Starch degradation by alpha-amylase in tobacco leaves during the curing process |
| |
| Authors: | Naoto Yamaguchi Shoichi Suzuki Amane Makino |
| |
| Institution: | 1. Graduate School of Agricultural Science, Tohoku University, Sendai 981–8555, Japan;2. Leaf Tobacco Research Center, Japan Tobacco Inc., Oyama 323–0808, Japannaoto.yamaguchi@jt.com;4. Leaf Tobacco Research Center, Japan Tobacco Inc., Oyama 323–0808, Japan |
| |
| Abstract: | Tobacco (Nicotiana tabacum L.) leaf starch is degraded to sugars through curing (42°C/82.3% relative humidity/72 h). Total carbohydrate content remained almost constant, starch content decreased markedly, and soluble sugar content (mostly glucose) increased. α-Amylase and starch phosphorylase activities increased sixfold and threefold, respectively, whereas β-amylase activity was unaltered and isoamylase activity decreased. Increased α-amylase activity was accompanied by increased α-amylase protein levels. Although tobacco has four α-amylase gene members, only NtAMY1 mRNA levels increased. For other starch degradation genes, such as NtBAM1 and NtBMY2 (β-amylase), NtISO1 and NtISO2 (isoamylase) and NtGWD1 and NtGWD3 (glucan water dikinase), the mRNA levels remained unaltered during the first 48 h of curing. NtAMY1 expression was induced by osmotic stress but was unaffected by high temperature and/or injury stresses. Similarly, soluble sugar contents were largely increased by osmotic stress. This suggests that starch is degraded by α-amylase during curing and that α-amylase is coded by NtAMY1, induced by osmotic stress. |
| |
| Keywords: | α-amylase curing process osmotic stress starch degradation tobacco leaf |
|
|
