[Changes in chlorophyll content and chloroplast fine structure in the bracts of davidia involucrata BAILL]

This paper deals with the destruction of plastid pigments and of chloroplast during the bleaching of the bracts of Davidia involucrata BAILL.Changes in pigment content have been analyzed both spectrophotometrically and by thin layer chromatography, whereas changes in the fine structure of leaf pieces have been examined by electronmicroscopy. After fixation in glutaraldehyde and osmium tetroxide, the leaf pieces were embedded in Epon. Thin sections were stained with lead citrate and examined under a Siemens Elmiskop I.In bracts and in normal leaves of Davidia two water soluble pigments were present which have been identified as flavone glycosides. The qualitative composition of the pigments in leaves and in different stages of the bracts was identical.During the 18 days of observation the surface of the bracts increased about 10 fold. The chlorophylls, on the contrary, were completely decomposed. No characteristic changes in the ratio a/b could be detected.With the beginning decomposition of chlorophyll, an alteration of the fine structure of the chloroplast was noted. The piles of thylakoids showed a swelling which began on the outside. At the same time the number of thylakoids was reduced. "Vacuoles" appeared in the stroma, and the osmiophilic globules increased in number. Under natural conditions, the grana-thylakoids in the chloroplasts of bracts from Davidia were disintegrated before the stroma-thylakoids. These findings are contrary to those of other authors.