Physiological and Proteomic Changes in the Apoplast Accompany Leaf Senescence in Arabidopsis

BORNIEGO, M.L.; MOLINA, M.C.; GUIAMET, J.J.; MARTÍNEZ D.E.

Frontiers in Plant Science

Frontiers Media

Lugar: Lausana; Año: 2020

The apoplast, i.e. the cellular compartment external to the plasma membrane, undergoesimportant changes during senescence. Apoplastic fluid volume increases quitesignificantly in senescing leaves, thereby diluting its contents. Its pH elevates by about0.8 units, similar to the apoplast alkalization in response to abiotic stresses. The levels of159 proteins decrease, whereas 24 proteins increase in relative abundance in theapoplast of senescing leaves. Around half of the apoplastic proteins of non-senescentleaves contain a N-terminal signal peptide for secretion, while all the identifiedsenescence-associated apoplastic proteins contain the signal peptide. Several of theapoplastic proteins that accumulate during senescence also accumulate in stressresponses, suggesting that the apoplast may constitute a compartment wheredevelopmental and stress-related programs overlap. Other senescence-relatedapoplastic proteins are involved in cell wall modifications, proteolysis, carbohydrate,ROS and amino acid metabolism, signaling, lipid transport, etc. The most abundantsenescence-associated apoplastic proteins, PR2 and PR5 (e.g. pathogenesis relatedproteins PR2 and PR5) are related to leaf aging rather than to the chloroplast degradationprogram, as their levels increase only in leaves undergoing developmental senescence,but not in dark-induced senescent leaves. Changes in the apoplastic space may berelevant for signaling and molecular trafficking underlying senescence.