Structural and Immunological Characterization of the Cuscuta pentagona L. Chloroplast

Structural and immunochemical studies were used to determine the photosynthetic potential of the dodder (Cuscuta pentagona) chloroplast. Ultrastructural studies revealed that thylakoid membranes of pre-parasitic phase Cuscuta pentagona are almost all organized into long, overlapping grana stacks of mainly two to five thylakoids with little space between adjacent stacks. Immunoblots reveal chloroplast proteins associated with PSI and 11, as well as cytochrome f and plastocyanin. Stromal extracts contained immmunologically-detectable RuBisCO and phosphoribulokinase. Cytochemical localizations of the oxidizing side of PSI showed product localization on the lumen side of the thylakoid. Immunocytochemical localizations of RuBisCO reveal exclusive labeling in the stroma, whereas antibodies to the PSII proteins, light-harvesting Chl a/b complex and the oxygen-evolving complex of PSII, are concentrated over the thylakoids. A limited capacity for C 0 2 fixation was found in seedlings by monitoring exchange rates in the presence and absence of atrazine. These data indicate that the chloroplast from this species of dodder contains a number of the proteins required for a successful fixation of C 0 2 and the proteins in the thylakoids are organized much like other higher plants, with the exception of the large percentage of the thylakoids organized into grana.