ABSTRACT: Investment in soil phosphorus (P) capital in the tropics is often constrained by poor availability of mineral fertiliser to small-scale farmers. Consequently, new sustainable agricultural cropping strategies are required to maintain fertility and maximise crop yields. The co-application of Tithonia diversifolia (Tithonia) green manure and mineral fertiliser (KH2PO4) together (integrated nutrient management) in comparison to the addition of one or the other alone has been hypothesized to promote crop P uptake. The aim of this study was to critically evaluate the benefits of integrated nutrient management practices in laboratory experiments. Wheat was grown as a test crop in microcosms to which either 32P-labelled mineral fertiliser or 33P-labelled Tithonia was added either singly or in combination. Exclusion meshes were used to determine the role of arbuscular mycorrhizal (AM) fungi in P uptake from the different P sources. The rate of uptake of both 32P and 33P by mycorrhizas was similar, and the rate of mycorrhizal P capture was comparable to that of roots. Generally, there was little difference in wheat P acquisition under integrated nutrient management treatments in comparison to P acquisition from 32P-mineral fertiliser or the addition of 33P-Tithonia alone. Overall, Tithonia residues were not very effective in supplying P to wheat over a short time evaluation period, suggesting that mineral fertilisers will still be required to satisfy crop demand.

Esta revisão considera a importância da compartimentação para a regulação do metabolismo de carboidratos nas folhas, com destaque especial para o papel do vacúolo como local de armazenamento de carboidratos solúveis derivados da sacarose e seu característico metabolismo. Inconsistências entre as propriedades dos vacúolos e o comportamento in vitro das enzimas de biossíntese de frutanos são também destacadas, uma vez que não dão suporte à hipótese de que o vacúolo, é o local de síntese e armazenamento desses compostos. A compartimentação do metabolismo de carboidratos em diferentes tipos de células também é considerada em folhas de gramíneas C3 de regiões temperadas. Através de estudos com células isoladas e de imunolocalização são apresentadas evidências de diferenças significativas entre o metabolismo de carbono em epiderme, mesófilo, bainha de feixes e tecidos vasculares; são discutidas as implicações dessas diferenças no controle do metabolismo foliar.

This review considers the importance of compartmentation in the regulation of carbohydrate metabolism in leaves. We draw particular attention to the role of the vacuole as a site for storage of soluble sugars based on sucrose, and discuss briefly their characteristic metabolism. We also point out inconsistencies between the observed properties of vacuoles and the behaviour in vitro of the enzymes of fructan biosynthesis that do not support the hypothesis that the vacuole is the site of synthesis as well as of storage. We also consider compartmentation of carbohydrate metabolism between different cell types, using mainly our studies on leaves of temperate C3 gramineae. Here we present evidence of significant differences in carbon metabolism between epidermis, mesophyll, bundle sheath and vasculature based upon both single-cell sampling and immunolocalisation. The implications of these differences for the control of metabolism in leaves are discussed.