Hours Of Illumination Research Articles

Wheel-running during anoestrus and oestrus in the ferret

Wheel-running activity was studied in female ferrets (Mustela putorius furo), during periods of anoestrus and oestrus, as well as after gonadectomy. During anoestrus wheel-running was restricted to the hours of illumination, but during oestrus extended into the dark period and was increased overall, with the number of wheel revolutions being doubled or trebled. In spayed females wheel-running was mostly limited to the light periods.

13C Nuclear Magnetic Resonance Studies of Crassulacean Acid Metabolism in Intact Leaves of Kalanchoë tubiflora

(13)C nuclear magnetic resonance spectroscopy of intact leaves of Kalanchoë tubiflora was used to observe Crassulacean acid metabolism in vivo. (13)C signals from C-4 of malate were observed after overnight exposure of leaves to (13)CO(2). Illumination of the labeled leaves resulted in a gradual decrease in the malate signals. After a period of darkness in normal air, (13)C signals were detected in all four carbons of malate in the previously labeled leaves. The (13)C nuclear magnetic resonance spectrum of malate in solution was pH dependent, which allowed an estimation of the vacuolar pH from the whole leaf spectrum. The pH was 4.0 following a 14-hour dark period, but rose to greater than 6.0 after 6 hours of illumination.

Blue light induces stomatal transpiration in wheat seedlings with chlorophyll deficiency caused by SAN 9789

Wheat seedlings (Truicum aestivum L. cv. Starke II, Weibull) grown in a solution of the herbicide SAN 9789 axe deficient in chlorophyll and carotenoids. Such seedlings were used in order to isolate a blue light response of stomata, not mediated by photosynthesis. When illuminated with blue light (430‐505 nm) SAN‐grown seedlings showed a considerable transpiration response, whereas red light (>590 nm) gave no response whatsoever with the intensities used. The transpiration was measured with hygrometers in an open air‐flow system. Furthermore, blue light had a superior effect, relative to red, in causing a transpiration response in untreated green seedlings. The transpiration level after two hours of illumination was higher in blue than in red light, although the blue light had its major effect immediately after the light was switched on. The difference between the effects of blue and red light was most pronounced at low light intensities. This, together with the high sensitivity of SAN‐grown seedlings to low ntensity blue light, led to the conclusion that blue light is of special importance at low quantum fluxes. Because of the very low carotenoid content in the SAN‐grown seedlings, the role of the carotenoids as photoreceptors for the blue light response of stomata was excluded.

Development of Nitrate Reductase Activity in Green Tissues of Soybean Seedlings (Glycine max. L. Merr.)

The pattern of in vivo activity of nitrate reductase was determined in chlorophyllous tissues of soybean seedlings cultivated under constant temperature and continuous light. Enzyme activity was detected in the cotyledons after approximately 20 hours of light exposure, the values being proportional to the concentration of nitrate in the irrigating solutions. In cotyledons watered with 15 mM of nitrate the peak of activity was reached after 120 hours of illumination. Chlorophyll accumulation preceded and approximately paralleled nitrate reductase activity in the cotyledons indicating that nitrate reduction is associated with the development of anabolic processes. Nitrate reductase activity in light-grown cotyledons was inhibited by cycloheximide when the inhibitor was added at the beginning of the illumination period. The effect progressively disappeared as the tissues were treated at later stages after having being exposed to light. On the other hand, actinomycin D did not affect enzyme activity, suggesting that the process does depend in part on de novo protein synthesis but does not require RNA synthesis. The appearance of enzyme activity in the primary leaves coincided with the time of maximum activity in the cotyledons. By the time nitrate reductase activity started decreasing in the primary leaves, the first trifoliate leaf showed increasing enzyme activity. The patterns determined in leaves showed low values of activity in the early stages of development, reached a peak when the leaves were almost expanded and declined thereafter. Maximum nitrate reductase activities were calculated as 2.3, 3.2 and 2.2 times higher in leaves infiltrated with nitrate than in the controls without exogenous nitrate, in the cotyledons, primary and first trifoliolate leaves, respectively.

Untersuchungen über den Kohlenhydratgehalt unterschiedlich beschatteter Küstentannen (Abies grandis (D. Don) Lindl.)

