Leaf anatomy of the mosaic Ficus benjamina cv. Starlight and interaction of source and sink chimera components

Abstract

Leaf anatomy was studied in the mosaic Ficus benjamina cv. Starlight and non-chimeric Ficus benjamina cv. Daniel. The number of chloroplasts in a white, chlorophyll-deficient tissue declines as compared to the green tissue. However, their functional activity is retained. The leaf of the mosaic F. benjamina contains two or, sometimes, three subepidermal layers. Mesophyll forms one layer in the green and white parts of leaf palisade and one white and one green layer in the transitional zone (edge). In the transitional zone, green spongy mesophyll is located between two white spongy layers and the proportion of photosynthesizing cells varies. In cv. Daniel, there are two subepidermal layers and one layer of columnar mesophyll cells. According to the morphometry data, the proportion of white zone in the leaf correlates with the leaf position in the whole shoot: the higher the branch order, the larger the proportion of white zone. The total leaf area depends also on its position in the shoot. No such correlation was found in non-chimeric F. benjamina cv. Daniel. In the mosaic chimera, the source-sink status appears to depend on the leaf position in the shoot. Experiments with individual shoots of the same order and elimination of all lateral shoots have shown that the proportion of white zone in new leaves on the shoot increases with the total area of green zone. Thus, the area of assimilating shoot surface affects the formation of leaves in the meristem. A hypothesis was put forward that the source-sink state affects the ratio of green and white parts in the leaf primordium. Products of photosynthesis (carbohydrates) are a possible metabolic signal affecting the meristem. It cannot be excluded as well that the hormonal state undergoes changes in the chimeric plant.