Autophagocytosis of carotenoid-rich lipid droplets into vacuoles during aeciospore ageing in Puccinia distincta.

•  Aeciospores of rust fungi contain numerous lipid droplets (LDs) which are stained yellow due to the presence of β-and γ-carotene, thereby facilitating observations of their fate during developmental processes. •  The ageing process of aeciospores of Puccinia distincta was examined by light and transmission electron microscopy. •  The cytoplasm of freshly harvested spores was filled with LDs but devoid of vacuoles. Within 12 h, numerous small vacuoles developed, and the LDs became associated with their cytoplasmic tonoplast surface. The vacuoles enlarged and fused together; they were also the destination of endocytotic uptake of the vital dye, Neutral Red. Within 36 h, LDs entered these vacuoles by autophagocytosis and were degraded in the vacuolar lumen. After 96 h, most lipid reserves had been used up and the highly vacuolated spores lost viability as indicated by their failure to germinate or take up Neutral Red. •  Spore maturation by vacuolation thus seems to occur at the direct expense of metabolic energy stored as LDs and is an extremely rapid process in aeciospores of P. distincta.