Light Activation of Contractile Roots of Easter Lily

Contractile roots provide for a type of movement in plants that occurs in many plant species but has been given little attention. In the case of Easter lily (Lilium longiflorum Thunb. cv. Nelly White), root contraction serves to pull a bulb down into the soil where environmental conditions are more constant. The contraction is evidenced by a formation of epidermal wrinkles, starting at the base of the root and advancing toward the root tip. The movement function occurs in shallowly planted materials, is lessened at deeper locations, and ceases at a vermiculite depth of ≈15 cm. Examination of the cell shapes and volumes in the contracting sector indicates that movement of the bulb in the soil is achieved by a hydraulic shift in cortical cells. Root contraction is stimulated by light. Perception of the light stimulus does not occur in the root but occurs in the bulblet or possibly in the subtending leaf. Responsiveness to light fades with aging of the root, and experiments with light of different wavelengths indicate that the contraction response is preferentially triggered by blue light.

Measurement of the pulling force of a single contractile root

A technique is described that can be used for direct measurement of the force of a single contractile root. This lifting technique has been tested on five species. It is shown that the results from direct measurement are in general agreement with those obtained with an indirect measurement. This new technique makes it possible to measure the pulling force of plants with specialized movements, e.g., Triteleia hyacinthina, in which contractile roots produce a channel for the movement of the offset. Although Triteleia contractile roots have what has been described as a 100% channel effect, measurements with the lifting technique show that a pulling force can, indeed, be measured. Key words: contractile root(s), monocotyledons, root contraction, plant movement, Triteleia hyacinthina, Sauromatum guttatum.

Phosphorylation of algal centrin is rapidly responsive to changes in the external milieu

Centrin, a calcium-sensitive contractile phosphoprotein, is the major component of the striated flagellar roots of the flagellate green alga, Tetraselmis striata. Flagellar roots contract in response to elevated calcium levels. Data presented here indicate that the level of centrin phosphorylation is rapidly responsive to changes in the cell's external environment. Centrin is dephosphorylated in response to elevated calcium or to heat shock. An increase in centrin phosphorylation accompanies pH shock or ethanol treatment. These changes are compared with flagellar excision, flagellar root contraction, and protein synthesis under the same treatments. We conclude that under certain conditions phosphorylation/dephosphorylation of centrin and extension/contraction of the flagellar root are uncoupled. Possible role(s) of centrin phosphorylation independent of force generation in the flagellar root are discussed.