Effects of enhanced UV-B radiation and different nitrogen conditions on protective matter and protective enzymes in millet(Setaria italica(L.) Beauv.) leaves Effects of enhanced UV-B radiation and nitrogen on photosynthetic pigments and non-enzymatic protection system in leaves of foxtail millet (Setaria italica (L.) Beauv.) 谷子显性雄性不育基因“Ms~(ch)”的细胞质转换