Planta 141, 191- 198 (1978) Planta �9 by Springer-Verlag 1978

Phytochrome-Mediated Control of Grana and Stroma Thylakoid Formation in Plastids of Mustard Cotyledons

Claud ia Gi rn th , Ra ine r Bergfeld, and Helga K a s e m i r

Biologisches Institut II, Universitfit Freiburg, Sch/inzlestrage 1, D-7800 Freiburg, Federal Republic of Germany

A b s t r a c t . The e t i o p l a s t - ~ c h l o r o p l a s t t r ans i t ion in the co ty ledons o f m u s t a r d seedlings (Sinapis alba L.) has been s tud ied by e lec t ron microscopy . I t was found tha t the active fo rm of p h y t o c h r o m e , es tab l i shed by a red l ight pulse p re t r ea tmen t , increases the ini t ia l ra te and e l iminates the lag o f g rana and s t roma thyla- ko id f o r m a t i o n after the onset of white l ight 60 h af ter sowing. The effect of a p r e t r ea tmen t with 15 s red l ight pulses is fully revers ible by 756 n m light pulses. This revers ib i l i ty is lost within 5 min. Evidence is p resen ted which suggests tha t the t ime course o f g rana and s t roma t h y l a k o i d f o r m a t i o n is no t corre- la ted with the t ime course o f the dispersal of the p r o l a m e l l a r body . The different func t ions of phy to - ch rome and ch lo rophy l l in con t ro l l ing t h y l a k o i d f o r m a t i o n are discussed.

K e y words : C h l o r o p h y l l - C h l o r o p l a s t s - G r a n a - P h y t o c h r o m e - Sinapis - Thylako ids .

I n t r o d u c t i o n

Recent ly K a s e m i r et al. (1975) have shown tha t the active fo rm of p h y t o c h r o m e (Pfr) 1 con t ro l s the for- m a t i o n of in terna l s t ruc tures of e t ioplas ts in m u s t a r d co ty ledons . I t has been d e m o n s t r a t e d that Pfr leads to an en la rgemen t a n d to a h igher o rgan i za t i ona l s tate o f the p r o l a m e l l a r body under l ight cond i t ions which do no t a l low a con t inuous sa tu ra t ed p h o t o c o n v e r s i o n of p ro toch lo rophy l l ( i de ) to ch lo rophyl l ( ide ) a. In the present p a p e r we have ana lyzed whether Per acceler- ates the e t i o p l a s t ~ c h l o r o p l a s t t r ans i t ion when the p ro toch lo rophy l l ( i de ) ~ Chl2a convers ion is no longer l imited. Our a t t en t ion has been d i rec ted to the fo rma- t ion of g rana and s t roma thy l ako ids since bo th are charac te r i s t i c s t ructures o f m a t u r e ch loroplas t s .

1 Pfr: far-red absorbing, active form of phytochrome system 2 Chl: any chlorophyll species regardless whether it is chloro- phyll(ide) a or chlorophyll b

There are only a few pub l i ca t ions ind ica t ing a Pf r -media ted acce le ra t ion of the deve lopmen t of chlo- roplas ts . Wi th seedlings o f Phaseolus vulgaris (Kle in et al., 1964; Bradbee r et al., 1974) and ba r ley (Berry

and Smith, 1971) it has been found tha t red l ight fo l lowed by a da rk pe r iod increases the f o r m a t i o n o f in terna l p las t id m e m b r a n e s u p o n a second light t rea tment . However , a pa r t i a l fa r - red l ight revers ion of the red l ight effect as evidence for the ac t ion o f Pr was only de tec ted by B r a d b e e r et al. (1974).

In the presen t p a p e r a s t r ik ing effect o f Ply on the f o r m a t i o n o f g rana and s t roma thy l ako ids will be demons t r a t ed . Moreove r , it has been found tha t the effect o f Pfr on the f o r m a t i o n o f t hy lako ids can be sepa ra t ed f rom the effect o f Pf~ on the conf igu ra t ion o f the p r o l a m e l l a r body.

M a t e r i a l s and M e t h o d s

Seeds of Sinapis alba L. were purchased in 1969 from Asgrow Company, Freiburg, Germany. For experiments investigating the disintegration of the prolamellar body seeds from 1971 were used.

