Chlorophyll-Protein Complexes and other Thylakoid Components at the Low Intensity Threshold in Euglena Chloroplast Development

The plastids of dark-grown resting cells of Euglena gracilisKlebs var. bacillaris Cori undergo only limited developmentwhen illuminated at the developmental threshold for light intensity7 foot-candles (ft-c) (27 µW/cm²). In the present work,we have found that these low intensity cells have substantialamounts of electron transport components such as ferredoxin-NADPreductase and Cyt c-552 but only trace amounts of the majorantenna components such as the light-harvesting Chl-proteincomplex (LHCP), the LHCP oligomer, CP la, Chi b and the 26.5kDa apo-LHCP; CP I and CPa are at levels comparable to the electrontransport components. Exposure of the low intensity cells tonormal light intensity causes large increases in major antennacomponents and small increases in electron transport components.The kinetics of accumulation of the antenna components Chi band apo-LHCP during greening of dark-grown resting cells atnormal intensities are the same as for Chi a. The low intensitywild-type cells strongly resemble mutants of Euglena low inChi b grown at normal intensities in lacking major antenna components. (Received April 7, 1987; Accepted June 19, 1987)     

The relative importance of food and temperature to copepod egg production and somatic growth in the southern Benguela upwelling system

The fecundity and somatic growth rates of Calanus agulhensisand Calanoides carinatus, the dominant large calanoid copepodsin the southern Benguela upwelling system, as well as the fecundityof several other common copepods, were measured between Septemberand March of 1993/94 and 1994/95. Mean egg production of mostcopepods was low at >30 eggs female^-1 day^-1 {Calanoides carinatus23.7, Calanus agulhensis 19.0, Neocalanus tonsus 16.1 and Rhincalanusnasutus 26.1), whereas the mean fecundity of Centropages brachiatuswas significantly greater (83.6 eggs female^–1 day^-1).This study also presents the first comprehensive field estimatesof the fecundity of Nanno-calanus minor (mean: 26.1 eggs female^–1day^–1, range: 0.0–96.2 eggs female^–1 day^–1)and of somatic growth of N6 and all copepodite stages of Calanoidescarinatus (decreasing from 0.58 day^–1 for N6 to 0.04 day^–1for C5). Somatic growth rates of Calanus agulhensis also declinedwith age: from 0.57 day1 for N6 to 0.09 day1 for C5. Data ongrowth rates were used to assess the relative importance offood [as measured by total chlorophyll (Chi) a concentration],phytoplankton cell size (proportion of cells >10 µm)and temperature to the growth of copepods. Multiple regressionresults suggested that fecundity and somatic growth rates werepositively related to both Chi a concentration and phytoplanktoncell size, but not to temperature. Although it was not possibleto separate the effects of Chi a concentration and phytoplanktoncell size, data from previous laboratory experiments suggestthat copepod growth is not limited by small cells per se, butby the low Chi a concentrations that are associated with theseparticles in the field. Despite growth not being directly relatedto temperature, a dome-shaped relationship was evident in somespecies, with slower growth rates at cool (<13°C) andwarm (>18°C) temperatures. The shape of this relationshipmirrors that of Chi a versus temperature, where poor Chi a concentrationsare associated with cool and warm temperatures. It is concludedthat the effect of food limitation on growth of copepods outweighsthat of temperature in the southern Benguela region. Sourcesof variability in relationships between growth and Chi a concentrationare discussed.     

Electrical Characteristics of the Tonoplast of Cham corallincr. A Study Using Permeabilised Cells

Use of permeabilised cells of Chara corallina provides a uniqueopportunity to study the electrical characteristics of the tonoplastwhilst being able to control ionic conditions on the outsideof the membrane. Current-voltage (I/V) analysis over wide voltagespans, and admittance measurements at 5 Hz showed that manypermeabilised cells had a similar conductance and capacitanceto the tonoplast of intact cells. Cells developed two regionsof negative-slope conductance upon addition of external Cl^–,which suggests the existence of potential-dependent Cl^–channels in the Chara tonoplast. With Cl^– concentrationssimilar to those expected in vivo, the resting potential wasmore sensitive to changes in external K⁺ than Cl^–; however,a decrease in external K⁺ did not significantly alter the shapeof the I/V relation. ¹Present address: Biopysics Laboratory, School of BiologicalSciences, A12, University of Sydney, Sydney, N.S.W., 2006, Australia ²Permanent address: Department of botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan (Received May 6, 1987; Accepted September 21, 1987)     

