Cotyledon cells of Vigna mungo seedlings use at least two distinct autophagic machineries for degradation of starch granules and cellular components

alpha -Amylase is expressed in cotyledons of germinated Vigna mungo seeds a nd is responsible for the degradation of starch that is stored in the starc h granule (SG). Immunocytochemical analysis of the cotyledon cells with ant i-alpha -amylase antibody showed that alpha -amylase is transported to prot ein storage vacuole (PSV) and lytic vacuole (LV), which is converted from P SV by hydrolysis of storage proteins. To observe the insertion/degradation processes of SG into/in the inside of vacuoles, ultrastructural analyses of the cotyledon cells were conducted. The results revealed that SC is insert ed into LV through autophagic function of LV and subsequently degraded by v acuolar alpha -amylase. The autophagy for SG was structurally similar to mi cropexophagy detected in yeast cells. In addition to the autophagic process for SG, autophagosome-mediated autophagy for cytoplasm and mitochondria wa s detected in the cotyledon cells. When the embryo axes were removed from s eeds and the detached cotyledons were incubated, the autophagosome-mediated autophagy was observed, but the autophagic process for the degradation of SG was not detected, suggesting that these two autophagic processes were me dia,ed by different cellular mechanisms. The two distinct autophagic proces ses were thought to be involved in the breakdown of SG and cell components in the cells of germinated cotyledon.