Inhibition of the Chloroplast Photochemical Reactions by Treatment of Wheat Seedlings with Low Concentrations of Cadmium: Analysis of Electron Transport Activities and Changes in Fluorescence Yield

The effect of treatment of wheat plants with Cd²⁺ ions on thephotochemical activity of the primary leaves was examined. Threeday-old etiolated seedlings were treated with Cd²⁺ ions for24 h in dark, and after this treatment the plants were grownin the light until the primary leaves were fully developed.Cd²⁺ ions (30–120 µM) induced a significant decreasein activities of both photosystem II and photosystem I. Theextent of the decrease in PS II activity was much greater thanthat in the PS I activity. Analysis of changes in the fluorescenceyield of chlorophyll also indicated that Cd²⁺ ions drasticallyaffect the photochemistry of photosystem II. Cd²⁺ ions induceddecrease in the rates of photoreduction of 2,6-dichlorophenolindophenol even in the presence of the exogenous electron donor,hydroxylamine, both in Tris-treated and untreated chloroplasts.This result suggests that the site of inhibition is near thesite of donation of electrons by hydroxylamine. Treatment withCd²⁺ ions impairs the electron transport system on the reducingside of PS II. The decrease in the fluorescence yield of Chi is less than that in the evolution of O₂ mediated by oxidizedphenylenediamine. This difference may be a result of inhibitionon the reducing side of PS II. In addition to inhibition onthe reducing side, Cd²⁺ ions may affect the oxidizing side ofPS II. A comparative study of the rates of evolution of O₂ withp-benzoquinone and dichloro-p-benzoquinone as electron acceptorswas performed since the halogenated benzoquinones have beenshown to accept electrons from both active and inactive centersof photosystem II while some of the benzoquinones accept electronsonly from active centers. The results suggest that Cd²⁺ ionsinduced a marginal increase in the number of inactive reactioncenters in PS II. Analysis of light-saturation-kinetics of theevolution of O₂ catalysed by PS II indicates a reduction inthe size of the antennae as well as in the concentration ofthe active (-type) reaction centers of PS II. Thus, the Cd²⁺-inducedeffects on the photochemistry of PS II involve changes on thereducing side of PS II as well as possible changes in the sizesof the populations of active and inactive centers. Thus, short-termexposure to Cd²⁺ ions during establishment of seedlings hasa severely detrimental effect on photochemical activities inchloroplasts. (Received October 17, 1990; Accepted July 3, 1991)     

Photochemical Apparatus Organization in the Diatom Cylindrotheca fusiformis: Photosystem Stoichiometry and Excitation Distribution in Cells Grown under High and Low Irradiance

The photochemical apparatus organization in the thylakoid membraneof the diatom Cylindrotheca fusiformis was investigated in cellsgrown under high and low irradiance. High light (HL, 200µE.m^–2.s^–1)grown cells displayed a relatively low fucoxanthin to chlorophyll(Chl) ratio, a low photosystem (PS) stoichiometry (PSII/PS I=1.3/1.0)and a smaller photosynthetic unit size in both PS I and PS II.Low light (LL, 30µE.m^–2.s^–1) grown cells displayeda 30% elevated fucoxanthin content, elevated PS II/PS I=3.9/1.0and larger photosynthetic unit size for PS II (a change of about100%) and for PS I (by about 30%). In agreement, SDS polyacrylamidegel electrophoresis of thylakoid membrane polypeptides showedgreater abundance of PS I, RuBP carboxylase and ATP synthasepolypeptides in HL cells. In contrast, LL grown cells exhibitedgreater abundance of light-harvesting complex polypeptides.Assuming an efficiency of red (670 nm) light utilization of1.0, the measured efficiency of blue (481 nm) light utilizationwas 0.64 (HL cells) and 0.72 (LL cells). The lower efficiencyof blue versus red light utilization is attributed to the quenchingof absorbed energy by non-fucoxanthin carotenoids. Differencesin the efficiency of blue light utilization between HL and LLgrown cells are attributed to the variable content of fucoxanthin.The results support the hypothesis of a variable Chl a-Chl c-fucoxanthinlight-harvesting antenna associated with PS II and PS I in Cylindrotheca. (Received February 10, 1988; Accepted April 6, 1988)     

Changes of Photosystem Stoichiometry during Cell Growth in Dunaliella salina Cultures