The seeds were spread in plastic boxes on moist chroma- tographic paper after being carefully washed with distilled water (Mohr, 1966). The 'time of sowing' was the moment when water was added to the seeds. The seedlings were grown at 25.0_+0.2 ~ C in the dark for 60 h after sowing. Thereafter they were illuminated with continuous white light at an illumination of 7000 lx (fluores- cent white light, Osram tubes, alternating L 40 W/15 and L 40 W/ 25).

Preirradiations were performed with standard red light (emis- sion maximum at 656nm, bandwidth 15nm, fluence rate 0.675 Wm 2), standard far-red light (emission maximum at 740 nm, bandwidth 123 nm, fluence rate 3.5 Wm -2) or with mono- chromatic light of higher fluence rates. This was obtained from a modified Leitz projector Prado 500 (Mohr and Schoser, 1959) equipped with appropriate filters.

The monochromatic red light was obtained with a plexiglass filter, PG 501/3 mm (R6hm& Haas, Darmstadt, Germany) com- bined with neutral glasses: 2-max 656 nm, bandwidth 15 rim, fluence rate 8.0 Wm 2. The long wave length far-red light (756 nm) was obtained with a PAL interference filter (Schott, Mainz, Germany) : 2m,x 756 nm, bandwidth 20 nm, fluence rate 9.2 Wm -2.

00 3 2-09 3 5/78/0141/0191/$01.60

192 C. Girnth et al. : Phytochrome-Mediated Thylakoid Formation

The pretreatments with light pulses were performed 36, 40, 44, and 48 h after sowing. Two different programs were used. Preirradiation program I: each pulse treatment consisted of 15 s red light (8.0 Wm 2) and/or 2 min 756 nm light (9.2 Wm 2). Preir- radiation program II: each pulse treatment consisted of 5 min stan- dard red light and/or 5 min standard far-red light.

Electron Microscopy

Fixation procedures were carried out on ice under dim green safe light. Pieces of cotyledons, approximately 1 mm in diameter, were fixed in 2% glutaraldehyde in 0.1 M phosphate buffer at pH 7.2 for 2 h at 4 ~ C. After several washings in phosphate buffer, the material was postfixed in 2% OsO4 for 2 h at 4 ~ C. Following dehydration in acetone, the tissue was embedded in araldite. Thin sections, cut with a Reichert ultramicrotome (OmU2, Reichert, Austria) were stained with uranyl acetate and lead citrate (Rey- nolds, 1963). For each treatment 4 portions of 25 different cotyle- dons were taken.

This procedure was repeated in 2 3 independent parallels. The mean values are based on data obtained from approximately 50 micrographs of plastids in mesophyll cells. The relatively small standard errors, represented by vertical bars in the Figures, indicate a high degree of uniformity among the plastids in the tissues exam- ined.

Definitions of the Evaluated Ultrastructures

For practical reasons we use the terms grana and stroma thylakoids as originally introduced by Menke (1962). This classification is based on the two-dimensional structures seen in the micrographs and does not consider the complicated three-dimensional models developed for the thylakoid system (Paollilo, 1970; Thomson, 1974). Stroma thylakoid: a double membrane which is at least two thirds as long as the plastid section. Granum: a thylakoid overlapping or stacking which is longer than the thickness of 2 thylakoids. Due to this definition even incipient grana were counted. Prolamellar body: an aggregation of tubular membranes irrespective of whether or not the arrangement is paracrystalline.

Results

Transition o f Etioplasts ~ Chloroplasts

The d e v e l o p m e n t of ch lo rop las t s was in i t ia ted by t rans fe r r ing m u s t a r d seedlings 60 h after sowing f rom d a r k into con t inuous white l ight ; thereaf te r the plas- t ids were ana lyzed dur ing 7 h of i l l umina t ion (Fig. l a - d ) . Wi th in the first 1 0 m i n of whi te l ight a r a p i d d i s in tegra t ion of the p r o l a m e l l a r b o d y cou ld be obse rved as i r id icated by the decrease of the n u m b e r of p las t id sect ions showing p ro l ame l l a r bod ies (Fig. 2a). Af te r 1 0 m i n this d i s in teg ra t ion proceeds m o r e slowly. Sixty min after the onset of white l ight ha l f o f the p las t id sect ions still con ta in p r o l a m e l l a r bodies . These p r o l a m e l l a r body r emnan t s r ema in for hours (Fig. 1 d, h) even in white l ight of a re la t ively high i l l umina t ion (28,0001x; Gi rn th , 1978).

