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Plastids division in shoot apical meristem during the tuberization of taro (Colocasia esculenta)
Scientia Horticulturae 150 (2013) 22–24
Contents lists available at SciVerse ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Short communication
Plastids division in shoot apical meristem during the tuberization of taro (Colocasia esculenta) Hongmei Du, Dongmei Tang, Danfeng Huang ∗ School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, PR China
a r t i c l e
i n f o
Article history: Received 13 February 2012 Received in revised form 22 August 2012 Accepted 26 October 2012 Keywords: Taro (Colocasia esculenta) Apical meristem Tuberization Proplastid Starch Amyloplast
a b s t r a c t This paper reports the first unambiguous observation of the differentiation of proplastids to amyloplasts in shoot apical meristem during the tuberization of taro. The differentiation mechanism from proplastids to amyloplasts was examined during tuberization of taro. Shoot tips during in vitro tuberization of taro were sampled and observed every 2 days using a transmission electron microscope. The enlargement of proplastids, accumulation of thylakoids and grana were observed in the cells of shoot apical meristem. After 8 days of the culture, starch grains deposition was distinctly observed in the amyloplasts. Binary fission and budding mode of proplastid division were found at the beginning of tuberization in taro. However, binary fission was the only division type shown by the amyloplasts. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Plastids are essential organelles in the cells of plants (Pyke, 2007). Proplastids are colourless, undifferentiated plastids occurring in the meristematic cells of shoots, roots, embryos, and endosperms (Neuhaus and Emes, 2000). In response to tissue-specific signals and environmental changes, proplastids differentiate into specialized plastid types, such as chloroplast, chromoplast, leucoplast and amyloplast (Thomson and Whatley, 1980). Amyloplasts are starch-storing, non-green plastids, which play an important role in the carbon assimilation of plants (Pyke, 1999). A key feature of tuber plants, such as taro, is that they accumulate starch as a storage reserve. This process can be affected by factors, such as short photoperiod (Ewing and Struik, 1992), high concentration of sucrose (Bánfalvi et al., 1996; Zhou et al., 1999) and exogenous hormonal stimuli (Miyazawa et al., 1999, 2002; Zhou et al., 1999), which regulate the expression of genes required for starch biosynthesis, starch grain deposition and proplastids transformation into amyloplasts. The study of the differentiation of the proplastid-amyloplast system is essential to clarify the mechanism of carbohydrate metabolism and the development of storage organs during tuber development. Most studies of plastid differentiation
∗ Corresponding author at: Shanghai Jiao Tong University, Shanghai 200240, PR China. Tel.: +86 21 34206943; fax: +86 21 34206943. E-mail address: [email protected] (D. Huang). 0304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2012.10.023
have focused primarily on the proplastid-chloroplast transition during the development of leaves (McCormac and Greenberg, 1992; Pyke, 2007; Taylor, 1989). By contrast, an overview of the differential mechanism of proplastid-amyloplast during tuberization has not been reported. Taro (Colocasia esculenta (L.) Schott) is an important socioeconomic crop in Southeast Asia and the Pacific (Lebot et al., 2004). Taro has an enlarged, starchy, underground stem which is designated as corm (Onwueme, 1999). The major obstacle in studying tuberization has been the problem of obtaining developmentally synchronized samples from whole plants. To solve this difficulty, the present study employed an in vitro tuberization system to explore the plastid division during the tuberization of taro with transmission electron microscopy (TEM). 2. Materials and methods 2.1. In vitro culture of plant materials Sterile plantlets of taro (C. esculenta var. antiquorum cv. ‘fragrant taro’) about 4 cm high, were obtained using the methods of Du et al. (2006). These were incubated in Murashige and Skoog (1962) liquid media with 8% sucrose, 1.0 mg l−1 BAP, 0.5 mg l−1 NAA and pH 5.8 to induce corm formation. The plantlets were held on absorbent cotton in 250 ml flasks containing 50 ml of the liquid medium. The cultures were maintained in a growth chamber at 24–26 ◦ C, a 12 h photoperiod and photosynthetically active radiation of 40 mol m−2 s−2 under cool-white fluorescent tubes.
