Immunochemical quantification of cytochrome f in leaves of a non-yellowing senescence mutant of Festuca pratensis

A non-competitive enzyme-linked immunosorbent assay (ELISA) which enables detection of as little as 0.1 ng cytochrome f in leaf extracts has been developed. No evidence for specific or non-specific interference by proteins other than cytochrome f was found. The assay was applied to a comparative study of age-related changes in the cytochrome f content of leaves of Festuca pratensis Huds. cv. Rossa, and a non-yellowing mutant genotype (Bf993) having a lesion in the mechanism responsible for thylakoid membrane disassembly. Cytochrome f in senescent leaves of the latter genotype was found to be present at significantly higher levels than in the wild-type, implying an inability on the part of the mutant to degrade this protein. The results obtained by ELISA were confirmed by antibody probing of Western blots.Abbreviations Ab antibody - BSA bovine serum albumin - chl chlorophyll - cyt cytochrome - ELISA enzyme-linked immunosorbent assay - Ig immunoglobulin - kDa kilodalton - LHCP-2 light-harvesting chlorophyll a/b binding protein - OEC oxygen-evolving complex - PAGE polyacrylamide gel electrophoresis - POase peroxidase - SDS sodium dodecyl sulphate - PS II Photosystem II - TBS Tris buffered saline - Tris tris (hydroxymethyl) aminomethane     

Gabaculine Inhibition of Chlorophyll Biosynthesis and Nodulation in Phaseolus lunatus L

Gabaculine (3-amino-2,3-dihydrobenzoic acid) was an inhibitor of in vivo chlorophyll biosynthesis in lima bean (Phaseolus lunatus L. cv Henderson). When applied to roots of 9-day-old plants, 10 micromolar gabaculine was sufficient to terminate biosynthesis of new chlorophyll. The trifoliolate leaves which emerged after gabaculine treatment were yellow. Gabaculine-treated plants had slightly lower dry weights; yet, overall plant size showed very little change. Chlorophyll fluorescence induction kinetics and CO₂ exchange measurements were used to monitor both immediate and long-term effects of gabaculine on photosynthesis. A lowered rate of the decline from the maximum level of fluorescence was observed after 10 hours for nitrate-supplemented plants, and all treated plants showed a slightly increased level of original fluorescence after 6 days. No change was observed in the rate of photosynthesis by unifoliolate leaves. The trifoliolate leaves, though not able to photosynthesize, were able to continue respiration. This suggested that heme biosynthesis for mitochondrial cytochromes was not abolished. In untreated lima bean, root nodules were induced by Rhizobium sp. 127E15. Following gabaculine treatment, root nodules formed, but were largely ineffective in nitrogen fixation. Nodule dry weight, nitrogen fixation activity, and leghemoglobin content were decreased by gabaculine.     

The Relationship Between the Phosphorus Status of Subterranean Clover Plants and Losses in Chlorophyll from Detached Leaves: A Basis for the Visual Diagnosis of Phosphorus Deficiency

Leaves detached from subterranean clover plants (Trifolium subterraneumL.), grown in solution cultures at different phosphorus levels,were placed in water and in phosphate solutions. Losses in totalchlorophyll (a+b) of leaves in water were greater the lowerthe previous phosphorus supply to the plants from which theywere detached. In comparable leaves placed in phosphate solutionschlorophyll was maintained at levels at least as high as inleaves from non-deficient plants. For the latter there wereno differences between treated and untreated leaves. The differencesin colour change between treated and untreated leaves, therefore,increased with the deficiency in the phosphorus supply to theplants from which the leaves were detached, thus visibly reflectingtheir phosphorus status. A light intensity of 300 ft c (27 lx) or higher was necessaryfor maximum differences in leaf colour between treated and untreatedleaves, mainly because lower light levels reduced chlorophylllosses from leaves in water. Differences in colour between treated and untreated deficientleaves decreased with their age. However, valid comparisonsbetween treated and untreated leaf tissue could be ensured bythe use of treated and untreated leaflets. It is suggested that the results provide the basis for a simple,direct and visual diagnostic method, requiring no laboratoryequipment. Trifolium subterraneum L., subterranean clover, phosphorus deficiency, chlorophyll     

Effect of Leaf Age and Shading on Photosynthesis in Potatoes (Solanum tuberosum)

