Current Genetics(1982) 6:129-135

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© Springer-Verlag 1982

Light and Benzylaminopurine Induce Changes in Ultrastructure and Gene Expression in Plastids of Petunia hybrida Cell Cultures C. M. Colijn, P. Sijmons, J. N. M. Mol, A. J. Kool, and H. J. J. Nijkamp Department of Genetics,BiologicalLaboratory,Vrije Universiteit,Post Box 7161, NL-1007 MC Amsterdam,The Netherlands

Summary. The regulatory effect of light and the cytokinin 6-benzylaminopurine (BA) on the plastid ultrastructure and plastid DNA gene expression is studied in white and mutant green cell suspension cultures o f Petunia hybrida. By electron microscopy we show that both light and 6-benzylaminopurine induce the formation of thylakoid membranes and grana structures in plastids of the green cultures. For membrane formation in plastids of white cultures, light in combination with BA is required. Light and benzylaminopurine also influence the plastid DNA gene expression. By in-organello protein synthesis with isolated plastids we show that light as well as benzylaminopurine affects the synthesis of plastid DNA encoded proteins. A characteristic effect of benzylaminopurine on plastids from white and green cultures is the reduction in the synthesis of the CF1 subunitsof55,000 and 57,000 D, and the reduction in the synthesis of large polypeptides with a molecular weight higher than 67,000 D. In contrast to benzylaminopurine, light only affects the DNA gene expression of plastids from white cell cultures, that are in a very early stage of plastid development. Light stimulates the synthesis of polypeptides with a molecular weight of 84,000, 70,000 and 46,000 D which are encoded by cpDNA in these white culture plastids. In green cell cultures both plastids with a etioplast-like phenotype and with a chloroplast-like morphology synthesize similar polypeptides, resulting in the same polypeptide pattern. Our results indicate that qualitative differences in plastid DNA gene expression as an effect of light do occur but only in plastids at very early stages of chloroplast development. We observe a gradual Abbreviations: LSU of RuBPCase: large subunit of Ribulose-1,

5-bisphosphate carboxylase, CF1: couplingfactor of.the ATPase complex, LCH: chlorophyll a/b protein, BA: 6-benzylaminopurine, cpDNA: chloroplast DNA Offprint requests to: A. J. Kool

reduction in the number of high molecular weight polypeptides at later stages of chloroplast development. This suggests that these large polypeptides are characteristic for plastids at an early developmental stage. Key words: Petunia hybrida - Cell cultures - Plastid gene expression - Protein synthesis

Introduction

Chloroplast development is controlled by a complex interplay of both chloroplast and nuclear genes (see review by Gillham 1978, Reinert 1980 and Ellis 1981). Light induces prominent changes in the structure and function of plastids during transition of etioplasts to chloroplasts. Under different light conditions the process of chloroplast biogenesis results in the appearance of various distinct chloroplast types which differ in ultrastructure, chlorophyll content and photosynthetic activity (Lichtenthaler and Buschmann 1978; Racio et al. 1979; Dubertret and Lefort-Tran 1981; Lichtenthaler et al. 1981). Light controls these changes in different ways: e.g., the amount of the NADPH protoctflorophyllide oxidoreductase mRNA in barley is diminished in the light. This means that the synthesis is negatively controlled by light (Apel 1981; Santel and Apel 1981): In contrast, positive control by light is observed in the expression of several nuclear genes coding for plastid proteins such as the small subunit of RuBPCase (SSU) and the chlorophyll a/b protein (LHC) (Apel 1979; Cuming and Bennet 1981 ;Sasaki et al. 1981 ; Smith and Ellis 1981 ; Tobin 1981aand b). In these cases, light increases the amounts of translatable mRNA. Light also positively controls the expression of several chloroplast DNA encoded proteins e,g. the large subunit of RuBPCase (LSU) and the 32,000 dalton chloroplast 0172.8083/82/0006/0129/$ 01.40

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C.M. Colljn et al.: Effects of Light and BA on Plastids in Petunia hybrida Cells

membrane protein (Bedbrook et al. 1978; Reisfeld et al. 1978; Smith and Ellis 1981 ; Link 1982). Cytokinins can also influence the ultrastructure and chlorophyll content of plastids (Seyer et al. 1975; Naito et al. 1981; Buschmann and Lichtenthaler 1982; Lew and Tsuji 1982). Axelos and P6aud-Leno61 (1980) showed that in tobacco suspension cells cytokinin affects the synthesis of a nuclear DNA encoded chloroplast protein: the chlorophyll a/b protein (LHC). In this paper we describe the effects of light and the cytokinin 6-benzylaminopurine on the chloroplast ultrastructure in suspension cultures of Petunia hybrida, and furthermore, we demonstrate that benzylaminopurineand light can qualitatively and quantitatively affect the expression of plastid genes.

