DEGRADATION OF PHOTOSYNTHETIC PROTEINS IN SENESCENCE-ASSOCIATED VACUOLES OF TOBACCO LEAVES

DANA MARTINEZ, LORENZA COSTA, MARISA OTEGUI, Y JUAN J. GUIAMÉT

Rosario, Santa Fé, Argentina

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2006

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

Chloroplast degradation is the hallmark of leaf senescence.However, the mechanism underlying the breakdown of chloroplast proteins is poorly understood. Several observations suggest that a novel class of “senescence-associated vacuoles”(SAVs) might be involved in the degradation of photosynthetic proteins. The abundance of SAVs correlates with rates of chloroplast degradation in tobacco, i.e., the number of SAVs decreases in cells where senescence is delayed by treatment with the plant hormone cytokinin, whereas acceleration of senescence with ethylene increases the number of SAVs. Immunolocalization experiments show that the chloroplastencoded large subunit of Rubisco (RbcL) is re-located to SAVs in senescing leaves. Autodigestion experiments with isolated SAVs incubated at pH 5.5 (the estimated lumenal pH of SAVs) show that RbcL is degraded by SAV proteases. These data strongly support the idea that chloroplast proteins are transferred to SAVs and degraded there during senescence of leaves