Deficiency symptoms and uptake of micronutrients by castor bean grown in nutrient solution

Castor bean is a nutrient-demanding species, but there is still little information on its micronutrient requirements. The objectives of this study were to evaluate the effects of levels of B (2.5, 12.5 and 25.0 µmol L-1), Cu (0.05, 0.25 and 0.50 µmol L-1), Mn (0.2, 1.0 and 2.0 µmol L-1) and Zn (0.2, 1.0 and 2.0 µmol L-1) in a nutrient solution on plant B, Cu, Mn and Zn concentrations and uptake, vegetative growth and fruit yield of castor bean "Iris", grown in greenhouse. The experiment was arranged in a completely randomized block design with three replicates. The first deficiency symptoms were observed for B, followed by Zn, Cu and Mn. The main changes in the cell ultrastructure due to lack of B were thickening of the cell walls and middle lamellae, distorted chloroplasts and tightly stacked thylakoids, besides the absence of starch grains. The Mn, Zn and Cu deficiencies led to disruption of chloroplasts, disintegration of thylakoids and absence of amyloplasts. The concentration and uptake of B, Cu, Mn, and Zn in castor bean plants increased with micronutrient supply in the solution. Fruit yield was drastically reduced by B and Mn deficiencies. On the other hand, the dry matter yield of the shoot and root of castor bean plants was not. In the treatment with full nutrient solution, the leaves accumulated 56 and 48 % of the total B and Mn taken up by the plants, respectively, and the seeds and roots 85 and 61 % of the total Cu and Zn taken up, respectively. This shows the high demand of castor bean Iris for B and Mn for fruit yield. A mamoneira é uma espécie exigente em nutrientes, porém ainda há pouca informação acerca da demanda por micronutrientes. Objetivou-se com este estudo avaliar os efeitos das doses de B (2,5, 12,5 e 25,0 µmol L-1), Cu (0,05, 0,25 e 0,50 µmol L-1), Mn (0,2, 1,0 e 2,0 µmol L-1) e Zn (0,2, 1,0 e 2,0 µmol L-1) nos teores e acúmulos desses elementos, no crescimento vegetativo e na produção de frutos da mamoneira Iris cultivada em casa de vegetação. O delineamento experimental foi o de blocos completos ao acaso, com três repetições. As primeiras manifestações de deficiência foram observadas em B, seguidas das de Zn, Cu e Mn. As principais alterações nas ultraestruturas celulares na carência de B foram o espessamento da parede celular e lamela média, a distorção no formato dos cloroplastos, com tilacoides muito agrupados, além da ausência de grãos de amido. As carências de Mn, Zn e Cu provocaram alterações nas conformações dos cloroplas