Gravitropic response inEichhornia cressipes (water hyacinth) I. process of gravitropic bending in the peduncle

Abstract

In the last half of the anthokinetic cycle inEichhornia cressipes the peduncle showed a two-step bending response which started after the completion of the flowering: the primary bending in the upper region and the second one in the base of the peduncle. In the present study, only the primary bending response was examined and the following results were obtained.

• (1) Under the condition in the Western Japan, the anthokinetic cycle completed in 36–40 hr. The inflorescence started to grow during night, reaching the full flowering stage next morning, and the bending was initiated in the evening and completed next morning.

• (2) The bending was a positive gravitropism since the peduncle did not show bending when it was placed on a horizontal clinostat rotating at 2–3 rpm, or when the plant was placed up-side-down.

• (3) Before the end of flowering phase, the peduncle showed a normal negative gravitropic response but afterward it acquired the property to show a positive gravitropic response.

• (4) The bending was due to the extension of convex side of the peduncle, accompanied by a shrinkage of the concave side. The extension of the upper side was caused by cell extension. At the turning point from negative to positive gravitropic response, the extension of the peduncle ceased for several hours.

From the above results it is concluded that the primary bending response of the peduncle in water hyacinth was a positive gravitropism.