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Flowering and fruiting in Valencia orange tree: anatomical, physiological, biochemical and molecular aspects


Commercial orange orchards from São Paulo state show low productivity and yield instability (biannual cycles). A better agricultural management aiming at stable yields depends on a better understanding of the interactions among environmental factors and the physiological processes controlling it. Yield depends on the environment, but also on the genetic constitution of the plant. The citrus plant is composed by organs (Ieaves) that function as sources of photoassimilates (sources) and by various other organs (Ieaves, roots, branches, flowers and fruits) which, at least at some stage of their development, consume carbohydrates produced by photosynthesis (drains). Any organ can accumulate storage resources when there is an excess of photoassimilate production by leaves. These resources can be re-mobilized to other organs when photosynthesis does not supply the demand. Productivity can be evaluated by the relation between production and utilization of carbohydrates. During spring, after induction, intense flowering occurs, followed by high levels of abscission of flower and immature fruits. Photosynthesis and the level of storage products may affect fertilization, as well as fruit set and growth. During summer, climatic conditions favor the production of photoassimilates, which maintain the supply of carbohydrates for the plant growth and the accumulation of storage products, providing nutrients and water for fruit growth. Fruits do not accumulate starch in the juice vesicles, but there is storage of organic acids, thus linking respiration cycles, the translocation from leaves and the sugar metabolism directly in the fruit. Little is known about the N metabolism in orange plants, despite the studies on foliar N nutrition. This project aims to analyze the physiological, biochemical and molecular interactions during photosynthesis, flowering and fruit set of the orange cultivar Valência. To achieve these goals, experiments will be performed in the field, under natural conditions, and in the greenhouse, with controlled environmental conditions. Besides flowering and fruit set, the seasonal and daytime variation of photosynthesis will be evaluated in the field experiments, as well as the water balance relations and the enzymes involved in carbon and nitrogen metabolism. The expression patterns of genes related to flower development will also be evaluated in different phenological stages. The hormones and carbohydrates involved in the flowering and fruit set processes will be evaluated under greenhouse conditions and these results will be related to anatomy and gene expression studies. (AU)

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Scientific publications (6)
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
RAFAEL VASCONCELOS RIBEIRO; EDUARDO CARUSO MACHADO; ERICK ESPINOZA-NÚÑEZ; RÔMULO AUGUSTO RAMOS; DANIELA FAVERO SÃO PEDRO MACHADO. Moderate warm temperature improves shoot growth, affects carbohydrate status and stimulates photosynthesis of sweet orange plants. Brazilian Journal of Plant Physiology, v. 24, n. 1, p. 37-46, . (05/57862-8)
RIBEIRO, RAFAEL V.; MACHADO, EDUARDO C.; HABERMANN, GUSTAVO; SANTOS, MAURO G.; OLIVEIRA, RICARDO F.. Seasonal effects on the relationship between photosynthesis and leaf carbohydrates in orange trees. FUNCTIONAL PLANT BIOLOGY, v. 39, n. 6, p. 471-480, . (05/57862-8)
DOVIS, VERONICA LORENA; RIEGER HIPPLER, FRANZ WALTER; SILVA, KARINA IOLANDA; RIBEIRO, RAFAEL VASCONCELOS; MACHADO, EDUARDO CARUSO; MATTOS, JR., DIRCEU. Optimization of the nitrate reductase activity assay for citrus trees. BRAZILIAN JOURNAL OF BOTANY, v. 37, n. 4, p. 383-390, . (10/02981-0, 05/57862-8)
RIBEIRO, R. V.; MACHADO, E. C.; SANTOS, M. G.; OLIVEIRA, R. F.. Photosynthesis and water relations of well-watered orange plants as affected by winter and summer conditions. Photosynthetica, v. 47, n. 2, p. 215-222, . (05/57862-8)
SAO PEDRO MACHADO, DANIELA FAVERO; RIBEIRO, RAFAEL VASCONCELOS; GOMES DA SILVEIRA, JOAQUIM ALBENISIO; MAGALHAES FILHO, JOSE RODRIGUES; MACHADO, EDUARDO CARUSO. Rootstocks induce contrasting photosynthetic responses of orange plants to low night temperature without affecting the antioxidant metabolism. THEORETICAL AND EXPERIMENTAL PLANT PHYSIOLOGY, v. 25, n. 1, p. 26-35, . (07/53520-0, 05/57862-8)
SANTOS, C. M. A.; RIBEIRO, R. V.; MAGALHES FILHO, J. R.; MACHADO, D. F. S. P.; MACHADO, E. C.. Low substrate temperature imposes higher limitation to photosynthesis of orange plants as compared to atmospheric chilling. Photosynthetica, v. 49, n. 4, p. 546-554, . (05/57862-8)

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