Effects of flooding, tilting of stems, and ethrel application on growth, stem anatomy, and ethylene production ofacer platanoidesseedlings

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Abstract
Flooding of soil, tilting of stems, and application of ethrel to stems variously influenced growth, stem anatomy and ethylene production of 12‐month‐old Acer platanoides L. seedlings. Flooding greatly suppressed height growth, stem diameter growth, and the rate of dry weight increase of leaves, stems, and roots, with root growth suppressed most. Flooding also increased bark thickness above the level of submergence, reduced the xylem increment, and stimulated ethylene production of stems and ACC accumulation in the roots. Tilting of stems inhibited height growth somewhat, increased diameter growth and fiber production on the upper side of the leaning stem, increased ethylene production somewhat on both the upper and lower side of the stem, and induced formation of tension wood on the upper side of the stem. Tilting did not affect dry weight increase of leaves, stems, or roots. Application of ethrel to upright stems increased xylem increment around the stem; in tilted, ethrel‐treated seedlings xylem increment was increased on the upper side of the stem only. Ethrel applied around the stem increased bark thickness in both upright and tilted seedlings. Local applications of ethrel to tilted seedlings increased xylem increment near the site of application. Ethrel also stimulated formation of axial parenchyma cells and increased the width of the xylem rays as well as the number of cells per ray. The following lines of evidence indicated that ethylene had no direct role in inducing formation of tension wood: (1) ethylene production of stems was stimulated more by flooding of soil than by tilting of stems, but only tilting induced formation of tension wood, (2) the increase in ethylene content of tilted seedlings was as great or greater on the lower side than on the upper side of the stem, but tension wood formed only on the upper side, (3) application of ethrel to upright stems did not cause formation of tension wood, and (4) application of ethrel to tilted stems blocked formation of tension wood.