H. Du et al. / Scientia Horticulturae 150 (2013) 22–24
23
Fig. 1. Morphological character of shoot apical meristem cells and division of proplastid (triangles showing the positions of binary fission) in vitro tuberization of taro (Colocasia esculenta) at 0 day (Panel A), 2 days (Panel B), 4 days (Panel C and D) and 6 days (Panel E) (bar = 1 m) of the culture. Ch, chloroplast; g, granum; P, proplastid; t, thylakoid.
2.2. Electron microscopy For ultrastructural analysis, shoot tips (0.5–1.0 mm diameter) with the same volume were harvested every 2 days, and immediately fixed in 4% glutaraldehyde in 0.1 M phosphate buffer (pH 7.2) for 24 h at room temperature. After washing in 0.1 M phosphate buffer (pH 7.2), samples were post-fixed in 1% osmium tetroxide in the same buffer for 2 h. After fixing, samples were dehydrated in a graded ethanol series and embedded in Spurr medium. Thin sections were double-stained with uranyl acetate and lead citrate and observed under a TEM (JEM-100CX, from JEOL company, Tokyo, Japan). 3. Results and discussion 3.1. Differentiation of plastids during in vitro tuberization of taro Although proplastids are the progenitors of all other plastid types, few studies on the division of proplastids could be found (Aldridge et al., 2005; Sakai et al., 1992). Using the above method, it was possible to observe division of plastids during the transformation of proplastids to amyloplasts during the in vitro tuberization of taro. Chloroplasts and proplastids were scattered in the cytoplasm of the shoot apical meristem cells at 0 day of the culture (Fig. 1A). At 2 days of the culture, the chloroplasts disappeared and a few thylakoids were found in proplastids (Fig. 1B). The volume of proplastids had increased significantly in the four day culture (Fig. 1C
and D) compared with 0 day (Fig. 1A) and 2 days of the culture (Fig. 1B), and the thylakoids were organized in the grana (Fig. 1C). At 6 days of the culture, the proplastids were even larger (Fig. 1E). After 8 days of the culture, the proplastids had accumulated starch grains and transformed to the amyloplasts (Fig. 2A and B). By 10 days, the amyloplasts had grown further and starch grains were deposited between grana (Fig. 2C). 3.2. The division type of proplastid and amyloplast The observations showed that binary fission was the primary division type of the proplastids for in vitro tuberization of taro (Figs. 1C–E and 2A). During the division process of the proplastids, several distinct stages of binary fission were found in the shoot apical meristem of taro. These are described by Aldridge et al. (2005) as slight proplastid elongation (Fig. 1E), dumbbellshaped dividing proplastids (Fig. 1C and E) and further constriction (Figs. 1D, E, and 2A). Proplastids with continual fragmentation phenomenon were also found in the cytoplasm (Fig. 1E). We also found that amyloplasts divided by binary fission during in vitro tuberization (Fig. 2B and C), as shown by Kawasaki et al. (1998) with the mature corm of taro. The central constrictions were observed during the division of amyloplasts (Fig. 2B and C). However, binary fission was not the sole type of plastid division, as also reported by Pyke (2007). We found budding type divisions where budding vesicles emanating from the proplastids after 4 days of the culture (Fig. 1C and D), as Kulandaivelu and Gnanam (1985) found in leaves of Bryophyllum pinnatum and Forth and Pyke (2006)
24
H. Du et al. / Scientia Horticulturae 150 (2013) 22–24
and Kawagoe, 2009), amyloplast budding was not found in the shoot apical meristem of taro. The reason why amyloplasts divided only by binary fission in this research need to be further discussed. Acknowledgements This work was supported by National 863 Project (Grant No. 2006AA10A311), Shanghai Leading Academic Discipline Project (Grant No. B209) and Shanghai Science and Technology Committee (Grant No. 09DZ1906100). We thank Associate Professor Y.J. Lu for assisting TEM analysis and Dr. Paul Burgess at Cranfield University for helpful review of our manuscript. References
Fig. 2. The division of plastids (triangles showing the positions of binary fission) at 8 days (Panel A and B) and 10 days (Panel C) of the culture and the accumulation of starch grains in amyloplast (Panel A–C). A, amyloplast; P, proplastid.
