Abstract
The shoots of a morning glory (Pharbitis nil) called Shidare-asagao display agravitropic and weeping growth. This shoot agravitropism is possibly due to the defective differentiation of endodermal cells. Shoots of the wild type morning glory exhibited distinct circumnutation with circular movements that increase as the plants grow. In weeping morning glory, however, nutation was limited to slight back and forth or side to side movements. The inflorescences of wild type Arabidopsis showed relatively large circular movements. Inflorescences of the pgm-1 mutant, which is defective in starch synthesis, showed reduced nutation. Even more seriously affected were the sgr1-1/scr-3 and sgr7-1/shr-2 mutants, which are defective in endodermal cell differentiation, and the auxin-resistant axr2-1 mutant showed no significant nutational movements at all. Thus, the gravitropic response is an essential component in plant shoot circumnutation. Endodermal cells are involved in such circumnutation possibly because of their role in inducing the gravitropic response.
