Molecular, functional and ultrastructural characterisation of plastids from six species of the parasitic flowering plant genus Cuscuta

Abstract

Plastids of Cuscuta reflexa Roxb., C. subinclusa D. et H., C. gronovii Willd. and C. campestris Yunck. possess thylakoids and contain both chlorophyll a and b in a ratio similar to that of stem tissue of the systematically closely related but 'normal' green Ipomoea tricolor. In contrast, plastids of C. odorata R. et P. and C. grandiflora H.B.K. do not contain any chlorophyll or possess thylakoids. Light-driven electron transport, as measured by oxygen evolution and indicated by analysis of chlorophyll fluorescence, was present in all chlorophyll-containing species. The photosystem II efficiency was low and ranged from 0.511 to 0.687. The plastid rbcL gene could not be detected in C. odorata, but was present in all other tested species. Neither rbcL transcripts nor the large subunit of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) could be detected in C. odorata and C. grandiflora. Low amounts of the large subunit of Rubisco were detected immunologically in all other Cuscuta species. Apparently, the genus Cuscuta comprises species with different degrees of plastid functionality, ranging from intact chloroplasts, via plastids with impaired protein production and gene expression to plastids with reduced plastome gene content.