Atrazine Resistance in a Velvetleaf (Abutilon theophrasti) Biotype Due to Enhanced Glutathione S-Transferase Activity

We previously reported that a velvetleaf (Abutilon theophrasti Medic) biotype found in Maryland was resistant to atrazine because of an enhanced capacity to detoxify the herbicide via glutathione conjugation (JW Gronwald, Andersen RN, Yee C [1989] Pestic Biochem Physiol 34: 149-163). The biochemical basis for the enhanced atrazine conjugation capacity in this biotype was examined. Glutathione levels and glutathione S-transferase activity were determined in extracts from the atrazine-resistant biotype and an atrazine-susceptible or “wild-type” velvetleaf biotype. In both biotypes, the highest concentration of glutathione (approximately 500 nanomoles per gram fresh weight) was found in leaf tissue. However, no significant differences were found in glutathione levels in roots, stems, or leaves of either biotype. In both biotypes, the highest concentration of glutathione S-transferase activity measured with 1-chloro-2,4-dinitrobenzene or atrazine as substrate was in leaf tissue. Glutathione S-transferase measured with 1-chloro-2,4-dinitrobenzene as substrate was 40 and 25% greater in leaf and stem tissue, respectively, of the susceptible biotype compared to the resistant biotype. In contrast, glutathione S-transferase activity measured with atrazine as substrate was 4.4- and 3.6-fold greater in leaf and stem tissue, respectively, of the resistant biotype. Kinetic analyses of glutathione S-transferase activity in leaf extracts from the resistant and susceptible biotypes were performed with the substrates glutathione, 1-chloro-2,4-dinitrobenzene, and atrazine. There was little or no change in apparent K_m values for glutathione, atrazine, or 1-chloro-2,4-dinitrobenzene. However, the V_max for glutathione and atrazine were approximately 3-fold higher in the resistant biotype than in the susceptible biotype. In contrast, the V_max for 1-chloro-2,4-dinitrobenzene was 30% lower in the resistant biotype. Leaf glutathione S-transferase isozymes that exhibit activity with atrazine and 1-chloro-2,4-dinitrobenzene were separated by fast protein liquid (anion-exchange) chromatography. The susceptible biotype had three peaks exhibiting activity with atrazine and the resistant biotype had two. The two peaks of glutathione S-transferase activity with atrazine from the resistant biotype coeluted with two of the peaks from the susceptible biotype, but peak height was three- to fourfold greater in the resistant biotype. In both biotypes, two of the peaks that exhibit glutathione S-transferase activity with atrazine also exhibited activity with 1-chloro-2,4-dinitrobenzene, with the peak height being greater in the susceptible biotype. The results indicate that atrazine resistance in the velvetleaf biotype from Maryland is due to enhanced glutathione S-transferase activity for atrazine in leaf and stem tissue which results in an enhanced capacity to detoxify the herbicide via glutathione conjugation.     

Biochemical and proteomic effects in Procambarus clarkii after chlorpyrifos or carbaryl exposure under sublethal conditions

In vivo effects of two sublethal doses of chlorpyrifos and carbaryl were studied in Procambarus clarkii after 2 and 7 days of exposure, and after pesticide removal. Chlorpyrifos inhibited carboxylesterase activity in a concentration-dependent manner, but acetylcholinesterase was less sensitive. Compared with chlorpyrifos, carbaryl had a less marked effect on esterase activity. The effects of selected pesticides on biotransformation or oxidative stress biomarkers were contradictory. Chlorpyrifos lowered ethoxyresorufin-O-deethylase (EROD), catalase and oxidized glutathione (GSSG) levels but raised glutathione-S-transferase activity, while carbaryl raised EROD, catalase and glutathione-S-transferase, but lowered glutathione peroxidase and reduced glutathione (GSH) levels. The effects on protein expression patterns depending on pesticide type and the tissue used for analysis were studied in parallel by 2-DE. In gill and nervous tissue about 2000 spots (pI 4–7) were resolved, with quite different expression patterns. Chlorpyrifos altered 72 proteins, mostly in nervous tissue, and carbaryl 35, distributed evenly between organs. Several specific spots were selected as specific protein expression signatures for chlorpyrifos or carbaryl exposure in gills and nervous tissue, respectively.     

