Chloroplasts Of Cotyledons Research Articles

Characterization of the plastid-specific germination and seedling establishment transcriptional programme

Upon imbibition, dry seeds rapidly gain metabolic activity and the switching on of a germination-specific transcriptional programme in the nucleus goes ahead, with the induction of many nucleus-encoded transcripts coding for plastid-localized proteins. Dedifferentiated plastids present in dry seeds differentiate into chloroplasts in cotyledons and into amyloplasts in the root and in the hypocotyl, raising the question of whether the beginning of a new plant's life cycle is also characterized by specific changes in the plastid transcriptional programme. Here the plastid transcriptome is characterized during imbibition/stratification, germination, and early seedling outgrowth. It is shown that each of these three developmental steps is characterized by specific changes in the transcriptome profile, due to differential activities of the three plastid RNA polymerases and showing the integration of plastids into a germination-specific transcriptional programme. All three RNA polymerases are active during imbibition; that is, at 4 °C in darkness. However, activity of plastid-encoded RNA polymerase (PEP) is restricted to the rrn operon. After cold release, PEP changes specificity by also transcribing photosynthesis-related genes. The period of germination and radicle outgrowth is further characterized by remarkable antisense RNA production that diminishes during greening when photosynthesis-related mRNAs accumulate to their highest but to very different steady-state levels. During stratification and germination mRNA accumulation is not paralleled by protein accumulation, indicating that plastid transcription is more important for efficient germination than translation.

Expression and Localization of Arachis Hypogaea 9-Cis Epoxycarotenoid Dioxygenase 1 (AhNCED1) of Peanut Under Water Stress

ABSTRACTThe oxidative cleavage of cis-epoxycarotenoids catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED) is considered to be the rate-limiting step in abscisic acid (ABA) biosynthesis. The optimal induction conditions for expressing the AhNCED1 (Arachis hypogaea 9-cis epoxycarotenoid dioxygenase 1) protein in E. coli BL21 (DE3) were established. The purified recombination AhNCEDl protein was used to generate a polyclonal antibody in rabbit. This purified antibody was used for western blotting analysis of protein samples extracted from different organs of peanut. Under normal growth conditions, water contents of leaves and stems in peanut were higher than that of roots, and AhNCED1 mRNA and protein were low in stems and leaves, but was not detectable in roots. After treatment with 20% PEG6000for 7 h, endogenous ABA predominantly accumulated in leaves and stems, and water contents of leaves and roots reduced more than that of stems. At the transcriptional level, AhNCED1 mRNA was strongly induced in roots and leaves. At expression of protein level, AhNCED1 were enhanced in both leaves and roots, but no change in stems. In transgenic Arabidopsis, AhNCED1-GFP fluorescence was detected in the root tips and cotyledons. Intense GFP-fluorescence signals were localized in chloroplasts of cotyledons in transgenic Arabidopsis treated with 20% PEG6000for 3h, and AhNCED1 targeted into chloroplasts was also indicated by western blotting in peanut. The results suggest that different spatio-temporal expression of AhNCED1 in leaves and roots related to water stress and these areas may be the main places that synthesize ABA in response to water stress.

OEP37 Is a New Member of the Chloroplast Outer Membrane Ion Channels

The chloroplast outer envelope protein OEP37 is a member of the growing beta-barrel protein family of the outer chloroplast membrane. The reconstituted recombinant protein OEP37 from pea forms a rectifying high conductance channel with a main conductance (lambda) of Lambda= 500 picosiemens (symmetrical 250 mm KCl). The OEP37 channel is cation-selective (P(K+)/P(K-) = 14:1) with a voltage-dependent open probability maximal at V(mem) = 0 mV. The channel pore reveals an hourglass-shaped form with different diameters for the vestibule and restriction zone. The diameters of the vestibule at the high conductance side were estimated by d = 3.0 nm and the restriction zone by d = 1.5 nm. The OEP37 channel displayed a nanomolar affinity for the precursor of the chloroplast inner membrane protein Tic32, which is imported into the chloroplast through a yet unknown pathway. Pre-proteins imported through the usual Toc pathway and synthetic control peptides, however, did not show a comparable block of the OEP37 channel. In addition to the electrophysiological characterization, we studied the gene expression of OEP37 in the model plant Arabidopsis thaliana. Here, transcripts of AtOEP37 are ubiquitously expressed throughout plant development and accumulate in early germinating seedlings as well as in late embryogenesis. The plastid intrinsic protein could be detected in isolated chloroplasts of cotyledons and rosette leaves. However, the knock-out mutant oep37-1 shows that the proper function of this single copy gene is not essential for development of the mature plant. Moreover, import of Tic32 into chloroplasts of oep37-1 was not impaired when compared with wild type. Thus, OEP37 may constitute a novel peptide-sensitive ion channel in the outer envelope of plastids with function during embryogenesis and germination.

