species of shady habitats (Geum urbanum, Solamun dulcamara)neither the levels of assimilation rate nor the ‘compensation-point’values are very different from those of the eight species fromopen situations (e.g. Hordeum vulgare, Pisum sativum, Fagopyrumesculentum). Nevertheless the intensity at which growth rateis maximal varies between species: it is 0•5 for G. urbanum,0•7 for H. annuus, full daylight for F. esculentum, whilefor Trifolium subterraneum the calculated value is 1·8daylight. Such specific differences can be largely accountedfor in terms of the differences in leaf-area ratio at the differentlight levels. On the basis of this analysis of the light factor, a ‘shade’plant is best redefined as a species in which a reduction ofthe light intensity causes a rapid rise in the leaf-area ratiofrom an initial low value in full daylight: for a ‘sun’plant the converse definition holds.     

The Carbohydrate Resources of Young Apple-trees under Four Levels of Illumination

Young apple-trees were grown in four light intensities to assessthe differentia dependence of growth on reserve carbohydratesand current products of photosynthesis. Low light intensitycaused no greater depletion of reserve carbohydrates duringinitial growth in spring, and during the growing season a similarcomposition was maintained with all treatments despite largedifferences in dry-weight increment. The results suggest thatthere is an ‘integrated phase of growth’ duringwhich carbohydrate composition is independent of external factors,and which may be followed by a ‘labile phase’ duringwhich accumulation of reserves can be influenced.     

Pattern of Respiration of a Perennial Ryegrass Crop in the Field

‘Dark’ respiratory losses of CO₂ were measured ona one year old sward of S24 perennial ryegrass (Lolium perenneL.) at intervals during a 74 day reproductive growth period,between April and June, and a 21 day vegetative growth period,in July and August. Part of the sward was shaded for one weekbefore measure ments commenced. Measurements of ‘dark’respiration continued for 46 hand it was possible to distinguishtwo components which are designated ‘maintenance’and ‘synthetic’ ‘Maintenance’ respiration was taken to be the meanrate of CO₂ efflux after 40–46 h darkness. When calculatedon a plant d. wt basis at 15°C it ranged between 6 to 32mgCO₂ g^-1 day^-1 during reproductive growth and 10–14 mgCO₂ g^-1 day^-1 during vegetative growth. During reproductivegrowth, sward protein content ranged between 7–23 percent and when maintenance respiration was recalculated on thebasis of protein content it changed relatively little throughoutthe growth period (90–140 mg CO₂ g pro tein^-1 day^-1);the value for vegetative growth ranged between 70–100mgCO₂ g protein-day^-1. Total ‘synthetic’ CO₂ flux was determined duringreproductive growth and a rate of ‘synthetic’ CO₂flux was determined during both reproductive and vegetativegrowth. Between 15 and 35 per cent of the CO₂ fixed in the previousphotoperiod was lost in ‘synthetic’ respirationof above-ground material in reproductive swards. Previous shadingincreased the proportion of ‘synthetic’ CO₂ lossfrom above ground. The rate of ‘synthetic’ CO₂ outputduring the first hours of darkness increased with amount ofCO₂ fixed in the previous photoperiod, although it was not proportionalto it. There is some evidence that assimilate is ‘carried-over’from one photoperiod to the next.     

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     

Growth and Dry-weight Distribution in Callistephus chinensis as Influenced by Lighting Treatment

Plants of two cultivars of Callistephus chinensis (Queen ofthe Market and Johannistag) were grown in 8 h of daylight perday with one of the following treatments given during the 16h dark period: (a) darkness—‘uninterrupted night’,(b) I h of light in the middle of the dark period—a ‘nightbreak’, (c) I min of light in every hour of the dark period—‘cycliclighting’, (d) light throughout—‘continuouslight’. The plants receiving uninterrupted dark periods remained compactand rosetted in habit with small leaves, while leaf expansion,stem extension, and flower initiation were promoted in all threeillumination treatments (b, c, d). Although these three treatmentsproduced similar increases in leaf area, continuous light wasthe most effective for the promotion of both stem growth andflower initiation while cyclic lighting was generally more effectivethan a I-h night break. Continuous light also caused more dry matter to be divertedto stems at any given vegetative dry weight and it was shownthat the stem weight ratio of both varieties was correlatedwith stem length.     