Summary In the summer and autumn at 1979 investigations on the sucrose and starch content of needles, bark and roots were carried out on four-year-old Grand-fir (Abies grandis (D. D on ) L indl .) seedlings. Since April 1978 the plants had been kept at the following light intensities: 100, 31 and 21 percent of full daylight. The shading led to a marked decrease of the growth (cf. Table 1). During the summer of 1979 the dry weight of the non-shaded plants increased by approx. 0.05 g per day and plant, whereas the shaded plants showed a daily increase of only 0.02 g resp. 0.01 g/plant. The resultes of repeated sampling of needles during the month of June showed that non-shaded firs on the average contained 2.5 mg sucrose per gram of dry weight, whereas the shaded firs averaged a content of only 1.8 resp. 1.5 mg/g-dry weight. Regression analyses revealed that the sucrose content of the needles was significantly dependent upon the time of day when the samples were collected. Needles collected in the afternoon contained almost twice as much Sucrose as needles collected in the time before noon. This increase was bigger in the non-shaded firs than in the shaded ones (cf. Table 4). Experiments in a growth chamber (air temp. 15 °C, rel humidity 100 %), where only the illumination was changed (5–25 klx), gave, due to a pre-treatment of the plants in darkness, information about the accumulation rates of sucrose in the needles. After two hours of illumination the sucrose content in the non-shaded firs was greater than in the shaded ones (cf. Table 5). In the non-shaded needles the sucrose content increased with increased illumination, in the shaded needles no such relationship could be found. Shading markedly decreased the starch content of bark and roots. A corresponding decrease was found in the accumulation rate of starch in these tissues during the time from September to November. It is concluded that the results of this paper help to (cf. Table 6) explain the poor growth of shaded Grand-firs, which apparently is an outcome of low production rate of carbohydrates during the summer and a very low accumulation rate of food reserves in the autumn.

Blue Light-Enhanced Phosphoenolpyruvate Carboxylase Activity in a Chlorophyll-free Chlorella Mutant

Summary The activity of phosphoenolpyruvate carboxylase (PEP carboxylase; EC 4.1.1.31) of a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris is enhanced by irradiation with blue light. The effect is pronounced in older cultures; more than 8 hours of illumination are necessary for its saturation. The enhancement of PEP carboxylase activity by blue light does not only result from an increase in V max but also from a decrease of k m (PEP). The respective energy requirements point to two possibly independent processes. All data show good agreement with corresponding results obtained for pyruvate kinase of the same organism.

Events surrounding the early development of Euglena chloroplasts : 18. Structure of the developing proplastid in the first hours of illumination from serial sections of wild-type cells

The structure of the proplastid in dark-grown nondividing cells of wild-type Euglena gracilis var. bacillaris and the changes which occur during the early hours of illumination have been studied using serial sections and transmission electron microscopy. The proplastid in dark-grown cells is a polyp-like structure with a number of tubular arms, each containing a noncrystalline prolamellar body composed of irregular tubules, at its extremity. The proplastid with membrane whorls attached is in intimate contact with the surrounding cytoplasm and is in close juxtaposition to microbody-like organelles and mitochondria. The plastid assumes a more globular shape after 30 min of illumination. During this period membrane whorls, similar to those described above, are found as transient structures at the interior of the prolamellar bodies and are found to be closely associated with mitochondria. Membrane whorls are also observed to penetrate to the cores of the microbodies. The thylakoids are attached to the remaining irregular tubular regions of the prolamellar body which surround the membrane whorls. There is a very close association of plastids, mitochondria, microbodies, and Golgi. After 1 to 2 hr the membrane whorls associated with the interior of the prolamellar bodies begin to disappear to be replaced by elongated straight tubules which, in turn, also disappear to leave a cavity surrounded by the remains of the original irregular tubules. There is a progressive pairing of thylakoids with the deposition of a dense matrix between the pairs; a different region of high density can be seen on either side of the paired thylakoids where single thylakoids adjoin them near the point of connection to the irregular tubules of the prolamellar bodies. No relations among the membrane whorls, straight tubules, and thylakoids have been detected. By 24 hr of development paired thylakoids are the rule. Reconstructions from serial sections are presented showing the three-dimensional structure of the proplastid before and after illumination.

