Molecular evidences on transport of thiocyanate into rice seedlings and assimilation by 13C and 15N labelling and gene expression analyses

Thiocyanate (SCN -) can be naturally produced by some plant species during assimilation of endogenous cyanide at very low levels, but higher concentration is detected in the environment from various industrial activities, which poses a potential threat to living organisms. In this study, uptake, transport, subcellular distribution and assimilation of SCN - were investigated using rice seedlings exposed to C-13 and N-15-labbled potassium thiocyanate. Our results showed that rice seedlings had a higher potential for SCN (-) uptake, and more was recovered in roots than shoots. Analysis of subcellular partition revealed that SCN- were mainly deposited in cell wall, and followed by cytosol and organelle fractions. Analysis of stable isotopes in rice tissues showed that the molar ratios of C-13 to N-15 content were inconsistent in roots (0.66) and shoots (0.98). PCR analysis revealed different expression arrangements to 20 selected genes in rice tissues, suggesting that involvements of genes encoding with different enzymes in SCN (-) assimilation are tissue specific. These unique genes should regulate and determine degradation pathway of SCN-. Data from stable isotopes and PCR analysis suggests that "TMT (thiol methylation) pathway", "COS (carbonyl sulfide) pathway" and "CNO (cyanate) pathway" are involved in detoxification of SCN- in rice tissues concurrently at the first-degradation phase; Rice seedlings are also able to degrade both CNO and COS in roots effectively, while innate pools of enzymes cyanase (CYN) and carbonyl sulfide hydrolase (COSase) are non-sufficient for further degrade both intermediates in shoots. Our results presented here provide convincing evidence to clarify transport and detoxification pathways of SCN - in rice seedlings.