Semi-viviparous embryo development and dehydrin expression in the mangrove Rhizophora mucronata Lam.

Rhizophora mucronata Lam. is a tropical mangrove with semi-viviparous (cotyledon body protrusion before shedding), non-quiescent and non-desiccating (recalcitrant) seeds. As recalcitrance has been thought to relate to the absence of desiccation-related proteins such as dehydrins, we for the first time systematically described and classified embryogenesis in R. mucronata and assessed the presence of dehydrin-like proteins. Embryogenesis largely follows the classic pattern till stage eight, the torpedo stage, with the formation of a cotyledonary body. Ovule and embryo express radical adaptations to semi-vivipary in the saline environment: (1) A large, highly vacuolated and persistent endosperm without noticeable food reserves that envelopes the developing embryo. (2) Absence of vascular tissue connections between embryo and maternal tissue, but, instead, transfer layers in between endosperm and integument and endosperm and embryo. Dehydrin-like proteins (55–65 kDa) were detected by the Western analysis, in the ovules till stage 10 when the integuments are dehisced. An additional 50 kDa band was detected at stages 6–8. Together these results suggest a continuous flow of water with nutrients from the integument via the endosperm to the embryo, circumventing the vascular route and probably suppressing the initially induced dehydrin expression

Pteridophyte fungal associations : current knowledge and future perspectives

Current understanding of the nature and function of fungal associations in pteridophytes is surprisingly patchy given their key evolutionary position, current research foci on other early‐branching plant clades, and major efforts at unravelling mycorrhizal evolution and the mechanisms underlying this key interaction between plants and fungi. Here we provide a critical review of current knowledge of fungal associations across pteridophytes and consider future directions making recommendations along the way. From a comprehensive survey of the literature, a confused picture emerges: suggestions that members of the Lycopsida harbour Basidiomycota fungi contrast sharply with extensive cytological and recent molecular evidence pointing to exclusively Glomeromycota and/or Mucoromycotina associations in this group. Similarly, reports of dark septate, assumingly ascomycetous, hyphae in a range of pteridophytes, advocating a mutualistic relationship, are not backed by functional evidence and the fact that the fungus invariably occupies dead host tissue points to saprotrophy and not mutualism. The best conclusion that can be reached based on current evidence is that the fungal symbionts of pteridophytes belong to the two fungal lineages Mucoromycotina and Glomeromycota. Do symbiotic fungi and host pteridophytes engage in mutually beneficial partnerships? To date, only two pioneering studies have addressed this key question demonstrating reciprocal exchange of nutrients between the sporophytes of Ophioglossum vulgatum and Osmunda regalis and their fungal symbionts. There is a pressing need for more functional investigations also extending to the gametophyte generation and coupled with in vitro isolation and resynthesis studies to unravel the effect of the fungi on their host

Leerboek der gynaecologie

Contents.--1. deel. Tekst.--2. deel. Afbeeldingen.Mode of access: Internet