"Boro em mamoneira: Aspectos morfológicos e fisiológicos relacionados à deficiência e toxicidade" / Boron in castor bean plants: Morphologic and physiologic aspects related to the deficiency and toxicity

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The castor bean production has highlighted as one of the most promising crops in cerrado and semi-arid farmlands, as the castor oil, besides being used in several industries, presents potential for biodiesel production. This work is based in the following hypotheses: a) the production of seeds and castor oil is related with appropriate supply of boron (B), and the interval between the deficiency and boron toxicity is narrow; b) The B toxicity is as serious as its deficiency; c) the phloem mobility in this plant is low or restricted. The objective was to evaluate the effects of boron deficiency and toxicity in castor bean plants (Ricinus communis L.), utilizing doses of this micronutrient in nutrient solution, and to evaluate the phloem mobility of boron using 10B enriched compound, through two experiments: 1) doses of 0; 0.025; 0.05; 0.10; 0.27; 2.70; 5.40 mg L-1 B in nutrient solution, with analysis of dry matter weight, ultra-structural evaluations, photosynthesis and transpiration rates, and viscosity and oil content in the produced seeds. 2) Three applications of acid boron solution in leaves (2.7 mg of B enriched in 10B per plant) and in nutrient solution (1 mg of B enriched in 10B per plant) with analysis of boron isotope ratio by ICP-MS. Among the results it was verified that there was not fruit yield in plants submitted to doses of 0 and 0.025 mg L-1 B. However, the fruit yields were not affected in plants with boron toxicity symptoms in leaves. The main ultra-structural alterations showed in boron deficiency was the thickness (or swollen) of medium lamellae and the absence of starch granules. The oil contents and viscosity in produced seeds did not show differences among the treatments. The photosynthesis and transpiration rates were lower in the plants with deficiency and and there was not significant differences among the treatments with B toxicity. In the second experiment, it was verified the occurrence of boron phloem mobility to fruits from the B applied to the leaves, and low phloem mobility of boron from leaves to the roots. The application of 1 mg of B per plant in each changes of nutrition solution was shown more efficient to increase the production and B rates in plants than applications of 2.7 mg of B per plant through the foliar application. It concludes that, in this species, the boron toxicity is not as harmful to fruit production as boron deficiency and the phloem mobility occurs from leaves to fruits, but not to roots

ASSUNTO(S)

isótopos estáveis foliar fertilization micronutrientes micronutrients adubação foliar stable isotopes photosynthesis fotossíntese

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