MANIPULATION OF XYLEM TRANSPORT AFFECTS ZN AND MN TRANSPORT INTO DEVELOPING WHEAT GRAINS OF CULTURED EARS

Zinc and manganese loading into developing wheat grain is little under stood at present. The objective of this work was to investigate factor s that may affect the rate of transport of Zn and Mn into developing w heat grain of cultured ears. Ears 18-22 days post-anthesis were cultur ed in solutions containing labelled Zn and Mn. The effect of additions of Cu, Fe, citrate, malate and EDTA to the culture solution was obser ved. The effect of humidity and awn removal as well as the sucrose sta tus of the ears on Zn and Mn transport was also investigated. The effe ct of high concentration of Zn and Mn on [C-14]-sucrose transport was determined High humidity almost completely blocked transport of Zn and Mn into the grain. Awn removal reduced the transport of Zn and Mn to the lemma but not the grain. When the ears were depleted of sucrose (b y maintaining them in the dark prior to labelling) transport of Zn and Mn to the grain was reduced compared to ears cultured with sucrose. T he presence of Cu reduced the loading of Zn into the grain. There was little effect of Cu on Mn transport or Fe on either Zn or Mn transport . High concentrations of Zn and Mn in the culture solution did not aff ect [C-14]-sucrose loading into the grain but loading of Zn and Mn was limited at high concentrations suggesting membrane saturation. This s tudy demonstrates that sucrose status and humidity clearly influence t he transport of Zn and Mn into the grain, and that other ions may infl uence Zn and Mn transport.