Plastid Protease Activity and Prolamellar Body Transformation during Greening

Two proteases active in and specific to oat etioplasts and up to 24-hour etiochloroplasts, only very slightly contaminated by other cellular compartments are described. The enzyme showed pH optima of 4.2 (acid) and 6.8 (neutral), temperature optima of 50 C and the highest level of enzyme activity was with prolamellar bodies (PLBs) as substrate. Both enzymes showed evidence of a sulfhydryl reagent requirement, particularly for the neutral enzyme. Levels of both proteases increased up to 4 hours of illumination of leaves, and then sharply decreased with the largest differences exhibited by the neutral protease. The pH values in the plastid stroma indicated that the neutral enzyme was likely to be the most important in PLB transformation. A comparison between plastid-associated and extra-plastidic protease activities showed similar properties, except the affinity toward PLBs, which was much higher for plastid proteases (K(m): 0.2 and 1.1 milligrams protein per milliliter, respectively).

Electrical field effects induced in membranes of developing chloroplasts

Etioplasts, etiochloroplasts, and chloroplasts of Avena sativa L. purified on a Percoll gradient were subjected to increasing electric field strengths in the orifice of a hydrodynamically focussing Coulter Counter. The change in resistance of the orifice when an organelle is present correlates well with the size of the plastid for field strengths up to about 3.5 kV cm(-1). Beyond this field strength, depending on the size of the organelle, the size is underestimated. The underestimation of the size is caused by the dielectric breakdown of the envelope membranes once a critical membrane potential has been exceeded. Beyond breakdown the signal of the particle is predominately determined both by the internal conductivity and the increased membrane conductivity. Measurements of the breakdown voltage of different developmental stages of the plastids reveal that the breakdown voltage decreases from 1.2 V in etioplasts to about 0.9 V in chloroplasts after 48 h illumination. The decrease in breakdown voltage can be explained in terms of increasing incorporation of proteins into the inner envelope membrane during development.This view is consistent with conclusions drawn by other authors from transport and biochemical studies. The underestimation of the size beyond breakdown is about 20% and increases to a constant value of about 40% during the first 3 h of illumination. The underestimation decreases again to about 10% when the chloroplast stage is reached. This result is consistent with the current view of chloroplast development. Mobilisation of glucans, the transformation of the prolamellar body of etioplasts into thylacoid membranes as well as an intensive synthesis of pigments and enhanced rates of ions transport in the first hour of illumination gives rise to an increased pool of ionic compounds within the plastid stroma.It should be noted that purification of the plastids on Percoll gradient leads to size distributions which are almost normally distributed over the whole field range, suggesting that the preparations are also electrically homogeneous (U. Zimmermann, F. Riemann and G. Pilwat: Biochim. Biophys. Acta 436, 460-474 (1976)). In contrast with results of Lürssen, K., Z. Naturforsch. 25b, 1113-1119 (1970) only a slight increase of the modal volume from the etioplast stage to the chloroplast stage is observed.

Further studies of the light-mediated change in the activity of pyruvate kinase of a chlorophyll-free Chlorella mutant

Summary The activity of pyruvate kinase (PK; EC 2.7.1.40) of a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris is enhanced by irradiation with blue light. The effect is most pronounced in cells which are depleted in carbohydrate reserves. 8 to 12 hours of illumination lead to maximal effect, only low light intensities being required. Light of wavelengths around 370 nm and 455 nm proves to be most effective. While the intensityand wavelength-dependences of the enhancement in PK activity show good agreement with corresponding data of other blue light-responses of that alga the duration of illumination does not.

Light-dependent Induction of Polyunsaturated Fatty Acid Biosynthesis in Greening Cucumber Cotyledons

Greening cucumber (Cucumis sativus L.) cotyledons exhibited dramatic increases in the ability to desaturate exogenously added [1-(14)C]oleic acid and [1-(14)C]linoleic acid within 2 to 3 hours of illumination. These increases were effectively inhibited by 10 micrograms per milliliter cycloheximide. Oleate desaturation remained at a high level in constant light for 5 to 6 days after induction and then declined by about 50%; when returned to the dark, the tissue showed a sharp decrease in conversion of [(14)C]oleate to [(14)C]linoleate. Linoleate desaturation reached a maximum about 15 hours after induction and declined immediately thereafter while the tissue still was in the light; after induction had peaked return of the tissue to the dark showed a dramatic fall of linoleate desaturation. The changes in desaturation were correlated with the conversion of the principal fatty acid in the etiolated cotyledons, linoleate, to alpha-linolenate, and with the assembly of the chlorophyll-containing photosynthetic membranes. The incorporation of [1-(14)C]acetate into lipids showed no significant light stimulation. The role of light in the regulation of certain aspects of plant metabolism during development is discussed.