A single protein research integrated advanced biochemistry laboratory course: design and general outline

An advanced biochemistry laboratory has been designed to focus on a detoxifying enzyme, glutathione-S-transferase, which is involved in the metabolism of polycyclic aromatic hydrocarbons (PAHs), pesticides, herbicides, and other electrophilic xenobiotic compounds. The enzyme is known to catalyze conjugation of glutathione to xenobiotics, which makes them water-soluble so that they can be easily discarded through further metabolism and excretion. About two-thirds of the laboratory course incorporates nine advanced biochemical techniques, all focused to analyze various chemical characteristics of the glutathione-S-transferase. The remaining third of the semester time students work on a project that involves application of all the newly acquired techniques to solve a biochemical problem that encompasses the same detoxifying enzyme.     

Enhancement of lipid peroxidation in rat liver on acute exposure to styrene and acrylamide a consequence of glutathione depletion

Lipid peroxidation, glutathione level and activity of glutathione-S-transferase were studied in liver and brain of rats 4 and 3 h after a single i.p. administration of 0, 25, 75, 100 mg/kg acrylamide or 0, 50, 100, 200, 600 mg/kg styrene, respectively. In liver both acrylamide and styrene caused an increase in lipid peroxidation and decrease in glutathione contents and activity of glutathione-S-transferase in a dose dependent manner, while in brain only acrylamide produced a decrease in glutathione content. The decrease in glutathione content was not always associated with increase of lipid peroxidation. The enhancement of lipid peroxidation occurred only when glutathione contents were depleted to certain critical levels. No effect of acrylamide or styrene was seen on lipid peroxidation under in vitro conditions. The addition of glutathione in the incubation mixture significantly inhibited the rate of lipid peroxidation of liver homogenates of acrylamide and styrene treated animals.The results suggest that enhancement of lipid peroxidation in liver on exposure to acrylamide or styrene is a consequence of depletion of glutathione to certain critical levels. The inhibition of glutathione-S-transferase activity by acrylamide and styrene suggests that detoxication of these neurotoxic compounds could be suppressed following acute exposure.     

Accumulation of calcium in the centre of leaves of coriander (Coriandrum sativum L.) is due to an uncoupling of water and ion transport

The aim of this study is to understand the parameters regulatingcalcium ion distribution in leaves. Accumulation of ions inleaf tissue is in part dependent on import from the xylem. Thisimport via the transpiration stream is more important for ionssuch as calcium that are xylem but not phloem mobile and cannottherefore be retranslocated. Accumulation of calcium was measuredon bulk coriander leaf tissue (Coriandrum sativum L. cv. Lemon)using ion chromatography and calcium uptake was visualized usingphosphor-images of ⁴⁵Ca²⁺. Leaves of plants grown in hydroponicshad elevated calcium in the centre of the leaf compared withthe leaf margin, while K⁺ was distributed homogeneously overthe leaf. This calcium was shown to be localised to the mesophyllvacuoles using EDAX. Stomatal density and evapotranspiration(water loss per unit area of leaf) were equal at inner and outersections of the leaf. Unequal ion distribution but uniformityof water loss suggested that there was a difference in the extentof uncoupling of calcium and water transport between the innerand outer leaf. Since isolated tissue from the inner and outerleaf were able to accumulate similar amounts of calcium, itis proposed that the spatial variation of leaf calcium concentrationis due to differential ion delivery to the two regions ratherthan tissue/cell-specific differences in ion uptake capacity.There was a positive correlation between whole leaf calciumconcentration and the difference in calcium concentration betweeninner and outer leaf tissue. Exposing the plants to increasedhumidity reduced transpiration and calcium delivery to the leafand abolished this spatial variation of calcium concentration.Mechanisms of calcium delivery to leaves are discussed. An understandingof calcium delivery and distribution within coriander will informstrategies to reduce the incidence of calcium-related syndromessuch as tip-burn and provides a robust model for the transportof ions and other substances in the leaf xylem. Key words: Calcium, Coriandrum sativum, distribution, ion chromatography, leaves, radioisotope, spatial variation, transpiration, uptake Received 29 August 2008; Accepted 16 October 2008     

An Empirical Model for Leaf Expansion in Cacao in Relation to Plant Water Deficit

