The chemical properties of the molybdate ion resemble those of sulphate and phosphate, which accounts for interactive effects of Mo, S and P in their assimilation and metabolism.


Molybdenum is taken up as the molybdate anion (MoOf). It has been suggested that uptake of molybdenum involves the same anion transporter

as is involved in the transport of phosphate (PO~4) (Heuwinkel et al. 1992). When phosphate supply was limiting (deficient), tomato plants showed as much as fivefold increase in uptake of radio-labelled MoO"4. Inhibition of molybdate uptake by large amounts of sulphate (SO|') (Marschner, 1995) also suggested that transport of M oO|' involves a common anion transporter. Mutant analysis of Chlamydomonas reinhardti (Limas, 2000) suggests involvement of more than one transporter in molybdenum uptake. Molybdenum uptake by Chlamydomonas involves two transporter systems, a 'high-affinity, low-capacity transporter', which is inhibited by 0.3 mM SO|", and a 'low-affinity, high-capacity transporter', that is not inhibited by S04'. While the former is insensitive to tungstate, the latter is inhibited by it. Bulk transport of molybdenum has, however, been suggested to take place through the low-affinity system described for tomato by Heuwinkel et al. (1992).