Photosynthetic apparatus in chilling-sensitive plants

Changes in the levels of both ATP and protein in relation to Hill reaction activity following cold and dark storage and illumination of leaves of Lycopersicon esculentum Mill. were studied. Loss of Hill reaction activity observed during cold and dark storage of leaves for 3-4 days was accompanied by about 50% decrease of both ATP and protein levels while the content of chlorophyll was not affected Illumination of cold and dark stored leaves (8000 lx for 2 h) resulted in almost a complete restoration of both ATP and protein levels as well as Hill reaction activity. The latter process proceeded, however with different kinetics than the former ones. The rate of Hill reaction activity increase very rapidly from the beginning of illumination while the ATP level diminished during the first hour of illumination. In addition there was a lag in the increases in protein content. By about two hours of illumination all these processes reached the maximum values. Following illumination of leaf dises stored in the cold and dark in the presence of either cycloheximide or DCMU, both ATP and proteins levels as well as Hill reaction activity were greatly diminished. These data seem to suggest that the lack of reactivation of Hill reaction activity in the presence of these two inhibitors is due to inhibition of ATP synthesis required primarily for manganese reincorporation into the thylakoid membrane and theraby restoration of Hill reaction activity (Kaniuga, Zabek and Sochanowicz, Planta 1978b). Contribution of cytoplasmic protein synthesis in this process appears to be of secondary importance, although the inactivation and reactivation of electron transport are accompanied by a large loss (as high as 50%) and the restoration of the initial protein content in leaves following illumination.

Intensity and Decay Half-Time of the Electron Paramagnetic Resonance Signal I in Bean Chloroplasts at Various Stages of Greening

The size of EPR signal I and its decay half-life were measured on chloroplasts isolated from primary bean leaves after illumination of 7 d old dark-grown seedlings. The results indicate that the ratio of P700/total chlorophyll decreased approximately 2-fold only between the 6th and 24th hour of illumination. The relative size of the signal increased with increasing light intensity up to 360 W m~2 in all stages of greening studied. Addition of HgCl2 (1 mM) caused an increase in the magnitude of the signal, especially at lower light intensities. Treat ment of isolated chloroplasts with DCMU (20 //M) did not have any effect on the intensity of the signal at the early stages of greening, that is 6 or 12 h of illumination, but it caused a slight enhance ment after 24 or 48 h of illumination. The higher intensity used for the signal production the smaller the enhancement observed. The addition of HgCl2 caused an increase in decay half-life of the signal 20-fold or 35-fold after 6 h or 48 h of greening, respectively. In DCMU-treated chloroplasts, an enhancing effect becomes visible after 12 h of greening and subsequently it gradually increased. The data obtained were interpreted in terms of an alteration in efficiency of the re-reduction of P700+ under different conditions and different stages of greening.

Kinetics of Membrane Transport during Chloroplast Development

In the course of plastid development there are changes in the permeability of the envelope membranes. An investigation of the kinetics of transport with largely uncontaminated and intact etioplast/etiochloroplast preparations from greening Avena sativa laminae demonstrates: (a) that etioplasts already possess specific translocators for the transporation of orthophosphate, dihydroxyacetone phosphate, 3-phosphoglycerate ("phosphate translocator"), and dicarboxylic acids ("dicarboxylate translocator"); (b) that changes in the rates of uptake during development are mainly due to changes in velocity for specific transport and not due to changes in the affinity for transport (K(m)) or nonspecific permeation. The very low competitive inhibition of transport of orthophosphate by dihydroxyacetone phosphate and 3-phosphoglycerate, observed for developmental stages corresponding to up to 3 hours of illumination of etiolated tissue, is discussed with respect to the possibility of an early phosphate transport mechanism that is different from the phosphate translocator of more developed plastids.

