Identification of genes expressed during ROL barrier formation in rice root

Potential components of the barrier to radial oxygen loss (ROL) are suberin and/or lignin, which accumulate at the cell wall in the cells of peripheral cell layers of the root. Chemical composition of the apoplastic barrier in rice roots was characterized and it was suggested that ROL can be restricted by the formation of a suberized exodermis and/or lignified sclerenchyma in the outer part of the root. To characterize reorganization of primary carbon metabolism in rice roots during the ROL barrier formation, we obtained the profiles of polar metabolites and the profiles of fatty acids of different zones of rice roots from plants growing in stagnant (anaerobic) and in well aerated medium. Biochemical data are combined with the results of microarray analysis. Nine days after germination, the seedlings were transferred to well aerated nutrient solution or stagnant deoxygenated nutrient solution. Stagnant solution contained 0.1% (w/v) dissolved agar and was deoxygenated (dissolved oxygen, <0.5 mg l–1) prior to use by flushing with N2 gas. After 14 d (23 d old), adventitious roots, 100-150 mm long, were harvested from rice plants grown either in aerated or stagnant conditions and RNA was extracted from 10 mm segments from the regions 0-10 mm, 10-20 mm and 20-30 mm from the root apex have been cut with sterile razor blade and collected and processed separately. Total RNAs were labeled with a Quick Amp Labeling Kit (Agilent Technologies) according to the manufacturer’s instructions. Aliquots of Cy5-labeled and Cy3-labeled cRNA (825 ng each) were used for hybridization in a rice 44K oligo-DNA microarray.