AOBPreview originally published online on May 16, 2005
Annals of Botany 2005 96(1):149-158; doi:10.1093/aob/mci160
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Soybean Genotypic Difference in Growth, Nutrient Accumulation and Ultrastructure in Response to Manganese and Iron Supply in Solution Culture
1 Instituto Venezolano de Investigaciones Cientificas, Centro de Microbiologia y Biología Celular, Apdo Postal 21827, Caracas 1020-A, Venezuela and 2 Agronomy Physiology Laboratory, University of Florida, PO Box 110965, Gainesville, FL 32611-0965, USA
* For correspondence. E-mail mizaguir{at}mail.ivic.ve
Received: 18 November 2004 Returned for revision: 17 January 2005 Accepted: 28 March 2005 Published electronically: 16 May 2005
• Background and Aims The objective of this research was to characterize the physiology and cell ultrastructure of two soybean genotypes subjected to nutrient solutions with increasing concentrations of manganese (Mn) at two contrasting iron (Fe) concentrations. Genotypes ‘PI227557’ and ‘Biloxi’ were selected based on their distinctly different capacities to accumulate Mn and Fe.
• Methods Bradyrhizobium-inoculated plants were grown in hydroponic cultures in a greenhouse. Nutrient solutions were supplied with Mn concentrations ranging from 0·3 to 90 µM, at either 5 or 150 µM Fe as FeEDTA.
• Key Results For both genotypes and at both Fe concentrations, Mn concentrations from 6·6 to 50 µM did not affect shoot, root and nodule mass, or leaf and nodule ureide concentration. Mn concentrations of 70 and 90 µM did not result in visible toxicity symptoms, but hindered growth and nodulation of ‘Biloxi’. An Mn concentration of 0·3 µM was, however, deleterious to growth and nodulation for both genotypes, and caused an accumulation of ureides in leaves and major alterations in the ultrastructure of chloroplasts, nuclei and mitochondria, regardless of the Fe concentration. In ‘PI227557’, there was also a proliferation of Golgi apparatus and endoplasmic reticulum in the cytoplasm of leaf cells, and nodules showed disrupted symbiosomes lacking poly-ß-hydroxybutirate grains concomitantly with a proliferation of endoplasmic reticulum as well as arrested bacterial division. At 15 µM Fe, ferritin-like crystals were formed in the lumen of chloroplasts of ‘PI227557’ plants. For both genotypes, there was an antagonism between the Fe and Mn concentrations in leaves, the higher values of both microelements being detected in ‘PI227557’. The absence of any detectable relationship between Fe or Mn and zinc, phosphorus and copper concentrations in leaves ruled out those micronutrients as relevant for Mn and Fe nutrition in soybeans.
• Conclusions The results confirmed the greater capacity of ‘PI227557’ for Mn and Fe accumulation than ‘Biloxi’ for most nutrient treatments. Hence, ‘PI227557’ may be a very useful genetic resource both in developing soybean cultivars for growth on low nutrient soils and in physiological studies to understand differing approaches to nutrient accumulation in plants.
Key words: Glycine max, manganese, iron, zinc, copper, phosphorus, leaf ultrastructure, nodule ultrastructure, ferritin, plant growth, ureide