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.     

Effects of Inorganic Phosphate on the Utilization of Sucrose by Suspension-cultured Catharanthus roseus Cells

The metabolic fate of [U-¹⁴C]sucrose in suspension culturesof Catharanthus roseus cells was monitored for 96 h after thecells were transferred to fresh complete (‘+Pi’)or to phosphate-deficient Murashige and Skoog (‘–Pi’)medium. Sucrose was hydrolysed extracellularly to glucose andfructose. The rate of uptake of sugars by the cells was 1.5–3times higher in ‘+Pi’ culture than in ‘–Pi’culture. Little difference in the rate of incorporation of radioactivityinto the ethanol-soluble fraction was found between the ‘+Pi’and ‘– Pi’ cultures during the initial 24h of culture, but after 48 h the rate in ‘ +Pi’cultures was higher than that in ‘–Pi’ cultures.Incorporation of radioactivity into ethanol-insoluble macromoleculeswas always significantly higher in the cells in ‘+Pi’cultures than in those in ‘–Pi’ cultures.The results suggest that Pi strongly affects the utilizationof sugars by cultured plant cells through the stimulation oftransport of sugars as well as through the activation of metabolism. Catharanthus roseus, Madagascar periwinkle, suspension culture, inorganic phosphate, sucrose, transport, metabolism     

Temperature Effects on Phenological Development and Yield of Muskmelon

Our goal was to construct a simple muskmelon phenology modelthat could be run with easily obtainable weather station dataand used by growers to quantify phenological development andaid in projecting harvest dates. A growth chamber experimentwas conducted with two cultivars of muskmelon (‘Gold Rush’and ‘Mission’) to determine how main vine leaf appearancerates responded to temperature. We identified three cardinaltemperatures for leaf appearance rate: the base temperature(10 °C) at which leaf appearance rate was zero; an optimumtemperature (34 °C) at which the rate of leaf appearancewas maximal; and an upper threshold temperature (45 °C)at which leaf appearance rate returned to zero. Using thesethree cardinal temperatures, we constructed a simplified thermalunit accumulator for hourly measurements of air temperature.Main vine plastochron interval (PI), thermal time to harvest,and final yield were determined for three cultivars of muskmelon(‘Explorer’, ‘Gold Rush’ and ‘Mission’)grown in the field at Overton, TX, USA, over six transplantingdates from March to June 1998. PI was calculated for each cultivarx transplanting date combination as the reciprocal of the slopeof main vine node number vs. accumulated hourly thermal units(     

Effects of Flooding and Drainage and their Alternation on the Growth and Uptake of Nutrients by Rice (Oryza sativa L., indica, var. IR-8)

Continuous flooding of the soil (‘flooded’ treatment)gave best growth of IR-8 variety of rice whereas soil drainedfor 4 weeks and then flooded for 8 (‘drained and flooded’treatment) resulted in poorest growth and chlorotic plants.Plants grown in the continuously drained soil (‘drained’treatment) and those in the soil flooded for 4 weeks and thendrained for 8 (‘flooded and drained’ treatment)showed intermediate growth. There were no differences in therelative water content of plants growing in the various treatments.Analyses of plant tissues showed that a consideration of therelative concentration of Fe, Mn, and P in the shoots is mostclosely related to the performance of rice under various culturalconditions. An increase in the concentration of Fe in the planttissues following flooding was correlated with the best growth(‘flooded’ treatment) unless it was accompaniedby high level of Mn (as in the ‘drained and flooded’treatment) which may have proved toxic, e.g. by interferencewith Fe metabolism as was evidenced by chlorosis. Measurementsof oxidation-reduction potentials, oxygen diffusion rates, andthe concentration of exchangeable and soluble Fe and Mn in thesoils have shown that the ‘drained and flooded’treatment caused the most extreme reducing conditions. Floodingaccompanied by the development of extreme reducing conditionsled to a greater accumulation of Mn in the shoots (‘drainedand flooded’ treatment) whereas flooding accompanied bythe maintenance of oxidizing conditions (‘flooded’treatment) resulted in a lower uptake of Mn. Growth of riceplants for 4 weeks in the drained soil did not fit them forthe reduced conditions which developed during subsequent flooding(‘drained and flooded’ treatment).     