Cloning of the Gene Encoding a Protochlorophyllide Reductase: the Physiological Significance of the Co-Existence of Light-Dependent and -Independent Protochlorophyllide Reduction Systems in the Cyanobacterium Plectonema boryanum

Cyanobacteria have two protochlorophyllide (Pchlide) reductasescatalyzing the conversion of Pchlide to chloro-phyllide, a keystep in the biosynthetic pathway of chlorophylls (Chls); a light-dependent(LPOR) and a light-independent (DPOR) reductase. We found anopen reading frame (ORF322) in a 2,131-bp EcoRI fragment fromthe genomic DNA of the cyanobacterium Plectonema boryanum. Becausethe deduced amino acid sequence showed a high similarity tothose of various plant LPORs and the LPOR activity was detectedin the soluble fraction of Esche-richia coli cells over-expressingthe ORF322 protein, ORF322 was defined as the por gene encodingLPOR in P. boryanum. A por-disrupted mutant, YFP12, was isolatedby targeted mutagenesiss to investigate the physiological importanceof LPOR. YFP12 grew as well as wild type under low light conditions(10-25 µE m^–2 S^–1). However, its growth wassignificantly retarded as a result of a significant decreasein its Chl content under higher light conditions (85-130 µEm^–2 s^–1). Furthermore, YFP12 stopped growing andsuffered from photobleaching under the highest light intensity(170 µE m^–2 s^–1). In contrast, a chlL-dis-rupted(DPOR-less) mutant YFC2 grew as well as wild type irrespectiveof light intensity. From these phenotypic characteristics, weconcluded that, although both LPOR and DPOR contribute to Chlsynthesis in the cells growing in the light, the extent of thecontribution by LPOR increases with increasing light intensity;without it, the cells are unable to grow under light intensitiesof more than 130 µ Em^–2s-^–. (Received September 26, 1997; Accepted November 21, 1997)     

NAD(P)H Dehydrogenase-Dependent Cyclic Electron Flow around Photosystem I in the Cyanobacterium Synechocystis PCC 6803: a Study of Dark-Starved Cells and Spheroplasts

Electron donation to P700⁺ through plastoquinone in the intersystemchain from both respiratory substrates and the photoreductantsin PSI has been shown to be mediated by the NAD(P)H-dehydrogenasecomplex (NDH) in Synechocystis PCC 6803 cells [Mi et al. (1992)Plant Cell Physiol. 33: 1233]. To confirm the participationof NDH in the cyclic electron flow around PSI, the redox kineticsof P700 and Chi fluorescence were analyzed in cells rendereddeficient in respiratory substrates by dark starvation and inspheroplasts. Dark-starved cells showed a high steady-state level of P700⁺under far-red (FR) illumination and the plastoquinone pool wasin a highly oxidized state. An NDH-defective mutant consistentlyshowed a high level of P700 oxidation under FR before and afterthe dark starvation. Donation of electrons either from exogenousNADPH or from photoreduced NADPH⁺ to the intersystem chain viaplastoquinone was demonstrated using spheroplasts from wild-typecells, but not those from the NDH-defective mutant, as monitoredby following changes in the kinetics of Chi fluorescence andthe redox state of P700. The electron flow to PSI via plastoquinone,mediated by NADPH, was sensitive to rotenone, Hg²⁺ ions and2-thenoyltrifluoroacetone, inhibitors of mitochondrial NDH andsuccinate dehydrogenase, but not to antimycin A. The pool sizeof electrons that can be donated to P700⁺ from the cytosol throughthe intersystem chain increased with increasing duration ofillumination time by actinic light and was sensitive to rotenonein both wild-type cells and spheroplasts, but no such resultswere obtained in the NDH-defective mutant of Synechocystis 6803.The results support our previous conclusion that NDH is a mediatorof both respiratory electron flow and cyclic electron flow aroundPSI to the intersystem chain in the cyanobacterium Synechocystis. (Received August 20, 1993; Accepted November 22, 1993)     

