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Expression of α‐amylases, carbohydrate metabolism, and autophagy in cultured rice cells is coordinately regulated by sugar nutrient
Author(s) -
Chen MinHuei,
Liu LiFei,
Chen YungReui,
Wu HsinKan,
Yu SuMay
Publication year - 1994
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1994.6050625.x
Subject(s) - amyloplast , vacuole , biochemistry , biology , carbohydrate metabolism , sugar , carbohydrate , starch , metabolism , microbiology and biotechnology , sucrose , amylase , gene expression , autophagy , cytoplasm , gene , enzyme , plastid , apoptosis , chloroplast
Summary A rice suspension cell culture system has been established to study how sugar depletion regulates α‐amylase expression, carbohydrate metabolism, and other physiological and cellular changes. It is shown here that a group of 44 kDa α‐amylases are constitutively expressed whether or not the cells are starved of sucrose. However, expression of a new group of α‐amylases of 46 kDa is dramatically induced when cells are starved of sucrose. Cellular sugar and starch were rapidly consumed and metabolic activity was decreased in the starved cells. Extensive autophagy also occurred in the starved cells, which caused an increase in vacuolar volume and degradation of cytoplasmic constituents including amyloplasts. Immunocytochemical studies revealed that α‐amylases are localized in starch granules within amyloplasts, in cell walls, and in some of the vacuoles. The presence of putative signal sequences in the N‐termini of nine rice α‐amylases suggests hitherto unidentified pathways for import of α‐amylases into amyloplasts. The studies show that differential α‐amylase expression, carbohydrate metabolism, metabolic activity, and vacuolar autophagy are coordinately regulated by the sugar level in the medium. As the starved suspension cells exhibit some sugar‐regulated characteristics of α‐amylase expression in germinating rice embryos as well as physiological changes similar to those in senescing cells, this system represents an ideal tool for studying cellular, biochemical, and molecular biological aspects of α‐amylase gene regulation, carbohydrate metabolism, senescence, and protein targeting in plants.