Genetic Analysis Of The Ability For Silicon Uptake By Rice (Oryza Sativa L.) Seedling

The silicon (Si) concentration of plant shoots varies greatly between plant species;ranging from about 0.1% to more than 10% (w/w) Si on a dry weight basis. Base on the Siconcentration of the plant tops and the Si to Ca ratio, plants are classified in to Siaccumulator, intermediate type, and Si excluder species. The variation in Si concentration islargely due to different capacities for Si uptake by plant roots. Three uptake modes havebeen suggested: active, passive, and rejective uptake, corresponding for the three Siaccumulator types respectively.Si was absorbed by roots in the form of silicic acid. After uptake, silicic acid in thexylem was immediately transported to the shoot together with the transpiration stream.Most of the Si deposited on the surface of leaf, stem, and the sclerenchyma of vascularbundles, in the form of silica gel. Si in plant can stimulate canopy photosynthesis byimproving leaf erectness, decrease susceptibility to disease and insect damage, preventlodging, and alleviate various abiotic and biotic stresses. But, usually the more Siaccumulates in the shoots, the larger is the effect that gained. The utilization of siliconfertilizer was one way to increase Si concentration in shoot of plant, however, improve theability of Si uptake by root is another way that scientists are dedicating to.Rice (Oryza sativa) is a typical plant that shows active uptake of Si, and canaccumulates Si to levels up to 10.0 % of shoot dry weight. Deficiency in Si, the growth ofrice is negatively affected, and the productivity decreases greatly due to reduced fertility. 40% of the paddy soil areas in the southern part of China, are Si deficient; and about 50% ofpaddy soil in the northern part of China are Si-deficient or potentially Si-deficient soils.However, the most strategy is to breed rice varieties with high ability of Si uptake that canget adequate Si from the Si-deficient soil. Thus, rice can get the beneficial from more Si inplant. Improves light interception characteristics by keeping the leaf blade erect, increasesresistance to diseases and pests and lodging, remediate nutrient imbalances, and other beneficial effects, and decrease the usage of pesticide and Si fertilizer, and this will beuseful for the rice sustaining productivity in China. Genetic dissection of silicon uptakeability in rice will be provide a better understanding of the mechanism of rice si uptakeability and a basis for higher Si uptake ability breeding in rice.In this study, three japonica rice varieties-Nipponbare, Asominori, Kinmaze -and threeindica rice varieties-Kasalath, IR24, DV85-was used to analysis the difference in Si uptakeamong rice genotypes, and two mapping population of recombinant inbreed lines (RIL)-Kinmaze (japonica) /DV85 (indica) RIL and Asominori (japonica) / IR24 (indica)RIL-were used to detect quantitative trait loci (QTL) for Si uptake by root and root dryweight. The results were followings:1. Significant difference in Si uptake ability was observed among rice varieties. The Siconcentration in shoot was affected by root Si uptake ability and the root to shoot ratio.Varieties with lower root Si uptake ability can get higher Si concentration in shoot throughhigher root to shoot ratio. Thus, Si concentration in shoot cannot reflect the ability of theroot Si uptake and it did not appropriate to be an index to detect the root Si uptake ability.Kinetics study indicated that the Si transporters in Kinmaze (japonica) and DV85 (indica)had the same affinity for silicic acid, but with different V_max. The same result was observedin the kinetic study of Asominori (J) and IR24 (I), they had same affinity for silicic acid, butwith different V_max, indicating that difference density of Si transporter in root of rice.2. Two mapping population of recombinant inbreed lines (RIL)-Kinmaze (japonica) /DV85 (indica) RIL and Asominori (japonica) / IR24 (indica) RIL-was used to detect theSi uptake ability in rice. The two RILs followed a continuous one-peak distribution andshow transgressive segregation in both directions for Si uptake by individual plants (SP), Siuptake per unit root dry weight (SR) and root dry weight (RDW). Therefore, these threetraits are polygenic inheritance. Low correlation was observed between the SP and SR, buthighly significant correlation between the SP and RDW in the both RILs populationssuggesting that SP was much more affected by RDW than by SR. Root biomass play animportant role in Si uptake per plant, and negative correlations between the SR and RDWwere observed in the two RIL populations.3. Composite interval mapping (CIM) was conducted by using Win QTL Cart 2.5 software to detected QTLs controlling the Si uptake and the root dry weight in the Kinmaze /DV85 RIL and Asominori / IR24 RIL populations.In the Kinmaze / DV85 RIL, three QTLs on chromosome 7, 8 and 10 were identified for SP with the phenotypic variation (PVE) of 13.2%, 11.0%, and 11.5%, respectively.Four QTLs on chromosomel, 3, 9, and 11 were identified for SR with PVEs of 11.7%, 7.2%, and 15.1%, respectively. And 3 QTLs for RDW were detected on chromosome 2, 3, 7with PVEs of 17.2%, 13.5%, and 8.1%, respectively.In the Asominori / IR24 RIL, three QTLs on chromosome 7, 8 were identified for SPwith PVE of 8.2%, 16.1%, and 10.7%, respectively. Three QTLs on chromosome 3, 7,and 9 were identified for SR with PVEs of 13.5 %, 12.1%, and 11.36 %, respectively. And6 QTLs for RDW were detected on chromosome 1, 2, 4, 7, 8 with PVEs of 8.9%, 7.4%,11.4%, 8.5%, 18.9%, and 12.8%, respectively.The QTL qSILr-3 for SR on the chromosome 3 was detected in both RIL. QTLs for SP,qSILp-7 and qslLp-8 were identified in both RILs, which on chromosome 7 and 8,respectively. And QTLs for RDW on chromosome 2 and 7 were detected in the both twoRILs.4. The AIS lines carried the QTL region for SR, which identified in the two RILsmapping populations, in the chromosome segment substitution lines (CSSLs) of IR24chromosome segments in the Asominori genetic background were selected to detect the Siuptake ability by root. The results showed that all the QTLs for SR detected in the Kinmaze/ DV85 RILs and Asominori / IR24 RILs had a corresponding effect. These showed therealty of these QTLs. Thus, the results from this study will provide a better understandingof the mechanism of rice Si uptake ability and the basis for fine-mapping the genesinvolved, and will be useful for the high Si uptake ability in rice breeding program.