A l t h o u g h the ini t ial p ro l ame l l a r body dispersal is very rapid , no s ignif icant changes at the t hy l ako id level cou ld be seen up to 1 h af ter the onset of white light. A t tha t t ime the n u m b e r of g rana star ts to increase (Fig. 2b) while there are a b o u t 4 s t roma thy- l ako ids up to 4 h (Fig. 2c). Two add i t i ona l s t roma thy l ako ids are f o r m e d be tween 4-7 h of i l luminat ion .

Response o f Grana Formation to a Light Pulse Pretreatment

Chlo rop l a s t deve lopmen t is acce le ra ted when the seedlings are p re t r ea t ed with 4 red l ight pulses equal ly d i s t r ibu ted be tween 36 and 48 h af ter sowing (Fig. 1 e h). The red l ight p r e t r e a tme n t increases the f o r m a t i o n of s t roma thy lako ids and grana. Fig. 3 shows the quan t i t a t ive eva lua t ions of the red l ight effect on the average n u m b e r of grana. Two var ious red l ight pulse p re t r ea tmen t s were given: 4 p u l s e s of 15 s each (Fig. 3 a) and 4 pulses of 5 min each (Fig. 3 b). In bo th cases the red l ight pulse p r e t r ea tmen t e l iminates the lag and increases the ini t ial ra te of g rana fo rmat ion .

The effect o f the p r e t r e a tme n t wi th 15 s red l ight pulses is fully revers ible by 756 nm light pulses (Fig. 3a). F r o m this resul t we can conc lude tha t the red l ight pulses act t h rough p h y t o c h r o m e (Mohr , 1977).

As ind ica ted by F igure 3 b there is a r ap id escape f rom revers ib i l i ty : the red l ight effect can no longer be reversed by pulses of fa r - red l ight when the length of each single pulse is ex tended to 5 min. F igure 3b shows ano the r in teres t ing fea ture : the n u m b e r of g rana is s t rongly affected by the p r e t r e a tme n t with 4 pulses of s t a n d a r d fa r - red l ight which p roduc e only a re la t ively smal l a m o u n t of Pfr (Mohr , 1977).

Pfr affects no t only the n u m b e r of g rana bu t also the g rana length. F igure 4 shows tha t the f requency d i s t r ibu t ion o f g rana length displays in pr inc ip le the same resul t as the t ime course o f g rana n u m b e r : a full escape f rom pho to revers ib i l i ty within 5 min and a sensit ive response to Pfr after a t r ea tmen t with 4 s t a n d a r d far - red l ight pulses.

Whi le the n u m b e r and length o f g rana are affected by Pfr, no specific response has been found with re- spect to the s tacking process. F igu re 5 shows a cont in- uous decrease in the f requency of g rana having 2 discs and a s imul taneous increase in the f requency of g rana having 3 and more discs. This process is i ndependen t of any l ight pulse p re t rea tment . Our result suppor t s the idea of a successive fo ld ing of m e m b r a n e po r t i ons on p r i m a r y thy lako ids to g rana s tacks (Wehrmeyer , 1966).

C. Girnth et al. : Phytochrome-Mediated Thylakoid Formation 193

Fig. la-h. Sections through plastids of mustard cotyledons after onset of white light 60 h after sowing, a d Etioplast - , chloroplast transformation : e ~ Development of chloroplasts after pretreating the seedlings with 4 x (5 min standard red light), see Methods. a and e Immediately before the onset of white light; b and f 1 h; c and g 4 h; d and h 7 h after the onset of white light

