Fine structure, pigment content and photosynthetic activity of variegated leaves of Euonymus fortunei var. radicans

Fine structure, pigment content and photosynthetic activity of variegated leaves of Euonymus fortunei var. radicans have been studied in detail. The middle dark-green leaf areas contain normal chloroplasts with large grana. Their chlorophyll content is high, as is their photosynthetic activity. The marginal leaf areas with mutant plastids are highly light-sensitive. When grown in the shade they are light-green and contain chloroplasts with small grana. In sunlight they are yellow, and in their plastids, in addition to a few single thylakoids, several abnormal membrane structures appear (tubular complexes, cup-shaped stacks of thylakoids, »bridges« between thylakoids). Both the chlorophyll content and the photosynthetic activity of the mutant plastids are low, especially in the yellow tissue. Their photosynthetic efficiency (photosynthetic activity calculated on a chlorophyll basis) is, on the contrary, much higher than that of the normal dark-green tissue chloroplasts. When the leaves are kept in the shade, the yellow leaf areas regreen in a short time and chloroplasts appear in them. This light-green tissue is able to yellow for the second time, when exposed to intense light. Plastids from this yellow tissue have only a few thylakoids. Membrane components, which either could not be built into thylakoids, or which originate from decomposed thylak­ oids, accumulate in special structures (prolamellar bodies, thylakoidal bodies, plastoglobules) which, in the course of further plastid differentiation, could be used or reused for the formation of new thylakoids.