reported in giant plastids of suffulta mutant in tomato (Solanum lycopersicum). During budding, the envelop of proplastid decomposed at the connection of the vesicle and proplastid. It was also found that binary fission and budding vesicles could occur simultaneously in the same proplastid (Fig. 1C and D). This phenomenon of simultaneous binary fission and budding was previously few reported and the mechanism is still unknown (Kuroda and Sagisaka, 2001). Moreover, we believe that, this is the first time that budding from proplasts has been observed in taro. Different with apical meristem cells of potato tubers (Platonova et al., 2010) and rice endosperm at later development stages (Yun
Aldridge, C., Maple, J., Møller, S.G., 2005. The molecular biology of plastid division in higher plants. J. Exp. Bot. 56, 1061–1077. Bánfalvi, Z., Molnár, A., Molnár, G., Lakatos, L., Szabó, L., 1996. Starch synthesis, and tuber storage protein genes are differently expressed in Solanum tuberosum and in Solanum brevidens. FEBS Lett. 383, 159–164. Du, H.M., Tang, D.M., Huang, D.F., 2006. ‘Fragrant taro’ [Colocasia esculenta (L.) Schott var. antiquorum] micropropagation using thidiazuron and benzylaminopurine. J. Hortic. Sci. Biotechnol. 81, 379–384. Ewing, E., Struik, P., 1992. Tuber formation in potato: induction, initiation, and growth. Hortic. Rev. 14, 89–197. Forth, D., Pyke, K.A., 2006. The suffulta mutation in tomato reveals a novel method of plastid replication during fruit ripening. J. Exp. Bot. 57, 1971–1979. Kawasaki, M., Matsuda, T., Chonan, N., 1998. Electron microscopy of plastidamyloplast system involved in starch synthesis and accumulation in eddoe corm (Colocasia esculenta var. antiquorum). Jpn. J. Crop Sci. 67, 200–207. Kuroda, H., Sagisaka, S., 2001. Ultrastructural changes in apical meristem cells of apple flower buds associated with dormancy and cold tolerance. J. Jpn. Soc. Hortic. Sci. 70, 553–560. Kulandaivelu, G., Gnanam, A., 1985. Scanning electron microscopic evidence for a budding mode of chloroplast multiplication in higher plants. Physiol. Plant. 63, 299–302. Lebot, V., Prana, M.S., Kreike, N., van Heck, H., Pardales, J., Okpul, T., Gendua, T., Thongjiem, M., Hue, H., Viet, N., Yap, T.C., 2004. Characterisation of taro (Colocasia esculenta (L.) Schott) genetic resources in Southeast Asia and Oceania. Genet. Resour. Crop Evol. 51, 381–392. McCormac, D.J., Greenberg, B.M., 1992. Differential synthesis of photosystem cores and light-harvesting antenna during proplastid to chloroplast development in Spirodela oligorrhiza. Plant Physiol. 98, 1011–1019. Miyazawa, Y., Kato, H., Muranaka, T., Yoshida, S., 2002. Amyloplast formation in cultured tobacco BY-2 cells requires a high cytokinin content. Plant Cell Physiol. 43, 1534–1541. Miyazawa, Y., Sakai, A., Miyagishima, S., Takano, H., Kawano, S., Kuroiwa, T., 1999. Auxin and cytokinin have opposite effects on amyloplast development and the expression of starch synthesis genes in cultured Bright Yellow-2 tobacco cells. Plant Physiol. 121, 461–469. Murashige, T., Skoog, F., 1962. A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiol. Plant. 15, 473–497. Neuhaus, H.E., Emes, M.J., 2000. Nonphotosynthetic metabolism in plastids. Annu. Rev. Plant Physiol. Plant Mol. Biol. 51, 111–140. Onwueme, I., 1999. Taro Cultivation in Asia and the Pacific. Food and Agriculture Organization of the United Nations, Regional Office for Asia and the Pacific, Bangkok, Thailand. Platonova, T.A., Evsyunina, A.S., Korableva, N.P., 2010. Changes in the plastid apparatus of apical meristem cells of potato tubers upon growth regulation with jasmonic acid. Appl. Biochem. Microbiol. 