Relationship between chloroplast structure and O2evolution rate of leaf discs in plants from different biotopes in South Finland

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Abstract
The chloroplast ultrastructure, especially the thylakoid organization, the polypeptide composition of the thylakoid membranes and photosynthetic O2evolution rate, chlorophyll (Chl) content and Chia/bratio were studied in leaves of nine plants growing in contrasting biotopes in the wild in South Finland. All the measurements were made at the beginning of the period of main growth on leaves approaching full expansion, when the CO2‐saturated O2evolution rate (measured at 20°C and 1500 μmol photons m−2s−1) was at a maximum, ranging from 19.2 to 6.9 μmol O2cm−2h−1. Among the species, the Chia/bratio varied between 3.75 and 2.71. In the mesophyll chloroplasts, the ratio of the total length of appressed to non‐appressed thylakoid membranes varied between 1.07 and 1.79, the number of partitions per granum varied between 2.8 and 12.0 and the grana area between 21 and 42% of the chloroplast area. There was a significant relationship between the rate of O2evolution of the leaf discs and the thylakoid organization in the mesophyll chloroplasts. The higher the O2evolution rate, the lower was the ratio of the total length of appressed to non‐appressed thylakoid membranes and also the lower the grana area. Although the relationship of the photosynthetic rate with the Chi content and the Chia/bratio of the leaves was not as clear, a significant negative correlation existed between the Chia/bratio and the ratio of appressed to non‐appressed thylakoid membranes, indicating lateral heterogeneity in the distribution of different Chl‐ protein complexes.