Characterization of Protoheme Levels in Etiolated and Greening Plant Tissues

The protoheme content of etiolated, greening, and fully greened bean (Phaseolus vulgaris L. var. Light Red Kidney) leaves has been studied. The protoheme level in etiolated and fully greened leaf tissue stays relatively constant from age 7 to 14 days. In agreement with the studies reported for barley (Castelfranco and Jones 1975 Plant Physiol 55: 485-490), the protoheme content of greening bean and barley (Hordeum vulgare var. Larker) leaves does not change appreciably during the first 9 hours of illumination, but the level rises significantly by the 24th hour of illumination (cf. Hendry and Stobart 1977 Phytochemistry 16: 1545-1548). This increase also occurs in seedlings returned to the dark for 24 to 48 hours following a 10-minute pulse of light. These results demonstrate a limited correlation with previous studies on the development of b-type cytochromes during greening of these tissues (Gregory and Bradbeer 1973; Planta 109: 317-326).

The Photochemical Activity of Chloroplasts and Subchloroplast Particles Isolated from Etiolated Bean Leaves Exposed to Continuous Light

The photochemical activity of chloroplasts and subchloroplast particles isolated from primary bean leaves between the 4th and 24th hour of illumination of etiolated seedlings is the subject of this paper. The photosystem I activity (oxygen uptake in the presence of MV, DCIP, ascorbate and DCMU), expressed on a unit chlorophyll basis, decreased approximately 10-fold between 4 and 8 h of greening. At the same time the photosystem II activity (DCIP photoreduction in the presence of DPC) was reduced to a half. The photosystem I activity also decreased in all hitherto investigated fractions which were isolated from the digitonin-treated chloroplasts. However, at the initial phase of greening this decrease was the most significant in the fraction containing heavy particles. After 24 h of greening DCMU, at concentrations higher than 10~10 M, limited the rate of ferricyanide photoreduction by isolated chloroplasts, whereas after 6 h of greening this effect was observable even in the presence of 10~12 M DCMU. The results obtained demonstrated that under those conditions both photosystems were active after 4 h of greening and PS I activity developed more rapidly than that of PS II. It also follows from the presented data that the water splitting reactions were delayed in development as compared to the other reactions investigated, and that PS

Changes in the polypeptide composition of internal membranes of barley plastids during greening

A method is described for obtaining good yields of purified internal membranes of plastids from greening barley seedlings. The procedure is suitable, without modification, for isolating intact plastids from etiolated seedlings and all early stages of greening. Electron microscopy was used to identify the types of contaminants present in preparations obtained by different methods, and to assess the degree of contamination in purified membranes. Gel electrophoresis of the sodium dodecyl sulphate-solubilised membrane polypeptides established that the proteins pelleted during flotation were a major component of unpurified membrane preparations from etioplasts and plastids greened for 9 hours or less. The polypeptide composition of purified etioplast membranes consisted of 35 bands. At least 15 of these disappeared during subsequent greening. After only 3 hours of illumination, the internal membranes contained almost all of the 43 polypeptides present in mature chloroplast thylakoids. The changes in polypeptide composition from 3–24h were mainly quantitative in nature.

Lipids and function of etiochloroplasts after ultraviolet, blue and red light-illumination.

