THE ULTRASTRUCTURE OF GRANA IN MESOPHYLL PLASTIDS OF ZEA MAYS

The compartments of the grana of mesophyll plastids of Zea mays are extensively interconnected. In median sections of grana, 16.5% of compartment margins were involved in a Y-shaped conjunction of the loculi of two consecutive compartments with the loculus of an attached fret. Various configurations accounted for the remainder of the compartment margins seen in median sections of grana. Tangential views of grana and serial sections revealed an oblique relationship between the frets and the grana. Analysis of serial sections allows the conclusion that the components of the fretwork are helically wound around a granum.