Journal of Biological Chemistry
Volume 274, Issue 16, 16 April 1999, Pages 10784-10789
Journal home page for Journal of Biological Chemistry

MEMBRANES AND BIOENERGETICS
Cosuppression of Photosystem I Subunit PSI-H in Arabidopsis thaliana: EFFICIENT ELECTRON TRANSFER AND STABILITY OF PHOTOSYSTEM I IS DEPENDENT UPON THE PSI-H SUBUNIT*

https://doi.org/10.1074/jbc.274.16.10784Get rights and content
Under a Creative Commons license
open access

PSI-H is an intrinsic membrane protein of 10 kDa that is a subunit of photosystem I (PSI). PSI-H is one of the three PSI subunits found only in eukaryotes. The function of PSI-H was characterized in Arabidopsis plants transformed with apsaH cDNA in sense orientation. Cosuppressed plants containing less than 3% PSI-H are smaller than wild type when grown on sterile media but are similar to wild type under optimal conditions. PSI complexes lacking PSI-H contain 50% PSI-L, whereas other PSI subunits accumulate in wild type amounts. PSI devoid of PSI-H has only 61% NADP+ photoreduction activity compared with wild type and is highly unstable in the presence of urea as determined from flash-induced absorbance changes at 834 nm. Our data show that PSI-H is required for stable accumulation of PSI and efficient electron transfer in the complex. The plants lacking PSI-H compensate for the less efficient PSI with a 15% increase in the P700/chlorophyll ratio, and this compensation is sufficient to prevent overreduction of the plastoquinone pool as evidenced by normal photochemical quenching of fluorescence. Nonphotochemical quenching is approximately 60% of the wild type value, suggesting that the proton gradient across the thylakoid membrane is decreased in the absence of PSI-H.

Cited by (0)

*

This work was supported by the Danish Biotechnology Program and the Danish National Research Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Present address: Dépt. de Biologie Moléculaire, Université de Genève, 30 Quai Ernest Ansermet, CH-1211 Genève 4, Switzerland.