The photosystem stoichiometry in Dunaliella salina thylakoidswas measured during cell growth in a fully contained culture.In dilute cultures, obtained after inoculation of cells intofresh growth medium, the PS II/PS I stoichiometry was about2.2/1.0. This ratio was gradually lowered to about 1.2/1.0 inmature cultures. The decrease of the PS II/PS I ratio is discussedin terms of increasing self-shading in the culture and increasingpH in the growth medium. Changes in the pH occurred from 7.7in young cultures to 8.9 in mature ones and caused a significantdepletion of soluble CO₂ from the growth medium. A correlationof the CO₂/HCO₃^– ratio in the growth medium with the PSII/PS I ratio in the thylakoid membrane is presented. ¹ Permanent address: Department of Physics, Palacky University,tr. Svobody 26, 771 46 Olomouc, Czechoslovakia (Received September 12, 1990; Accepted April 4, 1991)     

Preparation and Characterization of Heat-Stable and Very Active Oxygen-Evolving Photosystem II Particles from the Thermophilic Cyanobacterium, Synechococcus elongatu

Very active and heat-stable oxygen-evolving photosystem II particleswere isolated from the thermophilic cyanobacterium Synechococcuselongatus by treatment of thylakoid membranes with a non-ionicdetergent, sucrose monolaurate (SML). The particles were analyzedin a comparison with photosystem II particles prepared withß-octylglucoside (OG). The two preparations had similarpolypeptide compositions, which were caracterized by high levelsof polypeptides from phycobilisomes. The ratio of chlorophylla to QA was 45 and there were four Mn atoms and one tightlybound Ca²⁺ ion per QA in the particles prepared with SML. Thepreparations were thermophilic, showing substantial rates ofoxygen evolution at temperatures up to 60°C. The maximumrates attained at 45°C were as high as 6.0 mmoles O₂ mg^–1Chl h^–1. PS II particles prepared with OG were similarlythermostable but were less active in oxygen evolution at alltemperatures examined. Kinetic analysis of flash-induced absorptiontransients revealed that about 22% and 28% of photosystem IIreaction centers were not associated with the functional QBsite in the SML- and OG-particles, respectively. When correctedfor the inactive reaction centers, the maximum rates of oxygenevolution by SML- and OG-particles were 7.7 and 7.0 mmoles O₂mg^–1 Chl h^–1, which correspond to half times of1.9 and 2.1 ms for the first-order electron transfer, respectively.Comparison of these half times with those of the S-state transitionand the release of oxygen indicates that the overall photosystemII electron transport is limited by the reduction of added electronacceptors and not by release of oxygen. ³On leave from National Chemical Laboratory for Industry, Higashi1-1, Tsukuba, Ibaraki 305     

Nucleotide Sequence of cDNA Clones Encoding the PS I-H Subunit of Photosystem I in Tobacco

cDNA clones encoding the PS I-H subunit of photosystem I wereisolated from Nicotiana tabacum and Nicotiana sylvestris. Thenucleotide sequences of three clones showed that, in both species,the mature PS I-H protein consists of 95 amino acid residuesand has a calculated molecular mass of 10.3 kDa. ³ Present address: The Institute of Physical and Chemical Research,Tsukuba, 305 Japan.     

Chromatic Regulation of Cytochrome Composition and Electron Transfer from Cytochrome b6-f Complex to Photosystem I in Anacystis nidulans (Tx 20)

Cytochrome composition of the cyanobacterial photosyntheticsystem was studied with Anacystis nidulans (Tx 20) in relationto the chromatic regulation of photosystem composition. Comparisonof cytochrome compositions in cells with a high PS I/II ratio(3.0, grown under weak orange light) and with a low ratio (1.6,grown under weak red light) indicated that cytochrome compositionwas also changed in the chromatic regulation of photosystemcomposition. Two types of cytochrome change were observed: 1)contents of cytochromes C₅₅₃ and c₅₄₈ were changed in parallelwith the changes in PS I content, and 2) cytochrome b₅₅₃ andcytochrome b₆-f complex were held at a constant molar ratioto PS II. The molar ratio, PS II : cytochrome b₅₅₉ : cytochromeb₆-f complex : cytochrome c₅₅₃ : PS I : cytochrome C₅₄₈, inthe red-grown cells was 1 : 2.5 : 1.3 : 0.17 : 1.6 : 0.67, andthe ratio in the orange-grown cells, 1:2.4:0.9:0.32:3.0:1.2.In both types of cells, almost all cytochrome f in the cytochromeb₆-f complex was rapidly oxidized after multiple flash activation,indicating that all cytochrome b₆-f complexes in cells of bothtypes are functionally connected to PS I, even when the molarratio to PS I is largely changed. The content of cytochromeC₅₅₃ was at most 0.14 of PS I, suggesting that the cytochrometurns over several times per one turnover of PS I. ¹Present address: Department of Biology, Faculty of Science,Tokyo Metropolitan University, Fukazawa 2-1-1, Setagaya, Tokyo158, Japan. (Received January 20, 1986; Accepted March 17, 1986)     