Identification of Antheridic Acid as an Antheridiogen in Anemia rotundifolia and Anemia flexuosa

Antheridic acid was identified by retention time and full massspectra from GCMS analysis as an antheridiogen in Anemia rotundifoliaand A. flexuosa. In the dark spore germination assay, antheridicacid was active down to 10^–10 and 5 ? 10^–12g.ml^–1in A. rotundifolia and A.flexuosa, respectively. In the antheridiumformation assay, antheridic acid was active down to 10^–10g.ml^–1 in both A. rotundifolia and A.flexuosa (Received April 14, 1987; Accepted July 8, 1987)     

A Novel Carotenoid Ester, Loroxanthin Dodecenoate, from Pyramimonas parkeae (Prasinophyceae) and a Chlorarachniophycean Alga

A novel carotenoid ester, which had previously been assumedtentatively and without full supporting data to be loroxanthin19-dodecenoate (Kohata and Watanabe 1989), was isolated andpurified from cultured strains of Pyramimonas parkeae (Prasinophyceae)and a chlorarachniophycean alga. From spectroscopic and chemicalevidence, including results of analysis by ¹H-NMR, FD-MS, GLCand CD, the compound was clearly identified as loroxanthin dodecenoate,(3R,3'R,6'R)-ß,-carotene-3,19,3'-triol 19-(2-trans-dodecenoate).A double bond of the dodecenoate was located at the 12 positionand was in the trans form, as is the case for that in a siphonaxanthinester. However, loroxanthin itself was absent from these algae.Other algal pigments identified were Chls a and b, ß-carotene,lutein A, zeaxanthin, violaxanthin and neoxanthin. ³ Present address: Nippon Roche Research Center, Kajiwara 200,Kamakura, Kanagawa, 247 Japan.     

Cell-based imaging of sodium iodide symporter activity with the yellow fluorescent protein variant YFP-H148Q/I152L

The sodium iodide symporter (NIS) mediates iodide (I^–) transport in the thyroid gland and other tissues and is of increasing importance as a therapeutic target and nuclear imaging reporter. NIS activity in vitro is currently measured with radiotracers and electrophysiological techniques. We report on the development of a novel live cell imaging assay of NIS activity using the I^–-sensitive and genetically encodable yellow fluorescent protein (YFP) variant YFP-H148Q/I152L. In FRTL-5 thyrocytes stably expressing YFP-H148Q/I152L, I^– induced a rapid and reversible decrease in cellular fluorescence characterized by 1) high affinity for extracellular I^– (35 µM), 2) inhibition by the NIS inhibitor perchlorate, 3) extracellular Na⁺ dependence, and 4) TSH dependence, suggesting that fluorescence changes are due to I^– influx via NIS. Individual cells within a population of FRTL-5 cells exhibited a 3.5-fold variation in the rate of NIS-mediated I^– influx, illustrating the utility of YFP-H148Q/I152L to detect cell-to-cell difference in NIS activity. I^– also caused a perchlorate-sensitive decrease in YFP-H148Q/I152L fluorescence in COS-7 cells expressing NIS but not in cells lacking NIS. These results demonstrate that YFP-H148Q/I152L is a sensitive biosensor of NIS-mediated I^– uptake in thyroid cells and in nonthyroidal cells following gene transfer and suggest that fluorescence detection of cellular I^– may be a useful tool by which to study the pathophysiology and pharmacology of NIS. thyroid; fluorescence microscopy; FRTL-5 cells     

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)     