Matermls and Methods

Tissue Cultures. A white cell suspension culture (AK-1000) of Petunia hybricla was derived from PZ 505 D 1 (Colijn et al. 1979). A green mutant cell suspension culture (AK-2401) of Petunia hybrida was selected from a white cell suspension culture AK2000. This culture was derived from PZ 5407-2 (Colijn et al. 1982a). Callus initiation was performed as described previously (Colijn et al. 1979). The cell suspension cultures were grown in Murashige and Skoog medium (1962) supplemented with 2,4dichlorophenoxyacetic acid (2,4-D, 0.5 pg ml- I ) and sucrose (10 g 1-1). The cultures were grown at 26 °C and 60% relative humidity under fluorescent light (Philips no. 33) at 3,000 lx using a light/dark cycle of 18/6 h. They were diluted ten fold every week. Greening of the white AK-1000 culture was performed by the addition of 6-benzylaminopurine (1 #g m1-1) to the culture medium. A yellow-green mutant Petunia hybrida plant E 5059 and the wild-type Petunia hybricla plant Roter Vogel R27 are described previously (Colijn et al. 1982b). Chlorophyll content was estimated according to Arnon (1949).

Electron Microscopy. Suspension cells were washed in a buffer containing 67 mM phosphate, 4 mM MgC12and 29 mM sucrose. The cells were embedded at 40 °C in the same buffer supplemented with 2% agar. The agar blocs containing the suspension ceils were immediately fixed in 2% glutaraldehyde for 1 h at 4 °C and subsequently in 1% osmium tetroxide for 2 h at 4 °C. The blocs were dehydrated to absolute ethanol and embedded in epon. Ultrathin sections were prepared with a diamond knife, stained with lead citrate and examined in a Philips EM 300.

ln-organello Protein Synthesis. All operations were performed at 0 - 4 °C. Suspension cells were washed 3 times with 20 mM KC1/5 mM diaminetetra acetic acid (EDTA), and once with 20 mM KC1 on a scintered glass filter. The cells were mixed with I00 ml GR medium (Morgenthaler et al. 1975) and gently disrupted in a Polytron homogenizer. The homogenate was filtered through nylon nettings of 140, 80 and 30/~m. The filtrate was centrifuged at 270 g for 10 rain. The resulting supernatant was centrifuged at 2,500 g for 5 rain and the plastid pellet was resuspended with a paint brush in incubationmedium containing50 mM Tricine-KOH pH 8.3, 10 mM MgC12, 14 mM 2-mercaptoethanol, 80 mM NH4C1 supplemented with 2 mM ATP, 0.2 mM GTP, I0 mM creatine phosphate, and 200 gg/ml creatine phosphokinase (Colijn et al. 1982a). This plastid suspension was incubated for 60 min at 20 °C

in the presence of 35S-methionine (spec. activity 22.1012 Bq mmol-1, Radiochemical Centre, Amersham, U.K.). The plastids were spun down at 10,000 g for 1 s and resuspended in sample buffer (62.5 mM Tris-HC1pH 6.8, 2% SDS, 5% 2-mercaptoethanol, 10% glycerol). 35S4abeled proteins were separated on 12.5% potyacrylamide slab gels using the buffer system described by Laemmli (1970). The polypeptides were stained with Coomassie Brillant Blue and visualized by fiuorography as described by Bonnet and Laskey (1974).

