Structural reorganization of thylakoid systems in response to heat treatment

The structural reorganization of pea thylakoid systems in response to osmotic shock in a wide range of temperatures (36-70degreesC) was studied. At temperatures 40-46degreesC, the configuration of thylakoid systems changed from a flattened to a nearly round, whereas thylakoids themselves remained compressed. The percentage of thylakoids stacked into grana at 44degreesC decreased from 71% in the control to 40% in experimental samples, reaching 59% at 48degreesC. At 44degreesC and above, thylakoid systems ceased to respond to the osmotic shock by disordering, in contrast to what happened at lower temperatures (36-43degreesC) and in the control, and retained the configuration inherent in thylakoid systems at these temperatures. At 50degreesC and above, the packing of thylakoids in grana systems changed, and thylakoids formed extended strands of pseudograna. Simultaneously, single thylakoids formed a network of anastomoses through local fusions. At temperatures of 60-70degreesC, thylakoid systems appeared as spherical clusters of membrane vesicles with different degree of separation.