tions including sequestration, chemical modification and intracellular trafficking may be involved in delivering nutrients from their sites of origin (i.e. the chloroplast undergoing dis- assembly) to sites where long-distance transport originates. Long-distance transport of nutrients from senescing leaf tis- sue to the seeds or other parts of the plant is thought to take place via the phloem (Hill 1980). Hence, the phloem accessi- bility and phloem mobility of a nutrient influences the effi- ciency with which it is mobilized from senescing leaves (Bu- kovac and Wittwer 1957).