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     

Mycorrhizal Response of Two Tomato Genotypes Relates to their Ability to Acquire and Utilize Phosphorus

The purpose of this study was to determine how a plant's responseto colonization by mycorrhizal fungi relates to its abilityto acquire and utilize phosphorus for growth and reproduction.Two tomato genotypes previously found to be either responsive(‘LA1709’) or unresponsive (‘large cherry’)to mycorrhizal colonization during early vegetative growth wereexamined in detail. Plants were grown at four levels of addedphosphate or with mycorrhizal inoculum. Vegetative and reproductivegrowth, phosphorus uptake and root length density were measuredduring the course of plant development. Mycorrhizal symbiosissignificantly increased above-ground dry mass, root length,phosphorus content and yield under low phosphorus conditionsin ‘LA1709’, while it had less effect on these characteristicsin ‘large cherry’. When uninfected, however, ‘LA1709’grew and reproduced poorly unless high amounts of phosphoruswere added to the soil, while ‘large cherry’ grewwell under very low phosphorus conditions. This was because‘large cherry’ had significantly higher root lengthdensities than ‘LA1709’, enabling plants from thisgenotype to explore more soil volume and acquire greater amountsof phosphorus when grown without mycorrhizal fungi in low phosphorussoil. ‘Large cherry’ also had higher phosphorususe efficiency and allocated a greater proportion of phosphorusto reproduction when uninfected than ‘LA1709’. Itappears traits that affect a plant's ability to acquire andutilize phosphorus efficiently for growth and reproduction canalso affect its response to mycorrhizal colonization in tomato.Copyright1998 Annals of Botany Company. Tomato,Lycopersicon esculentum,mycorrhiza,Glomus etunicatum,phosphorus, reproduction, lifespan.     

Factors Determining Petal Colour of Baccara Roses II: THE EFFECT OF PIGMENT CONCENTRATION

‘Blueing’ in young and senescing petals was comparedin the red rose cv. Baccara. The ‘blueing’ of senescingflowers is accompanied by a bathochromic shift in the lightreflectance curve, a rise in the pH value and a decrease inthe malic acid concentration of the petal tissue. These factorsindicate that a complex with a co-pigment is produced. Similarchanges were not found in the ‘blueing’ of youngflowers, where a decrease was found in pigment concentrationper unit weight as well as per unit area of petal. A similar‘blueing’ was achieved by diluting a solution ofcrystalline cyanin. The phenomenon of ‘blueing’by dilution is discussed in the light of Bougeur's law.     

The Potassium Relations of Lemna minor L.: I. POTASSIUM UPTAKE AND PLANT GROWTH

A simple expression has been derived to predict the rate ofnet K uptake into exponentially growing plants of Lemna minor.Net uptake predictions are in good quantitative agreement withmeasurements of ‘steady-state’ K influx, indicatingthat, in the ‘steady state’, K movements in theplant are essentially undirectional and that efflux is small.This close matching of inward K movement to the demands of theexpanding tissue is temporarily disturbed if plants are transferredto media of different K status. Uptake rates in the ‘step-up’are initially enhanced and then fall gradually towards a new‘steady-state’ rate. In contrast, the ‘step-down’causes an initial depression of uptake and then rates increasegradually towards the new ‘steady-state’ rate. Itis argued that these changes in uptake rates are associatedwith alterations in the cytoplasmic K content.     

The Growth and Carbon Economy of Selection Lines of Lolium perenne cv. S23 with Differing Rates of Dark Respiration: 2. Grown as Young Plants from Seed

Young plants of two selection lines of Lolium perenne cv. S23with ‘fast’ and ‘slow’ rates of ‘maturetissue’ respiration were individually grown from seed,together with plants of S23, their common parent, in 9.2 cmpots in a controlled environment at 20/15 °C day/night temperatures. No significant differences were found between the genotypesin leaf extension and tiller production during this early stageof their growth. They did differ however, by an average of 26%,in the rate of dark respiration of fully expanded leaf laminae.The use of a simple model demonstrated that such a differencein respiration could alone account for the different rates ofdry matter production shown by the selection lines when grownas young crops from seed. Possible penalties of ‘slow’respiration are also considered. Lolium perenne L., ryegrass, respiration, maintenance respiration, stimulated swards, leaf growth, tiller production, carbon economy