Polymorphism in the GBSS gene affects amylose content in US and European rice germplasm

The present study was conducted to investigate the relationship between waxy allelic forms and amylose in European and US rice germplasm. These allelic forms were defined according to the single-nucleotide polymorphisms (SNP) found in the leader intron 5′ splice site (G → T), exon 6 (A → C) and exon 10 (C → T). The combination of these three SNPs accounted for 89.2% of the variation in apparent amylose content in a pedigree of 85 US rice varieties and 93.8% of the variation among 279 accessions in a European germplasm collection. The allelic forms TAC and TCC were found in low amylose varieties. All varieties with intermediate levels of apparent amylose had the GCC allele. High levels of apparent amylose varieties had either the GAT and GAC allele. The sequence AGTTATA in the intron 1 distinguished the low amylose varieties from the other classes regardless of any other base changes. Intermediate amylose varieties can be distinguished from those with high apparent amylose by changes in either exon 6 or exon 10. However the simplest interpretation of the data is that the tyrosine/serine change in exon 6 is responsible for the lower levels of Granule bound starch synthase (GBSS) protein and thus lower levels of amylose in intermediate vs. high amylose verities.     

Morphological and geochemical properties of soil accumulated in hedge-induced terraces in the Massif Central, France

Hedges are part of the landscape in many regions of the world. Among many important roles, they limit soil translocation. Hedges perpendicular to the slope at the lower end of sloping fields result in the formation of soil terraces. Quantification of fluxes of matter at the landscape scale has shown that terraces cannot be neglected. In this study, we try to quantify and explain the origin of the morphological and geochemical properties of terraces. The morphology of the terraces and corresponding stocks of soil material and chemical elements are assessed through a microtopographic study. The 11-ha study area is located on a rolling landscape in the Massif Central (France). The study is focused on three particular terraces. Two DEMs (2.5-m resolution) were established on the study area. The first DEM (DEM₁) represents the actual elevation, using 4600 elevation spots. Elevation cross-sections were computed to determine the extent of the terraces, and a second DEM (DEM₂) was then calculated, excluding all the elevation spots located in terraced areas. The thickness of soil material stored in each terrace is given by DEM_st = DEM₁ − DEM₂. It varies between 0 and 0.63 m, representing a soil accumulation of 3–7 m³ m⁻¹ hedge length. One-hundred and seventy-three samples were taken in the topsoil, and the content in some major and trace elements (Ca, Mg, K, Fe, Mn, Cr and Co) measured and mapped using ordinary kriging. The stock of these elements accumulated in the terraces was computed and compared to the stock eroded considering uniform erosion from the upper part of the fields. Results show a difference in stocks exceeding more than 20% for several elements, showing that uniform erosion is not a satisfactory explanation for the accumulations observed in the terraces. A higher contribution of the area located immediately upslope form the terraces results in a better agreement in the stocks comparison for most of the chemical elements studied. Evidence from coarse fragments study, particle size distribution, soil depth in the upslope part of the fields and microtopography show that the formation of the terraces is probably mainly due to redistributions through tillage. The geochemical properties of the terraces are probably exclusively the result of this mechanical redistribution, except for Mn and Co. Indeed, it is likely that since the plantation of the hedges, seasonal waterlogging conditions have significantly affected the mobility of these two elements through geochemical processes that resulted in their leaching downwards as well as perhaps out of the field.