The morphogenesis of whole plants and the development of cell organelles are highly affected or regulated by light-treatment. Chloroplasts normally develop from proplastids when illuminated. In complete darkness, proplastids develop into etioplasts with an assembly of characteristic prolamellar bodies. Light-treatment induces the disappearance of the prolamellar bodies and the development of photosynthetically active thylakoids. Besides chlorophyll, nearly all lipids are already present in etioplasts. Some authors divide the thylakoid lipids into more functional moieties as chlorophylls, carotenoids or lipophilic plastidquinones, and into more structural lipids as the glycerolipids, but it must be said that the function of glycoand phospho-lipids has not yet been elucidated. Further, it is not clear what role the glycerolipids play during physiological plastid development and how the lipid synthesis is regulated. Therefore we performed experiments with etiolated tissues and isolated etioplasts from Hordeum vuIgure L. (cv. Breuns Villa) tQ obtain information about the participation of glycerolipids in etiochloroplast development following continuous illumination. The etiochloroplasts were isolated from illuminated tissues by a density-gradient procedure, the fractions were checked for contamination with other organelles by marker-enzyme measurements. The plastid fraction showed contamination with other material of less than 1 %. In further experiments we used short-time irradiation with different light-qualities for studying regulation phenomena for lipid metabolism. As reported earlier, the lipid composition of etiolated barley seedlings changed by continuous irradiation with white and red light (Tevini & Herm, 1974). Especially within the first 8 h of illumination, a special metabolism of glycerolipids and their fatty acids could be seen. We used light with the following intensities: white light, 0.8 W/mZ; red light, 0.5W/mZ; blue light, 0.8W/mZ. In these early stages of development white, red and blue light enhanced the phospholipid synthesis, whereas the glycolipid synthesis showed the opposite effect (Figs. la and lb). The same holds true when lipid values are related to a constant plastid number (lo9). We infer that a part of the galactolipids as the main constituents of the prolammellar system and plastoglobuli in etioplasts must be hydrolysed before use for thylakoid assembly. Phospholipids may play the role of fatty acid carriers for newly formed galactolipids. Long-wave U.V. light (interference filter with Amax. = 366nm, 0.5 W/mZ) on the other hand enhances the galactolipid synthesis during the first hours of illumination. This may be a reflection of partly inhibited prolamellar-body breakdown and small chlorophyll synthesis, so that all newly formed galactolipids can be measured. Protochlorophyll-absorption measurements show no 'Shibata-shift' meaning that no phytylation takes place under these low light-intensity conditions. In contrast with all other light-qualities U.V. light causes inhibition of phospholipid synthesis during the first hours of illumination and later on even the breakdown of phospholipids can be seen by the formation of lysoglycerides. Blue light, given at the same intensity as red light, induces higher chlorophyll amounts and an earlier appearance of normal chlorophyll a/chlorophyll b ratios than red light. The photosynthetic activity of greening etioplasts, isolated from redand blue-light-illuminated tissues by repeated density-gradient centrifugation, develops somewhat earlier under blue light. Even on a chlorophyll basis the dichlorophenolindophenoland ferricyanide-reduction rates of blue-light-illuminated chloroplasts are considerably higher than those of red-light-illuminated chloroplasts (Table 1). The analysis of the ultrastructure of etiochloroplasts (M. Tevini & K. Herm, unpublished work) proves the earlier appearance of multilayered grana stacks ,

Changes in Ascorbic Acid Content during Growth and Development of Panicum miliaceum

The present paper deals with changes in the ascorbic acid content of the shoot apex during its transformation from the vegetative to the reproductive state and its further development in Panicum miliaceum var. Samai Co. 1. Seedlings were exposed to 24-hour illumination, natural day, and 8 hours of illumination per day. Ascorbic acid was determined for the growing apex, stem, and leaf of the main shoot and for the individual branches produced on it at successive developmental stages.A several-fold increase in ascorbic acid content of the growing apex of the main shoot of plants grown under 8-hour illumination synchronizes with its transformation from the vegetative to the reproductive state. In plants grown under natural day and continuous illumination, which continue to grow vegetatively, the ascorbic acid content remains at a low level. Moving these plants to 8-hour illumination results in floral initiation and an increase in the ascorbic acid content. The high level of ascorbic acid is maintained through the gametogenic and embryogenic phases, but decreases during seed formation. A rise in ascorbic acid content of branch apices always occurs later than that in the main shoot but the increase again coincides with floral initiation in the branch apex. The ascorbic acid contents of stem and leaf are not significantly affected by the photoperiod. Hence, a massive upsurge in ascorbic acid content synchronizes with the transformation of the vegetative branch and shoot apices to the reproductive state.

Synthesis and translation site of light-induced mRNAs in etiolated Euglena gracilis

Poly(A)-mRNA synthesis has been studied in etiolated Euglena gracilis exposed to 1 or 2 h of illumination. 1. 1. Labeling kinetics of mRNAs containing poly(A) sequences, during illumination or after return to darkness, reach a plateau in 10 or 20 min according to nutritional conditions. When the cultures are returned to darkness, the mRNA synthesis decreases rapidly. Thus, the synthesis of these mRNAs (light-induced mRNAs) is dependent on light and their half-life can be evaluated. 2. 2. Cycloheximide induces accumulation of label in poly(A)-containing mRNA; such an accumulation is not observed after addition of lincomycin. Labeling during illumination of mRNA in a chloroplast mutant is similar to that in the wild type strain. These data suggest that the poly(A)-mRNAs synthesized in the two first hours of illumination are translated on cytoplasmic polyribosomes.