Size structures of microplankton biomass and production in Jiaozhou Bay, China

Seasonal investigations of size-fractionated biomass and productionwere carried out from February 1992 to May 1993 in JiaozhouBay, China. Microplankton assemblages were separated into threefractions: pico- (0.7–2 µm), nano- (2–20 µm)and netplankton (20–200 µm). The biomass was measuredas chlorophyll a (Chi a), paniculate organic carbon (POC) andparticipate organic nitrogen (PON). The production was determinedby ¹⁴C and ¹⁵N tracer techniques. The seasonal patterns in biomass,though variable, were characterized by higher values in springand lower values in autumn and summer (for Chi a only). Theseasonal patterns in production, on the other hand, were moreclear with higher values occurring in summer and spring, andlower values occurring in autumn and winter. Averaged over thewhole study period, the respective proportions of total biomassaccounted for by net-, nano- and picoplankton were 26, 45 and29% for Chi a, 32, 33 and 35% for POC, and 26, 32 and 42% forPON. The contributions to total primary production by net-,nano- and picoplankton were 31, 35 and 34%, respectively. Therespective proportions of total NH₄⁺–N uptake accountedfor by net-, nano- and picoplankton were 28, 33 and 39% in thedaytime, and 10, 29 and 61% at night. The respective contributionsto total NO₃^–-N uptake by net-, nano- and picoplanktonwere 37, 40 and 23% in the daytime, and 13, 23 and 64% at night.Some comprehensive ratios, including C/N biomass ratio, Chla/C ratio, C uptake/Chl a ratio, C:N uptake ratio and the f-ratio,were also calculated size separately, and their biological andecological meanings are discussed.     

Respiration-Dependent Proton and Sodium Pumps in a Psychrophilic Bacterium, Vibrio sp. Strain ABE-1

Respiration-dependent proton and sodium flows in a psychrophilicbacterium, Vibrio sp. strain ABE-1, were examined. At alkalinepH, this bacterium grew without being affected by a proton conductor,carbonylcyanide m-chlorophenylhydrazone (CCCP). O₂-pulse intoanaerobic cell suspensions prepared with Na^$-free buffers inducedtransient alkalization in the presence of CCCP and acidificationat pH 8.5 and 6.5, respectively. However, using cells preparedwith Na^$-containing buffer, the transient pH changes of thecell suspension could be simultanously detected at both pHs.Several inhibitory experiments suggested that the acidificationand alkalization should be attributed to a respiration-dependentprimary H^$ pump and Na^$ pump, respectively, and that the latterwas similar to that first reported in a marine bacterium, Vibrioalginolyticus. This Na^$ pump may have supported the CCCP-resistantgrowth at alkaline pH. The H^$ and Na^$ pumps operated very actively at low temperatures,such as 5?C, and should markedly help sustain bacterial growthat low temperatures. (Received May 30, 1987; Accepted November 13, 1987)     

Potassium Transport Across the Membranes of Chara: I. THE RELATIONSHIP BETWEEN RADIOACTIVE TRACER INFLUX AND ELECTRICAL CONDUCTANCE

Smith, J. R., Smith, F. A. and Walker, N. A. 1987. Potassiumtransport across the membrane of Chara. I. The relationshipbetween radioactive tracer influx and electrical conductance.—J.exp. Bot. 38:731–751. The ⁴²K influx () and the electrical conductance (G_m) were measured simultaneously for the ‘membrane’of internodal cells of Chara australis as a function of theexternal [KCl] (K?. In bathing solutions of pH = 5?0, progressively increased from 20?5to 430?60 nmol m^–2 s^–1 and G_m increased from 0?36?0?02to 3?8?0?8 S m^–2 when K? was increased from 0?1 to 10mol m^–3. The resting membrane potential difference (p.d.)was approximately -135 mV for low K? and approached the expectedNernst equilibrium p.d. for K⁺ ions when K? > 1?0 mol m^–3.Measurements of ³⁶Cl influx suggested that the ⁴²K influx waspredominantly electrogenic. The equivalent Goldman permeabilityto K⁺ ions (P_k) was approximately 20–30 nm s^–1 anddid not vary significantly with increasing K?. The equivalentconductance attributable to the electrogenic transport of K⁺ ions was calculated from assuming passive, independent diffusionof K⁺ ions and the ratio was found to be typically close to one. It was also found that themagnitudes of and G_m measuredsimultaneously for each individual cell were also well correlatedfor K? 1?0 mol m^–3, and that the slope of the line ofbest fit was close to one. For each K? it was found that theconductance not attributable to K⁺ translocation and presumablyassociated primarily with the transport of protons or theirequivalents was typically 0?2–0?5 Sm^–2. For K? >1?0 mol m^–3 the results indicated that the transport ofK⁺ ions was essentially independent, i.e. there was no evidencefor flux interactions. The results also indicated that the equivalentconductance derived from the measured ⁴²K influx could usefullyindicate the fraction of the electrical conductance attributableto the translocation of K⁺ ions. Key words: Potassium, conductance, influx     