Response of Stroma Thylakoid Formation to a Light Pulse Pretreatment

I f the seed l ings a re p r e t r e a t e d wi th Pfr the p las t ids

inc rease the i r a v e r a g e n u m b e r o f s t r o m a t h y l a k o i d s

f r o m 4 to a p l a t e a u o f 6 w i th in 1 h (Fig. 6). W i t h o u t

Pfr six s t r o m a t h y l a k o i d s pe r p la s t id sec t ion a re n o t

r e a c h e d unt i l 7 h a f te r t he onse t o f wh i t e l ight . T h e

r e s p o n s e o f s t r o m a t h y l a k o i d f o r m a t i o n to Pfr seems

to be s imi la r to t ha t o f g r a n a f o r m a t i o n s ince the

194 C. Girnth et al, : Phytochrome-Mediated Thylakoid Formation

~ eq

~ 60 o "U o[~

"o E

20

o _ _ / + l i I 1 - - � 8 9 ; 4 ; [ h i 7 2~

c o g l S

"5 .,., 10

~as

44

l _ I l

4 5 [h] 7 I I +.+

2 ~ 6

ql 4,

E ~ 2 2

o

E

i I i I

1 2 - ; ~ ; [h+ ; t i m e a f t e r o n s e t o f w h i t e l i g h t

6 0 h e f t e r s o w i n g

Fig. 2a-c. Time course of etioplast ~ chloroplast transition. Onset of white light: 60 h after sowing. No light pretreatment

d

20

15 s red--~

15

10

g u

J

=T 1#5 rain r e d +

201- ~' 5 rain f o r - r e d

5 rain r e d

~, 15

E

c 10

5 ~ I

i

t i m e a f t e r o n s e t of w h i t e l i gh t (?O00tx)

60 h a f t e r s o w i n g

Fig. 3a and b. Time course of grana formation after the onset of white light 60 h after sowing, a Preirradiation program I ; b Preir- radiation program tI (see Methods)

o =

+5 eJ tn

o Q.

L 5

"B

J= E

'3 red

I~1~1 ~ - - ~ l , ~ - r ' T 7 1 2 3 4 5 6 7

red +756nm 756nm dark c o n t r o l

1 2 3 1 2 3 1 2 3 4[nm]x3~

p r o g r a m II

i r"r'~ i i I-i-I I ~ 1 2 3 4 5 6 7 1 2 3 4 " 5 6 1 2 3 4 5 [rim]x33

g r a n o l eng th c l a s s e s

Fig. 4. Frequency distribution of grana lengths. The grana lengths were measured 1 h after the transfer of dark-grown seedlings to continuous white light at 60 h after sowing. UpFer part: Preirrad]ation program I. Lower part: Preirradiation program II (see Methods)

escape from reversibility is also rapid (Fig. 6b). In contrast to the grana formation, standard far-red light pulses do not exert an increase over the dark control. It is remarkable that chloroplast development ceases as soon as the plastids have approximated the stage

of et io-chloroplasts after 7 h of white light i l lumina- tion. Thus, in the red light pretreated seedlings the format ion of new stroma thylakoids stops within 1 h while the deve lopment of grana ceases 4 h after the onset o f white light. After 7 h o f white l ight a develop-

C. Girnth et al. : Phytochrome-Mediated Thylakoid Format ion 195

E D

0

m o u~

o

c

D

100

9O

80

70

[%)

5O

CO

30

20

10

0

,, 2 d i s c s �9 \\\/

\ \

\

/ /

/ /

/

/ /

0 1 2 3

x \ t

" \ / . . / f f

/ \ \ \ O0~

/

,,IV" / \ / /

t I I I

/, 5 [h] 7

3 - 6 discs Z.-2 / j "

J t ime after onset of whi te t ight (7000 tx) 60 haf ter sowing

Fig. 5. Changes in the degree of grana stackings, Symbols with regard to the pretreatment with 4 l ight pulses: rn- , red light; zxA red+fa r - red light; o * , far-red light; o no light pretreatment. Filled symbols: program II (see Methods). Symbols with diagonal bars: grana with 3 6 discs. The lines are determined by the means of all respective values at any given time

-O~o ~// ~ / ~ 2 m i n 756nm

o_ / , ~ - i / < ~ , I~.._ 15 s red + 2mln 756nm

no l ight pretreotment u)

~ I t 1 I I I I 0

>, b

2

"S

b 5

E

Z /,I ~ ~,no tight pretreatment

~5 min far - red

0~ i I t I I I I

1 2 3 4 5 [h] 7 I time after onset of white t ight

60halter sowing

Fig. 6a and b. Time course of s t roma thylakoid formation after the onset of cont inuous white light 60 h after sowing, a Preirradia- tion program I. b Preirradiation program II (see Methods)

80

70

60

5O

o [%] C

~- 30 O0 L.

