Chloroplast thylakoids are the site of photosynthetic light reactions, electron transport, adenosine triphosphate (ATP) synthesis and nicotinamide adenine dinucleotide phosphate (NADP) reduction in plant cells. Isolated thylakoids are therefore the necessary prerequisite for many in vitro studies of photosynthetic mechanisms. They are also used to elucidate aspects of photosynthetic responses to freezing, chilling, heat, and high light stress. For many of these studies it is important to work with membranes of closely similar properties over extended periods of time to facilitate direct comparisons of the results. The pigment, protein, and lipid composition of thylakoid membranes, however, vary with plant growth conditions (1–3). Even the solute permeability properties of thylakoids are significantly different between warm-and cold-grown spinach plants (4).