Immunoprecipitation 'Procedure. Immunoprecipitation of CF 1 subunits from the 3SS-labeled polypeptides synthesized in the in-organello protein system was carried out as follows: Plastids were spun down at 10,000 g for 5 s. The pellet was resuspended in 50 ~1 of 1% SDS, boiled for 2 min and centrifuged at 20,000 g for 5 min. The supernatant was diluted ten times in 50 mM TrisHC1 pH 7.4, 5 mM EDTA, 150 mM NaC1, 0.05% Triton X-100. Antiserum raised against the CF 1 subunits ofSpirodeia oligorhiza (a generous gift of H. de Hey, Vrije Universiteit, Amsterdam, The Netherlands) was added and the mixture was incubated for 2 h at 20 °C. After addition of 2 mg of Sepharose-protein A (Pharmacia) and incubation for 1.5 h at 20 °C the antigen-antibody complex was spun down at 10,000 g for 1 min. The pellet was washed once in 50 mM Tris-HC1pH 7.4, 5 mM EDTA, 1 M NaC1, 1% Triton X-100 and twice in 50 mM Tris-HC1pH 7.4, 5 mM EDTA, 150 mM NaC1, 1% Triton X-100. The pellet was resuspended in 30 ~/1 sample buffer (62.5 mM Tris-HC1 pH 6.8, 2% SDS, 5% 2-mercaptoethanol 10% glycerol), and boiled for 2 min. This sample was analyzed on an SDS-polyacrylamide slabgel (Laemmli 1970).

Results

The Effect of Light and Benzylaminopurine on Plastid Ultrastructure Light and cytokinins influence the ultrastructure of plastids in leaves and tissue cultures (Seyer et al. 1975; Lichtenthaler and Buschmann 1978; Naito et al. 1981). Several groups have shown that in tissue cultures of Nicotiana tabacum and Streptanthus tortuosus, cytokinins induce chloroplast differentiation during the stationary phase and not during exponential growth (Stetler et al. 1965; Sj olund and Weier 1971 ; Seyer et al. 1975). To confirm and extend these observations, we studied the effect of light and 6-benzylaminopurine(BA) on plastid morphology in petunia cells. For this purpose, we grew a white (AK-1000) and green (AK-2401) suspension culture of Petunia hybrida to the stationary phase (10 days after subculturing) und studied plastid ultrastructure b y electron microscopy. The results of these experiments on white tissue (AK-1000) plastids are shown in Fig. 1 Plastids present in light-grown white cultures contain large amounts of starch with some occasional thylakoid4ike structures (Fig. 1A). Similar plastid structures are observed in darkgrown white cultures (Fig. 1B), indicating that light does not cause any visible change in plastid ultrastructure. Growth in a combination of light and BA (1 /~g m1-1) results in greening of the white AK-1000 culture. The

C. M. Colijn et al.: Effects of Light and BA on Plastids in Petunia hybrida Cells

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Fig. IA-D. Electron micrographs of AK-1000 plastids. The cultures were grown: in the light A, in the dark B, in light in the presence of BA C, in the dark in the presence of BAD. Bar = 0.5 #m

plastids in this culture are partially differentiated chloroplasts, they contain a lot of thylakoid membranes and some appressed membranes (Fig. 1C). BA fails to induce thylakoid development and chlorophyll synthesiswhen the white AK-1000 culture is grown in the dark (Fig. 1D), indicating that only a combination of light and BA stimulates the formation of thylakoids and greening of the white culture. Figure 2 illustrates the effect of light and BA on plastid morphology in the green AK-2401 cell cultures. The plastids of the light-grown AK-2401 cell culture have a chloroplast-like phenotype; they contain a large amount of thylakoid membranes with grana structures (Fig. 2A). The plastids of the dark-grown AK-2401 culture have an etioplast-like phenotype; they contain numerous thylakoid membranes with only a few appressed membranes and a prolamellar body (PLB) (Fig. 2B). Addition of BA (1 pg ml-1) to the light-grown culture causes enlargement of the grana, resulting in broader grana stacks (Fig. 2C). Addition of BA to the dark-grown AK-2401 cultures results in the formation of a chloroplast-like phenotype of the plastids (Fig. 2D), which resembles the plastid

morphology of the light-grown AK-2401 cell cultures (Fig. 2A). This result suggests that light and BA have the same effect on plastid morphology in this green cell culture; both induce the formation of grana structures.

