## 研究ブログ

2019/08/23

#### 植物の葉の枝分かれに見られる非対称性のルールについて その１

| by A.Nakamasu

A rule of asymmetries observed in leaf divarications 1

When we look a divaricated leaf, it may show several levels of axes in the divarication. The axis along from the apex to the basal of a leaf is main (primary) axis, then lateral axes on the main axis are secondary axes. If the secondary axis has axes, they are tertiary axes and so on. The secondary axes often show bilateral (i.e., apicobasal with respect to the main axis) asymmetry. It means the number of tertiary axes on either side of a secondary axis are greater than another side. The directions of the asymmetry may not be determined at random, those seem to be species specific. That is, a species has leaves with more axes on either of apical or basal side with respect to a primary axis. Though it is species specific, in some plants, a leaf has the both secondary axes with apical-rich or basal-rich asymmetry. Such plants almost always show the leaves with mixed directions of asymmetry. As another exception, some heterophyllous plants show heterophylls with different directions of asymmetry in a plant. Such heterophyllous plants almost always show the leaves with different directions of asymmetry as the change of leaf shape. That is, the direction of asymmetry in a leaf divarication is a characteristic index of the plant species.

①まず、適当なところ（半分より上）で１次軸を切ります。

②切った先端の枝が２次軸をいくつ持っているか数えます。

③１つ飛ばしてその下の2次軸を切り取ります。

④切り取った2次軸が3次軸をいくつ持っているか数えます。

②と④の数に違いがありましたか？
②と④がほぼ同じ場合は、先ほど１つ飛ばした2次軸の左右の枝の数が対称になることが多いです。もし、②と④の数に違いがあった場合は、１つとばした2次軸は左右で非対称になっているのではないでしょうか？

②の先端の2次軸の数が多い場合。。。１次軸に対する先端側（点線で囲った2次軸の右側）が多くなります。

④の２次軸の3次軸の数が多い場合。。。１次軸に対する基部側（同左側）が多くなります。

Please prepare some divaricated leaves of several plant species, then select leaves with spread (i.e., increase the number of lateral axes) toward the bottom.

1) Cut the tip at shorter than the half of the main axis in a leaf.

2) Count the number of secondary axes in the tip.

3) Cut the secondary axis next to the secondary axes on the most apical side in the remaining basal part.

4) Count the number of tertiary axes on the secondary axis.

When you compare the 2) and 4), is there any difference? If there is no (some) difference, secondary axis on the most apical side show symmetry (asymmetry). Moreover, the remaining secondary axis indicates the either (side) of divarication has more axes. Why does this happen? If you are interested in, please refer the following paper.

Asymmetries in leaf branch are associated with differential speeds along growth axes: A theoretical predictionA. Nakamasu, N. J. Suematsu, S. Kimura (2017) Dev. Dyn. 246 (12); 981-991

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