Mechanisms and regulation of aluminum-induced secretion of organic acid anions from plant roots / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Aluminum (Al) is the most abundant metal element in the earth’s crust. On acid soils, at pH 5.5 or lower, part of insoluble Al-containing minerals become solubilized into soil solution, with resultant highly toxic effects on plant growth and development. Nevertheless, some plants have developed Al-tolerance mechanisms that enable them to counteract this Al toxicity. One such well-documented mechanism is the Al-induced secretion of organic acid anions, including citrate, malate, and oxalate, from plant roots. Once secreted, these anions chelate external Al ions, thus protecting the secreting plant from Al toxicity. Genes encoding the citrate and malate transporters responsible for secretion have been identified and characterized, and accumulating evidence indicates that regulation of the expression of these transporter genes is critical for plant Al tolerance. In this review, we outline the recent history of research into plant Al-tolerance mechanisms, with special emphasis on the physiology of Al-induced secretion of organic acid anions from plant roots. In particular, we summarize the identification of genes encoding organic acid transporters and review current understanding of genes regulating organic acid secretion. We also discuss the possible signaling pathways regulating the expression of organic acid transporter genes.

Mechanisms and regulation of aluminum-induced secretion of organic acid anions from plant roots / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Aluminum (Al) is the most abundant metal element in the earth's crust. On acid soils, at pH 5.5 or lower, part of insoluble Al-containing minerals become solubilized into soil solution, with resultant highly toxic effects on plant growth and development. Nevertheless, some plants have developed Al-tolerance mechanisms that enable them to counteract this Al toxicity. One such well-documented mechanism is the Al-induced secretion of organic acid anions, including citrate, malate, and oxalate, from plant roots. Once secreted, these anions chelate external Al ions, thus protecting the secreting plant from Al toxicity. Genes encoding the citrate and malate transporters responsible for secretion have been identified and characterized, and accumulating evidence indicates that regulation of the expression of these transporter genes is critical for plant Al tolerance. In this review, we outline the recent history of research into plant Al-tolerance mechanisms, with special emphasis on the physiology of Al-induced secretion of organic acid anions from plant roots. In particular, we summarize the identification of genes encoding organic acid transporters and review current understanding of genes regulating organic acid secretion. We also discuss the possible signaling pathways regulating the expression of organic acid transporter genes.

Study of Microbial Population and Enzyme Activities in Intercropped Peanut Rhizosphere with Different Nutrient Application.

The aim of this study was to investigate the effect of different levels of chemical fertilizers (CF) alone or in combination with farmyard manure (FYM) under lime or no lime amelioration on biological properties of the rhizosphere soil of peanut, grown as intercrop with sabai grass (Eulaliopsis binata (Retz.) C.E. Hubb) in an acid lateritic soil. The effect of five fertilization levels viz., no CF (F0), CF @ 20:40:30 (F1), CF @ 40:80:60 (F2) kg ha-1 NPK, F1 + 2.5 t FYM ha-1 (F3) and F2 + 5 t FYM ha-1 (F4) with (2 t ha-1) and without lime application were studied on the bacterial density, dehydrogenase and phosphatase enzyme activities (i.e. acid and alkaline phosphomonoesterases), nitrogen accumulation in nodules and phosphorus solubilizing power at 25, 50, 75 and 100 days after sowing of peanut for two years. Results showed significant effects of fertilization levels and growth stages of the crop on the microbial activities. Populations of symbiotic nitrogen fixing and phosphorus solubilizing bacteria, soil enzyme activities, nitrogen accumulation in nodules and phosphorus solubilizing power in the FYM+CF treated plots significantly increased compared to sole CF treatments under both lime and no lime application. Lime application improved the activity of dehydrogenase and alkaline phosphomonoesterase enzymes, while decreased acid phosphomonoesterase activity. This study revealed that integrated application of optimum level of inorganic fertilizer, farmyard manure along with lime could improve the biological properties of an acid lateritic soil as well as the growth of peanut under sabai grass-peanut intercropping system.

Influence of Soil Ameliorants, Manures and Fertilizers on Bacterial Populations, Enzyme Activities, N Fixation and P Solubilization in Peanut Rhizosphere under Lateritic Soil.