The Effect of Light and Benzylaminopurine on Poly. peptide Synthesis in Isolated Plastids The synthesis of chloroplast proteins requires the coordinated activities of both nuclear and plastid systems (Ellis 1981). Light controls the synthesis of several chloroplast and nuclear DNA encoded plastid proteins (Bedbrook et al. 1978;Ape11979;Smith and Ellis 1981 ;Tobin 1981 ; Link 1982). Axelos and P6aud-LenoOl (1980) have shown that cytokinin affects the synthesis of the nuclear DNA encoded chlorophyll a/b protein. To determine whether not only light but also BA can affect the expression of chloroplast DNA encoded genes, we performed inorganello protein synthesis in the presence of 3SS-methionine with plastids isolated from light- and dark-grown AK-1000 and AK-2401 cultures grown in the presence

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C.M. Colijn et al.: Effects of Light and BA on Plastids in Petunia hybrida Cells

Fig. 2A-D. Electron micrographs of AK-2401 plastids. The AK-2401 suspension cultures were grown: in the light A, in the dark B, in light in the presence of BA C, in the dark in the presence of BAD. Bar = 1 tzrn.The arrow in panel B indicates the prolamellarbody

and absence of BA. 35S-methionine labeled polypeptides synthesized by these plastids were separated on polyacrylamide slab gels. The results of these experiments are shown in Fig. 3. Plastids fromlight- and dark-grown white AK-1000 suspension cells synthesize two polypeptides of 57,000 and 21,000 D respectively in large amounts (Fig. 3A, lane 1 and 2). Plastids from the light-grown culture synthesize six to eight polypeptides with high molecular weight (> 67,000 D). Three polypeptides with a molecular weight of 84,000, 70,000 and 46,000 D are specifically synthesized by plastids from the light-grown AK-1000 culture, and are hardly detectable in plastids from the dark-grown AK-1000 culture (Fig. 3A, lane 1 and 2). This suggests that light specifically stimulates the synthesis of the three above-mentioned polypeptides. The synthesis of the LSU of RuBPCase, which has a molecular weight of 52,000 D (Colijn et al. 1982b), is hardly detected in these plastids (observed by immunoprecipitation, results not shown). Growth of these cell cultures in light and in the presence of BA results in a decreased synthesis of polypeptides with a molecular weight of 84,000, 70,000 and 46,000 D. Also the amount

of the polypeptide with a molecular weight of 57,000 D is strongly diminished (Fig. 3A, lane 3). By immunoprecipitation this polypeptide band is identified as a component of the coupling factor of the ATPase complex (¢F1) (Fig. 3A, lane 4). The addition of BA also causes a stimulation in the synthesis of one or more polypeptides with a molecular weight in the range from 27,000-34,000 D (Fig. 3A, lane 3). One of these polypeptides could very well be the 32,000 D membrane polypeptide identified by Reisfeld et al. (1978). The effect of light and BA on the polypeptide synthesis by plastids isolated from the green AK-2401 cell cultures is shown in Figure 3B. Plastids from light- and dark-grown AK-2401 cultures synthesize identical polypeptides (lane 5 and 6), however, the overall synthesis is decreased by a factor of 2 in dark-grown AK-2401 plastids (not shown). Three polypeptides with a high molecular weight of 135,000, 115,000 and 95,000 D are observed. Two prominent bands of 57,000 and 55,000 D that are synthesized in both plastid types, were identified as subunits of the CF1 (Fig. 3B, lane 8, the immunoprecipitated bands overlap). The synthesis of these polypeptides is

C. M. Colijn et al. : Effects of Light and BA on Plastids in Petunia hybrida Cells

133

Fig. 3. Effects of light and BA on the synthesis of 35S-labeled polypeptides by isolated plastids. Fluorogram of translation products and immuno-precipitates. Inputs: 10 s cpm TCA-precipitable material per slot. Panel A: AK-1000 grown in the light (lane 1), grown in the dark (lane 2), grown in the light in the presence of BA (lane 3). Immunoprecipitation of CF 1 from translation products of lane 1, (lane 4). Panel B: AK-2401 grown in the light (lane 5), grown in the dark (lane 6), grown in the light in the presence of BA (lane 7). Immunoprecipitation of CF 1 from translation products of lane 5, (lane 8). Panel C: white mutant Petunia hybrida plant (lane 9), wildtype petunia plant (lane 10)

descreased when the culture is grown in the light in the presence of BA and in addition, the synthesis of the polypeptide with a molecular weight of 95,000 D is decreased (Fig. 3B, lane 7). The inhibitory effect of BA on the synthesis of the CFt subunits and on the synthesis of the high molecular weight polypeptides is also observed in the white AK-1000 culture plastids. The data mentioned above indicate that both light and BA influence the expression of plastid DNA encoded genes. The proplastid stage and the synthesis of polypeptides with a high molecular weight is not specific for plastids from white suspension cultures but is also found at the plant level. The results mentioned above resemble those obtained from a yellow-green leaf mutant (Colijn et al. 1982b). The plastid morphology of these yellowgreen leaf plastids resembles the one of the AK-1000 plastids; only a few thylakoid structures are observed (Colijn et al. 1982b). The yellow-green leafplastids also synthesize polypeptides with a high molecular weight of 135,000, 105,000, 95,000, 84,000 and 72,000 (Fig. 3C, lane 9), which are absent in chloroplasts from wild-type petunia plants (Fig. 3C, lane 10). Furthermore, we observe the synthesis of polypeptides with a molecular weight of 27,000-33,000 D in the yellow-green leafplastids. These results indicate that concerning plastid morphology and

