Surface density and volume density measurements of chloroplast thylakoids in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) under chilling conditions

Measurements of ultrastructural characteristics of chloroplast thylakoids are important for studies of ontogenic or ecological limitations of leaf photosynthetic functions. Most frequently, volumetric proportion of thylakoids in the chloroplast is measured; however, such measurement does not provide a direct information about the surface area of thylakoids which is most important from the functional point of view. Therefore, we adapted the stereological method using “local vertical windows” for estimating thylakoid surface area in the chloroplast volume and compared thus obtained surface density results with results of conventional volume density measurements. The methods were tested in the study of chloroplast ultrastructure in the leaves of plants of two maize (Zea mays L.) hybrid combinations, 2013×CE810 and CE704×CE810, developing in control and chilling conditions. Correlation analysis revealed a tight relationship between the granal/intergranal thylakoid surface density and volume density results, both indicating that under chilling conditions the development of the system of thylakoids in maize leaves is suppressed, while the difference is more pronounced in CE704 than in CE810 genotype, known to have a better photosynthetic performance.