The effects of external NaCl on thylakoid stacking in lettuce plants

The average degree of thylakoid stacking was determined for loose‐leaf lettuce plants which were grown in complete nutrient solutions containing either 10 or 100mol m −3 NaCl. Digitonin fractionation and differential centrifugation were used to assay the level of thylakoid stacking. Based on a comparison between 10mol m −3 NaCl‐grown and 100mol m −3 NaCl‐grown lettuce plants of equal ages, digitonin assays indicated that significantly less stacking occurred in 100mol m −3 NaCl‐grown plants. Isolated thylakoid membranes from 100mol m −3 NaCl‐grown plants were also characterized by a greater capacity to absorb divalent cations and by a higher chlorophyll a/b ratio. Since plants from both growth salinities were capable of a marked increase in thylakoid stacking upon a transition from high to low irradiance, the observed differences in thylakoid stacking were not attributed to a salinity‐related impairment of stacking mechanisms. Instead, the salinity‐induced differences in thylakoid stacking appear to represent a process of controlled adjustment.