Photosynthesis of enlarged chloroplasts in transgenic tobacco plants

Abstract

Transgenic tobacco (Nicotiana tabacum, Xanthi) plants that contain enlarged chloroplasts in leaf mesophyll cell were constructed. Independent 3 lines of plants were generated by introducing a sense construct of NtFtsZf-2, which is a tobacco nuclear gene encoding a chloroplast localized homolog of the bacterial cell division protein. In T1 progeny, two different types of transgenic plants were observed: (1) plants with cells containing 1-3 enlarged chioroplasts (severe type) and (2) plants with cells containing a mixture of many small chioroplasts and 1-3 enlarged chioroplasts (intermediate type). The outward appearance of the severe and intermediate types of the transgenic plants did not differ noticeably from the wild type plants. However, the severe type plants were most retarded in growth under both high and low light conditions, followed by intermediate type plants. The two types of the transgenic plants exhibited comparable growth with wild type plants under medium light conditions. Transgenic tobacco leaf cells showed comparable contents of photosynthetic components such as PSII, PSI, Cyt f, Lhcal and Lhcbl, Rubisco, and total Chlorophylls to those of cells of wild type plants. Further, no appreciable differences were noticed in ultrastructure between the gigantic chioroplasts and those of the wild type. Despite the similarities in photosynthetic components and ultrastructure of photosynthetic machinery between the wild type and transgenic plants, the overall growth of transgenic plants under low and high light conditions was retarded. In the wild type plants the chloroplasts moved toward the face position under low light and toward the profile position under high light conditions. However, chloroplast rearrangement in transgenic plants in response to light conditions was not evident. In addition, transgenic plant leaves showed greatly diminished changes in leaf transmittance values under both light conditions, indicating that chloroplast rearrangement wa...