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  • Author or Editor: J. Aguirre R. x
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Abstract  

Phosphate rocks are used for phosphoric acid production, which is the basis of agricultural phosphate fertilizers. It is known that phosphate ores contain, due to geological reasons, important amounts of natural radioactivity, mainly U-isotopes and daughters. By studying a specific case in Southwestern Spain, it is shown that the operation of phosphate fertilizer factories clearly enhance the natural radiation levels of its close environment. Levels of U-, Th-isotopes, and other natural radionuclides are given for a wide set of different samples, which support such a conclusion. In addition, the study of isotopic ratios gives information on the environmental behavior of such radionuclides.

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The effect of substrate water potential (Ψ W ) in root growth and proline content of maize seedlings of Tuxpeño Sequía C0 (TSC0) and Tuxpeño Sequía C8 (TSC8), sensitive and resistant to drought respectively, were evaluated. Seventy two hours old seedlings, with 5 cm root length, were maintained for 24 h in vermiculite at Ψ W between −0.03 and −2.35 MPa. Root length, fresh and dry weight, number of lateral roots and proline content were evaluated. Root enlargement of TSC0 was significantly higher than TSC8 at −0.03 MPa, but the response was opposite at low substrate Ψ W . The number of lateral roots was reduced in 23% in TSC8 at the lowest substrate Ψ W (−2.35 MPa) but it was not significantly affected in TSC0. A higher proline content was quantified in the cell division root region than in differentiation root region in both maize populations (5.64 and 6.96 μmol 100 mg −1 of dry weight in TSC0 and TSC8, respectively); and Ψ W between −0.65 and −2.35 MPa induced a drastic and significant increase of proline content in both populations. The statistical interaction between maize population, substrate Ψ W , and root region was highly significant (P≤0.0039) for proline content. The results demonstrated that eight cycles of recurrent selection of Tuxpeño for drought tolerance induced a reduction of the number of secondary roots and proline content in the differentiation root region, but a proline increase in the cell division region when root seedling grow under no restrictive water conditions (Ψ W =−0.03 MPa), beside recurrent selection modified root reaction to low substrate Ψ W by accumulation of dry matter and proline.

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Cereal Research Communications
Authors: Cecilia Peña-Valdivia, Adriana Sánchez-Urdaneta, Carlos Trejo, J. Aguirre R., and Elizabeth Cárdenas S.

The effect of substrate water potential (Ψ W ) in anatomical characteristics of root seedlings of maize Tuxpeño Sequía C0 (TSC0), drought sensitive, and Tuxpeño Sequía C8 (TSC8), drought resistant, were evaluated. Seventy two hours old seedlings, having an average root length of 5 cm, were maintained for 24 h in vermiculite at Ψ W of −0.03, −0.65, −1.48 and −2.35 MPa. Anatomical characteristics from both differentiation and cell division root regions were evaluated. Lowest Ψ W diminished significantly (P=0.0020) transverse root area, number of cells in the cortex parenchyma, thickness of epidermis, exodermis and cortex, and number of metaxylem vessels in both maize populations. Number of metaxylem vessels and cortex thickness was affected only in TSC0 (15% in both cases); in contrast, the number of cortex cells in the differentiation root region increased 25%, independently of the Ψ W , and the thickness of the xylem wall from the differentiation root region increased 93% at Ψ W of −2.35 MPa, in both maize populations. Results suggest that the recurrent selection for drought tolerance induced a significant thinning of the protoderm (78%), endodermis (17%), and xylem vessels (14%) in Tuxpeño maize root and modified the response of root to substrate Ψ W , including several anatomical changes.

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