DNA gene expression the yellow-green leaf plastids resemble the plastids isolated from the light-grown AK-1000 cultures and those from the AK-1000 cultures grown in the light in the presence of BA. Most of the high molecular weight polypeptides (> 67,000 D) that are synthesized in plastids from the white AK-1000 culture and from the yellow-green leaf mutant are no longer synthesized in more mature plastids such as the plastids from light-grown AK-2410 cells or the wild-type leaf chloroplasts. This suggests that the synthesis of these polypeptides is characteristic for an early stage of chloroplast development.

Discussion In this paper we have analyzed the effects of light and benzylaminopurine (BA) on plastid morphology and plastid DNA gene expression. For this purpose we have used a white and a green cell suspension culture of Petunia hybrida. Several authors describe the stimulation of chlorophyll synthesis in the presence o f a cytokinin (Seyer et al. 1975; Lichtenthaler and Buschmann 1978; Buschmann and Lichtenthaler 1982; Lew and Tsuji 1982). Petunia cell

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C.M. Colijn et al.: Effects of Light and BA on Plastids in Petunia hybrida Ceils

cultures are able to grow in the presence of an auxin without the addition of a cytokinin. However, for greening of the culture a cytokinin is required. The mutant petunia cell culture AK-2401 is green also without the addition of a cytokinin to the culture medium and therefore, we suggest that in these green cells the genes involved in the synthesis of cytokinin are, at least in part, derepressed resulting in the synthesis of chlorophyll. Light in combination with BA not only changes the ultrastructure of the white AK-1000 plastids, but also the radioactive polypeptide pattern obtained after in-organello protein synthesis with these isolated plastids. The pattern thus obtained resembles the one obtained from green AK-2401 plastids. Both polypeptide patterns are characterized by prominent synthesis of polypeptides with a molecular weight of 27,000-34,000 D, and by diminished synthesis of polypeptides of 84,000, 70,000 and 46,000 D. The number of high molecular weight polypeptides synthesized by isolated plastids decreases as chloroplast development proceeds: In plastids from the light-grown white AK-1000 cultures six to eight high molecular weight polypeptides are synthesized while in the presence of BA this amount is diminished to four. In plastids of light-grown green AK-2401 cultures we observe the synthesis of only two or three high molecular weight polypeptides. In AK-2401 plastids from cells grown in the light in the presence of BA polypeptides larger than 67,000 D are not detectable. Proplastid stages of chloroplast development are not only present in cells from suspension cultures but also in leaves of a yellow-green mutant plant E 5059 of Petunia hybrida (Colijn et al. 1982). Proplastids isolated from this mutant synthesize five polypeptides with a molecular weight of 135,000, 105,000, 95,000, 84,000 and 72,000 D which are not synthesized in mature chloroplasts (Fig. 3c). This indicates that the synthesis of these high molecular weight polypeptides is specific for the proplastid stages of chloroplast development and that qualitative differences of plastid DNA gene expression occur during the various stages of chloroplast biogenesis. Siddell and Ellis (1975) observed that there is no qualitative difference in plastid DNA gene expression between etioplasts and chloroplasts of pea;only the overall synthesis in isolated etioplasts is lower. Similar results are obtained for plastids isolated from light-grown and dark-grown AK-2401 cultures; In the dark the plastids have an etioplast-like phenotype, whereas in the light these plastids have a chloroplast-like morphology. Both plastid types synthesize identical p olypeptides,indicating that light does not cause qualitative differences in gene expression in these plastid types. On the other hand, we observed that plastids from the light-gown AK-1000 culture synthesize several polypeptides of high molecular weight, which are not synthesized by plastids from the AK-1000 culture grown in the dark. Therefore, we

conclude that light can cause qualitative differences in plastid DNA gene expression, but only in plastids at a very early stage of chloroplast development. Our future research is focussed on the identification of these high molecular weight polypeptides. These polypeptides could be either precursors ofpolypeptideswhlch are also synthesized in mature chloroplasts, or they represent polypeptides that are only synthesized and required at an early stage of chloroplast development. Furthermore, additional experiments are required to find out whether light and BA affect the plastid DNA gene expression at the transcriptional or translational level, and whether these differences in gene expression could be correlated with the ob served changes in plastid ultrastucture.

