NUKLEONIKA 2005, 50(Supplement 1):S3-S8

Both theoretical models and pharmacological dissection suggest that Cs⁺ influx to arabidopsis root cells occurs through voltage-insensitive cation channels (VICCs), encoded by members of the AtCNGC and AtGLR gene families, and ‘high-affinity’ K⁺/H⁺ symporters (KUPs), encoded by members of the AtKUP/AtHAK gene family. When arabidopsis have sufficient K, it is observed that VICCs mediate most Cs⁺ influx to root cells. However, KUPs contribute more to Cs⁺ influx in roots of K-starved plants. This phenomenon has been attributed to an increased expression of AtHAK5 in roots of K-starved plants. Curiously, although arabidopsis mutants lacking some AtCNGCs show reduced Cs accumulation, mutants lacking other AtCNGCs accumulate more Cs in their shoot than wildtype plants. It is hypothesised, therefore, that the expression of genes encoding diverse K⁺-transporters might be altered to compensate for the absence of AtCNGCs that contribute significantly to cellular K homeostasis. Increased Cs⁺ influx and accumulation could then be explained if the lack of an AtCNGC caused a physiological K-deficiency that increased the expression of AtKUPs. Such observations imply that the consequences of a simple genetic manipulation, such as the mis-expression of a AtCNGC gene, on Cs⁺ influx and accumulation might not be predicted a priori. Finally, since AtCGNCs, AtGLRs and AtKUPs have contrasting Cs⁺:K⁺ selectivities, and their relative expression is determined by diverse environmental variables, both the Cs:K ratio in plant tissues and the absolute rates of Cs⁺ influx and accumulation will depend critically on environmental conditions. This will impact on strategies for phytoremediation and/or the development of ‘safer’ crops for radiocaesium-contaminated land.