The aim of this study was to investigate relative efficacy of different organic wastes like farmyard manure (FYM) and water hyacinth (WH) and industrial wastes like paper factory sludge (PFS) on balancing with chemical fertilizers (CF) along with soil ameliorants viz., lime (L) or rice husk ash (RHA), another industrial waste, on dry matter production and biological properties of the rhizosphere soil of peanut (Arachis hypogaea), grown as intercrop with sabai grass (Eulaliopsis binata) in acid lateritic soil. Population of symbiotic nitrogen fixing and phosphorus solubilizing bacteria, activity of dehydrogenase and phosphatase enzymes (i.e. acid and alkaline phosphomonoesterases), nitrogen accumulation in nodules and phosphorus solubilizing power of rhizosphere soil were measured after 25, 50, 75 and 100 days after sowing (DAS) of peanut for two years. Results showed significant effects of nutrient sources and growth stages of the crop on the microbial activities. Higher values of all the biological properties and plant growth parameters were recorded significantly under the integrated application of CF and any of the organic or industrial wastes over sole application of CF. Among three organic or industrial wastes WH was superior to others regarding microbial activities at 25 DAS, whereas PFS became superior at 50, 75 and 100 DAS. Application of lime or RHA improved the activity of dehydrogenase and alkaline phosphomonoesterase enzymes, while decreased acid phosphomonoesterase activity. This study revealed that integrated application of organic or industrial wastes, soil ameliorants and inorganic fertilizer, could improve the biological properties of an acid lateritic soil as well as the dry matter production of peanut, intercropped with sabai grass under lateritic soil.

Performance de populações de Milho (Zea Mays L.) em terras altas sob cerrado no Centro-sul do estado do Tocantins, Brasil1

In the state of Tocantins, the crop of maize in the high land under "cerrado" has levels of yield variable, whose average does not exceed 2 t/ha. Events of soil, as acidity, low levels of Ca, Mg, and and organic matter, concur to decrease the yields. The development of genetics materials improved fetching to contribute in the overcoming of there limitations. As initial ativity in a program of genetic improvement, the present study it evaluated a whole of 160 maize populations, in seasons 1994/95, 1995/96 and 1998/99, in the cities of Pedro Afonso and Gurupi, in terms of grain weight (GW), plant height (PH), ear height (EH) and days for feminine flowering (FF). For GW, the effects of the populations were significant in whole the evaluations, occurring yields between 1,59 t/ha the 7,46 t/ha. Populations IAPAR 51, EGO 17, CMS 08, CMS 50, COMPOSTO TERRAS BAIXAS, TAIÚBA, TAITINGA, CMS 28, CMS 15, and SIKALQ, had been distinguished in Pedro Afonso; and 9201, CMS 39, BR 105, and CMS 03, in Gurupi, with yields above of the 5 t/ha. The differences in the productive and agronomics performances in Pedro Afonso and Gurupi, together with significant effect of the interactions populations locals, alert for the conduction of the specifics improvement programs for each local.

No estado do Tocantins, o cultivo de milho em "terras altas sob cerrado" apresenta níveis de produtividade variáveis, cuja média não ultrapassa 2 t/ha. Fatores de solo, como acidez, baixos teores de Ca, Mg, e e matéria orgânica, concorrem para reduzir as produtividades. O desenvolvimento de materiais genéticos melhorados busca contribuir na superação dessas limitações. Como atividade inicial em um programa de melhoramento genético, o presente estudo avaliou um total de 160 populações de milho, nas safras 1994/95, 1995/96 e 1998/99, nos municípios de Pedro Afonso e Gurupi, em termos de produtividade de grãos (PG), altura da planta (AP), altura da espiga (AE) e dias para florescimento feminino (FF). Para PG, os efeitos de populações foram significativos em todas as avaliações, ocorrendo produtividades entre 1,59 t/ ha a 7,46 t/ha. Destacaram-se as populações IAPAR 51, EGO 17, CMS 08, CMS 50, COMPOSTO TERRAS BAIXAS, TAIÚBA, TAITINGA, CMS 28, CMS 15 e SIKALQ, em Pedro Afonso, e K9201, CMS 39, BR 105 e CMS 03, em Gurupi, com produtividades acima de 5 t/ha. As diferenças nas performances produtivas e agronômicas em Pedro Afonso e Gurupi, juntamente com efeitos significativos das interações populações locais, alertam para a condução de programas de melhoramento específicos para cada local.