We investigated the effects of low-dose in planta irradiation on red pepper plants treated with gamma rays of 2, 4, 8, and 16 Gy. Growth was stimulated at 2 and 4 Gy but inhibited at 8 and 16 Gy. Photochemical quenching (qP) increased slightly in all treatment groups for 1 d after irradiation (DAI), whereas non-photochemical quenching (NPQ) decreased more noticeably. These changes in qP and NPQ were transient and had almost recovered to the control level by 2 DAI. Although carotenoid pigments also fluctuated during the experimental period, chlorophylls were almost entirely insensitive to the gamma rays. Irradiation also partially protected leaves from a decrease in photochemical efficiency (Fv/Fm) under conditions of UV-B $(2.2;W;m^{-2})$ and high light intensity $(800{mu}mol;m^{-2};s^{-1})$. This enhanced stress resistance could be partly explained by higher levels of SOD and APX activities, as well as ascorbate content. Our results demonstrate for the first time that the carotenoid pigments are the most radio-sensitive and fastest recovering compounds in plants, and that SOD, APX, and ascorbate are important inducible factors for improving stress resistance through the use of in planta gamma-irradiation.