The effect of mechanical stress (partial defoliation and/or shoot decapitation) were studied on gas exchanges and growth of radish and rapeseed plants. Removal of older leaves increased transpiration rate (E) but it didn’t have any influence on net photosynthesis rate (Pn). Shoot decapitation and defoliation of young leaves didn’t influence the Pn of radish but it greatly decreased photosynthesis rate of rapeseed plants. The stress also changed pattern of assimilates distribution and the organs’ growth. In radish plants photoassimilates were translocated to hypocotyls whereas in rapeseed they were mostly used for the growth of leaves and roots. It is concluded that mechanical stress plays important role in sink/source regulation. In this way it has an influence on gas exchange, biomass distribution and the growth of plants. That processes also depend on the types (donor or acceptor) and age of defected organs and plants cultivars.