Role of the epidermis in auxin-induced elongation of light-grown pea stem segments

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Effects of auxin on elongation and cell wall properties were studied using 5th internode segments of light-grown pea epicotyl. The results were: 1. The optimum concentration of 2,4-D for elongation induction was about 1 μg/ml, both for unpeeled and peeled segments. 2. Using stress-relaxation analysis, mechanical properties of the cell wall were expressed by the parameters 1/τ_1, T_0 and T_m. Unpeeled segments were first treated with 2,4-D, then the epidermis was peeled off. Parameters of the epidermal cell wall were conspicuously changed by 2,4-D but those of the inner tissue were not. 3. Actinomycin D and cycloheximide inhibited 2,4-D-induced changes in cell wall parameters, as well as in elongation, of unpeeled segments and of epidermis. 4. 2,4-D did not induce elongation of the isolated epidermis but promoted that of peeled segments. This promotion was smaller as compared with unpeeled segments. 2,4-D did not significantly influence the diffusion pressure deficit of peeled segments but did increase their elastic and plastic extensibilities. 5. We conclude that auxin primarily induces cell wall loosening of the epidermis, most likely through nucleic acid and protein synthesis.
日本植物生理学会の論文