Leaves are specialized photosynthetic organs and the plant
invests much energy and nutrients in leaf production. After a
photosynthetically productive period, the leaf’s contribution
of photosynthate to the plant diminishes and the leaf then enters its
last stage of development: senescence. During senescence, nutrients
such as nitrogen, phosphorus and metals that were invested in the
leaf are reallocated to younger leaves and to growing seeds, or are
stored for the next growing season1. Indeed, leaf senescence can be
viewed as a recycling program at the organismal level