The effects of leaf age and of shading on photosynthetic rateand on other leaf parameters of potato (Solanum tuberosum L.)were studied using a portable gas exchange system. A rapid decreasein the rate of photosynthesis during leaf senescence was observed.This was accompanied by an increase in stomatal resistance,and as a result a fairly constant level of sub-stomatal CO₂concentration was maintained at all leaf ages. The reductionin the photosynthetic rate in older leaves was therefore assumedto be essentially mesophyllic in origin, whereas the stomatalresponse was probably secondary. Canopy density significantly affected the rate of photosyntheticreduction with leaf age. Leaves maintained under high radiationintensities manifested a slower decline in their photosyntheticrate, especially in the early stages of their senescence, thanleaves kept under shade conditions. The latter leaves were foundto be more adapted to low radiation intensities, as indicatedby changes in their chlorophyll a:b ratio and specific leafweight Solanum tuberosum L, potato, photosynthetic rate, mesophyll, stomata, leaf age, radiation intensity, chlorophyll a:b ratio     

Leaf Characteristics and Net Gas Exchange of Diploid and Autotetraploid Citrus

The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) ‘Valencia’ sweet orange (Citrus sinensis (L.)Osb.) and ‘Femminello’ lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 5–15% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO₂assimilation rate (A_CO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerA_CO2than their diploids. There were no significant differencesin A_CO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower A_CO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO₂diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; ‘Valencia’ sweet orange; ‘Femminello’ lemon     

Haem synthesis during cytochrome P-450 induction in higher plants. 5-Aminolaevulinic acid synthesis through a five-carbon pathway in Helianthus tuberosus tuber tissues aged in the dark.

Chlorophyll and haem synthesis in illuminated Jerusalem artichoke tuber tissues were very efficiently inhibited by gabaculine (3-amino-2,3-dihydrobenzoic acid). This inhibition seems to be due specifically to a blockade of the pathway for 5-aminolaevulinate biosynthesis which used glutamate as a substrate (the so-called C5 pathway) since we could not detect any inhibition of protein synthesis in the treated tissues and there was no effect of gabaculine on the glycine-dependent yeast 5-aminolaevulinate synthase used as a model. In dark-aged artichoke tissues, gabaculine also effectively blocked cytochrome P-450 induction, peroxidase activity and 5-aminolaevulinic acid synthesis, thus suggesting the involvement of a C5 pathway in cytoplasmic and microsomal haemoprotein synthesis in this higher plant. Allylglycine and (2-amino-ethyloxyvinyl)glycine, two olefinic glycine analogues which are potential suicide inhibitors of pyridoxal phosphate enzymes, were also demonstrated to be effective blockers of chlorophyll synthesis in artichoke tuber and Euglena cells exposed to light.     

Changes of Anatomical Features, Photosynthesis and Ribulose Bisphosphate Carboxylase-Oxygenase Content of Mango Leaves

Changes in anatomical and physiological features, includingchanges in amount per unit area of anthocyanin and chlorophyll,in leaves of seedling mango (Mangifera indica L. cv. Irwin)trees were determined to understand what controls the rate ofphotosynthesis (Pn) at various stages of development. The youngleaves of seedling trees contained high concentrations of anthocyanin.During enlargement of leaves, the disappearance of anthocyaninand the accumulation of chlorophyll occurred concomitantly;the anthocyanin content began to decrease markedly once theleaf area had reached a maximum. During the early period ofleaf development, the thickness of mesophyll tissue decreasedtemporarily, but when the length of the leaf reached half thatof a mature leaf, the mesophyll began to thicken again. Smallstarch grains appeared in the chloroplasts of the young leavesand chloroplast nucleoids (ct-nuclei) were distributed throughoutthe chloroplasts. When leaves matured, ct-nuclei were displacedto the periphery of chloroplasts because of the accumulationof large starch grains. Compared with young leaves, green andmature leaves contained greater concentrations of ribulose bisphosphatecarboxylase-oxygenase (RuBisCO) protein. The results of immunocytochemicalexamination of RuBisCO under the light microscope reflectedthe results of electrophoresis measurements of RuBisCO. Pn waslow during the chocolate-coloured stage of early leaf development.In green and mature leaves Pn was higher; the average Pn was7·6 mg CO₂ dm^-2 h^-1 under light at intensities above500 µmol m^-2 s^-1.Copyright 1995, 1999 Academic Press Mangifera indica L., mango leaf, chloroplast nucleoids, chloroplast ultrastructure, starch accumulation, anthocyanin, chlorophyll, DAPI staining, SDS-PAGE, immunocytochemical technique     

Growth and Physiology of One-year old Poplar (Populus) Under Elevated Atmospheric CO2 Levels