Cacao (Theobroma cacao L.) seedlings at the onset of a flushcycle were exposed to five different irrigation treatments.The expansion of all leaves in an emerging flush was followed,and estimates of leaf water potential(_w) were made on each daythat leaf areas were measured. The growth in area of the leaveswas fitted with a modified logistic curve of the form y = a/[1+ be ^–(ct+dt2)], and parameters of leaf growth were derivedfrom the fitted constants. A coefficient of stress exposure,S, was derived as the slope of the relation between cumulative_w and time. Three parameters of the logisitc function (a, cand d) were strongly associated with S. By fitting regressionsfor the relations between S and estimates of each parameterfor the five treatments, values of a, b, c and d may be estimatedat any level of S encompassed by these data. The effects ofwater stress on leaf expansion rate and on the final leaf areaattained by the emerging flush can be adequately predicted bythis technique. Theobroma cacao L.cacao, leaf expansion, logistic model, water stress     

The Effect of Current Photosynthesis on the Origin of Translocates in Old Tomato Leaves

The rate of carbon transport from an old tomato leaf (54 days),grown at 80 W m^–2, was measured under light flux densitiesbetween 7 and 90 W m^–2. Under low light, the rate of carbontransport over a 6 h period was about 1 mg C dm^–2 h^–1,well in excess of the concurrent photosynthetic rate. The lossfrom these leaves of ¹⁴C-leaf assimilate which was fixed beforethe experimental period amounted to 62 per cent of the totalinitial uptake and was higher than that from leaves with higherconcurrent photosynthetic rates. The higher loss of ¹⁴C fromleaves with low photosynthetic rates was due to a greater contributionof ¹⁴C from the starch and residue fractions. The rate of transportappeared to be determined by the concentration of the labilesucrose, not the total sucrose concentration. In comparisonwith young fully-expanded tomato leaves (Ho, 1976) the sizeof the labile sucrose pool appeared to decrease with age. Thephotosynthesistranslocation coefficient was low (k₁k₂=0•21)for an old tomato leaf. Based on these results a scheme of carbonpartitioning in relation to translocation is proposed. Criteriafor assessing the efficiency of translocation in leaves arediscussed.     

Temporal and Spatial Development of the Cells of the Expanding First Leaf of Arabidopsis thaliana (L.) Heynh

The three-dimensional quantitative leaf anatomy in developingyoung (9–22 d) first leaves of wild type Arabidopsis thalianacv. Landsberg erecta from mitosis through cell and leaf expansionto the cessation of lamina growth has been studied. The domainsof cell division, the relative proportion of the cell typespresent during development and the production of intercellularspace in the developing leaf have been determined by image analysisof entire leaves sectioned in three planes. Mitotic activityoccurs throughout the youngest leaves prior to unfolding andcell expansion is initiated firstly at the leaf tip with a persistentzone of mitotic cells at the leaf base resulting in a gradientof development along the leaf axis, which persists in the olderleaves. Major anatomical changes which occur during the developmentare, a rapid increase in mesophyll volume, an increase in thevein network, and expansion of the intercellular spaces. Thepattern of cell expansion results in a 10-fold variation inmesophyll cell size in mature leaves. In the youngest leavesthe plan area of mesophyll cells varies between 100 µm²and 400 µm² whereas in mature leaves mesophyll cells rangein plan area from 800 µm² to 9500 µm². The volumesof mesophyll tissue and airspace under unit leaf area increase3-fold and 35-fold, respectively, during leaf expansion. Thevolume proportions of tissue types mesophyll:airspace:epiderrnal:vascularin the mature leaf are 61:26:12:1, respectively. This studyprovides comparative information for future identification andanalysis of leaf development mutants of Arabidopsis thaliana. Key words: Arabidopsis, quantitative leaf anatomy, leaf expansion, image analysis     

Ochna pulchra Hook: Leaf Growth and Development Related to Photosynthetic Activity