The Distribution of Zinc-65 in Agrostis tenuis sibth. and A. stolonifera L. Tissues4

The distribution of ⁶⁵Zn in zinc-tolerant and copper-tolerantplants of Agrostis spp. from toxic mine-tailings in Enflandand Wales was compared with zinc distribution in non-tolerantplants. Isotope was applied in culture solution in which theplants were growing. No differences could be demonstrated betweenthe plants were growing. No differences could be demonstratedbetween the plants by whole-plant radioautography, or by zincanalyses of the tops. Root/shoot ratios calculated from specificactivity values varied with population, the non-tolerant plantshaving the lowest and the zinc-tolerant plants the highest ratio.After solvent (80 per cent ethanol and water) extractions, theroot residue of zinc-tolerant plants contained a higher percentageof ⁶⁵Zn than that of non-tolerant plants. Chemical fractionationof the roots revealed that the main high difference was thatthe amount of ⁶⁵Zn in the pectate extract of the cell wall washigh in zinc-tolerant plants and low in non-tolerant plants.The ⁶⁵Zn distribution in the copper-tolerant plants was similarto that in the non-tolerant plants, indicating that the tolerancemechanisms for the elements are different. Soluble protein andRNA preparations were made but they contained low levels of⁶⁵Zn. An exception was the relatively high value for RNA fromzinc-tolerant A. stolonifera shoots. An anionic complex of ⁶⁵Znin the soluble fraction was investigated. This complex accountedfor most of the radioactivity in A. tennis extracts of shootsbut the concentration of the complex was low in A. stoloniferashoots, and in root extracts of all plants examined.     

Chromatic Regulation of Photosystem Composition in the Photosynthetic System of Red and Blue-Green Algae

A chromatic adaptation in the photosynthetic quantum yield forthe light mainly absorbed by chlorophyll a (Chl a light) firstfound by Yocum (1951) was studied with one red and three blue-greenalgal strains. When the cells were grown under a weak Chl alight, the quantum yield in all the strains increased. Comparisonof photosystem (PS) compositions, including phycobilin (PBP)and Chl a antennae, reaction centers I and II, in the cellsgrown under the light mainly absorbed by PBP and Chl a revealedthat changes in quantum yield could be attributed to changesin the ratio of PS I/II; PS I/II becomes larger than 1 underPBP light but decreases to 1 in most cases under Chl a light.The change in the PS I/II ratio is due solely to the changesin the PS I population in the cell; PS II remains constant.These results are similar to the intensity-dependent responsein PS composition. A common hypothesis for both the chromatic and intensity-inducedregulation of PS composition was proposed based on the ideaof balance between the electron flow from H₂O to NADP drivenby PS I and II and the cyclic one driven by PS I. (Received May 16, 1985; Accepted September 4, 1985)     

Photosynthetic Responses of Different Varieties of Wheat to High Temperature: II. EFFECT OF HEAT STRESS ON PHOTOSYNTHETIC ELECTRON TRANSPORT

The effect of heat stress on photosynthetic electron transportwas investigated in thylakoids isolated from the wheat (Triticumaestivum L.) varieties APU (Finland) and K65 (India) grown underboth cool (13 °C day, 10 °C night) and warm (30 °Cday, 25 °C night) regimes which gave rise to varietal differencesin photosynthetic temperature acclimation. The responses ofthe uncoupled activities of both whole-chain electron transportand photosystem II to heat stress were similar. Both activitiesexhibited higher rates in thylakoids isolated from warm-grownplants and were more resistant to high temperature pretreatmentthan in those isolated from cool-grown plants, but varietaldifferences were not observed. Uncoupled photosystem I activity driven by either reduced 2,6-dichlorophenol indophenol (DCPIPH₂) or N,N,N',N'-tetramethyl-p-phenylenediamine (TMPDH₂) showed a stimulation following high temperaturepretreatment which was more marked in thylakoids isolated fromwarm-grown plants, followed by inhibition at extreme high temperatures.This stimulation was due largely to an increase in V_max butdid not occur when reduced diaminodurene, which is highly lipophilic,was used as the electron donor. It appears that stimulationof PS I activity may involve increased accessibility of someartificial electron donors to the native acceptor sites withinthe thylakoid membrane in a process which is influenced by growthtemperature. Key words: Photosynthetic electron transport, heat stress, Triticum aestivum     

