GREEN TISSUE WITHIN THE HAUSTORIUM OF THE DWARF MISTLETOE KORTHALSELLA (VISCACEAE) - AN ULTRASTRUCTURAL COMPARISON BETWEEN CHLOROPLASTS OF SUCKER AND AERIAL STEM TISSUES

Korthalsella (Viscaceae) is a dwarf mistletoe attached to its host bra nch by a single haustorium. Plants are leafless with flattened or cyli ndrical stems that function in photosynthesis. When a fresh haustorium is cut the sucker within the host appears bright green. Transmission electron microscopy reveals that this greening is due to chloroplasts, but that their organization differs from those of the aerial stem. Th e three representatives of Korthalsella endemic to New Zealand were th e main species investigated. In the stem, chloroplasts have short stac ks of cylindrical grana interconnected by stroma thylakoids typical of normal chloroplasts. Sucker chloroplasts have a more variable organiz ation, with most containing extensive granal stacks and poorly differe ntiated stroma thylakoids. These granal thylakoids exhibit extensive p artitions formed by appression of adjacent membranes. Some sucker plas tids also approach etioplasts in having a prominent prolamellar body f rom which radiate thylakoids with short partitions. Sucker chloroplast s usually contain a few large starch grains, plastoglobuli, and someti mes also a stroma centre. The extensive granal thylakoids in sucker ch loroplasts of Korthalsella resemble that found in certain shade plants and tissue grown under low light conditions. Sucker chloroplasts prob ably have a low level of photosynthesis. This activity might provide a local source of osmotically active material used to assist transport between host and parasite.