Catherine Cheniclet

A Ubiquitous Plant Housekeeping Gene, PAP, Encodes a Major Protein Component of Bell Pepper Chromoplasts

We have isolated a cDNA (PAP) corresponding to a single nuclear gene that encodes an approximately 30-kD major protein of bell pepper (Capsicum annuum L.) fruit chromoplasts. RNA and protein analyses revealed that, although at a low level, this gene is also expressed in every organ of the plant, the amount of the corresponding transcript and protein dramatically increasing in the latter stages of fruit development. Western-blot and immunocytochemical analyses of purified chloroplasts from leaves and fruits and of chromoplasts from red fruits showed that the encoded protein is the major component of plastoglobules and fibrils and is localized on the outer surface of these lipid structures. Analyses of PAP in plants belonging to different taxa revealed that it is expressed and highly conserved in both monocotyledonous and dicotyledonous plants. The presence of the protein in plastids not differentiating into chromoplasts indicates that PAP is expressed irrespective of the ontogeny of various plastid lines. In light of our results and since the encoded protein, identical to that previously named ChrB or fibrillin, is present in plastoglobules from several species and accumulates in the fibrils of bell pepper chromoplast, we propose to designate it as a plastid-lipid-associated protein.

PRESENCE OF LEUCOPLASTS IN SECRETORY CELLS AND OF MONOTERPENES IN THE ESSENTIAL OIL: A CORRELATIVE STUDY

ABSTRACT Analytical and structural studies were performed on 45 species of higher plants containing specialized secretory structures and/or producing essential oils or resins. Significant amounts of volatile compounds, mainly monoterpenes and sesquiterpenes, were recovered from these species. The specialized structures included glandular hairs, resin ducts, secretory cavities and idioblasts. During the ultrastructural investigation, special attention was paid to the plastidome. A number of secretory cells contain true leucoplasts, devoid of thylakoids and ribosomes. The comparison between analytical and structural data showed a very close correlation between the presence of leucoplasts in secretory cells and the significant quantities of monoterpenes (hydrocarbons or oxygenated compounds) in the volatile extract. Moreover, a morphometric estimation of leucoplast development in the cells suggested a quantitative relationship between the expansion of this plastidome and the ratio of monoterpenes in the oil....

Interspecific potato somatic hybrids between Solanum berthaultii and Solanum tuberosum L. showed recombinant plastome and improved tolerance to salinity

In this study three somatic hybrid lines originating from protoplast fusion between Solanum tuberosum cv. BF15 and Solanum berthaultii were subjected to a detailed molecular analysis using the I-SSR-PCR technique based on 5′-anchored microsatellite primers. The data obtained revealed a polymorphism between the different lines, suggesting that they correspond to symmetric hybrids. The analysis of chloroplast genome of these hybrids showed that they are resulting from a recombination between parental plastomes. When transferred to a greenhouse, these hybrid lines displayed an improved vigour compared to the cultivated potato BF15 parent. Indeed, an important growth rate and high tuber yield and weight were obtained for these hybrids compared to the parent. Some of these hybrids showed also an improved ion homeostasis control and they seem to display a better tolerance to salt stress compared to the potato BF15 parent.

Localization of the enzyme geranylgeranylpyrophosphate synthase in Capsicum fruits by immunogold cytochemistry after conventional chemical fixation or quick‐freezing followed by freeze‐substitution. Labelling evolution during fruit ripening

The enzyme geranylgeranylpyrophosphate synthase (GGPPS), which plays a key role in the synthesis of diterpene compounds, carotenoids and higher terpenoids, has been localized in Capsicum fruit cells by ultrastructural immunogold cytochemistry, after conventional chemical fixation of tissues and quick‐freezing followed by freeze‐substitution of isolated chloroplasts and chromoplasts. In agreement with previous biochemical studies on cell fractions, the enzyme seems restricted to the plastid compartment. Together with the phenotypic changes of the fruit and the ultrastructural modifications of the plastids during the transition of chloroplasts to chromoplasts, the amount of immunolabelling over plastid sections increases more than a ten‐fold factor in the course of fruit ripening. In chemically fixed tissues, the gold labelling of chloroplasts is very faint and erratically localized whereas in further transition stages, and in chromoplasts, most of the gold particles surround the developing plastoglobuli, which are the characteristic carotenoid‐bearing structures. Because of the very low and inconstant labelling of chloroplasts in green fruits after chemical fixation, cryofixed and acetone freeze‐substituted purified plastids were used as a model system for an accurate localization of the enzyme in these organelles. Quick‐freezing in buffered sucrose by slam‐freezing on a cold copper block results in optimal preservation of the plastids and improved labelling of GGPPS. The enzyme is not scattered at random throughout the stroma. Gold particles are concentrated in distinct stroma regions, and especially at the sites of initiation of stroma globuli which are the early structural event of carotenoid accumulation. A few gold particles are also present on the margins of thylakoids and, presumably, on the plastid envelope. This paper reports further evidence of the central role of the plastid compartment in the production of C20 isoprenoid intermediates in the plant cell, shows the spatial relationship of the enzyme geranylgeranylpyrophosphate synthase with the plastid substructures and the existence of several GGPPS pools within the plastids. It demonstrates the interest of cryo‐methods for an accurate localization of various enzymes in plant cells.

Differentiation of leucoplasts: Comparative transition of proplastids to chloroplasts or leucoplasts in trichomes ofStachys lanata leaves

SummaryThe development of proplastids to chloroplasts or leucoplasts was followed in uniseriate nonglandular hairs, containing chloroplasts, and in glandular hairs, containing leucoplasts, ofStachys lanata leaves. Both hairs grow at the same time from the epidermis.Both chloroplasts and leucoplasts originate from structurally identical proplastids in meristematic cells. At the early stage, ribosomes are absent. After production of the first ribosomes, each plastid population differentiates along its own developmental pathway.In nonglandular hairs, ribosome multiplication occurs within the plastid stroma and a thylakoid system with grana stacks is formed. Ribosomes are attached to membrane vesicles produced by the inner membrane of the plastid envelope, to thylakoids, or are clustered in specialized areas of the stroma. Further development produces typical, small differentiated chloroplasts.In glandular hairs, the production of additional complete ribosomes ceases early. Smaller, transient dense particles are seen within the stroma in the course of the developmental process. The plastids increase in size and there is a transient tubular system but no thylakoids develop. Plastid division proceeds by neck constriction. The latter stage of leucoplast differentiation is characterized by the complete disappearance of ribosomal material and of tubular inner membranes. DNA nucleoids are obvious throughout the developmental period.Unlike chloroplasts, the development of these nonphotosynthetic heterotrophic organelles and the expression of their specialized metabolic activity probably does not involve the synthesis of specific peptides via plastoribosomes.

Immunocytochemical detection of ribulose bisphosphate carboxylase in capsicum plastids

Ribulose bisphosphate carboxylase (RUBPCase) was localized by fluorescence and gold immunocytochemistry in Capsicum fruits. Chloroplasts of the green fruit are heavily labelled. A positive staining is also obtained with chromoplasts of the ripe rad fruit, but gold labelling is fainter. The presence of reactive RuBPCase in chromoplasts is discussed in relation with the absence of ribosomes in these plastids.