Negative Phototropism Of Rice Root And Its Influencing Factors

Some characteristics of the rice (Oryza saliva L.) root were found in the experiment of unilaterally irradiating the roots which were planted in water. To properly explore the effects of IAA on the negative phototropism of rice root, immunoussay of ELISA (Enzyme linked immunosorbcnt assay) was employed lo determine IAA concentration in root tip, unilateral application of agar block containing IAA on root tip was carried out to investigate the effect of exogenous IAA on phototropic response. And the bending part of the rice root was sliced into semi-thin sections to study its microstructure. (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 compared with that of the shaded side. (3) Root cap was the site of light perception. If root cap was shaded while the root was irradiated the root showed no negative phototropism, and the root lost the characteristic of negative phototropism when root cap was divested. Rice root could resume 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 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 to 40 . (6) Blue-violet light could prominently induce the negative phototropism of rice root, while red light had no such effect. (7) The auxin (IAA) in the solution as a very prominent influencing factor, 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 (8) The results showed that the growth of seminal roots could be regulated by exogenous IAA as well as light, the root was induced to bend toward the site of application with IAA. (9) IAA concentration on the shaded side of adventitious root increased much greater. 1.5 h after the start of irradiation. (10) Caused asymmetric growth of the root cells at the elongation zone and resulted in the bending growth. The unequal lateral IAA distribution can be concluded to be the main cause for the negative phototropism of rice root.