Regulation of the Stoichiometry of Thylakoid Components in the Photosynthetic System of Cyanophytes: Model Experiments Showing that Control of the Synthesis or Supply of Chl a can Change the Stoichiometric Relationship between the Two Photosystems

Regulation of the assembly of the photosystem I (PS I) complexin response to the light regime in the photosynthetic systemof cyanophytes was studied in Synechocystis PCC 6714. The relationshipbetween the assembly of the PS I complex and synthesis of Chla was examined by model experiments in which synthesis of Chla was controlled by two inhibitors, gabaculine (GAB) and 2,2'-dipyridyl(DP). Both inhibitors caused a change to a lower ratio of PSI to PS II even under light that normally induces a high ratioof PS I to PS II. The change in stoichiometry induced by theseinhibitors was suppressed when protein synthesis was inhibitedby chloram-phenicol, similarly to the change in the stoichiometryinduced by light that excites mainly PS I (PS I light). Comparisonof the levels of PS I, PS II and Cyt b₆-f complexes per cellindicated that a selective suppression of the assembly of thePS I complex was induced by the inhibitors: the stoichiometricrelationship among PS I, PS II and Cyt b₆-f complexes was identicalto that induced by PS I light or white light of high intensity.GAB induced a decrease in size of the phycobilisome also, whileDP did not, similarly to PS I light. The results indicate thatthe ratio of PS I to PS II can be changed by the control ofsynthesis of Chl a. They also suggest that control of the synthesisor supply of Chl a probably exerted at site(s) in or after theprocess of the Mg-protoporphyrin branch, is involved in themechanism of regulation of the assembly of the PS I complexin cyanophytes. (Received September 7, 1989; Accepted November 20, 1989)     

Uptake and distribution of 65Zn and 54Mn in wheat grownat sufficient and deficient levels of Zn and Mn: I. During vegetative growth

The uptake and distribution of ⁶⁵Zn and ⁵⁴Mn by wheat (Triticumaestivum cv. Aroona) was investigated. Plantswere grown in achelate-buffered nutrient solution with either sufficient Znand Mn, low Zn or low Mn. A single representative seminal rootfrom 14-d-old and 42-d-old plants was dual-labelled with ⁶⁵Znand ⁵⁴Mn. The 14-d-old plants were harvested every 10 min from10–140 min of labelling, whilst the 42-d-old plants wereharvested after 2 h of labelling. At harvest, each plant wasseparated into leaves, main stem, unexposedroots, and tillers.In addition, the crown was separatedfrom the stem in the 14-d-oldplants In the control plants labelled at 14 d, ⁶⁵Zn was firstdetectedand accumulated in the crown of the roots after 40–60min. Labelled Zn was then detected in the stem, followed bythe leaves. The oldest and youngest leaves received less ⁶⁵Znthan the second and third oldest leaves. The plants grown underlow Zn conditions accumulated more ⁶⁵Zn in their older leavesand transferred ⁶³Zn to the unexposed roots. Distribution of⁵⁴Mn was similar in the controls to that of ⁶⁵Zn, except theolder leaves received no HMn, At the second harvest, a similardistribution pattern of ⁶⁵Zn and ⁵⁴Mn was observed with regardto leaf age. Large amounts of ⁶⁵Zn and ⁵⁴Mn were detected withinthe unexposed roots of all treatments. It is suggested thatthe distribution of root-supplied Zn and Mn may be determinedby micronutrient status and its relationship with leaf transpirationrates. Key words: Distribution, manganese, vegetative growth, wheat, zinc     

Purification and properties of the photoactive particle corresponding to photosystem II

1. 1) Purification of the photoactive particle corresponding tophotosystem II (particle II) was achieved using a combinationof procedures including digitonin- and Triton X-100-treatments,sonication, and differential- and density-gradient centrifugations.
2. 2) The "purified" particle II preparation showed only oxygenevolution activity and showed no NADP⁺ photoreduction activityeven when an electron donor couple was added.
3. 3) The chemicalcompositions of this particle and of the particlecorrespondingto photosystem I (particle I) were compared withrespect tothe composition and contents of their chlorophylls,carotenoids,cytochromes, plastoquinones, protein and lipid.Marked differenceswere found.
4. 4) Using the two photoactive particles I and IIlacking therespective counterpart activity, a partial successwas attainedin reconstituting a system, in which photoinducedelectron flowfrom water to NADP⁺ was observed, provided thatsuitable intermediateelectron carriers, e. g. plastoquinoneand plastocyanin, wereadded.
5. 5) The nature of the two photoactiveparticles obtained andtheir relationship to particles so farreported are discussed.

