Quantification of fine root responses to selenium toxicity

The morphological changes of lettuce and ryegrass roots in response to Se t oxicity were quantified by image analysis. Based on the assumption that soi l stresses increase endogenous ethylene production in plants, changes indic ating higher construction costs for roots, such as decreased specific root length, were expected. As lettuce roots in soil without Se addition (contro l) became older, their width increased whereas their specific length, speci fic surface area and specific volume decreased. In younger lettuce, large S e additions induced changes resembling those identified in the control plan t upon senescence. In older plants, Se fertilisation reversed these changes or made them smaller. Ryegrass roots were not as sensitive to added Se as lettuce roots; a lower dosage stimulated root growth but a higher one reduc ed it.