Prone - prone

Japanese: 傾性 - けいせい

Tropism is when a part of a plant responds directional to a stimulus from one direction, while toclination is when the plant moves in a fixed direction regardless of the direction of the stimulus. Therefore, the direction of movement in toclination is structurally determined, and organs that exhibit toclination must have a dorsoventral orientation morphologically or physiologically. Types of toclination include phototropism, thermotropism, seismic toclination, and tactile toclination, but some plants show various toclination reactions but the mechanism of movement is the same, such as the opening and closing movement of the leaves of the Mimosa pudica. Toclination reactions include both growth movement and turgor movement.

[Masayuki Katsumi]

Phototropy

Also called phototropism. A periodic movement that repeats day and night, seen in the opening and closing of flowers. Flowers that open during the day and close at night include wood sorrel and ray flowers of Asteraceae plants, while flowers that open at night include evening primrose and tobacco. In most cases, phototropism in flowers is due to growth, with the opening and closing occurring due to the difference in the growth rate on either side of the petals.

The nyctination movement of leaves that occurs at night is often caused by photoclimatism. In plants of the Balsam family, the leaves droop downward at night and become horizontal during the day. In contrast, in the case of Chinese pigweed, the leaves stand almost vertically at night. These growth movements are caused by the difference in growth rate on both sides of the petiole, and are only seen in leaves that are growing. Plants of the Fabaceae and Oxalidaceae families that have a pulvinus (a joint-like thickening that occurs at the lower or upper end of the petiole) at the base of the leaf show photoclimatism-induced turgor movement based on the volume change of motile cells in the pulvinus. In this case, too, there are plants whose leaf blades droop at night, such as the primary leaves of the scarlet runner bean and the leaves of the wood sorrel, and plants whose leaflets stand up, such as Lotus japonicus and Mimosa pudica. The mechanism of the reversible volume change of the pulvinus motile cells is not yet fully understood.

[Masayuki Katsumi]

Thermophilic

Also called a thermogradient. A movement that occurs in response to temperature differences. Typical examples are the opening and closing of crocus and tulip flowers. These flowers open when the temperature rises by 0.2°C and 1°C, respectively, and close when the temperature falls. This is a type of growth movement. When the temperature rises in the base one-quarter to one-sixth of the petal, the growth rate of the inner cells increases first, whereas when the temperature falls, the growth rate of the outer cells increases first.

[Masayuki Katsumi]

Seismic

Also called seismic inclination. A plant's tendency to react to stimuli such as wind or vibration. It is seen in leaves with pulvinars, with Mimosa pudica being a particularly striking example. The seismic inclination can also be seen with electrical stimulation (electroclination). The seismic inclination is a temporary turgor movement that occurs much faster than tropism or other inclinations. The reaction of Mimosa pudica leaves occurs within one second and is complete in five to six seconds. Electroclination occurs even faster, in a tenth of a second. The sensory hairs on the trapping leaves of the Venus flytrap and the Venus flytrap also show seismic inclination.

[Masayuki Katsumi]

Other tendencies

A tactile reaction caused by touch is called tactile or tactile stimulation, and the movement of the tentacles on the trapping leaves of the sundew is a typical example. There is also tactile stimulation (chemotaxis) seen in the trapping leaves of carnivorous plants.

[Masayuki Katsumi]

[Reference] | Sense | Tropism

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

植物体の一部が、一方向からの刺激に対して方向性をもって反応することを屈性というが、刺激の方向とは無関係に、いつも一定方向へ運動する現象を傾性という。したがって、傾性における運動の方向は構造的に決まっており、傾性を示す器官は、形態的または生理的に背腹性をもたねばならない。傾性の種類には傾光性、傾熱性、傾震性、傾触性などがあるが、なかにはオジギソウの葉の開閉運動のように、種々の傾性反応を示しても運動の仕組みは同じものもある。傾性反応には成長運動と膨圧(ぼうあつ)運動の両方がある。

［勝見允行］

傾光性

光傾性ともいう。昼夜周期的に繰り返される運動で、花の開閉などでみられる。昼間開いて夜閉じるものではカタバミ、キク科植物の舌状花などがあり、夜開くものではオオマツヨイグサ、タバコなどがある。花の傾光性運動は、ほとんどの場合、成長運動によるもので、花弁の両側の成長率の違いによって開閉が行われる。

　夜になるとおこる葉の就眠運動も傾光性による場合が多い。ホウセンカの仲間は夜になると葉は下方に垂れ、昼間は水平になる。逆にアカザでは、夜になると葉はほぼ垂直に立つ。これらは葉柄の両側の成長率の差による成長運動であるから、成長中の葉にだけみられるものである。葉の基部に葉枕(ようちん)（葉柄の下端部や上端部に生じる関節状の肥厚）をもつマメ科、カタバミ科などの植物では、葉枕の運動性細胞の容積変化に基づく傾光性膨圧運動を示す。この場合も、ベニバナインゲンの初生葉やカタバミの葉のように、夜になると葉身が垂れ下がるものや、ミヤコグサ、オジギソウのように小葉が立ち上がるものもある。葉枕運動細胞の可逆的な容積変化の仕組みはまだよくわかっていない。

［勝見允行］

傾熱性

温度傾性ともいう。温度差に反応しておこる運動で、クロッカスとチューリップの花の開閉が代表的な例である。これらの花は、それぞれ0.2℃および1℃以内の温度上昇で開き、下降で閉じる。これは成長運動の一種である。花弁の基部4分の1から6分の1の部分で温度が上昇すると、まず初めに内側の細胞の成長率が増加するのに対し、温度が下降すると、まず初めに外側の細胞の成長率が増す。

［勝見允行］

傾震性

震動傾性ともいう。風や振動などが刺激となって植物が示す傾性反応をいう。葉枕のある葉でみられるが、とくにオジギソウは顕著な例である。傾震性反応は電気的刺激（傾電性）によっても同じことがみられる。傾震性反応は、屈性や他の傾性に比べて非常に速くおこる一時的な膨圧運動である。オジギソウの葉の反応は1秒以内でおこり、5～6秒で終了する。傾電性になるとさらに速く、10分の1秒の範囲でおこる。ムジナモやハエジゴクの捕虫葉の感覚毛も傾震性を示す。

［勝見允行］