Phloem loading. A reevaluation of the relationship between plasmodesmatal frequencies and loading strategies. (1/4)
The incidence of plasmodesmata in the minor vein phloem of leaves varies widely between species. On this basis, two pathways of phloem loading have been proposed: symplastic where frequencies are high, and apoplastic where they are low. However, putative symplastic-loading species fall into at least two categories. In one, the plants translocate raffinose-family oligosaccharides (RFOs). In the other, the primary sugar in the phloem sap is sucrose (Suc). While a thermodynamically feasible mechanism of symplastic loading has been postulated for species that transport RFOs, no such mechanism is known for Suc transporters. We used p-chloromercuribenzenesulfonic acid inhibition of apoplastic loading to distinguish between the two pathways in three species that have abundant minor vein plasmodesmata and are therefore putative symplastic loaders. Clethra barbinervis and Liquidambar styraciflua transport Suc, while Catalpa speciosa transports RFOs. The results indicate that, contrary to the hypothesis that all species with abundant minor vein plasmodesmata load symplastically, C. barbinervis and L. styraciflua load from the apoplast. C. speciosa, being an RFO transporter, loads from the symplast, as expected. Data from these three species, and from the literature, also indicate that plants with abundant plasmodesmata in the minor vein phloem have abundant plasmodesmata between mesophyll cells. Thus, plasmodesmatal frequencies in the minor veins may be a reflection of overall frequencies in the lamina and may have limited relevance to phloem loading. We suggest that symplastic loading is restricted to plants that translocate oligosaccharides larger than Suc, such as RFOs, and that other plants, no matter how many plasmodesmata they have in the minor vein phloem, load via the apoplast. (+info)Glandulocalyx upatoiensis, a fossil flower of Ericales (Actinidiaceae/Clethraceae) from the Late Cretaceous (Santonian) of Georgia, USA. (2/4)
(+info)Triterpene saponins from Clethra barbinervis and their hyaluronidase inhibitory activities. (3/4)
An extract of Clethra barbinervis with an inhibitory effect on hyaluronidase activity was fractionated guided by the results of an assay. From the active fractions, seven new triterpene saponins (1-4, 6-8) and a new lignan glycoside (14) were isolated together with 14 known compounds (5, 9-13, 15-22). Some of the saponins (2, 3, 9) were revealed as hyaluronidase inhibitors similar to epicatechin (17). (+info)Structures of ryobunins A-C from the leaves of Clethra barbinervis. (4/4)
From a MeOH extract of the leaves of Clethra barbinervis Sieb. et Zucc., ryobunins A-C, three new triterpene glucosides, i.e. one ursane, one seco-ursane and one oleanane-type glucoside, along with four known compounds were isolated. Their structures were elucidated based on chemical and spectral evidence. (+info)Clethraceae is a family of flowering plants that includes shrubs and small trees. It is primarily found in eastern Asia, with a few species in southeastern North America. The family is characterized by simple, alternate leaves and showy, bell-shaped flowers. Clethra alnifolia, also known as summersweet or coastal sweetpepperbush, is a common species in this family that is native to the eastern United States and is often grown for its fragrant, white flowers.
Actinidiaceae is a family of plants in the order Ericales, which includes shrubs and trees. It contains around 350 species, with the most well-known genus being Actinidia, which includes the kiwi fruit (Actinidia deliciosa). These plants are native to temperate regions of Asia, particularly China, Japan, and Korea. They typically have simple, alternate leaves and small flowers with both male and female reproductive structures. The fruits of these plants can be edible and are often eaten fresh or used in jams and other products.