Senescence-Related Changes in the Leaf Apoplast

Abstract

The extracellular space of leaves is a highly dynamic compartment harboring a number of activities involved in signal recognition, import/export of organic and inorganic compounds, and defense against pathogens. Although this has not been extensively studied, there is evidence for the involvement of the extracellular space in signal perception and nutrient remobilization during senescence. Integration of the apoplast into the larger picture of cellular activities during senescence may help understand key events in the terminal phase of leaf development. Important events associated with senescence occur in the apoplast, and these events may offer targets for genetic manipulation to modulate senescence. In this paper we look into changes in the extracellular space of leaves accompanying senescence, with a special focus on apoplastic proteins and plasma membrane proteins related to signaling and export of amino acids. Other not less relevant senescence-related metabolic changes such as NH4 accumulation and the oxidative burst are beyond the scope of this review.