20

10

o ram p i a s l i d s w i th PLB

0 I 2 3 J time after

60 h a f te r sowing

o n s e t

a

I I 1 I

s [hl 7 of w h i t e t i g h t (7000 Ix)

Fig. 7. Time course of the dispersal of the prolamellar bodies (PLB) after the onset of white light 60 h after sowing. Preirradiation program I was used. Symbols are the same as those of Figure 6a. The curve is determined by the means of all respective values at any given time

196 C. Girnth et al. : Phytochrome-Mediated Thylakoid Format ion

mental acceleration of the red light pretreated seed- lings is hardly detectable (Figs. 3,5). These findings can be explained by the assumption that the Pf~ formed in white light will especially affect the mem- brane-forming capacity of previously etiolated seed- lings. Experiments with dichromatic irradiation (Girnth, 1978) support this interpretation.

Prolamellar Body Dispersal

It is a well-known fact that a great deal of the newly formed thylakoid membranes emerge from the disin- tegrating prolamellar body (Henningsen and Boyn- ton, 1969; Weier et al., 1970). In the present context the question arises whether Pfr increases the amount of grana or stroma thylakoids by accelerating the dispersal of the prolamellar body. Pertinent results are shown in Figure 7. After transferring the mustard seedlings 60 h after sowing from dark to continuous white light we determined the changes in the fre- quency of plastid sections without prolamellar bodies. This parameter seems to be a suitable gauge for the prolamellar body decay (Henningsen and Boynton, 1970). It is obvious from Figure 7 that the time course of the prolamellar body dispersal does not vary signi- ficantly after different light pretreatments.

From this result we may conclude that under our experimental conditions no correlation exists between the rate of grana and stroma thylakoid formation and the extent of the prolamellar body disintegration.

Structural Development and Chlorophyll Accumulation

Since the formation of chloroplasts requires Chl (Ar- gyroudi-Akoyunoglou etal . , 1976; Armond etal . , 1976) we have finally posed the question whether a relationship exists between the grana and stroma thy- lakoid formation and the accumulation of Chl after the onset of continuous white light. To study this question the kinetics of ultrastructural development have been compared with the kinetics of Chl accumu- lation (Fig. 8). It has been found that without any light pretreatment the time course of grana formation is similar to the time course of Chl accumulation (Fig. 8a). However, such a correlation does not exist in the red light-pretreated mustard seedlings (Fig. 8 b), where the number of grana increases more rapidly than the Chl content. This discrepancy occurs al- though Pfr also accelerates the Chl accumulation (Kasemir et al., 1973).

Under all experimental conditions the time course of stroma thylakoid formation differs greatly from the time course of Chl accumulation (Fig. 8a, b).

E 0

~l > 0J

O .

0

0

t~

100 - -" ~ Y [%3 a I s f roma -

80- thy{akoids-'-~ .-" //

0 t I i I I 1 I

100" b / w . . . . . . . . - [ ~

-o ,." ....... / ..-,0 ,/..,..o>. 2

/ -o grano

Z_ /'g O

o t a+b

0 I I I I I I 0 ~ 2 3 z. 5 [h i 7

I t ime af ter onset of wh i te Light 60h after sawing

Fig. 8a and b. Compar ison of the time course of ultrastructural development and the time course of chlorophyll (Chl) accumulat ion after the onset of white light 60 h after sowing, a No light pretreat- ment. b Seedlings pretreated with 4 x (5 min standard red light) pulses. The Chl data were obtained from Kasemir et al. (1973)

D i s c u s s i o n

]'he data of Figures 3, 4 and 6 show distinct effects o f Pfr on the formation of the thylakoid system during the transition ofetioplasts into chloroplasts. By which mechanism Pfr exerts its control in this special case is uncertain at present. Three possibilities can be con- sidered (Fig. 9). Pfr could act (1) by increasing the membrane material stored in the prolamellar body before the onset of white light (Pfr I in Fig. 9), (2) by increasing the rate of Chl accumulation after the onset of white light (Pfr 2 in Fig. 9) or (3) by increasing the rate of the completion of the photosynthetic mem- brane (Pfr 3 in Fig. 9).

