A novel class of MADS box genes is involved in ovule development in petunia.

We isolated and characterized two ovule-specific MADS box cDNAs from petunia, designated floral binding protein (fbp) genes 7 and 11. The putative protein products of these genes have approximately 90% of their overall amino acid sequence in common. In situ RNA hybridization experiments revealed that both genes are expressed in the center of the developing gynoecium before ovule primordia are visible. At later developmental stages, hybridization signals were observed only in the ovules, suggesting that these genes are involved in ovule formation. To test this hypothesis, we raised transgenic petunia plants in which both fbp7 and fbp11 expression was inhibited by cosuppression. In the ovary of these transformants, spaghetti-shaped structures developed in positions normally occupied by ovules. These abnormal structures morphologically and functionally resemble style and stigma tissues. Our results show that these MADS box genes belong to a new class of MADS box genes involved in proper ovule development in petunia.

Ultrastructural changes of Arabidopsis thaliana pollen during final maturation and rehydration.

Several ultrastructural changes occur during dehydration and subsequent rehydration of Arabidopsis thaliana pollen. The cytoplasmic channels, present in the outer part of the intine of the mature, dehydrating pollen grain, degenerate and develop into electron-dense inclusions. At the same time a large quantity of electron-dense material is deposited in the cavities of the exine. A large number of vesicles is produced in the vegetative cell, and they become predominantly located in the peripheral region near the intine. Starch of amyloplasts is consumed and the lipid bodies which originally surround the sperm cells become randomly distributed. In addition, the individual lipid bodies become enveloped by single rough endoplasmic reticulum cisterns.

Unequal distribution of plastids during generative cell formation in Impatiens.

This paper describes the unequal distribution of plastids in the developing microspores of Impatiens walleriana and Impatiens glandulifera which leads to the exclusion of plastids from the generative cell. During the development from young microspore to the onset of mitosis a change in the organization of the cytoplasm and distribution of organelles is gradually established. This includes the formation of vacuoles at the poles of the elongate-shaped microspores, the movement of the nucleus to a position near the microspore wall in the central part of the cell, and the accumulation of the plastids to a position near the wall at the opposite side of the cell. In Impatiens walleriana, the accumulated plastids are separated from each other by ER cisterns, and some mitochondria are also accumulated. In both Impatiens species, the portion of the microspore in which the generative cell will be formed is completely devoid of plastids at the time mitosis starts.

Ultrastructure and histochemistry of Citrus limon (L.) stigma.

Citrus limon has a "wet" stigma which can be divided in two zones: a glandular superficial one formed by papillae, and a non-glandular one formed by parenchymatic cells. The stigmatic exudate is produced by the papillae after the latter have reached their ultimate size. The papillae of the mature pistil are of varying size and composition. Both the unicellular and multicellular ones are present. The cells at the base of the papillae are rich in cytoplasm, whereas the tip cells are vacuolated. Histochemical analysis has shown that the exudate of Citrus is composed of lipids, polysaccharides, and proteins. Our results indicate that the lipidic component is produced and secreted first, followed by production and secretion of the polysaccharidic component. The lipidic component of the exudate is produced in the basal papillae cells and accumulates as droplets in dilated parts of the smooth endoplasmic reticulum (SER). Subsequently the lipid droplets are transported to the plasma membrane, and transferred by the latter into the cell walls. Then the exudate component is accumulated in the intercellular spaces and in the middle lamellar regions of the walls. Subsequently, the polysaccharidic component of the exudate is produced and secreted by the tip cells of the papillae.

Ultrastructure of transmitting tissue of Lycopersicon peruvianum style: Development and histochemistry.

The development of the transmitting tissue of the style of Lycopersicon peruvianum goes, after the completion of cell division and cell wall formation, through two distinct phases. During the first phase, the cells enlarge and the main part of the intercellular substance, consisting of pectins, is formed. During the second phase, the cells form an extensive rough endoplasmic reticulum (RER) and proteins are incorporated in the intercellular substance. A possible role of these proteins in the incompatibility reaction is proposed.

Callose deposition and plug formation in Petunia pollen tubes in situ.

In Petunia pollen tubes growing in the style there appear to be two ways of callose deposition. The first one is callose deposition outside the plasma membrane as a distinct layer closely appressed to the cell wall. The second one is callose deposition within the cytoplasm as distinct callose grains, leading to the formation of callose plugs. This second way is accompanied by a characteristic ultrastructure of the cytoplasm, namely strong electron-density of the plasma matrix, partial absence of the plasma membrane and the absence of plastids and dictyosomes. For both ways of callose deposition a mechanism is proposed and the function of callose plugs is discussed.