Chloroplast Differentiation in Tomato Root Galls Induced by the Root Knot Nematode Meloidogyne incognita

Primary roots of tomato, Lycopersicon esculentum cv. Marglobe, were cultured aseptically on agar containing a standard nutrient formulation with or without kinetin. When secondary roots developed, cultures were inoculated with the root-knot nematode, Meloidogyne incognita. Following inoculation, the cultures were divided into two groups which were incubated either in total darkness or in 16-h light-8-h dark cycles. At 24 h, 1, 2, 3, and 4 wk after incubation, roots from all cultures were processed for transmission electron microscopy. Fine structural observation of the parenchyma tissue in galls from the inoculated cultures indicated that starch containing plastids or amyloplasts, which are usually present and remain undifferentiated in these root cells, developed into chloroplasts. These chloroplasts contained a membrane system indistinguishable from those found in leaves of intact plants. Although plastid development was not affected when uninoculated cultures were incubated in the light, differentiation of the amyloplast was induced when roots were cultured on the medium containing kinetin. These results suggest that plastid differentiation in the inoculated tissue may be influenced by an accumulation of kinetin in the gall, which is induced by the nematode and serves as the nutrient sink for its feeding.