Nuclear and Cell Sizes in Different Regions of Root Meristems of Zea mays L.

Nuclear volumes and cell areas were determined for seven regionsof the meristem of roots of Zea mays. Roots were fixed in 10per cent neutral buffered formalin, in 3 per cent glutaraldehydeor in acetic acid/alcohol; they were prepared as sections oralls were teased apart. Mean volumes of interphase nuclei weresimilar in all regions of the root except the vascular tissueof the stele. Mean nuclear volumes and the overall range ofvolumes were similar in sub-populations of cells with differentproportions of G¹, S and G² cells, e.g. in row I of root capinitials, whose cells lack a G¹ phase, and in quiescent centrecells, which are mainly in G¹. Nuclear volume does not appearto be closely correlated with DNA content. Nuclear volumes covereda 6 to 12-fold range within a meristem and even within specificregions, in which cells are part of the same cell lineages,there was a 4- to 9-fold range. Nuclear volumes were comparedin sister cells in rows I and II of the root cap initials. In10 per cent of the pairs, sister nuclei had identical volumes;the other pain had different volumes and mean difference was68 µm³. Mechanisms by which this variability could begenerated are discussed, particularly asymmetry, at mitoses,of factors that regulate nuclear growth. Zea mays L., nuclear volume, cell size, root mcristem, DNA content, mitosis     

Methionine as a Dominant Precursor of Phytosiderophores in Graminaceae Plants

Nine ¹⁴C-labeled amino acids and ¹⁴C-acetic acid from root tipsof Fe-deficient Graminaceae plants (Hordeum vulgare, Oryzaesativa and Avena saliva) were surveyed to determine the precursoramino acid of phytosiderophores. The dominant precursor wasmethionine, which was incorporated into avenic acid deoxymugineicacid mugineic acid epihydroxymugineic acid and/or hydroxymugineicacid in this order. Methionine sulfoxide or methionine sulfonemay be important intermediates in going from methionine to avenicacid. (Received May 6, 1987; Accepted June 12, 1987)     

Oxidative Damages and Repair in Euglena gracilis Exposed to Ozone. I. SH Groups and Lipids

Malondialdehyde, a product of lipid oxidation, increased graduallywhen Euglena gracilis cells were bubbled with 240 µ1.liter^–1ozone (delivery rate of 1µmolO₃.min^–1) for 120 min.Simultaneously, the sulfhydryl group content decreased by 36%during the treatment, which was mainly due to oxidation of proteinsulfhydryl groups. The molar amount of SH groups oxidized was3 times higher than that of fatty acid oxidized, indicatingthat sulfhydryl groups were more accessible or more easily oxidizedby O₃ than fatty acids. When Euglena cells were allowed to recoverunder autotrophic growth conditions following O₃ treatment,viable cells were incapable of dividing during the first 5 hof the recovery period but regenerated SH groups nearly to thecontrol level. The increase of SH content during this periodpreceded the resumption of cell division and the restorationof normal growth. These results suggest that the regenerationof SH groups by Euglena cells is a part of a mechanism involvedin the repair of oxidative damage caused by ozone and is anessential step for the initiation of cell division. (Received July 20, 1987; Accepted December 14, 1987)     