An Arabidopsis cotyledon-specific albino locus: a possible role in 16S rRNA maturation.

We report here the isolation and characterization of a cotyledon-specific albino locus of Arabidopsis, WHITE COTYLEDONS (WCO). This recessive mutation in the WCO locus, located on the top of Chromosome 1, results in albino cotyledons but green true leaves. An accumulation profile of chlorophylls and ultrastructure of chloroplasts indicate that WCO is necessary for development of functional chloroplasts in cotyledons but is dispensable in true leaves. This was further supported by the fact that the mutants request feeding of sucrose for their survival at the early seedling stage where true leaves have not emerged, but the mutants which have developed true leaves are able to grow autotrophically without sucrose supplementation. The wco mutants accumulate low levels of chloroplast mRNA encoding photosynthesis-related proteins and have a specific defect in 16S rRNA maturation in a cotyledon-specific manner. Although wco mutants exhibited abnormal chloroplasts and chloroplast gene expression in cotyledons, nuclear genes for photosynthetic components are expressed at similar levels to those found in wild-type siblings. This lack of suppression of the nuclear genes is not due to a defect in the signaling of the so-called "plastid factor" to the nucleus since normal suppression of the nuclear genes was observed in response to the photo-oxidative damage due to norflurazon application.

Isolation and characterisation of 14-S RNA from spinach chloroplasts

14-S RNA was purified from spinach chloroplasts. It has a molecular weight of 0.43 · 10 6 and the following nucleotide composition: 20% CMP, 23.9% AMP, 24.2% GMP and 31.9% UMP. The accumulation of 14-S RNA in chloroplasts of cotyledons of dark-grown plants is stimulated by light. Conditions are described for the isolation of 14-S RNA in the absence of appreciable fragmentation of chloroplast 23-S rRNA and the evidence that it represents a distinct type of chloroplast RNA is discussed. Translation of 14-S RNA in a protein synthesising system from Escherichia coli gives rise to two polypeptides with molecular weights of 13 200 and 12 600 and the possible role of 14-S RNA as a chloroplast messenger is discussed.

Phenolic Synthesis in Relation to Chloroplast Ultrastructure in Flax Callus and Cell Suspension Cultures

Summary The distribution of phenolic compounds, chlorophyll content and enzymes of phenolic synthesis were studied in relation to the ultrastructure of chloroplasts in cotyledons, callus tissue and cell suspension cultures of the oil flax (Linum usitatissimum L.). Significant biochemical changes were observed in the cultured tissues as compared with the intact cotyledons which involved: (a) a marked decrease in the amounts of p-coumaric, caffeic and ferulic acids, as well as the chlorophyll content, and a concomitant decrease in phenolic acid/chlorophyll ratios; (b) a significant drop in the activity of enzymes of phenylpropanoid metabolism (phenylalanine ammonia-lyase, cinnamate-4-hydroxylase and caffeate-O-methyltransferase); (c) the absence of chalcone-flavanone isomerase activity and a resulting loss of potential for the synthesis of C-glycoflavones; (d) the disappearance of sinapic acid and the formation of a number of unidentified phenolic compounds. While the chloroplast ultrastructure of intact cotyledons exhibited the normal features of light-grown tissues those of the cultured tissues appeared to be partially differentiated and exhibited marked ultrastructural changes which involved: (a) the absence of starch grains and an increase in the number and size of plastoglobuli; (b) a loosely packed thylakoidal system with few lamellae and occassional granal stackings in callus-tissue chloroplasts; (c) a rather “primitive” type of chloroplast with vesiculated lamellar structure and containing phytoferritin bodies in the cultured cells. The parallelism between the biochemical modifications and the changes in chloroplast ultrastructure of callus tissues and cultured cells is discussed in relation to the possible involvement of chloroplasts in penylpropanoid and flavonoid biosynthesis in cultured flax tissues.

Ricerche Comparate Sulla Morfologia e Sulla fisiologia di Larix e di Picea

Abstract Comparative researches on morphology and physiology of PICEA and LARIX. Infrastructure of chloroplasts of cotyledons of seedlings kept in darkness and light. — In proplastides of cotyledons of seedlings of Larix decidua kept in darkness there is a single and well evident prolamellar body, with a lamellar system without grana and very reduced. After exposure to light, the progressive disappearance of the prolamellar body is, as a rule, noticed and one can observe the organisation of the usual structure of the chloroplasts, although with underdeveloped grana. In the cotyledons of Picea kept in darkness, the chloroplasts have several prolamellar bodies; from each of them a lamellar system, with many differentiated grana is formed. Picea chloroplasts, therefore, are initially more advanced than Larix, and light induces a more rapid evolution. These results are particularly interesting as they permit a deeper insight into those striking differences in the physiological behaviour of the two above-mentioned species, that were put in light by the same Author.