Ochna pulchra Hook. is a deciduous broad-leaved tree in theMixed Bushveld vegetation of the Northern Transvaal. The growthand development of leaves taken from trees in the field werestudied from a stage shortly before bud break, in late spring,until they were fully expanded and at the peak of photosyntheticactivity. Leaf area was measured by photographing the leaf against a transparentmm² grid. Finally a constant relationship between leaf area(A) and the linear dimension of length (L) and breadth (B) wasestablished: A = b x LB, where coefficient b = 0.72. Transverse sections of the lamina of the youngest leaves showeda five-layered plate meristem with a few functional conductingelements in the midrib. During further leaf development, celldivision was followed by means of autoradiography using [³H]thymidine.It was most active during the week after bud break. Leaf cell increment following on cell division made the majorcontribution to leaf growth resulting in a lamina that was atleast 90% expanded 4 weeks after bud break. The histologicalchanges accompanying cell division were observed using lightand electron microscopy. Even in late stages of leaf development mature and differentiatingstomata occurred together, limited to the abaxial epidermisand the midrib. Scanning electron microscopy showed stomataldistribution, their increasing density and gradual opening.The structure of these sunken stomata could reduce the outwarddiffusion of water vapour and increase the diffusion resistanceto carbon dioxide. Carbon assimilation rates of the developing leaves were measuredusing an IRGA (infra-red gas analyser) and their chlorophyllvalues were calculated. Photosynthesis was first measured amonth after bud break when the leaves were fully expanded, over50 % of the stomata exposed and leaf mesophyll tissue differentiatedwith mature chloroplasts. Net photosynthetic rates and chlorophyllvalues peaked 1 month later. Ochna pulchra Hook., photosynthesis, leaf development, leaf area, stomata, chlorophyll, savanna     

The Influence of Prior Water Stress and Abscisic Acid Foliar Spraying on Stomatal Responses to CO2, IAA, ABA, and Calcium in Leaves of Solanum melongena

The influence of a water stress or foliar ABA spraying pretreatmenton stomatal responses to water loss, exogenous ABA, IAA, Ca²⁺,and CO₂ were studied using excised leaves of Solanum melongena.Both pretreatments increased stomatal sensitivity of water loss,in the presence and absence of CO₂, but decreased stomatal sensitivityto exogenous ABA. CO₂ greatly reduced the effect of exogenouslyapplied ABA. IAA decreased leaf diffusion resistance for controland ABA sprayed leaves, but did not influence the LDR of previouslywater-stressed leaves. CA²⁺ did not influence LDR of any leavesof any treatments. Key words: Water stress, stomatal response, pretreatments     

Glandular Trichomes in Satureja thymbra Leaves

The leaves of the aromatic plant Satureja thymbra have numerousglandular trichomes of two morphologically distinct types glandularhairs and glandular scales Investigations of the anatomy ofthese glandular trichomes with serial thick sections revealedthat the glandular hairs consist of three cells a foot, stalkand head cell Glandular scales also have a unicellular footand stalk Their heads, however, are composed of 12 cells Fourof these cells are small, occupying the central region of thehead, whereas the remainder are large and peripherally arrangedMorphometric analysis showed that, in leaf surface view, glandularscales are about 17-fold larger than glandular hairs In addition,glandular scales were found to occupy 5 7 % of the entire leafsurface area In each glandular scale the total amount of essentialoil, contained within both the subcuticular space and the interiorof the secretory cells, was calculated to be 2 51 x 10^–4mm³ The volume of the essential oil produced by all glandularscales on a single mature leaf was correspondingly determinedto be 0.059 mm³ Finally, the theoretical essential oil yieldof 100 g dry leaves of S thymbra was estimated to be 3 54 %(secretory activity of glandular scales only) Satureja thymbra, glandular trichomes, morphology, morphometry     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

Leaf-like Structure in the Photosynthetic, Succulent Stems of Cacti

This research examined the hypothesis that as cacti evolve tothe leafless condition, the stem epidermis and cortex becomemore leaflike and more compatible with a photosynthetic role.All cacti in the relict genus Pereskia have non-succulent stemsand broad, thin leaves. All members of the derived subfamilyCactoideae are ‘leafless’, having an expanded cortexthat is the plant's only photosynthetic tissue. In Pereskia,leaves have a high stomatal density (mean: 50.7 stomata mm^–2in the lower epidermis, 38.1 mm^–2 in the upper epidermis),but stems have low stomatal densities (mean: 11.3 mm ₂, threeof the species have none). Stems of Cactoideae have a high stomataldensity (mean: 31.1 mm^–2, all species have stomata). Theouter cortex cells of stems of Cactoideae occur in columns,forming a palisade cortex similar to a leaf palisade parenchyma.In this palisade cortex, the fraction of tissue volume availablefor gas diffusion has a mean volume of 12.9%, which is identicalto that of Pereskia leaf palisade parenchyma. Pereskia stemcortex is much less aerenchymatous (mean: 5.3% of cortex volume).Cactoideae palisade cortex has a high internal surface density(0.0207 cm₂ cm^–2 which is higher than in Pereskia stemcortex (0.0150 cm₂ cm^–3) but not as high as Pereskia leafpalisade parenchyma (0.0396 cm₂ cm^–3). Pereskia stem cortexhas no cortical bundles, but Cactoideae cortexes have extensivenetworks of collateral vascular bundles that resemble leaf veins. Cactaceae, cactus, intercellular space, stomatal density, internal surface/volume, evolution     

The Dynamics of Leaf Growth and Photosynthetic Capacity in Capsicum frutescens L.