46, 352–358. Pyke, K.A., 1999. Plastid division and development. Plant Cell 11, 549–556. Pyke, K.A., 2007. Plastid biogenesis and differentiation. In: Bock, R. (Ed.), Cell and Molecular Biology of Plastids, vol. 19. Springer, Berlin and Heidelberg, pp. 1–28. Sakai, A., Kawano, S., Kuroiwa, T., 1992. Conversion of proplastids to amyloplasts in tobacco cultured cells is accompanied by changes in the transcriptional activities of plastid genes. Plant Physiol. 100, 1062–1066. Taylor, W.C., 1989. Regulatory interactions between nuclear and plastid genomes. Annu. Rev. Plant Physiol. Plant Mol. Biol. 40, 211–233. Thomson, W.W., Whatley, J.M., 1980. Development of nongreen plastids. Annu. Rev. Plant Physiol. 31, 375–394. Yun, M.S., Kawagoe, Y., 2009. Amyloplast division progresses simultaneously at multiple sites in the endosperm of rice. Plant Cell Physiol. 50, 1617–1626. Zhou, S.P., He, Y.K., Li, S.J., 1999. Induction and characterization of in vitro corms of diploid-taro. Plant Cell Tissue Organ Cult. 57, 173–178.
Contents lists available at SciVerse ScienceDirect
Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Short communication
Plastids division in shoot apical meristem during the tuberization of taro (Colocasia esculenta) Hongmei Du, Dongmei Tang, Danfeng Huang ∗ School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, PR China
a r t i c l e
i n f o
Article history: Received 13 February 2012 Received in revised form 22 August 2012 Accepted 26 October 2012 Keywords: Taro (Colocasia esculenta) Apical meristem Tuberization Proplastid Starch Amyloplast
a b s t r a c t This paper reports the first unambiguous observation of the differentiation of proplastids to amyloplasts in shoot apical meristem during the tuberization of taro. The differentiation mechanism from proplastids to amyloplasts was examined during tuberization of taro. Shoot tips during in vitro tuberization of taro were sampled and observed every 2 days using a transmission electron microscope. The enlargement of proplastids, accumulation of thylakoids and grana were observed in the cells of shoot apical meristem. After 8 days of the culture, starch grains deposition was distinctly observed in the amyloplasts. Binary fission and budding mode of proplastid division were found at the beginning of tuberization in taro. However, binary fission was the only division type shown by the amyloplasts. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Plastids are essential organelles in the cells of plants (Pyke, 2007). Proplastids are colourless, undifferentiated plastids occurring in the meristematic cells of shoots, roots, embryos, and endosperms (Neuhaus and Emes, 2000). In response to tissue-specific signals and environmental changes, proplastids differentiate into specialized plastid types, such as chloroplast, chromoplast, leucoplast and amyloplast (Thomson and Whatley, 1980). Amyloplasts are starch-storing, non-green plastids, which play an important role in the carbon assimilation of plants (Pyke, 1999). A key feature of tuber plants, such as taro, is that they accumulate starch as a storage reserve. This process can be affected by factors, such as short photoperiod (Ewing and Struik, 1992), high concentration of sucrose (Bánfalvi et al., 1996; Zhou et al., 1999) and exogenous hormonal stimuli (Miyazawa et al., 1999, 2002; Zhou et al., 1999), which regulate the expression of genes required for starch biosynthesis, starch grain deposition and proplastids transformation into amyloplasts. The study of the differentiation of the proplastid-amyloplast system is essential to clarify the mechanism of carbohydrate metabolism and the development of storage organs during tuber development. Most studies of plastid differentiation
