Abstract
Etioplasts of 5-day-old dark-grown barley seedlings synthesize most of the soluble and membrane proteins found in chloroplasts of illuminated plants. Prominent among these proteins are the large subunit of ribulose bisphosphate carboxylase and the alpha- and beta-subunits of the chloroplast ATPase. However, etioplasts do not synthesize four chloroplast-encoded proteins which are major constituents of the chloroplast thylakoid membrane: two chlorophyll apoproteins of photosystem I (68 and 65 kDa) and two chlorophyll apoproteins of photosystem II (47 and 43 kDa). Pulse-labeling experiments show that the lack of radiolabel accumulation in the chlorophyll apoproteins in etioplasts is due to inhibition of synthesis rather than apoprotein instability. Illumination of 5-day-old dark-grown barley selectively induces synthesis of the plastid-encoded chlorophyll apoproteins and proteins of 32, 23, and 21 kDa. Synthesis of the chlorophyll apoproteins was significant in plants illuminated for 15 min and was near maximum by 1 h. The induction of photosystem I chlorophyll apoprotein synthesis was not accompanied by an increase in mRNA for these proteins. These results demonstrate that the synthesis of the plastid-encoded photosystem I chlorophyll apoproteins is blocked at the translational level in dark-grown barley. Translation of the chlorophyll apoproteins is induced rapidly by light with a time course which is similar to the light-dependent formation of chlorophyll from protochlorophyllide.
Highlights
In oats, bean, and spinach ptlhaestid-encoded photosystem I (PSI)’ chlorophyll apoproteins were reported to accumulate in dark-grown plants [8].In contrast, these proteins did not accumulate in dark-grownbarley ( 7 ) .When dark-grown barley seedlings were illuminated, synthesis of PSI chlorophyll apoproteins was observed within 15 min
In this paper we have examined the effect of light on the synthesis of the plastid-encodedchlorophyll-binding proteins during light-induced development
Our results demonstrate that etioplasts are translationally competent and synthesize most of the soluble and membrane proteins found in mature chloroplasts
Summary
Tissue Selection-The growth of the barley primary leaf is only marginallydifferent for the first days whendark-grown plants are compared to light-grown plants. Regulation of Chlorophyll-bPSinryodntitenhignesis by autoradiography of NaDodSO, gels (Fig. 1) This experi- of cycloheximide), etioplasts synthesize the(Y- and &subunits ment indicated that major light-induced changes in the syn- of the ATPase, a low level of a 32-kDa polypeptide 8).It was noted that illuminatioonf dark-gown barley altered cantly in illuminated plants (Fig. 1, lane 3 uersus 4 ) These the synthesis of only a few nuclear-encoded soluble proteins results indicated that while etioplasts are translationally ac-. In contrast numerous differences tive and are capableof synthesizing a nearly complete set of were observed when radiolabeled membraneproteins from plastid-encoded polypeptides, light selectively stimulated the dark-grown plants were compared to illuminated plants
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
