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Alterations in Chloroplast Thylakoids during an in Vitro Freeze-Thaw Cycle ¹

^a Department of Floriculture and Ornamental Horticulture, Cornell University, Ithaca, New York 14853

Plastocyanin and chloroplast coupling factor 1 (CF₁) are released from spinach (Spinacia oleracea L.) thylakoids during a slow freezethaw cycle. CF₁ addition increases the proton uptake of thylakoids previously frozen in sucrose concentrations of 15 mM to 100 mM. Addition of CF₁ and plastocyanin restores the proton uptake of thylakoids frozen in 100 mM sucrose. Plastocyanin and CF₁ release is a manifestation, not the cause, of freeze-thaw damage.

Frozen-thawed thylakoids appear to exhibit two levels of response to sucrose as measured by light-dependent proton uptake. Different levels of protection afforded by sucrose may be due, in part, to quantitative differences in CF₁ release. The results suggest at least three freeze-induced lesions in light-dependent proton uptake by thylakoids: plastocyanin release, CF₁ release, and disruption of the semi-permeability of thylakoids.

¹ This work is part of the Ph.D. thesis of M. P. G.