∗ Corresponding author at: Shanghai Jiao Tong University, Shanghai 200240, PR China. Tel.: +86 21 34206943; fax: +86 21 34206943. E-mail address: [email protected] (D. Huang). 0304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scienta.2012.10.023
have focused primarily on the proplastid-chloroplast transition during the development of leaves (McCormac and Greenberg, 1992; Pyke, 2007; Taylor, 1989). By contrast, an overview of the differential mechanism of proplastid-amyloplast during tuberization has not been reported. Taro (Colocasia esculenta (L.) Schott) is an important socioeconomic crop in Southeast Asia and the Pacific (Lebot et al., 2004). Taro has an enlarged, starchy, underground stem which is designated as corm (Onwueme, 1999). The major obstacle in studying tuberization has been the problem of obtaining developmentally synchronized samples from whole plants. To solve this difficulty, the present study employed an in vitro tuberization system to explore the plastid division during the tuberization of taro with transmission electron microscopy (TEM). 2. Materials and methods 2.1. In vitro culture of plant materials Sterile plantlets of taro (C. esculenta var. antiquorum cv. ‘fragrant taro’) about 4 cm high, were obtained using the methods of Du et al. (2006). These were incubated in Murashige and Skoog (1962) liquid media with 8% sucrose, 1.0 mg l−1 BAP, 0.5 mg l−1 NAA and pH 5.8 to induce corm formation. The plantlets were held on absorbent cotton in 250 ml flasks containing 50 ml of the liquid medium. The cultures were maintained in a growth chamber at 24–26 ◦ C, a 12 h photoperiod and photosynthetically active radiation of 40 mol m−2 s−2 under cool-white fluorescent tubes.
H. Du et al. / Scientia Horticulturae 150 (2013) 22–24
23
Fig. 1. Morphological character of shoot apical meristem cells and division of proplastid (triangles showing the positions of binary fission) in vitro tuberization of taro (Colocasia esculenta) at 0 day (Panel A), 2 days (Panel B), 4 days (Panel C and D) and 6 days (Panel E) (bar = 1 m) of the culture. Ch, chloroplast; g, granum; P, proplastid; t, thylakoid.
2.2. Electron microscopy For ultrastructural analysis, shoot tips (0.5–1.0 mm diameter) with the same volume were harvested every 2 days, and immediately fixed in 4% glutaraldehyde in 0.1 M phosphate buffer (pH 7.2) for 24 h at room temperature. After washing in 0.1 M phosphate buffer (pH 7.2), samples were post-fixed in 1% osmium tetroxide in the same buffer for 2 h. After fixing, samples were dehydrated in a graded ethanol series and embedded in Spurr medium. Thin sections were double-stained with uranyl acetate and lead citrate and observed under a TEM (JEM-100CX, from JEOL company, Tokyo, Japan). 3. Results and discussion 3.1. Differentiation of plastids during in vitro tuberization of taro Although proplastids are the progenitors of all other plastid types, few studies on the division of proplastids could be found (Aldridge et al., 2005; Sakai et al., 1992). Using the above method, it was possible to observe division of plastids during the transformation of proplastids to amyloplasts during the in vitro tuberization of taro. Chloroplasts and proplastids were scattered in the cytoplasm of the shoot apical meristem cells at 0 day of the culture (Fig. 1A). At 2 days of the culture, the chloroplasts disappeared and a few thylakoids were found in proplastids (Fig. 1B). The volume of proplastids had increased significantly in the four day culture (Fig. 1C
