Thermal Dissipation of Excess Light inArabidopsis Leaves is Inhibited after Gamma-irradiation |
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Authors: | Yu Ran Moon Jin-Hong Kim Min Hee Lee Jae-Sung Kim Byung Yeoup Chung |
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Institution: | (1) Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, 1266 Sinjeong-dong, jeongeup-si, 580-185 Jeollabuk-do, Korea |
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Abstract: | To elucidate the effect of ionizing radiation on the non-photochemical quenching (NPQ) oir chlorophyll fluorescence, we analyzed
the buildup and release of NPQ inArabidopsis wild-type (WT) andnpq1- 2 mutant plants after gamma-irradiation. Thenpqi- 2 mutant cannot normally induce the buildup of NPQ by a mutation in the violaxamthin de-epoxidase gene. A dose of 50 Gy h for
4 h significantly suppressed such buildup in the mutant and, more noticeably, in the WT. Both the initial rise and maximum
level of NPQ were gradually inhibited after gamma-irradiation. In contrast, the release of NPQ and the maximum photochemical
efficiency (Fv/Fm) of Photosystem II were largely unaffected in either genotype. This inhibition of NPQ buildup could be partly
attributable to a significant decrease in the content of carotenoids, including xanthophyll pigments. Moreover, inhibition
that was dependent on the xanthophyll cycle substantially enhanced the sensitivity of irradiated leaves to a photoinhibitory
illumination of 800 |imol photons m 2 s"1. The difference in Fv/Fm values between the WT andnpq1- 2 under that photoinhibitory level of illumination was much smaller in the irradiated leaves than in the control. However,
NPQ inhibition did not cause a significant difference in efficiency between WT and mutant when both were treated with UV-B
irradiance of 2.4 W m 2. Therefore, we suggest that a significant decrease in carotenoid content after gamma-irradiation should
partially contribute to the enhanced sensitivity of irradiated plants, at least to high-ligtil photoinhibition. This is accomplished
by suppressing the thermal dissipation of excess light absorbed by photosynthetic pigments. |
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Keywords: | gamma ray high light non-photochemical quenching (NPQ) ultraviolet (UV) ray xanthophyll cycle |
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