¹This study was aided by grants from the Ministry of Education(407160-1965, 91402-1966, 1967). Financial support from SanyoBroadcasting Scientific Foundation is also acknowledged withcordial thanks. (Received October 23, 1968; )     

Further investigation of the light-induced cytochrome b-559 reaction in membrane fragments of the blue-green alga Anabaena variabilis

Oxidation-reduction reactions of the low redox potential cytochromeb-559 were studied for membrane fragments of the blue-greenalga Anabaena variabilis. Cytochrome photooxidation was observableat room temperature when the membrane fragments had been preincubatedat room temperature in the dark. A CCCP addition (10^–4M) strongly enhanced the reaction. Oxidation consisted of a DCMU-sensitive and an insensitive reaction.The former depended on actinic illumination of short wavelength.The latter showed a dependency on longer wavelength light. Theformer was assumed to be induced by the action of photosystemII and the latter by that of photosystem I. The photosystem II oxidation was small before preincubation,and was enhanced by added DPIP or Ferro. This was interpretedas photosystem II action inducing oxidation as well as reduction;reduction being inactivated during dark incubation or beingsuppressed by added redox reagents which compete for electronacceptance from photosystem II so that oxidation was apparentlyenhanced. The oxidationreduction reactions of this cytochromewith low redox potential were assumed to be almost identicalwith those of the high redox potential form, at least in themembrane fragments of Anabaena variabilis. (Received June 8, 1975; )     

Phytotoxicity of Phthalate Plasticisers: 2. SITE AND MODE OF ACTION

The effects of phthalate esters on chlorophyll a₂ fluorescencein radish plants (Raphanus sativus L. cv. Cherry Belle) wereexamined Fluorescence yield was increased in those plants exposedto an aerial concentration of 120 ng dm^–3 dibutyl phthaiatc(DBP) at a rate of 3.0 dm³ min^–1 for 13 d. Comparisonof fluorescence enhancement ratios and F_red/F_ox, suggests thatDBP inhibits photosynthesis in radish plants at a site afterQ_A. Both DBP and diisobutyl phthalate (DIBP) strongly inhibiteduncoupled (PS2+PS1) electron transport rates in thylakoids isolatedfrom spinach. At a chlorophyll concentration of 10 µgcm^–3 the concentrations of DBP and DIBP exhibiting 50%inhibition were 44 mmol m^–3 and 42 mmol m^–3 respectively.Basal electron transport rates were also inhibited, with 87mmol m^–3 of DBP or DIBP producing 50% inhibition. Measurementof photosystcm 1 activity suggested that the main site of actionof these phthalates was localized at a site near the reducingside of photosystem 2. Key words: Phthalate, plasticiser, chlorophyll, fluorescence, photosynthesis, inhibition     

Characteristics of the Cl- Action Site in the O2 Evolving Reaction in PS II Particles: Electrostatic Interaction with Ions

The role of Cl^– in the reactivation of O₂ evolution inphotosystem II (PS II) particles derived from spinach chloroplastswas studied in the presence of various salts. Multivalent ion(especially anion) salts were found to strongly suppress thereactivation of O₂ evolution by Cl^– in the Cl^–-depletedPS II particles in a competitive manner. The effectiveness ofanions in the suppression of Cl^–-supported O₂ evolutionwas in the order of trivalent>divalent>monovalent ones.Multivalent anions similarly suppressed O₂ evolution in theuntreated PS II particles under low and moderate Cl^– concentrations.pH dependence of the Cl^–-affinity (K_m) value for Cl^–)was also studied. Within the pH range 5.5 to 8 the K_m valuebecame higher as the pH of the medium increased. These resultssuggest that the membrane surface in the vicinity of the Cl^–action site is net positively charged and attracts Cl^–electrostatically, and that the site is almost freely accessibleto various anions. The origin and role of the local net positivedomain and the role of peripheral proteins are discussed. (Received May 27, 1985; Accepted October 8, 1985)     

Light-induced Changes of the Electrical Potential in Chloroplasts Associated with the Activity of Photosystem I and Photosystem II