The effects of elevated atmospheric CO₂ concentrations on theecophysiological responses (gas exchange, chlorophyll a fluorescence,Rubisco activity, leaf area development) as well as on the growthand biomass production of two poplar clones (i.e. Populus trichocarpax P. deltoides clone Beaupré and P. x euramericana cloneRobusta) were examined under open top chamber conditions. Theelevated CO₂ treatment (ambient + 350 µmol mol^-1) stimulatedabove-ground biomass of clones Robusta and Beaupré afterthe first growing season by 55 and 38%, respectively. This increasedbiomass production under elevated CO₂ was associated with asignificant increase in plant height, the latter being the resultof enhanced internode elongation rather than an increased productionof leaves or internodes. Both an increased leaf area index (LAI)and a stimulated net photosynthesis per unit leaf contributedto a significantly higher stem biomass per unit leaf area, andthus to the increased above-ground biomass production underthe elevated CO₂ concentrations in both clones. The larger LAIwas caused by a larger individual leaf size and leaf growthrate; the number of leaves was not altered by the elevated CO₂treatment. The higher net leaf photosynthesis was the resultof an increase in the photochemical (maximal chlorophyll fluorescenceFm and photochemical efficiency Fv/Fm) as well as in the biochemical(increased Rubisco activity) process capacities. No significantdifferences were found in dark respiration rate, neither betweenclones nor between treatments, but specific leaf area significantlydecreased under elevated CO₂ conditions.Copyright 1995, 1999Academic Press Biomass, chlorophyll a fluorescence, elevated CO₂, growth, Populus, poplar, photosynthesis, respiration, Rubisco     

Leaf development in Lolium temulentum: plastid membrane polypeptides in relation to assembly of the photosynthetic apparatus and leaf growth

Cellular and compositional changes related to tissue growth and assembly of the photosynthetic apparatus were established with reference to the developmental gradient along the expanding fourth leaf of Lolium temulentum L. Ba 3081. The number of cells and the fresh weight per leaf segment fell with increasing cell age (distance from the leaf base). Components of the photosynthetic apparatus increased in concentration towards the more mature part of the leaf. Appreciable levels of chlorophyll and carotenoid could be detected in basal tissue enclosed in the sheaths of previous leaves prior to emergence into full light. The distributions of NADPH-protochlorophyllide oxidoreductase (PCR. EC 1.6.99.1) and cytochrome f along the age gradient were visualized by Western blotting. Leaf base tissue contained two forms of PCR, 41 and 39 kDa, the smaller of which diminished with increasing cell age and proximity to full light. Cytochrome f comprised a 52 kDa species, which also declined with distance from the base, and a group of polypeptides at around 30–33 kDa which greatly intensified with tissue maturity. The significance of multiple forms of plastid proteins and the role of the light gradient penetrating the leaf sheath in regulating growth and plastid assembly processes are discussed.     

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     

Effects of 6N-Benzyladenine on Primary Leaves of Intact Bean Plants and on their Sodium Absorption Capacity

The application of ⁶N-benzyladenine (BA) to primary bean-leaves attached to the intact plant resulted in increased leaf area. This was due to an extension of the duration of the period of leaf expansion. The dry-weight percentage of untreated leaves decreased continuously from emergence to abscission. In BA treated leaves this decrease stopped with the cessation of leaf expansion. Net chlorophyll synthesis occurs in untreated leaves as long as they continue to expand, shortly afterwards net chlorophyll decomposition starts. Benzyladenine treatments diminished the rate of chlorophyll synthesis immediately after its first application, but prevented the loss of chlorophyll afterwards. The abscission of primary leaves was also delayed by BA. During the period of rapid leaf expansion in slices cut from BA treated leaves, sodium absorption rates were lower than in those from untreated leaves. From the age of 14 days after sowing, till abscission time of untreated primary leaves, the BA treatment did not significantly affect sodium absorption rates by leaf slices.     

Regulation of Leaf Senescence by Reproductive Sink Intensity in Cowpea (Vigna unguiculata L. Walp)

The relationship between seed number per pod and senescenceof the leaf in its axil was examined in a determinate cowpea(Vigna unguiculata L. Walp) variety C.779. The seed number perpod was reduced at all fruiting nodes by surgical excision ofpart of the 4-d-old pod. Leaf senescence as measured by lossof leaf area, chlorophyll content and soluble protein was sloweddown in leaves supporting the development of an artificiallyreduced number of seeds. Diminished nitrogen mobilization fromthe leaf could not account for the reduced rate of leaf senescence.The result suggests the involvement of a senescence signal fromthe developing seeds to the leaf in its axil. Development ofthe basal half of the excised pod in the cowpea provides a uniquesystem for manipulating seed number per pod. Senescence, monocarpic, chlorophyll, protein, Vigna unguiculata, cowpea     

Rate-Limiting Steps of Electron Transport in Chloroplasts during Ontogeny and Senescence of Barley

