Developmental Pattern and Structural Organisation of Leaf Chloroplasts in Lepidozamia peroffskyana

Abstract

The ontogenesis of chloroplasts during leaf development in Lepidozamia peroffskyana Regel is described; this cycad lives in the ground layer of the evergreen subtropical closed forest of south-eastern Australia. Characteristic features in young plastids are long bands of multilayered thylakoids, resembling photosynthetic structures of some green algae and ferns. 'Optional' structures, namely prothylakoid bodies and crystalline inclusions, are present in the pre-grana stages, in relation to the slow rate of leaf development. Mature chloroplasts are characterised by a great number of randomly oriented high grana stacks, a lack of starch, a high ratio of appressed to exposed thylakoids, and a low ratio of Chl a to Chl b; these shade features appear coherent with the natural habitat of Lepidozamia. However, since similar structures have been reported in mature chloroplasts of other cycads living in exposed sites, the existence of a genetically superimposed structural pattern is hypothesised, reflecting a primitive adaptation to weak light conditions of this group of ancient seed plants.