The electric potential changes induced by flashing and continuouslight were measured with microcapillary electrodes in isolatedwhole chloroplasts of Peperomia inetallica. In continuous lightthe chloroplast electrical potential rose in two phases. Theinitial rapid phase coincided in extent with the flash-inducedpotential and was insensitive to the electron transfer inhibitorDBMIB. The subsequent phase was relatively slow (20–30ms) and was inhibited by DBMIB. Electron acceptors of photosystemII (p-phenylendiamine, p-benzoquinone) added to DBMIB-treatedchloroplasts produced a suppression of the flash-induced responseand a considerable increase in the steady level of the potentialin the light. The electrical potential associated with the activityof photosystem II rose in continuous light much more slowlythan that associated with the activity of photosystem I aloneor the activities of both photosystems. Illumination of chloroplastswith successive flashes at a repetition rate 5 Hz in the presenceof oxaloacetate, a terminal acceptor of photosystem I, was accompaniedwith a gradual decline of the flash-induced potential. The specificrole of two photosystems in the light-induced H⁺ transport andthe electrogenesis across the chloroplast thylakoid membranesis discussed.     

Immunogold localization of light-harvesting and photosystem I complexes in the thylakoids ofFucus serratus (Phaeophyceae)

Summary The repartition of light-harvesting complex (LHC) and photosystem I (PS I) complex has been examined in isolated plastids ofFucus serratus by immunocytochemical labelling. LHC is distributed equally all along the length of thylakoid membranes, without any special repartition in the appressed membranes of the three associated thylakoids ofFucus. PS I is present on all the thylakoid membranes, but the external membranes of the three associated thylakoids are largely enriched relatively to the inner ones. This specific repartition of PSI on non-appressed membranes can be compared to the localization of PSI on stroma thylakoid membranes of higher plants and green algae. Consequently, although they share some common features with those of higher plants and green algae, the appressions of thylakoids in brown algae has neither the same structure nor the same functional role as typical grana stacked membranes in the repartition of the harvested energy.Abbreviations BSA bovine serum albumin - GAR goat anti-rabbit immunoglobulin G - LHC light-harvesting complex - PBS phosphatebuffered saline - PS I photosystem I - PS II photosystem II     

Contents of Cytochromes, Quinones and Reaction Centers of Photosystems I and II in a Cyanobacterium Synechococcus sp.

The contents of photosystem I and photosystem II reaction centers,cytochrome c-553, cytochrome c-550, cytochrome f, cytochromeb-559, cytochrome b-563, plastoquinone and vitamin K₁ in thecyanobacterium Synechococcus sp. were determined. About threephotosystem I reaction centers were present for each photosystemII reaction center. The amounts of cytochromes functioning betweenthe two photosystems were approximately half those of the photosystemI reaction center. Plastocyanin was not detected, while plastoquinoneand vitamin K₁ were present in excess of other electron carriersand reaction centers. The results indicate the importance ofplastoquinone and cytochrome c-553 for cooperation of the tworeaction centers through electron transport. ¹Present address: Toray Basic Research Laboratory, 1111 Tebiro,Kamakura, Kanagawa 248, Japan. (Received June 17, 1982; Accepted January 17, 1983)     

Freeze-etched membrane faces and photosynthetic activity in normal and mutantTradescantia chloroplasts

Summary Membrane structure and photosynthetic activity was investigated in normal and mutant plastids ofTradescantia albiflora cv.aureo-vittata. In the stacked membrane regions (the macrograna) of mutant plastids, the B fracture faces lack both 170 Å particles and photosystem II (PS II) activity. The C face has the normal 110 Å particles, and photosystem I (PS I) activity is also similar to that in normal chloroplasts. In dilated macrograna the particle size on the C face significantly decreases, and as progressive plastid destruction occurs so PS I activity also disappears. It has been concluded that the integrity of B face particles is related to PS II activity, rather than for membrane stacking. A similar correlation seems to be valid for C face particles and PS I activity.     

EFFECTS OF WOUND HEALING ON ZINC DISTRIBUTION AND ALKALINE PHOSPHATASE ACTIVITY OF HELIX ASPERSA (GASTROPODA: PULMONATA)

Helix aspersa were loaded with ⁶⁵zinc and after 2 and 5 daysstarvation there was no significant reduction in the zinc concentrationof the digestive gland and shell. Wounding of the optic tentacle,foot tissue and partial shell removal of H. aspersa resultedin deposition of ⁶⁵zinc in the wound area. Alkaline phosphataseshowed no increase in concentration at the sites of wounding. (Received 15 October 1985;