Acknowledgement. We thank Mrs. Rita Divendal and Dr. E. W. Roubos (Department of Histology, Vrije Universiteit, Amsterdam) for their help and advice with electron microscopic techniques.

References Apel K (1979) Eur J Biochem 97:183-188 Apel K (1981) Eur J Biochem 120:83-93 Arnon DJ (1949) Plant Physiol 14:1-15 Axelos M, P6aud-Leno~l C (1980) Plant Sei Lett 19:33-41 Bedbrook JR, Link G, Coen DM, Bogorad L, Rich A (1978) Proc Nail Acad Sci USA 75:3060-3064 Bonnet WM, Laskey RA (1974) Eur J Biochem 46:83-88 Buschmann C, Liehtenthaler HK (1982) Photochem Photobiol 35:217-221 Colijn CM, Kool AJ, Nijkamp HJJ (1979) Protoplasma 99:335340 Colijn CM, Kool AJ, Nijkamp HJJ (1982a) Planta 155:37-44 Colijn CM, Mol JNM, Kool AJ, Nijkamp HJJ (1982b) (submitted) Cuming AC, Bennett J (1981) Eur J Biochem 118:71-80 Dubertret G, Lefort-Tran M (1981) Biochem Biophys Acta 634: 52-69 Ellis RJ (1981) Ann Rev Plant Physiol 32:111-137 Gillham NW (1978) In: Organelle heridity. Raven Press, New York, pp 1-38 Laemmii UK (1970) Nature (London) 227:680-685 Lew R, Tsuji H (1982) Plant Physiol 69:663-667 Lichtenthaler H, Buschmann C (1978) In: Akoyunoglou G, Argyroudi-Akoyunoglou HJ (eds) Chloroplast development. Elsevier/North-Holland Biomedical Press, Amsterdam New York Oxford, pp 801-816 Lichtenthaler HK, Buscbmann C, Dt~ll M, Fietz HJ, Bach T, Kozel U, Meier D, Rahmsdorf U (1981) Photosynthesis Research 2:115-141 Link G (1982) Planta 154:81-86 Morgenthaler JJ, Marsden MPF, Price CA (1975) Arch Bioehem Biophys 168:289-301 Murashige T, Skoog F (1962) Physiol Plant 15:473-497 Naito K, Ueda K, Tsuji H (1981) Protoplasma 105:293-306 Ratio N, Casadoro G, di Chio L (1979) Protoplasma 100:45-52 Reinert J (1980) In: Reinert J (ed) Results and problems in cell differentiation, vol. 10. Springer, Berlin Heidelberg New York

C. M. Colijn et al.: Effects of Light and BA on Plastids in Petunia hybrida Cells Reisfeld A, Gressel J, Jakob KM, Edelman M (1978) Photochem Photobiol 27:161 - 165 Santel I-U, Apel K (1981) Eur J Biochem 120:95-103 Sasaki Y, Ishiye M, Sakihama T, Kamikubo T (1981) J Biol Chem 256:2315-2320 Seyer P, Marry D, Lescure AM, P6aud-Leno~l C (1975) Cell Diff 4:187-197 Siddell SG, Ellis RJ (1975).Biochem J 146:675-685 Sjolund RD, Weier TE (1971) Am J Botany 58:172-181 Smith SM, Ellis RJ (1981) J Mol Appl Genet 1:127-137

Stetler DA, Laetscha WM (1965) Science 149:1387-1388 Tobin EM (1981a) Plant Physiol 67:1078-1083 Tobin EM (1981b) Plant Mol. Biol 1:35-51

Communicated by F. Kaudewitz Received August 6, 1982

135

Light and benzylaminopurine induce changes in ultrastructure and gene expression in plastids of Petunia hybrida cell cultures.

The regulatory effect of light and the cytokinin 6-benzylaminopurine (BA) on the plastid ultrastructure and plastid DNA gene expression is studied in ...
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