Transmission electron micrographs showing leaf chloroplast and mitochondrial ultrastructure of Arabidopsis grown at three temperatures. Samples were taken at ambient temperature (A and D), elevated temperature I (B, E and F), and elevated temperature II (C). Note that there were larger starch grains in the chloroplasts of A. thaliana leaves grown at ambient temperature than at elevated temperatures I and II. In addition, there were more mitochondria nearby chloroplasts at elevated temperatures I and II than at ambient temperature. St, starch grain; Mi, mitochondrion; Ch, chloroplast. Bar, 1 μm (A-F).