In senescent Sw-leaves also yellow fluorescent ‘spots’ were observed
(Fig. 4B–e). They might be putative lipid droplets, as also
seen in senescent banana leaves [13]. Indeed, in senescent leaves
chloroplasts develop into a distinct plastid type, the gerontoplasts,
which are formed by loss of thylakoid membranes and accumulation
of lipid globules [29,35]. At a late stage, rupture of the gerontoplast
envelope was observed to lead to release of globules to the
cytoplasm
leaves (Fig. 4A-c). Senescent leaves lacked the red Chl- fluorescence;
only in the guard cells of their stomata were intact chloroplasts
marked by their red fluorescence (Fig. 4B-e and h). Indeed,
stomata remain functional during (early phases of) senescence
[34]. Green Sw-leaves showed bright red Chl-fluorescence in the
whole mesophyll, which lacked the marked blue fluorescence of
the senescent cells