Transport and Fixation of Inorganic Carbon during Photosynthesis in Cells of Anabaena Grown under Ordinary Air: III. Some Characteristics of the HCO3--Transport System in Cells Grown under Ordinary Air

In cells of cyanobacterium Anabaena variabilis grown under ordinaryair (low-CO₂ cells), the transport of both CO₂ and HCO₃^–was significantly enhanced by Na⁺. This effect was pronouncedas the external pH increased. When low-CO₂ cells were treatedwith an inhibitor of carbonic anhydrase (CA), only CO₂ transportbut not HCO₃^– transport, was inhibited. The initial rateof photosynthetic carbon fixation as a function of the concentrationof internal inorganic carbon (IC) was practically the same irrespectiveof whether CO₂ or HCO₃^– was externally supplied. Theseresults suggest that IC is actively transported through theplasma membrane in a form of HCO₃^– probably by some transporterand that the transmembrane Na⁺ gradient is involved in thisIC transport system. Free CO₂ may be hydrated by CA to HCO₃^–and then transported to the cells by this transporter. On the other hand, CO₂ is actively taken up by cells grown withair containing 5% CO₂ (high-CO₂ cells) though the enhancingeffect of Na⁺ was much smaller in high- CO₂ cells than in low-CO₂cells. The initial rate of fixation as a function of internal IC concentrationindicated that the rate of the carboxylation reaction of accumulatedIC is higher in I0W-CO₂ cells than in high-CO₂ cells. The studieswith ethoxyzolamide indicated that even in low-CO₂ cells, CAdoes not function inside Anabaena cells. These results suggestthat inside the low-CO₂ cells of Anabaena, some mediator(s)facilitates the transport of IC to RuBPCase. (Received January 23, 1987; Accepted April 24, 1987)     

Specific Inhibition of Electron Transfer for Nitrate Reduction by a Low Concentration of Cyanide in Rhodobacter sphaeroides f. s. denitrificans

The effects of cyanide on the electron flow in NO₃^– andNO₂^– reductions and photosynthetic electron transfer wereinvestigated with intact cells of a photodenitrifier, Rhodobactersphaeroides f. s. denitrificans. In the presence of 30 µMKCN, electron transfer for NO₃^– reduction was inhibitedby about 70% and the concomitant H translocation was completelyinhibited. However, neither NO₂^– reduction nor photosyntheticcyclic electron transfer was affected at 30 µM. Theseresults suggested that the electron transfer pathway to NO₃^–has, in addition to a b-type cytochrome and the nitratereductase,a component sensitive to a low concenration of cyanide whichis not involvedin the cytochrome bc₁ complex. (Received April 13, 1987; Accepted July 23, 1987)     

Regulation of Tubulin Degradation in Isolated Zinnia Mesophyll Cells in Culture

Tubulin degradation in isolated Zinnia mesophyll cells in culturewas investigated by pulse-chase labeling with [³⁵S]-methionineand two-dimensional electrophoresis. Tubulin degradation changesdynamically during culture. Almost no tubulin degradation occursin the cells on the first day in culture. Treatment of thesecells with colchicine activates the degradation of tubulin,but not of proteins other than tubulin. In the presence of colchicine,the and ß-subunits of tubulin are degraded togetherand the half life of each subunit is approximately 6 h. After2 d in culture, there is active degradation of tubulin evenin the absence of colchicine. Colchicine did not inhibit new synthesis of tubulin in Zinniacells. This is very different from the results reported in culturedmammalian cells, whereby unpolymerized tubulin elevated by colchicine-treatmentdepresses its own synthesis. These and previous results dealing with changes in the leveland synthesis of tubulin in cultured Zinnia cells (Fukuda 1987),are discussed in relation to the regulation of tubulin metabolismin cultured Zinnia cells. ¹Present address: Biological Institute, Faculty of Science,Tohoku University, Aoba-yama, Sendai, 980 Japan. (Received September 5, 1988; Accepted December 20, 1988)