Altered branched-chain amino acid metabolism due to boron deficiency

The importance of boron (B) for living organisms is a puzzling matter. Despite the long established essential micronutrient role of B for vascular plants, only recent research gave insights on the mechanisms of its uptake, transport and direct participation in cell-wall formation. Despite that its precise role in plant metabolism remains elusive. In an attempt to clarify the role of B in plant metabolism the gene expression profile of a persistent response to B suppression was evaluated. For that purpose, the transcriptional profile of Arabidopsis thaliana subjected to 2 days of B deficiency was analyzed and the genes that kept responding 4 days after B deficiency were selected. The gene expression profile of Arabidopsis plants submitted to Ca deficiency was also evaluated and this data cross-compared with the 2 days transcriptional profile obtained under B deficiency. Plants were grown on perlite, which has a low B content. After a period of 2 days at 4 ºC, the containers were transferred to a growth chamber at a temperature of 16/22 ºC (night/day), with a 16 h photoperiod and a light intensity of 150 µmol m-2 s-1, PAR. The plants were watered every other day with a complete nutrient solution in which the B concentration was 25 µM and the Ca concentration of 3 mM. Boron or Ca deficiencies were imposed 19 days after sowing by daily watering the plants with a B-free nutrient solution or with a Ca-free nutrient solution corrected for the nitrate content with magnesium and potassium salts. The gene expression profiles of the plants grown under B deficiency for 2 and 4 days or Ca deficiency for 2 days was analysed with Affymetrix ATH1 Genome Array.The expression profile of the selected genes was further evaluated by RT-qPCR.