Study On The Mechanism Of Negative Phototropism Of Rice Root

From the rice root growth and curve in water culture, all the seminal roots, adventitious roots and their branched roots bent away from light. To properly study the mechanism of negative phototropism of rice root, four rice (Orysa sativa L.) varieties"Yaodaoliuhao","Sanlicun"(large panicle variety),"xianyou 63"(too many roots variety) and"Ribenqing"(Japonica) were used in this experiment"Yaodaoliuhao","Sanlicun"were used for the investigation of the rice root growth and curve in water culture,"xianyou 63"was used for the experiments of photoreceptor of negative phototropism of rice root, and"Ribenqing"(Japonica) was for the study of the effect of cpt1 gene on negative phototropism of rice root. Chemical reagent(such as CaCl2,EDTA)and hormones(IAA, TIBA, CTK, ABA,GA and ethephon)with different concentrations were applied to investigate their contribution on negative phototropism of rice root. Rurthermore, the photoreceptor, signal transduction elements and the express of cpt1 gene that encoded for IAA carrier protein during negative phototropism of rice root were invesgated, too. Some fruits were acquired after corresponding experiments as followed:1 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.2 The effect of light quality on phototropic bending could be induced prominently by blue/UV light, while not be induced by red or far-red light. Absorption spectrum of the extracted solution from rice cap had two peaks under 350nm and 450nm accordingly, and the molecular weight of the 120KD protein of the cap under unilateral light was larger than that under the dark. It suggested that the blue light receptor might be the photoreceptor might be the photoreceptor for the negative phototropism in rice root3 Ca2+, EDTA, EGTA, EB, inositol, LiCl, FC, Vanadate, CTX, PTX, H2O2, sucrose, pH with different concentrations were employed to investigate their effects on phototropic bending. From the results, Ca2+, IP3, LiCl, G protein and sucrose showed positive regulation for signal transduction during negative phototropism of rice roots; the negative phototropism of rice roots prefer proper concentration of H+-ATPase on plasma membrane and pH, or will be reversed; H2O2 had different effects on rice root for it had a positive regulation for rice lateral roots, while negative to rice primary roots. The present experiments suggested that many signal transduction during negative phototropism of rice (Oryza sativa L.) root should be attributed the coorperation of different signal transduction elements more than a single elements.4 Hormones with different concentrations were applied and it was found that they had different effects on negative phototropic bending. Results showed that (1) ABA, GA and ethephon had almost no effect on the negative phototropism of rice root, while CTK obviously inhibited the growth and negative phototropic bending of rice root. (2) 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. (3) The negative phototropic bending could be regulated by exogenous IAA as well as light, the root was induced to bend toward the site of the application, caused asymmetric growth of the root cells at the elongation zone and resulted in the bending growth. IAA concentration on the shaded side of adventitions root increased much greater 1. 5 h after the start of irradiation. The une qual lateral IAA distribution can be concluded to be the main cause for the negative phototropism of rice root.5 From the effect on the cpt1gene on the correlation of asymmetric distribution of IAA with negative phototropism of rice root we found that the negative phototropism of rice root was improved by 1 mg·L-1 CaCl2 and 0.001 mg·L-1 IAA after 24h light but constrained by 1 mg·L-1 EDTA, which is similar to the expression of cpt1 gene. It could be concluded that the asymmetric distribution of IAA was an important step on the negative phototropism of rice root, which probably be taken by CPT1 as a carrier of IAA.