This work is dedicated to Professor Shu-Chen Grace Chen (1948–2007).
Alkaline α-galactosidase degrades thylakoid membranes in the chloroplast during leaf senescence in rice
Article first published online: 24 AUG 2009
© The Authors (2009). Journal compilation © New Phytologist (2009)
Volume 184, Issue 3, pages 596–606, November 2009
How to Cite
Lee, R.-H., Hsu, J.-H., Huang, H.-J., Lo, S.-F. and Grace Chen, S.-C. (2009), Alkaline α-galactosidase degrades thylakoid membranes in the chloroplast during leaf senescence in rice. New Phytologist, 184: 596–606. doi: 10.1111/j.1469-8137.2009.02999.x
- Issue published online: 16 OCT 2009
- Article first published online: 24 AUG 2009
- Received: 7 July 2009 Accepted: 9 July 2009
- alkaline α-galactosidase;
- leaf senescence;
- thylakoid membrane
- •Here, we studied the functional role of a chloroplast alkaline α-galactosidase (OsAkαGal) in the breakdown of thylakoid membranes during rice (Oryza sativa) leaf senescence.
- •We assayed the enzyme activity of recombinant OsAkαGal with different natural substrates and examined the effect of ectopic OsAkαGal expression in rice plants.
- •Recombinant OsAkαGal showed at least a two-fold greater substrate-binding affinity and a 10-fold greater turnover rate to galactolipid digalactosyl diacylglycerol than the raffinose family of oligosaccharides (verbascose, stachyose, raffinose) and melibiose. The OsAkαGal null mutant (osakαgal) displayed a delayed leaf senescence phenotype. OsAkαGal complementation in osakαgal recovered OsAkαGal expression and showed a senescence phenotype similar to that of wild-type plants. Transgenic plants overexpressing OsAkαGal (UbiP-OsAkαGal) exhibited retarded plant growth and development, and showed a pale-green phenotype coupled with a reduced chlorophyll content to 42% in newly unfolded leaves. UbiP-OsAkαGal leaves also showed a 29-fold increase in alkaline α-galactosidase activity compared with wild-type leaves. An ultrastructural study of Ubi-OsAkαGal chloroplasts in newly unfolded leaves revealed abnormal grana organization.
- •Our findings strongly suggest that OsAkαGal is a thylakoid membrane-degrading enzyme involved in the degradation of digalactosyl diacylglycerol during rice leaf senescence.