and D) compared with 0 day (Fig. 1A) and 2 days of the culture (Fig. 1B), and the thylakoids were organized in the grana (Fig. 1C). At 6 days of the culture, the proplastids were even larger (Fig. 1E). After 8 days of the culture, the proplastids had accumulated starch grains and transformed to the amyloplasts (Fig. 2A and B). By 10 days, the amyloplasts had grown further and starch grains were deposited between grana (Fig. 2C). 3.2. The division type of proplastid and amyloplast The observations showed that binary fission was the primary division type of the proplastids for in vitro tuberization of taro (Figs. 1C–E and 2A). During the division process of the proplastids, several distinct stages of binary fission were found in the shoot apical meristem of taro. These are described by Aldridge et al. (2005) as slight proplastid elongation (Fig. 1E), dumbbellshaped dividing proplastids (Fig. 1C and E) and further constriction (Figs. 1D, E, and 2A). Proplastids with continual fragmentation phenomenon were also found in the cytoplasm (Fig. 1E). We also found that amyloplasts divided by binary fission during in vitro tuberization (Fig. 2B and C), as shown by Kawasaki et al. (1998) with the mature corm of taro. The central constrictions were observed during the division of amyloplasts (Fig. 2B and C). However, binary fission was not the sole type of plastid division, as also reported by Pyke (2007). We found budding type divisions where budding vesicles emanating from the proplastids after 4 days of the culture (Fig. 1C and D), as Kulandaivelu and Gnanam (1985) found in leaves of Bryophyllum pinnatum and Forth and Pyke (2006)
24
H. Du et al. / Scientia Horticulturae 150 (2013) 22–24
and Kawagoe, 2009), amyloplast budding was not found in the shoot apical meristem of taro. The reason why amyloplasts divided only by binary fission in this research need to be further discussed. Acknowledgements This work was supported by National 863 Project (Grant No. 2006AA10A311), Shanghai Leading Academic Discipline Project (Grant No. B209) and Shanghai Science and Technology Committee (Grant No. 09DZ1906100). We thank Associate Professor Y.J. Lu for assisting TEM analysis and Dr. Paul Burgess at Cranfield University for helpful review of our manuscript. References
Fig. 2. The division of plastids (triangles showing the positions of binary fission) at 8 days (Panel A and B) and 10 days (Panel C) of the culture and the accumulation of starch grains in amyloplast (Panel A–C). A, amyloplast; P, proplastid.
reported in giant plastids of suffulta mutant in tomato (Solanum lycopersicum). During budding, the envelop of proplastid decomposed at the connection of the vesicle and proplastid. It was also found that binary fission and budding vesicles could occur simultaneously in the same proplastid (Fig. 1C and D). This phenomenon of simultaneous binary fission and budding was previously few reported and the mechanism is still unknown (Kuroda and Sagisaka, 2001). Moreover, we believe that, this is the first time that budding from proplasts has been observed in taro. Different with apical meristem cells of potato tubers (Platonova et al., 2010) and rice endosperm at later development stages (Yun
