Effects of trace element stress on the morphology of developing seedlings of lettuce (Lactuca sativaL. grand rapids) as shown by scanning electron microscopy

Abstract

Abstract Five‐day old lettuce seedlings, cultured in 1/10 Hoagland's solution to which copper was added in stepwise increments from 0 to 30 μeq./L., were examined by scanning electron microscopy. Morphological features of control and experimental specimens were analyzed. Observed changes were correlated with concentrations equal to or greater than the toxicity threshold of 14 μeq./L. of copper. The toxicity threshold is marked by a right‐angle bend of the primary root at the hypocotyl‐root junction, an increase in the number of secondary roots, and a reduction in number and length of root hairs. Increased concentrations of copper above the toxicity threshold were correlated with morphological alterations such as loss of the right‐angle curvature of the primary root, decrease in number and length of secondary roots, reduction in number and length of secondary roots, altered distribution and reduction in number of root hairs, reduction in size of the eophyll and cotyledons, and abnormalities in trichome and...