A comparison of glutaraldehyde and formaldehyde fixation of isolated pea chloroplasts and its implications for the treatment of herbage for nutritional studies

Abstract

SummaryPhotosynthetic electron transport, osmotic volume changes and protein loss on osmotic shock were measured in isolated pea chloroplasts after treatment with a range of aldehyde concentrations at various temperatures and times. ADP+Pi-stimulated oxygen production was the most sensitive to inhibition by the aldehyde treatment. With suitable conditions, osmotic volume changes could be prevented and protein losses on osmotic shock reduced to about 1% of the control value, whilst NH3-uncoupled electron transport retained about 40% of its activity. Results showed that basal, ADP + Pi-stimulated and NH3-stimulated O2 production could be used together to indicate the extent of chloroplast fixation thus providing a way of assessing fixation in preparations where osmotic changes are difficult to measure.Glutaraldehyde (M.W. 100) was found to be 60–80 times as effective as formaldehyde (M.W. 30), on a molar basis, in preventing osmotic volume changes and protein loss on osmotic shock.The application of this work for the production of large amounts of glutaraldehyde fixed chloroplasts and of fixed herbage for use as a tool in nutritional studies in ruminant animals is discussed.