The compensatory effect is a phenomenon recently found in mutants and transformants with defects in cell proliferation at the leaf base. This is a phenomenon in which the volume of leaf cells is significantly increased compared to normal as if to compensate for the reduction in leaf area caused by the lack of cell proliferation. For example, the Arabidopsis AN3 gene is a positive regulator of leaf cell proliferation, and its loss leads to a drastic reduction in the number of leaf cells. However, the leaf cell size of the an3 mutant is much larger than that of the wild type. This implies that there is some linkage between cell number and cell size as a regulatory system for organ size. Our study revealed that the compensatory action in an3 is regulated by intercellular communication at the leaf base. To elucidate the molecular mechanism, we are working with former members of our lab (Horiguchi Lab. at Rikkyo University and Ferjani Lab. at Tokyo Gakugei University).