| To properly study the mechanism of negative phototropism of rice (Oryza sativa L.) root, chemical reagent (CaCl2, EDTA) and plant hormone (IAA, TIB A, CTK) were used in our experiment, IAA concentration in the irradiated side and the shaded side of the root tip after irriadiation was determined, and microstructure of the bending part of rice root was observed. All the results were shown as the follows: (1) All the seminal roots, adventitious roots and their branched roots bent away from light, and their curvatures ranged from 25 to 60 °. The curvature of adventitious root of the . higher node was often larger than that of the lower node, and even larger than that of the seminal root. (2) The negative phototropic bending of the rice root was mainly due to the larger growth increment of root-tip cells of the irradiated side than that of the shaded side. (3) Root cap was the site of light perception. If root cap was shaded when the root was irradiated, the root showed no negative phototropism' And the root lost the characteristics of negative phototropism when root cap was divested completely. Rice root could restore the characteristic of negative phototropism when the new root cap grew up, if the original cells of root cap were well protected while root cap was divested. (4) The growth increment and curvature of rice root were both influenced by light intensity. Within the range of 0~ 100 μ mol · m-2 · s-1, the increasing of light intensity resulted in the decreasing of the growth increment and the increasing of the curvature of rice root. (5)The growth increment and the curvature reached the maximum at 30℃ with the temperature treatment of 10~40℃. (6) Blue-violet light could prominently induce the negative phototropism of rice root, while red light had no such effect. (7) The negative phototropism of rice root had nothing to do with the upper part of rice, when the upper part of rice was cut, the root can show the characteristics of negative phototropism with little influence. (8) When rice root was subjected to intermitted irridation, rice root was subjected to the action of light and gravity, it showed the shape as a saw. (9) The growth and negative phototropism of rice root was promoted when the pH value under a certain degree, but when the pH value of the concentration wasabove certain degree, the growth and negative phototropism was inhibited. (10) From the absorbtion spectrum of the abstracts, it could be said that the extractives of the root caps mainly absorb at the field of ultra-violet and blue/UV. (11) In the experiment of EDTA, the chelator EDTA inhibited the growth and negative phototropism of rice root remarkably. (12) The auxin (IAA) in the solution as a very prominent influencing factor, in the range of 0~ 100 mg · L-1 , the auxin inhibited the growth, the negative phototropism and the gravitropism of rice root when the concentration of IAA increased. The response of negative phototropism of rice root disappeared when the concentration of IAA was above 10 mg· L-1 (13) The growth and negative phototropism of rice root was inhibited by auxin transported inhibitor the plant hormone CTK and TIBA, the inhibition degree was enhanced with the enhancement of the hormone of CTK or TIBA. (14) The results showed that the growth of seminal roots could be regulated by exogenous IAA as well as light, and the root bent toward the side applied with IAA in darkness.
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