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

Toyooka K, Okamoto T, Minamikawa T - J. Cell Biol. (2001)

Bottom Line: The results revealed that SG is inserted into LV through autophagic function of LV and subsequently degraded by vacuolar alpha-amylase.When the embryo axes were removed from seeds 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 mediated by different cellular mechanisms.The two distinct autophagic processes were thought to be involved in the breakdown of SG and cell components in the cells of germinated cotyledon.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Tokyo Metropolitan University, Tokyo, 192-0397 Japan.

ABSTRACT
alpha-Amylase is expressed in cotyledons of germinated Vigna mungo seeds and is responsible for the degradation of starch that is stored in the starch granule (SG). Immunocytochemical analysis of the cotyledon cells with anti-alpha-amylase antibody showed that alpha-amylase is transported to protein storage vacuole (PSV) and lytic vacuole (LV), which is converted from PSV 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 SG is inserted into LV through autophagic function of LV and subsequently degraded by vacuolar alpha-amylase. The autophagy for SG was structurally similar to micropexophagy detected in yeast cells. In addition to the autophagic process for SG, autophagosome-mediated autophagy for cytoplasm and mitochondria was detected in the cotyledon cells. When the embryo axes were removed from seeds 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 mediated by different cellular mechanisms. The two distinct autophagic processes were thought to be involved in the breakdown of SG and cell components in the cells of germinated cotyledon.

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Electron micrographs showing autophagosome-mediated autophagy in attached (A–C) and detached (D and E) cotyledon cells. (A) Two autophagosomes containing cytoplasm were observed. Mitochondria and the cytoplasm appeared to be enclosed with an ER-like double membrane. (B) An autophagosome containing mitochondria and cytoplasm was fused with LV (arrowheads). (C) Autophagic body containing mitochondria was found in LV. (D) An autophagosome containing mitochondria and cytoplasm was observed. The PSV was not converted into the LV. (E) Autophagic body was observed in the PSV of detached cotyledon cells. AB, autophagic body; AP, autophagosome; ER, endoplasmic reticulum; LV, lytic vacuole; Mt, mitochondrion; PSV, protein storage vacuole; SG, starch granule. Bars, 200 nm.
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fig6: Electron micrographs showing autophagosome-mediated autophagy in attached (A–C) and detached (D and E) cotyledon cells. (A) Two autophagosomes containing cytoplasm were observed. Mitochondria and the cytoplasm appeared to be enclosed with an ER-like double membrane. (B) An autophagosome containing mitochondria and cytoplasm was fused with LV (arrowheads). (C) Autophagic body containing mitochondria was found in LV. (D) An autophagosome containing mitochondria and cytoplasm was observed. The PSV was not converted into the LV. (E) Autophagic body was observed in the PSV of detached cotyledon cells. AB, autophagic body; AP, autophagosome; ER, endoplasmic reticulum; LV, lytic vacuole; Mt, mitochondrion; PSV, protein storage vacuole; SG, starch granule. Bars, 200 nm.

Mentions: In the course of the ultrastructural observation of the cotyledon cells, the autophagic process for cytoplasm and mitchondrion, which is distinct from that for SGs, was detected. Two autophagosomes containing cytoplasm with a double membrane were observed in the attached cotyledon cells, and mitochondria and cytoplasm appeared to be enclosed with double-membranous structure similar to that of the endoplasmic reticulum (Fig. 6 A). Autophagosome containing mitochondria and cytoplasm was fused with the LV (Fig. 6 B), and an autophagic body containing mitochondria was observed in LVs (Fig. 6 C). These results are consistent with the reports that vacuoles in the cotyledon cells of Vigna radiata function as autophagic organelles (van der Wilden et al., 1980; Herman et al., 1981). When the detached cotyledons were incubated at 27°C in darkness for 3 d and then analyzed by conventional electron microscopy, as shown in Fig. 6, A–C, autophagosomes and autophagic bodies were observed in the detached cotyledon cells (Fig. 6, D and E), although the conversion of PSV to LV did not occur (Figs. 4 I and 6, D and E). This indicates that autophagosome-mediated autophagy functions in detached cotyledons as well as attached cotyledons.


