Aberrant chloroplasts in transgenic rice plants expressing a high level of maize NADP-dependent malic enzyme

 NADP-dependent malic enzyme (NADP-ME) is a major decarboxylating enzyme in NADP-ME-type C₄ species such as maize and Flaveria. In this study, chloroplastic NADP-ME was transferred to rice (Oryza sativa L.) using a chimeric gene composed of maize NADP-ME cDNA under the control of rice light-harvesting chlorophyll-a/b-binding protein (Cab) promoter. There was a 20- to 70-fold increase in the NADP-ME activity in leaves of transgenic rice compared to that in wild-type rice plants. Immunocytochemical studies by electron microscopy showed that maize NADP-ME was mostly localized in chloroplasts in transgenic rice plants, and that the chloroplasts were agranal without thylakoid stacking. Chlorophyll content and photosystem II activity were inversely correlated with the level of NADP-ME activity. These results suggest that aberrant chloroplasts in transgenic plants may be caused by excessive NADP-ME activity. Based on these results and the known fact that only bundle sheath cells of NADP-ME species, among all three C₄ subgroups, have agranal chloroplasts, we postulate that a high level of chloroplastic NADP-ME activity could strongly affect the development of chloroplasts.

Authors and Affiliations

1. Life Sciences Laboratory, Mitsui Chemicals, Inc., Togo 1144, Mobara, 297-0017 Japan, , , , , , JP

   Yuu Takeuchi, Hiromori Akagi & Hideo Honda

2. Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, 2-8-1, Mejiro-dai, Bunkyo-ku, Tokyo, 112-8681 Japan, , , , , , JP

   Naomi Kamasawa & Masako Osumi

Received: 27 January 1999 / Accepted: 20 January 2000

Reprints and permissions