Structural and immunological characterization of the Cuscuta pentagona L-chloroplast

Structural and immunochemical studies were used to determine the photosynth etic potential of the dodder (Cuscuta pentagona) chloroplast. Ultrastructur al 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. Im munoblots reveal chloroplast proteins associated with PSI and II, as well a s cytochrome f and plastocyanin. Stromal extracts contained immmunologicall y-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 exclusiv e labeling in the stroma, whereas antibodies to the PSII proteins, light-ha rvesting Chl a/b complex and the oxygen-evolving complex of PSII, are conce ntrated over the thylakoids. A limited capacity for CO2 fixation was found in seedlings by monitoring CO2 exchange rates in the presence and absence o f atrazine. These data indicate that the chloroplast from this species of d odder contains a number of the proteins required for a successful fixation of CO2 and the proteins in the thylakoids are organized much like other hig her plants, with the exception of the large percentage of the thylakoids or ganized into grana.