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

Toyooka K, Okamoto T, Minamikawa T - J. Cell Biol. (2001)

Electron micrographs showing autophagosome-mediated autophagy in attached (A–C) and detached (D and E) cotyledon cells. (A) Two autophagosomes containing cytoplasm were observed. Mitochondria and the cytoplasm appeared to be enclosed with an ER-like double membrane. (B) An autophagosome containing mitochondria and cytoplasm was fused with LV (arrowheads). (C) Autophagic body containing mitochondria was found in LV. (D) An autophagosome containing mitochondria and cytoplasm was observed. The PSV was not converted into the LV. (E) Autophagic body was observed in the PSV of detached cotyledon cells. AB, autophagic body; AP, autophagosome; ER, endoplasmic reticulum; LV, lytic vacuole; Mt, mitochondrion; PSV, protein storage vacuole; SG, starch granule. Bars, 200 nm.
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Related In: Results  -  Collection

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fig6: Electron micrographs showing autophagosome-mediated autophagy in attached (A–C) and detached (D and E) cotyledon cells. (A) Two autophagosomes containing cytoplasm were observed. Mitochondria and the cytoplasm appeared to be enclosed with an ER-like double membrane. (B) An autophagosome containing mitochondria and cytoplasm was fused with LV (arrowheads). (C) Autophagic body containing mitochondria was found in LV. (D) An autophagosome containing mitochondria and cytoplasm was observed. The PSV was not converted into the LV. (E) Autophagic body was observed in the PSV of detached cotyledon cells. AB, autophagic body; AP, autophagosome; ER, endoplasmic reticulum; LV, lytic vacuole; Mt, mitochondrion; PSV, protein storage vacuole; SG, starch granule. Bars, 200 nm.
Mentions: In the course of the ultrastructural observation of the cotyledon cells, the autophagic process for cytoplasm and mitchondrion, which is distinct from that for SGs, was detected. Two autophagosomes containing cytoplasm with a double membrane were observed in the attached cotyledon cells, and mitochondria and cytoplasm appeared to be enclosed with double-membranous structure similar to that of the endoplasmic reticulum (Fig. 6 A). Autophagosome containing mitochondria and cytoplasm was fused with the LV (Fig. 6 B), and an autophagic body containing mitochondria was observed in LVs (Fig. 6 C). These results are consistent with the reports that vacuoles in the cotyledon cells of Vigna radiata function as autophagic organelles (van der Wilden et al., 1980; Herman et al., 1981). When the detached cotyledons were incubated at 27°C in darkness for 3 d and then analyzed by conventional electron microscopy, as shown in Fig. 6, A–C, autophagosomes and autophagic bodies were observed in the detached cotyledon cells (Fig. 6, D and E), although the conversion of PSV to LV did not occur (Figs. 4 I and 6, D and E). This indicates that autophagosome-mediated autophagy functions in detached cotyledons as well as attached cotyledons.

Bottom Line: The results revealed that SG is inserted into LV through autophagic function of LV and subsequently degraded by vacuolar alpha-amylase.When the embryo axes were removed from seeds 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 mediated by different cellular mechanisms.The two distinct autophagic processes were thought to be involved in the breakdown of SG and cell components in the cells of germinated cotyledon.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Tokyo Metropolitan University, Tokyo, 192-0397 Japan.

ABSTRACT
alpha-Amylase is expressed in cotyledons of germinated Vigna mungo seeds and is responsible for the degradation of starch that is stored in the starch granule (SG). Immunocytochemical analysis of the cotyledon cells with anti-alpha-amylase antibody showed that alpha-amylase is transported to protein storage vacuole (PSV) and lytic vacuole (LV), which is converted from PSV 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 SG is inserted into LV through autophagic function of LV and subsequently degraded by vacuolar alpha-amylase. The autophagy for SG was structurally similar to micropexophagy detected in yeast cells. In addition to the autophagic process for SG, autophagosome-mediated autophagy for cytoplasm and mitochondria was detected in the cotyledon cells. When the embryo axes were removed from seeds 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 mediated by different cellular mechanisms. The two distinct autophagic processes were thought to be involved in the breakdown of SG and cell components in the cells of germinated cotyledon.

Show MeSH
Related in: MedlinePlus