THE ULTRASTRUCTURE OF PLASTIDS IN THE PETALS OF CALTHA PALUSTRIS L

The petals of Caltha palustris are unusual in that they contain chromoplasts belonging to two different ultrastructural classes. Other forms of plastid are also present and one of these provides the petal with a reflective starch layer. These different types of plastid and several distinctive features of petal morphology all point to a type of petal which is particularly well-adapted to encourage pollination of the flower by insects. chromoplast. It is common for plastids in adjacent cell layers of the same organ to differ from each other in structure and for these differences first to become apparent during very early stages of organ development. The developing chloroplasts in adjacent layers within the primary leaf of Phaseolus vulgaris L. and those within the green root of Azolla pinnata R. Br. both show such cell layer-related differences (Whatley, 1979; Whatley & Gunning, 1981). However, these layer-related variations in plastid ultrastructure are mainly minor and quantitative, as illustrated by small differences in plastid size and in the amounts of starch and thylakoid material present. More fundamental qualitative differences in plastid ultrastructure are typical of only a few specialized types of cell like the bundle sheath cells of some C4 plants and the sieve elements of seed plants (Whatley, 1983a). The petals of Caltha are unusual in that just such major qualitative differences in ultrastructure are shown by the plastids (including the two classes of chromoplast) in each of the three uppermost cell layers. In addition, a fourth type of plastid - a true chloroplast - is present in cells adjacent to the veins.