Architecture of the chloroplast PSI-NDH supercomplex in Hordeum vulgare.

The chloroplast NADH dehydrogenase-like (NDH) complex is composed of at least 29 subunits and has an important role in mediating photosystem I (PSI) cyclic electron transport (CET)1-3. The NDH complex associates with PSI to form the PSI-NDH supercomplex and fulfil its function. Here, we report cryo-electron microscopy structures of a PSI-NDH supercomplex from barley (Hordeum vulgare). The structures reveal that PSI-NDH is composed of two copies of the PSI-light-harvesting complex I (LHCI) subcomplex and one NDH complex. Two monomeric LHCI proteins, Lhca5 and Lhca6, mediate the binding of two PSI complexes to NDH. Ten plant chloroplast-specific NDH subunits are presented and their exact positions as well as their interactions with other subunits in NDH are elucidated. In all, this study provides a structural basis for further investigations on the functions and regulation of PSI-NDH-dependent CET.

Induction, identification and characterization of polyploidy in Stevia rebaudiana Bertoni.

Stevia rebaudiana Bertoni produces sweet steviol glycosides; these are regarded as the most promising substitute for sucrose and have a wide range of applications with high economic value. To improve steviol glycosides yields, we established an efficient method for inducing polyploidy in S. rebaudiana. Treatment with 0.05% colchicine for 48 h or with 0.1% colchicine for 24 h efficiently induced polyploidy in germinating seeds and polyploidy could be accurately identified using flow cytometry. Most of the tetraploid S. rebaudiana plants exhibited apparent variations in cytological and morphological characteristics, and had higher contents of the two main steviol glycosides, stevioside and rebaudioside A, than the diploid controls. These tetraploid plants may be further selected for breeding purposes or micropropagated for commercial production.