Probing the effects of light and temperature on diurnal rhythms of phytosiderophore release in wheat

* The existing literature is ambiguous as to whether the diurnal pulse in phytosiderophore (PS) release in the Poaceae is mediated by light or temperature, or both. * Here, wheat (Triticum aestivum cv. Yecora Rojo) seedlings were grown in Fe-sufficient (pFe = 16.5) and Fe-deficient (pFe = 17.8) chelator-buffered nutrient solutions. Six different light/temperature regimes were tested over 8 d in paired growth chambers. * Phytosiderophore release patterns under a square-wave light regime were similar, irrespective of whether temperature was varied diurnally or held constant, but PS release was negligible when the light was removed. Release patterns of PS for Fe-deficient and Fe-sufficient plants grown under the square-wave vs ramped light and temperature regimes were similar in the corresponding Fe treatments. * Our results strongly support the notion that the diurnal pulse in PS release in the Poaceae is mainly mediated by changes in light rather than temperature. Our comparison of square-wave with more natural ramped light/temperature regimes suggests that the diurnal response patterns of PS release in wheat can be confidently studied using traditional square-wave regimes, and this is likely to be the case with other Poaceae as well.