Etioplasts

Proplastids are small colorless or pale green undifferentated plastids that occur in the meristematic cells of roots and stems. Proplastids are precursors of more highly differentiated plastids. Etioplasts are proplastids containing prolemellar bodies and are precursors of chloroplasts developmentally arrested by low light levels. 

Etioplasts Specific stage in the transformation of proplastids to chloroplasts,... 

Daniell, H. and McFadden, B.A. (1987). Uptake and expression of bacterial and cyanobacterial genes by isolated cucumber etioplasts. Proc. Natl. Acad. Sci U.S.A. 84 6349-6353. 

In plastids of etiolated radish seedlings, far-red light stimulated the synthesis of all prenyl chains, but it did not alter the relative concentrations of the various chains synthesized under dark conditions. White light further stimulated chain synthesis, particularly the formation of phytyl chains,370 and a similar situation occurred with barley.371 In contrast, both far-red and white light changed the pattern of carotenoid synthesis in etioplasts of Raphanus seedlings372 and it seems that phytochrome in its excited state controls light-induced synthesis of carotenoid. This synthesis was also... 

Luetke-Brinkhaus, R and Kleinig, H. (1987) Formation of isopentenyl diphosphate via mevalonate does not occur within etioplasts and etiochloroplasts of mustard Sinapis alba L.) seedlings. Planta, 171, 401-6. 

In etioplasts there are pre-existing functional protein complexes. 

Fig. 12.8 depicts some steps in the light-induced assembly of the photosystem 1 reaction center. In this case, subunit I exists in etioplasts as an inactive unit. Light induces its initial activity within a few minutes, and it takes hours to synthesize and assemble the fully functional protein complex. 

Although there is much evidence to suggest that the envelopes of photosyntheti-cally competent plastids are relatively impermeable to MVA, the origin of the MVA required for chloroplastidic terpenoid biosynthesis in plastids that are not able to fix CO2 is not yet certain. Studies using silicone-oil centrifugal filtration have shown that etioplasts and 1—2 h etiochloroplasts have envelopes that are permeable to acetate and MVA, but plastids from etiolated tissues that have been illuminated for periods of 4 h or longer show progressive impermeability to these precursors. 

Physical Methods.—Separation and Assay. A range of isomers of astaxanthin (8) diacetate (9-cis, 13-cis, 15-cis, 9,9 -di-cis, 9,13-di-cw, 9,13 -di-cw, 13,13 -di-cw, 13,15-di-cw), prepared by thermal and iodine-catalysed isomerization of irans-(S) have been separated by h.p.l.c.126 A procedure has been developed for separation of bean leaf etioplast pigments, including carotenoids,127 by h.p.l.c. H.p.l.c. separations of esters of all-trans-, 9-cis-, 11-cw-, and 13-cw-retinol,128-130 and determinations of retinol in serum,131 retinol and 13-cw-retinoic acid,132 and the aromatic retinoid (195)133 in plasma have been described. A reversed-phase ion-pair... 

Ito H, Tanaka Y, Tsuji H, Tanaka A (1993) Conversion of Chlorophyll b to Chlorophyll a by Isolated Cucumber Etioplasts. Arch Biochem Biophys 306 148... 

Dahlin C and Franzen LG (1997) Carotenoid deficient young wheat etioplasts are able to bind precursor proteins on the plastid surface but are impaired in theirtranslocation ability. Physiol Plant 99 279-285... 

Kuttkat A, Edhofer 1, Eichacker LA and Paulsen H (1997) Light harvesting chlorophyll a/b binding protein stably inserts into etioplast membranes supplemented with Zn pheophytin a/b. J Biol Chem 272 20451-20455... 

In confirmation of earlier indieations that enf-kaurene synthesis is localised in plastids [60-62], Aaeh et al. [44] demonstrated clearly the presence of CPS/EKS activity in the stroma of wheat and pea etioplasts and leucoplasts from C. maxima endosperm. They showed, furthermore, that mature chloroplasts contain no CPS/EKS activity and that the activity is associated with dividing cells in the meristem [45]. These findings, together with the demonstration that CPS is targeted to plastids, provide firm evidence that the first part of GA biosynthesis takes place in plastids. 

Haise, K.P. and G. Jacobi Comparative smdies on the lipid composition of etioplasts and chloroplasts from fisum and of chloroplasts from a mutant Nicotiana, Planta 111 (1973) 137-148. 

Muller B, Eichacker LA, Assembly of the D1 precursor in monomeric photosystem II reaction center precomplexes precedes chlorophyll a-triggered accumulation of reaction center II in barley etioplasts. Plant Cell 1999 11 2365-2378. 

Eichacker LA, Soil ], Lautcrbach P et al. In vitro synthesis of chlotophyll-A in the dark triggers accumulation of chlotophyll-a apoproteins in barley etioplasts. ] Biol Chem 1990 265 13566-13571. 

Guera A, De Nova PG, Sabater B. Identification of the Ndh(NAD(P)H-plastoquinone-oxidoreductase) complex in etioplast membranes of barley Changes during photomorphogenesis of chloroplasts. Plant Cell Physiol 2000 41 49-59. 

The outer chloroplast and etioplast envelope contains carotenoids (36). By illuminating this subcellular fraction at various wavelengths in a spectrophotometer and obtaining a difference spectra in the presence of DPE herbicides, the direct interaction between herbicide and pigment can be evaluated. The wavelength at which the interaction is observed will implicate the pigment involved. 

The ultrastructure of the tissue treated with AFM for 6 h in darkness (Figure 3A) was the same as untreated tissue. However, massive cellular and membrane damage was apparent in the AFM-treated tissue within 30 to 45 min following light-activation of the herbicide (Figure 3B). Some etioplasts and chloroplasts... 

Early signs of injury appeared in the outer chloroplast or etioplast envelope and in the tonoplast. This information supports the proposed mechanism of action of DPE herbicides. Carotenoids are known to be present in the outer plastid envelope... 

ALBRECHT, M., SANDMANN, G., Light-stimulated carotenoid biosynthesis during transformation of maize etioplasts is regulated by increased activity of isopentenyl pyrophosphate isomerase.. Plant Physiol. 1994,105,529-534. 

Acifluorfen-methyl and LS 820340, fi-nitro and fi-chloro diphenyl ethers, respectively, had Uq s of less than 1 /iM for the synthesis of Mg-PPIX from ALA in a maize etioplast preparation (57). 

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