Fig. 4.

Biophysical basis of cell elongation in the coleoptile and mesocotyl of maize (Zea mays) seedlings. Split sections (length: 1 cm), placed on water, display a rapid outward bending response, indicating that the outer epidermal wall is under longitudinal tension (a). Upon incubation in IAA (10 μM) for 24 h, mesocotyl sections respond with the typical inward bending, as documented before for coleoptile segments (b). This result indicates that the epidermis is the primary target tissue for IAA action in this organ