The effect of chronic gamma ray irradiation on lignocellulose of Brachypodium distachyon

The effects of chronic gamma ray irradiation on Brachypodiumdistachyon were investigated to lignocellulose composition and enzymatic hydrolysis. Four-week-old plants of B. distachyon were exposed to gamma-ray irradiation at doses of 50, 100, 150, 200, 250, and 300 Gy. Gamma-ray irradiation negatively influenced biomass related morphology including plant height and cell size; however, it increased tiller number and internode diameter. SEM image analysis showed that the cell size of 300-Gy gamma irradiated plants was 45 % lower than that of the control. Destroyed regions on the cell wall surface were observed according to the dose of radiation. Cell wall yield, lignin content, and neutral sugar content were decreased in a dose-dependent manner. Glucose yield via enzymatic hydrolysis was positively correlated with radiation dose. In addition, 250-Gy and 300-Gy irradiated plants showed significantly better saccharification efficiency than non-irradiated controls. Initial glucose yields from 250-Gy- and 300-Gy-irradiated plants were 121.5 and 139.4 % of yields from non-irradiated controls, and final yields were 184.7 and 213.7 % of control yields, respectively. Reverse-transcription polymerase chain reaction (RT-PCR) analysis of lignin pathway-related genes showed increase of F5H, COMT, and CAD expression in 250-Gy- and 300-Gy-irradiated Brachypodium plants. Chemical composition analysis further verified that chronic gamma ray irradiation degraded lignocellulose as a pretreatment.