Aldridge, C., Maple, J., Møller, S.G., 2005. The molecular biology of plastid division in higher plants. J. Exp. Bot. 56, 1061–1077. Bánfalvi, Z., Molnár, A., Molnár, G., Lakatos, L., Szabó, L., 1996. Starch synthesis, and tuber storage protein genes are differently expressed in Solanum tuberosum and in Solanum brevidens. FEBS Lett. 383, 159–164. Du, H.M., Tang, D.M., Huang, D.F., 2006. ‘Fragrant taro’ [Colocasia esculenta (L.) Schott var. antiquorum] micropropagation using thidiazuron and benzylaminopurine. J. Hortic. Sci. Biotechnol. 81, 379–384. Ewing, E., Struik, P., 1992. Tuber formation in potato: induction, initiation, and growth. Hortic. Rev. 14, 89–197. Forth, D., Pyke, K.A., 2006. The suffulta mutation in tomato reveals a novel method of plastid replication during fruit ripening. J. Exp. Bot. 57, 1971–1979. Kawasaki, M., Matsuda, T., Chonan, N., 1998. Electron microscopy of plastidamyloplast system involved in starch synthesis and accumulation in eddoe corm (Colocasia esculenta var. antiquorum). Jpn. J. Crop Sci. 67, 200–207. Kuroda, H., Sagisaka, S., 2001. Ultrastructural changes in apical meristem cells of apple flower buds associated with dormancy and cold tolerance. J. Jpn. Soc. Hortic. Sci. 70, 553–560. Kulandaivelu, G., Gnanam, A., 1985. Scanning electron microscopic evidence for a budding mode of chloroplast multiplication in higher plants. Physiol. Plant. 63, 299–302. Lebot, V., Prana, M.S., Kreike, N., van Heck, H., Pardales, J., Okpul, T., Gendua, T., Thongjiem, M., Hue, H., Viet, N., Yap, T.C., 2004. Characterisation of taro (Colocasia esculenta (L.) Schott) genetic resources in Southeast Asia and Oceania. Genet. Resour. Crop Evol. 51, 381–392. McCormac, D.J., Greenberg, B.M., 1992. Differential synthesis of photosystem cores and light-harvesting antenna during proplastid to chloroplast development in Spirodela oligorrhiza. Plant Physiol. 98, 1011–1019. Miyazawa, Y., Kato, H., Muranaka, T., Yoshida, S., 2002. Amyloplast formation in cultured tobacco BY-2 cells requires a high cytokinin content. Plant Cell Physiol. 43, 1534–1541. Miyazawa, Y., Sakai, A., Miyagishima, S., Takano, H., Kawano, S., Kuroiwa, T., 1999. Auxin and cytokinin have opposite effects on amyloplast development and the expression of starch synthesis genes in cultured Bright Yellow-2 tobacco cells. Plant Physiol. 121, 461–469. Murashige, T., Skoog, F., 1962. A revised medium for rapid growth and bioassays with tobacco tissue cultures. Physiol. Plant. 15, 473–497. Neuhaus, H.E., Emes, M.J., 2000. Nonphotosynthetic metabolism in plastids. Annu. Rev. Plant Physiol. Plant Mol. Biol. 51, 111–140. Onwueme, I., 1999. Taro Cultivation in Asia and the Pacific. Food and Agriculture Organization of the United Nations, Regional Office for Asia and the Pacific, Bangkok, Thailand. Platonova, T.A., Evsyunina, A.S., Korableva, N.P., 2010. Changes in the plastid apparatus of apical meristem cells of potato tubers upon growth regulation with jasmonic acid. Appl. Biochem. Microbiol. 46, 352–358. Pyke, K.A., 1999. Plastid division and development. Plant Cell 11, 549–556. Pyke, K.A., 2007. Plastid biogenesis and differentiation. In: Bock, R. (Ed.), Cell and Molecular Biology of Plastids, vol. 19. Springer, Berlin and Heidelberg, pp. 1–28. Sakai, A., Kawano, S., Kuroiwa, T., 1992. Conversion of proplastids to amyloplasts in tobacco cultured cells is accompanied by changes in the transcriptional activities of plastid genes. Plant Physiol. 100, 1062–1066. Taylor, W.C., 1989. Regulatory interactions between nuclear and plastid genomes. Annu. Rev. Plant Physiol. Plant Mol. Biol. 40, 211–233. Thomson, W.W., Whatley, J.M., 1980. Development of nongreen plastids. Annu. Rev. Plant Physiol. 31, 375–394. Yun, M.S., Kawagoe, Y., 2009. Amyloplast division progresses simultaneously at multiple sites in the endosperm of rice. Plant Cell Physiol. 50, 1617–1626. Zhou, S.P., He, Y.K., Li, S.J., 1999. Induction and characterization of in vitro corms of diploid-taro. Plant Cell Tissue Organ Cult. 57, 173–178.