Variation in [⁷⁵ Se]selenate uptake and partitioning among tomato cultivars and wild species

Eight Lycopersicon esculentum cultivars and six wild taxa from four Lycopersicon species were tested for their ability to transport and distribute Se under low and high sulphate salinity conditions. Plants were exposed to [⁷⁵ Se]selenate for 1 h. Significant variation was observed in both morphological and transport characteristics that control the short-term uptake and accumulation of selenate in tomato species. Among L. esculentum cultivars under low salinity, selenate uptake ranged from 126-184 pmol g f. wt root^-1 h^-1 and shoot ⁷⁵ Se concentrations ranged from 40-66 pmol g f. wt shoot^-1 . Shoot accumulation was affected by both specific root weight (SRW, root fresh weight/total plant fresh weight) and uptake of the cultivar. Distribution of tracer between root accumulation and transport to the shoot, expressed on a root weight basis, was similar in all cultivars. High sulphate salinity reduced uptake to around 22 pmol g f. wt root^-1 h^-1 in all cultivars and only small differences in shoot ⁷⁵ Se concentration (7.4-10.5 pmol g f. wt shoot^-1 ) were observed, indicating that root uptake rate was the primary determinant of shoot ⁷⁵ Se concentration under these conditions. In the low-salinity treatment wild accessions showed a wider range of uptake rates (52-190 pmol g f. wt root^-1 h^-1 ) and shoot Se concentrations (12-79 pmol g f. wt shoot^-1 ) than the cultivars. High sulphate salinity had a less inhibitory effect on Se uptake in the wild taxa than in the cultivars, with uptake rates of 18-63 pmol g f. wt root^-1 h^-1 and shoot concentrations of 7-28 pmol g f. wt shoot^-1 measured. Differences in uptake, partitioning and SRW all contributed to the variation in shoot ⁷⁵ Se uptake in these taxa at both salinity levels. One cultivar (UC82B) was tested under high chloride salinity. Uptake was reduced by 40% relative to the low salt control, compared with the 87% reduction observed under high sulphate salinity. The apparent inhibition in the presence of chloride salinity could be explained by the 40% reduction in selenate activity calculated for this solution relative to the control. Reduced selenate activity was insufficient to account entirely for the reduced uptake observed in this taxon under high sulphate salinity. In contrast, after allowing for reduced selenate activity, uptake by L. pennellii LA716 was little affected by an increase in sulphate from 2.9 and 38 mM, showing that considerable variation in selectivity of the transport system for selenate versus sulphate exists among Lycopersicon species.