抄録
Physiological damage showing rapid yellowing was widely observed on the fully expanded upper leaves of flue-cured tobacco, cv. MC, in Kanto provinces, in July, 1979 and 1980, just after the continuous course of unusually low temperature and little sunshine. The ultrastructure of damaged leaf tissues was examined by electron microscope. The ultrastructures of naturally senescent leaf tissues and of rapidly yellowing ones by foliar spraying of two chemicals (2-chloroethyl phosphonic acid and maleic hydrazide) and infection with bacterial wilt, were also examined by comparison. In the mesophyll cells of reddish-yellow spots on the damaged leaves, the choroplasts showed some singular ultrastructural changes, such as the presence of electron-dense membrane-bound bodies, striped or latticed unidentified bodies with complex structure, and pseudocrystalline bodies. Many unidentified protuberances were also observed on the cell walls adjoining to intercellular space, whose inner structure was filled with electron-dense and small granular materials. In the mesophyll cells of naturally senescent leaves and of rapidly yellowing ones by other causes, the chloroplasts showed same well-known and usual degenerative changes, such as destruction of lameller system, increase in plastoglobules and so on. Ultrastructural differences mentioned above suggest that some metabolic abnormality might have occurred in the rapidly yellowing leaves with the progress of this damage.
