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Extra‐plastidial degradation of chlorophyll and photosystem I in tobacco leaves involving ‘senescence‐associated vacuoles’
Author(s) -
Gomez Facundo M.,
Carrión Cristian A.,
Costa María L.,
Desel Christine,
Kieselbach Thomas,
Funk Christiane,
Krupinska Karin,
Guiamet Juan
Publication year - 2019
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14337
Subject(s) - photosystem ii , chlorophyll , photosystem , photosystem i , vacuole , chlorophyll a , chloroplast , biology , chlorophyll fluorescence , photosynthetic reaction centre , photosynthesis , chemistry , botany , biochemistry , cytoplasm , gene
Summary 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’ ( SAV s) contain Chl raises the question of whether SAV s might also contribute to Chl breakdown. Previous confocal microscope observations (Martínez et al ., 2008) showed many SAV s containing Chl. Isolated SAV s contained Chl a and b (with a Chl a / b ratio close to 5) and lower levels of chlorophyllide a . Pheophytin a and pheophorbide a were formed after the incubation of SAV s at 30°C in darkness, suggesting the presence of Chl‐degrading activities in SAV s. Chl in SAV s was bound to a number of ‘green bands’. In the most abundant green band of SAV s, Western blot analysis showed the presence of photosystem I ( PSI ) Chl‐binding proteins, including the PsaA protein of the PSI reaction center and the apoproteins of the light‐harvesting complexes (Lhca 1–4). This was confirmed by: (i) measurements of 77‐K fluorescence emission spectra showing a single emission peak at around 730 nm in SAV s; (ii) mass spectrometry of the most prominent green band with the slowest electrophoretic mobility; and (iii) immunofluorescence detection of PsaA in SAV s observed through confocal microscopy. Incubation of SAV s at 30°C in darkness caused a steady decrease in PsaA levels. Overall, these results indicate that SAV s may be involved in the degradation of PSI proteins and their associated chlorophylls during the senescence of leaves.