A fine structural analysis of chloroplast developmental stages in the fern Davallia fejeensis with comparisons to chloroplasts of other major plant groups.

摘要

Chloroplast development has been widely studied in angiosperms (flowering plants) and gymnosperms (naked seed plants). However, relatively little work on chloroplast ontogenesis, differentiation and division has been done in pteridophytes (ferns). Even less is understood about gametophytic fern chloroplast ultrastructural development, especially in homosporous leptosporangiate ferns which generally release non-green spores from the under-surfaces of their sporophytic leaves or fronds.; In this research, chloroplast development was primarily characterized in sequential stages of gametophytic tissues of Davallia fejeensis by transmission electron microscopy. Methods of scanning electron and light microscopy were also used. Duvallia fejeensis was selected for its relatively thin outer spore wall characteristics, its epiphytic nature and production of abundant spores. This research further describes similarities and differences in chloroplast ultrastructure and development between gametophytic and sporophytic chloroplasts of Davallia fejeensis. Comparisons were made to chloroplasts of other major plant groups including, Pogonatum urnigerum (a bryophyte), Woodwardia virginica (Virginia chain fern), Dennstaedtia punctilobula (hay-scented fern), Pinus strobus (white pine) and Ginkgo biloba (two gymnosperms), and Chrysanthemum leucanthemum (an angiosperm).; The fine structure of Davallia fejeensis chloroplasts were analyzed in gametophytic tissues. Ungerminated spores contain undifferentiated chloroplasts, few grana and numerous membrane-bound vesicles. Chloroplasts within primary emergent protonemal and apical filament cells contain lobes and constrictions possibly mediating ontogenesis and plastid division. Starch deposits and membrane-bound vesicles are present. Undifferentiated proplastids within mature gametophyte prothallus cells contain single, elongated spans of transverse thylakoids with numerous plastoglobuli.; Gametophyte chloroplasts possess elongated, thinly-stacked grana and prolamellar body-like membrane membrane organizations, while sporophyte chloroplasts contain thicker granal thylakoids. Davallia fejeensis spores visibly swell before germination and develop localized green chloroplast clusters. The external spore morphology of Davallia fejeensis, determined by scanning electron microscopy, has characteristics similar to other members of this genus.; Specific findings of this research on gametophyte ultrastructure and development in Davallia fejeensis may further link information on chloroplast differentiation and division in the ferns, with other lower plant groups and angiosperms.