The Effect of 2,4-Dichlorophenoxyacetic Acid and Related Compounds on the Fine Structure of the Primary Leaves ofPhaseolus vulgaris

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Abstract
The epidermal cuticle of the abaxial surface of the primary leaves of Phaseolus vulgaris used for these experiments is not more than 0.15 μm thick except on the walls of basal cells of epidermal hairs. The cuticle apparently has no internal structure; neither channels or canals can be seen passing through it. An examination of the fine structure of leaf tissue 24 h after the application of 1.6 × 10−3 M solutions of 2-chlorophenoxyacetic acid (2-CPA), 4-chlorophenoxyacetic acid (4-CPA), 2,6-dichlorophenoxyacetic acid (2,6-D), and 2,4-dichlorophenoxyacetic acid (2,4-D) has shown that 2,4-D alone, and then only in the light, induces changes in the morphology and internal structure of the chloroplast. As early as 4 h after application, there is an apparent breakdown in the structure of the membrane systems of the cells of the epidermis, palisade, and mesophyll. After 8 h the chloroplasts are distorted and contain electron-dense granules, and the cells appear to be plasmolysed. Subsequently these changes become more pronounced. It is possible that the specific disturbances brought about by 2,4-D reflect its phytotoxic properties.

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