As shown by Kasemir et al. (1975) Pfr increases the size and the organizational state of the prolamellar body in plastids of mustard cotyledon mesophyll cells. Nevertheless, it is unclear in which way this Pfr effect

C. Girnth et al. : Phytochrome-Mediated Thylakoid Formation 197

p r e c u r s o r s

I 1 i I

-, l,

precursors --"--~----~ 0 0 0 t I PCht(ide) poot I

D 3 ptastid membrane material Ifr.

white Light ~ grana and stroma t ~ thyLakoids

�9 0 - 0 , 0 \

Chl.(ide) o ' f r Cht b

Fig. 9. A scheme to account for the available information regarding the Per-mediated control of grana and stroma thylakoid formation in developing chloroplasts of mustard cotyledons. For clearness the biosynthetic pathways of plastid membrane material and Chl are drawn separately although in situ they may be localized in a close proximity. 1, Kasemir et al. (1975); 2, Kasemir et al. (1976); 3, this paper, Girnth (1978); 3', Jabben and Mohr (1975)

contributes to the regulation of grana and stroma thylakoid formation. We may assume that during the first hours o f ' g r e e n i n g ' the grana and s t roma thyla- koids are formed at the expense of the prolamellar body (Henningsen and Boynton, 1969; Bradbeer et al., 1970). However, the development of ultrastruc- tures in white light is neither determined by the size or the organizational state of the prolamellar body (Girnth, 1978) nor by the time course of the prolamel- lar body dispersal (Fig. 7). Obviously, Per 1 (Fig. 9) and the Per effect on grana and s t roma thylakoid forma- tion proceed independently. This assumption is supported by the fact that these two plastid responses cannot be traced back to the same 'initial act ion ' of Pfl which is thought to commence at the moment when a red light effect can no longer be reversed by far-red light (Mohr, 1977). As previously shown (Kasemir et al., 1975) the red light effect on the pro- lamellar body is fully reversible within 5 rain by a pulse of far-red light. However, there is an escape f rom reversibility after 5 rain with regard to the for- mation of grana and s t roma thylakoids (Figs. 3, 4, 6).

Per 2 in Figure 9 stresses the point that phyto- chrome also increases the capacity of the mustard coty- ledons for synthesizing Chl via an acceleration of pro- tochlorophyll(ide) formation. Since chloroplast devel- opment requires the continuous accumulation of Chl (Argyroudi-Akoyunoglou et al., 1976; Armond et al., 1976) this Per effect could be part of the control sys- tem. However, no correlation exists between the Prr- mediated increase of grana and stroma thylakoid for- mation and that of Chl accumulation in white light (Fig. 8). Hence, the contribution of an increased rate of Chl accumulation to the rate of ultrastructural development of chloroplasts remains to be clarified.

It is suggested in Fig. 9 that a continuous protochlo- rophyll(ide) ~ C h l photoconversion may contribute to the format ion of the thylakoid system only insofar as the resulting Chl molecules become integral ele- ments of the developing membranes (Bogorad et al., 1968). The participation of Chl formation in control- ling the formation of chloroplast ultrastructures may cease at the moment when the pigment conversion is no longer limited.

Since the Pf~-mediated increase of prolamellar body formation and of the capacity of the Chl-synthe- sizing system do not seem to contribute to the in- creased rate of grana and s t roma thylakoid formation, a direct influence of Per on the completion of the photosynthetic membrane (indicated by P e r 3 in Fig. 9) can be assumed. This concept agrees with findings concerning the Prr-mediated control of the 'Shibata shift ' (Jabben and Mohr, 1975). The term Shibata- shift designates the in vivo spectral shift of the Chl a absorption maximum from a longer to shorter wave- length following the p ro toch lorophyl l ( ide)~Chl a photoconversion after a brief, saturating light pulse. While the mechanism of this shift is not yet fully understood it has been proposed that it reflects organ- isational changes in the thylakoid membrane (Butler and Briggs, 1966). Surprisingly, the response of the Shibata-shift to Per is as rapid as in the case of grana and stroma thylakoid formation (Jabben and Mohr, 1975). Probably these findings suggest that both re- sponses are manifestations of a single effect of Per on the arrangement of plastid membrane constituents.

Supported by a grant from the Deutsche Forschungsgemeinschaft (SFB 46) to Prof, H. Mohr. We thank Miss E. Baumann for compe- tent technical assistance and our coIleagues for stimulating discus- sions.

198 C. Girnth et al. : Phytochrome-Mediated Thylakoid Formation

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Berry, D.R., Smith, H. : Red-light stimulation of prolamellar body recrystallization and thylakoid formation in barley etioplasts. J. Cell Sci. 8, 185 200 (1971)

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Received 17 February; accepted 7 April 1978