In Capsicum frutescens L. cv. California Wonder the specificleaf weight (dry weight per unit laminar area) at leaf unfoldingis three times higher in the eighth leaf than in the first leafproduced. Intermediate leaves exhibit a trend between the twoThe change in specific leaf weight during laminar expansionis greatest in leaf 1 and least (sometimes zero) in leaf 8.Large changes in specific leaf weight during laminar expansionare associated with a large degree of palisade cell expansion,while leaves showing smaller rates of change have less palisadecell expansion but cell division is more evident. At leaf unfoldingthe fraction I protein content per unit laminar area is higherin upper than in lower leaves. Ribulose diphosphate carboxylaseactivity per unit laminar area and ¹⁴CO₂ fixation per unit laminararea have a similar pattern of development in all leaves andshow no correlation with the changes in specific leaf weight.The peak of activity in all leaves occurs when the laminar areais 10 cm². These results are compared with previous data onlaminar expansion and are seen as in accord with current ideason leaf growth.     

Inhibition of Light-Stimulated Leaf Expansion by Abscisic Acid

Abscisic acid (ABA) applied to intact bean (Phaseolus vulgaris)leaves or to isolated leaf discs inhibits light-stimulated cellenlargement This effect may be obtained with 10^–4 molm^–3 ABA, but is more significant at higher concentrations.The inhibition of disc expansion by ABA is greater for discsprovided with an external supply of sucrose than for discs providedwith KC1, and may be completely overcome by increasing the KC1concentration externally to 50 mol m^–3. Decreased growthrate of ABA-treated tissue is not correlated with loss of solutesfrom growing cells, but is correlated with a decrease in cellwall extensibility. ABA does not prevent light-stimulated acidificationof the leaf surface, and stimulates the acidification of theexternal solution by leaf pieces. However, the capacity of thecell walls to undergo acid-induced wall loosening is diminishedby ABA-treatment. The possibility that ABA acts directly byinhibiting growth processes at the cellular level, or indirectlyby causing stomatal closure, is discussed. Key words: Phaseolus vulgaris, ABA, Inhibition, Leaf expansion     

Effects of Leaf Age and Position on the Shoot Axis on Potassium Absorption by Tomato Leaf Slices

The effect of leaf age on K (⁸⁶Rb) influx into tomato (Lycopersiconesculentum Mill.) leaf lamina slices was determined for leaves5, 9 and 13 counting acropetally. Potassium influx rates expressedon a leaf fresh weight basis declined rapidly during leaf elongationat external KCI concentrations between 0.5 and 20.0 mM. In fullyexpanded leaves, K influx rates declined more slowly with age.The onset of senescence in mature leaves did not result in alarge loss in K uptake capability. Leaf position on the shootaxis and the stage of whole plant development had little influenceon K influx into leaf cells. It is suggested that the rapiddecrease in K influx in growing leaves is related to a dilutionin the concentration of K transporter sites resulting from anincrease in cell volume and weight. Lycopersicon esculentum Mill, tomato, free space, potassium, influx rate, ion uptake, leaf slices, leaf age leaf ontogeny     