Partial photochemical activities and concentrations of electron carriers were measured relative to chlorophyll in barley (Hordeum vulgare L.) thylakoids, isolated from primary leaves during ontogeny and senescence. Thylakoids from mature leaves generated somewhat higher quantum efficiencies than thylakoids from premature or senescing leaves; this phenomenon did not appear to be caused by any deficiency of water-splitting enzyme. Under conditions of saturating light, the noncyclic electron flux from water to the reducing side of photosystem I increased during leaf ontogeny, peaked at maturity, and declined during senescence. However, electron fluxes appeared to be limited at different steps before and after leaf maturity. Before leaf maturity, the rate-limiting step was located prior to the reoxidation of plastohydroquinone. After leaf maturity, the decline in noncyclic electron flux correlated with a decrease in the concentration of cytochromes f and b₆. This correlation, together with a consideration of mechanisms of entry and exit of electrons in 3-(3,4-dichlorophenyl)-1,1-dimethylurea-treated thylakoids, suggests that the cytochrome f/b₆-containing complex, and not plastocyanin or P700, is the site of entry of electrons from the reduced forms of 2,6-dichlorophenolindophenol and diaminodurene. It is therefore proposed that in senescing leaves the cytochrome f/b₆-containing complex limited electron transport by constraining the rate of reduction of cytochrome f by plastohydroquinone.     

Ineffectiveness of cytokinin-induced chlorophyll retention in hypostomatous leaf discs

Kinetin retarded the decrease in chlorophyll content in leafdiscs from 5 species of plants with amphistomatous leaves, wherethe upper surface was exposed to air, but not in Rumex acetosera.When leaf discs were floated so that the lower surface was exposed,the effect of kinetin was less evident. Kinetin also stimulatedtranspiration in leaf discs from Nicotiana tabacum (amphistomatous),but not in leaf discs from Paederia chinensis (hypostomatous).Nor kinetin did retard chlorophyll breakdown in this specieswhen leaf discs were floated so that the stomatal surface wasin contact with the solution. The ineffectiveness of cytokininsin chlorophyll retention in leaf discs from hypostomatous leaveswas not due to reduced uptake of benzylaminopurine-¹⁴C. Chlorophyll retention was severely inhibited by coating theleaf surface with vaseline either in the presence or absenceof kinetin. Leaf discs floated on a solution exposed to CO₂-lessair retained more chlorophyll than those in normal air. Thereis thus a close relationship between stomatal opening (as measuredby stimulation of transpiration) and chlorophyll retention,as influenced by cytokinins. It is suggested that cytokinin-induced chlorophyll retentionand odier effects on leaf tissues could be mediated throughits effects on stomatal opening. (Received January 22, 1976; )     

Chlorophyll Content and the Pattern of Yellowing in Senescent Leaves

In senescent leaves of four species, leaf chlorophyll contentwas approximately linearly related to the estimated area ofyellow tissue, but the species differed in the amount of chlorophylllost before yellowing became apparent. Cotoneaster and Vicia leaves and Sinapis cotyledons, which produceddistinct yellowing patterns lost about 40 per cent, whereasSolanumleaves, which yellowed more uniformly lost over 60 percent of the chlorophyll before yellowing was visible. It issuggested that the leaf-cell population of Solanum may senescerather more synchronously than the other species, and that chlorophyllloss before yellowing may be a useful index of synchrony ofsenescence in leaves.     

Leaf senescence in a non-yellowing mutant of Festuca pratensis: Proteins of photosystem II

The senescence of leaves is characterized by yellowing as chlorophyll pigments are degraded. Proteins of the chloroplasts also decline during this phase of development. There exists a non-yellowing mutant genotype of Festuca pratensis Huds. which does not suffer a loss of chlorophyll during senescence. The fate of chloroplast membrane proteins was studied in mutant and wild-type plants by immune blotting and immuno-electron microscopy. Intrinsic proteins of photosystem II, exemplified by the light-harvesting chlorophyll a/b-binding protein (LHCP-2) and D1, were shown to be unusually stable in the mutant during senescence, whereas the extrinsic 33-kilodalton protein of the oxygen-evolving complex was equally lable in both genotypes. An ultrastructural study revealed that while the intrinsic proteins remained in the internal membranes of the chloroplasts, they ceased to display the heterogenous lateral distribution within the lamellae which was characteristic of nonsenescent chloroplasts. These observations are discussed in the light of possible mechanisms of protein turnover in chloroplasts.Abbreviations kDa kilodalton - LHCP-2 light-harvesting chlorophyll a/b-binding protein - M_r relative molecular mass - PSII photosystem II - SDS sodium dodecyl sulphate     

