Effects of Season and Low Temperature on Polypeptides from Thylakoids Isolated from Chloroplasts of Pinus silvestris

Thylakoids isolated from pine chloroplasts were solubilized by sodium dodecyl sulphate and the polypeptides were separated by polyacrylamide gel electrophoresis. The chlorophyll-protein complexes, P700-CPa₁ and LH-CPa/b, had apparent molecular weights of 92,000 and 25,000, respectively. When the chlorophyll of P700-CPa₁ was extracted or photobleached, the apoprotein of P700-CPa₁ appeared as a pronounced peak in the polypeptide scan profile. The molecular weight of the apoprotein was 70,000. During autumn and winter the complex P700-CPa₁ was destroyed. This was primarily caused by bleaching of chlorophyll, as the 70,000 apoprotein increased in the scan profile when the complex P700-CPa₁ decreased. The winter destruction of P700-CPa₁ was less pronounced in old needles than in young. Freezing of frost-hardened seedlings did not change the polypeptide scan profile, unless the temperature was lowered below the frost-killing point followed by thawing and post-treatment in light or darkness above 0°C. Again the main destruction occurred in the P700-CPa₁ complex, but in this case no significant increase of the apoprotein was observed. These alterations in the polypeptide scan profile of frost-killed needles were not caused by the low temperature treatment as such, but they occurred after thawing of the needles.