Temperature Response of Early Foliar Expansion of Potato and Wheat

We studied the course of early leaf area expansion and specificleaf area (S_LA) in potato (Solanum tuberosum L.) and wheat (Triticumaestivum L.) genotypes and tested whether air temperature explainsdifferences in these courses within different environments.Such knowledge can be used to improve crop growth modelling.The relative rate of leaf area expansion (R_L) of potato andwheat decreased with thermal time, but was nearly linear upto a leaf area index (L) of 1.0. TheR_L (L < 1; mean: 17.9x 10^-3°C^-1 d^-1) of potato showed an interaction betweengenotype and environment, and varied with year. TheR_L (L <1; mean: 7.1 x 10^-3°C^-1 d^-1) of winter wheat was lower thanthat of spring wheat (mean: 10.9 x 10^-3°C^-1 d^-1), and bothvaried with year. S_LAof potato increased nearly linearly withthermal time from 5 to 15 m² kg^-1at 50% emergence, to 20 to25 m² kg^-1at 155°Cd, and then decreased slightly. The S_LAofboth winter and spring wheat began at 16 to 23 m² kg^-1and inmost cases increased slightly with thermal time. In potato,regression parameters of S_LAwith thermal time were affectedby environment (management conditions and year) and genotype;in wheat they were affected by environment (year and site).Treatment effects on R_Lof potato were not correlated with thoseon S_LA , and were only partly correlated for wheat. Thereforewe conclude that the early foliar expansion of potato is associatedwith a strong increase in S_LA , and not so for wheat. For bothcrops the course of early leaf area expansion and ofS_LA withair temperature is not robust over environments and genotypes.The consequences of these results for modelling are discussed.Copyright 2000 Annals of Botany Company Triticum aestivum, spring wheat, winter wheat, Solanum tuberosum, leaf area expansion, specific leaf area, early growth, genotype, environment, modelling     

Respiration Rate and Adenosine Triphosphate Formation in Tissues4

When leaves of Nicotiana tabacum L. var. Xanthi were inoculatedwith TMV, local lesion formation gave enhanced ATP concentrationaccompanied by increased respiration. Phosphorus metabolismin healthy and infected leaves was investigated either by floatingleaf tissue on ³²P₁-phosphate buffer or by allowing intact leavesto take up ³²P₁-phosphate buffer through the petioles. Bothmethods gave increased ³²P₁ incorporation into inorganic andorganic acid-soluble phosphorus fractions of the infected leaf.Comparison of the specific activity of ³²P₁-phosphate buffersupplied with the specific activity of the -phosphate groupof ATP demonstrated that 50 per cent of the ATP in the healthyleaf compared with over 78 per cent of the ATP in the infectedleaf was metabolically active in respiration. As the ATP concentrationin the infected leaf is much greater than that in the healthyleaf, this means that the amount of ATP being utilized and resynthesizedas a result of respiratory metabolism in the infected leaf ismore than twice that in the healthy leaf. Pulse-labelling experimentsdemonstrated that the rate of ATP turnover was very similarin healthy and infected leaves; therefore the increased respirationin the infected leaf results from the larger ATP pool with aturnover rate of ATP similar to that in the healthy leaf. Withtobacco callus tissue cultures infected by TMV, where infectiondoes not result in local-lesion formation, phosphorus metabolismwas unaltered in the infected tissue. It is concluded that necroticlocal-lesion formation results from increased availability ofATP at sites of ATP utilization, and this is aggravated by over-productionof ATP in the infected leaf.     

Abscisic Acid and the Regulation of Water Loss in Plantlets of Brassica oleracea L. var. botrytisRegenerated Through Apical Meristem Culture

Water loss was studied in regenerated plantlets of Brassicaoleracea var. botrytis cv. Currawong derived through apicalmeristem culture. Hardening of plantlets was eliminated by asingle application of a polyvinyl resin (S600) sprayed immediatelyafter transplanting. Plantlets sprayed with S600 had highercuticular resistances than unsprayed plantlets; this treatmenthad no effect on stomatal resistance. Leaves formed during theculture period showed very little wax formation and using markedleaves it was found that only reduced levels of wax formed onthese leaves even after transplanting. New leaves formed aftertransplanting, showed typical wax formation compared to seedgrown plants. Abscisic acid (ABA) at 10^–4 M applied as a leaf sprayto transplants did not cause a substantial increase in stomatalresistance in leaves which had been initiated during the cultureperiod. Leaves of seed-grown plants as well as leaves of plantletsformed after transplanting did respond to a leaf spray of ABAat 10^–4 M by a large increase in stomatal resistance. Relative concentrations of K, Na, Ca, P, S and Mg in guard cellswere calculated for each leaf type by X-ray micro-probe analysis.K/Na values decreased in the order: seedling > leaves formedafter transplanting > leaves intiated during culture. A highpositive correlation was also found between K/Na and K/P forthe three leaf types. K:Mg and K:Ca ratios for leaves formedduring culture were low in comparison to the values obtainedfor leaves formed after transplanting and seedlings for whichthe values were similar. Brassica oleracea var. botrytis, cauliflower, regenerated plantlets, meristem culture, stomatal resistance, water loss, abscisic acid, X-ray micro-probe analysis     

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