Effect of a brassinosteroid analogue and high temperature stress on leaf ultrastructnre of Lycopersicon esculentum

The ultrastructure of tomato leaf disks treated with a biostimulator (0.01 mg dm(-3) BB6, brassinosteroid analogue from Cuba), and subjected to high t emperature (40 degreesC for 1.5 h) was studied. High temperature stress cau sed the appearance of granules in the nucleus, nucleolus and cytoplasm. In chloroplasts and in mitochondria the internal membrane system was disorgani sed and in chloroplasts some starch granules were detected. These symptoms were more marked in the cells treated with BB6. The influence of BB6 on the ultrastructure of leaf cells was apparent also before being subjected to h eat stress.