RUBIDIUM EXPORT FROM INDIVIDUAL LEAVES OF MATURING WHEAT

Rubidium (similar to the highly mobile macronutrient K) and strontium (immobile in the phloem) were fed through a flap into one of the three uppermost leaves of field grown wheat. In all cases rubidium (supplied to the plants shortly after ear emergence) was mainly translocated into shoot parts above the feeding position. Strontium accumulated in the fed leaf and was essentially not detectable in other plant parts. These results indicate that direct contamination with the feeding solution was negligible and Rb was redistributed through long distance translocation. A considerable amount flowed from the flag leaf into the maturing grains. Rb fed into the two lower leaves accumulated in the internode below the flag leaf and only a minor portion reached the ear. A high percentage of the Rb was lost from the shoots at the end of maturation. This decrease was most pronounced after feeding the lowest leaf. The proper consideration of losses caused by leakage in the rain and of export patterns from individual leaves might allow a further insight into the redistribution physiology and the K-economy of field grown cereals.