Theodore C. Fox

Mollusc/algal chloroplast symbiosis: how can isolated chloroplasts continue to function for months in the cytosol of a sea slug in the absence of an algal nucleus?**

A marine sea slug, Elysia chlorotica, has acquired the ability to carry out photosynthesis as a result of forming an intracellular symbiotic association with chloroplasts of the chromophytic alga, Vaucheria litorea. The symbiont chloroplasts (kleptoplasts) are functional, i.e. they evolve oxygen and fix CO(2) and actively transcribe and translate proteins for several months in the sea slug cytosol. Considering the dependency of plastid function on nuclear genes, the level of kleptoplast activity observed in the animal cell is quite remarkable. Possible factors contributing to this long-lasting functional association that are considered here include: the presence of an algal nuclear genome in the sea slug, autonomous chloroplasts, unusual chloroplast/protein stability, re-directing of animal proteins to the kleptoplast, and lateral gene transfer. Based on our current understanding, the acquisition and incorporation of intact algal plastids by E. chlorotica is aided by the robustness of the plastids and the long-term functional activity of the kleptoplasts appears to be supported by both plastid and protein stability and contributions from the sea slug.

Biochemical Adaptations to Anoxia in Barnyard Grass

Although higher plants require oxygen for growth, they frequently experience low oxygen environments which occur in natural wetlands and during flooding or irrigation. Plants tolerate these conditions for only a short period of time before irreversible damage occurs. We have been studying a group of rice weeds which, like cultivated rice (Oryza sativa), can germinate and grow without oxygen. Echinochloa crus-galli var. oryzicola (hereafter oryzicola) metabolizes its seed reserves under N2 and produces a larger seedling from a smaller seed than rice (Kennedy, Rumpho and VanderZee, 1983b). In response to temperature, oryzicola and rice exhibit similar germination characteristics under aerobic conditions. Under anaerobic conditions, however, oryzicola germinates better and tolerates colder temperatures than rice. Thus, both Echinochloa and rice provide excellent opportunities to study metabolic adaptations to low oxygen stress. In addition, the Echinochloa ‘complex’ is composed of several species that differ in their ability to germinate under anoxia (Kennedy et al., 1983b), each exhibiting a full range of habitat preference and weediness in rice cultivation — an ideal natural system for comparative studies on the biochemistry of these important weed species.