Phosphorus uptake commences at the earliest stages of seedling development in rice

Seed phosphorus (P) reserves are essential for seedling development, however, we hypothesise that the quantity of P in seeds will lose importance in cultivars that rapidly acquire P via roots. Our objective was to investigate the onset of seedling P uptake in rice (Oryza sativa). This question was addressed through 33P labelled P supply and through measuring P depletion in combination with the detection of P transporter activity in root tissue of three rice cultivars during early seedling development.33P supplied to roots four days after germination (DAG) was detected in shoots two days later, indicating P was taken up and translocated to shoots during early seedling development. Measurements of P depletion from the growth medium indicated P uptake occurred even at 2 DAG when roots were only 3 cm long. By day three, P depletion was rapid and P transporter activity was detected in roots, regardless of levels of seed P reserves present. We conclude that P uptake commences at the earliest stages of seedling development in rice, that the amount of P taken up will be limited by root size and that genotypes with more rapid root development should more rapidly complement seed-P reserves by root P uptake.