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Involvement of Ca 2+ signalling in the sugar‐inducible expression of genes coding for sporamin and β‐amylase of sweet potato
Author(s) -
Ohto Masaaki,
Hayashi Koji,
Isobe Minoru,
Nakamura Kenzo
Publication year - 1995
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.1995.7020297.x
Subject(s) - biochemistry , aequorin , sucrose , fructose , chemistry , gene expression , egta , calcium , gene , organic chemistry , intracellular
Summary Genes coding for sporamin and β‐amylase of sweet potato are inducible not only by high levels of metabolizable sugars, such as sucrose, but also by a low concentration of polygalacturonic acid (PGA). Calmodulin inhibitors and EGTA inhibited both the PGA‐inducible and the sucrose‐inducible accumulation of mRNAs for sporamin and β‐amylase in sweet potato. Calmodulin inhibitors, EGTA and La 3+ , also inhibited the sucrose‐inducible expression, in leaves of transgenic tobacco, of a fusion gene, β‐ Amy :GUS, which consists of the promoter of the β‐amylase gene and the coding sequence for β‐glucuronidase. The sucrose‐inducible expression of the β‐ Amy :GUS fusion gene was also inhibited by two inhibitors of Ca 2+ channels, diltiazem and nicardipine. These results suggest that the sugar‐inducible expression of genes for sporamin and β‐amylase involves, at least in part, Ca 2+ ‐mediated signalling, and that the cytosolic free Ca 2+ may mediate cross‐talk between signals related to carbohydrate metabolism and other stimuli. Treatment of coelenterazine‐loaded leaf discs of tobacco expressing a Ca 2+ ‐binding photoprotein, aequorin, with 0.2 M sucrose for 24 h significantly reduced the level of luminescence that could be induced by cold shock, as compared to cold shock‐induced luminescence in coelenterazine‐loaded leaf discs treated with water. Repression of cold shock‐induced luminescence was due to the conversion of holoaequorin to apoaequorin during the treatment with sucrose. Treatment of coelenterazine‐loaded leaf discs with a 0.2 M solution of glucose or fructose, but not of mannitol or sorbitol, also reduced the cold shock‐induced luminescence. It is suggested that non‐synchronous increases in cytosolic level of free Ca 2+ occur in leaf discs during treatment with high levels of metabolizable sugars.