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.