Extra-plastidial degradation of chlorophyll and photosystem I in tobacco leaves involving "Senescence-associated- vacuoles"

CARRIÓN, CRISTIAN A.; KIESELBACH, THOMAS; GUIAMÉT, JUAN J.; COSTA, MARÍA LORENZA; FUNK, CHRISTIANE; GOMEZ, FACUNDO M.; DESEL, CHRISTINE; KRUPINSKA, KARIN

PLANT JOURNAL

WILEY-BLACKWELL PUBLISHING, INC

Año: 2019

0960-7412

Chlorophyll (Chl) loss is the main visible symptom of senescence in leaves. The initial steps of Chl degradation operate within the chloroplast, but the observation that ?senescence-associated vacuoles? (SAVs) contain Chl raises the question whetherSAVs might also contribute to Chl breakdown.Previous confocal microscope observations (Martínez et al. 2008) showed many SAVs containing Chl. Isolated SAVs contained Chla and b (with a Chl a/b ratio close to 5) and smaller amounts of chlorophyllide a. Pheophytin a and Pheophorbide a were formed after incubation of SAVs at 30ºC in darkness, suggesting the presence of Chl-degrading activities in SAVs. Chl in SAVs was bound to a number of ?green bands?. In the most -abundant green band of SAVs, Western blot analysis showed the presence of PSI Chl-binding proteins, including the PsaA protein of PSI reaction center and the apoproteins of light -harvesting complexes (Lhca 1-4). This was confirmed by -1 measurements of 77K fluorescence emission spectra showing a single emission peak at around 730 nm in SAVs, -2 mass spectrometry of the most prominent green band with the slowest electrophoretic mobility, and -3 immunofluorescence detection of PsaA in SAVs observed through confocal microscopy. Incubation of SAVs at 30ºC in darknesscaused a steady decrease in PsaA levels . Overall, these results indicate that SAVs may be involved in the degradation of PSI proteins and their associated chlorophylls during senescence of leaves.