Prolonged Survival of CAM-Mode Mesembryanthemum crystallinum in Darkness and its Possible Dependence on Malate

A remarkable difference was found in the survival of leavesof Mesembryanthemum crystallinum with plants grown in the C₃versus the CAM mode. With excised leaves (petiole in solution)of C₃-mode plants subjected to 6 days of darkness, there wasa large reduction in the chlorophyll content of the leaf andleaf turgor had decreased. By day 9, the chlorophyll had disappeared,except at the major veins, and the leaf tip had dried and turnedbrown. In contrast, the leaf tissue in the CAM mode showed onlya partial loss of chlorophyll during the same period, and evenafter 17 days of darkness, the tissue at the base was stillalive. Similarly, intact plants grown in the C₃ mode deterioratedmuch faster during 20 days of darkness than did plants grownin the CAM mode. Chlorophyll content, chlorophyll a/b ratio,phosphoenolpyruvate carboxylase, NADP-malic enzyme, malate andstarch content were measured. In both C₃- and CAM-mode plants,the starch content decreased rapidly during the dark periodand was nearly depleted after two days. In the CAM-mode tissue,there was a relatively high level of malate during prolongeddarkness (up to 17 days), with a transitory rise early in thedark period. In contrast, the malate content was low and rapidlydepleted in the C₃-mode leaves kept in darkness. These findingssuggest that malate may be an important source of carbon forsustaining leaves of CAM-mode M. crystallinum during prolongeddarkness. (Received May 20, 1987; Accepted October 23, 1987)     

Development of Photochemical Activity and the Appearance of the High Potential Form of Cytochrome b-559 in Greening Barley Seedlings

The development of photochemical activity during the greening of dark-grown barley seedlings (Hordeum vulgare L. cv. Svalöfs Bonus) was studied in relation to the formation of the high potential form of cytochrome b-559 (cytochrome b-559_HP). Photosynthetic oxygen evolution from leaves was detected at 30 minutes of illumination. The rate of oxygen evolution per gram fresh weight of leaf was as high at 2 to 2.5 hours of greening as at 24 hours or in fully greened leaves. On a chlorophyll basis, the photosynthetic rate at 90 minutes of greening was 80-fold greater than the rate at 45 hours. It is concluded that the majority of photosynthetic units are functional at an early stage of greening, and that chlorophyll synthesis during greening serves to increase the size of the units.     

Acclimation in Seedlings of a Tropical Tree, Bischofia javanica, Following a Stepwise Reduction in Light

Acclimation of fully developed leaves of Bischofia javanicaBlume to shadelight was examined. Seedlings were grown undersimulated daylight (1000 µmol m^–2 s^–1), thentransferred to a simulated shadelight (40 µmol m^–2s^–1). When a high-light leaf was transferred to low light, large negativenet photosynthetic rates (P_m) were recorded. This decrease wasrapid, but within 7 d the rate increased and became equal tothe low-light control leaf. These changes in photosynthesisdid not follow the pattern of changes in stomatal conductance(g_s). Transfer to the low light resulted in a dramatic decreasein leaf weight per unit area (L_w), and most of the decreasesin L_w occurred within 3 d of transfer when the P_m of the transferredleaf was well below that of the low-light control leaf. There was a significant decrease in chlorophyll a in the transferredleaf without an appreciable change in chlorophyll b resultingin a large decrease in the chlorophyll a to chlorophyll b ratio.Leaf chlorophylls per unit area were higher in the transferredleaf than the low-light control leaf. Maximum photosyntheticrate in the transferred leaf was decreased by 40% compared tothat for the high-control leaf, but was almost at the same extenthigher than the low-light control leaf The results are discussedin the context of carbon gain capacity of its seedlings underlight-limiting forest understorey habitats. Bischofia, chlorophylls, light, photosynthesis, shade acclimation, tree seedlings, tropical tree     

Cytochrome Oxidase and Mitochondrial Protein in Extracts of Leaves of Nicotiana glutinosa L. Infected with Tobacco Mosaic Virus

Leaves of N. glutinosa were inoculated with tobacco mosaic virus,and infection allowed to develop in situ or in discs cut fromthe leaves and floated on water or culture solution. Extracts,made from the leaves and discs when their respiration was greaterthan that of comparable uninfected tissue, contained amountsof protein N, chlorophyll, glycollic oxidase, and mitochondrialprotein N, similar to those in extracts from uninfected tissue,but slightly less cytochrome oxidase and considerably more polyphenoloxidase.No evidence was obtained for the view that the virus-inducedrespiration reflects an increase in the amount of mitochondrialmaterial.