Regulation of photosynthetic performance and antioxidant capacity by 60Co γ-irradiation in Zizania latifolia plants

• The responses of Zizania latifolia plants to 60Co γ-irradiation were examined.
• Plant growth was suppressed by high doses of irradiation but slightly affected by low doses.
• γ-irradiation reduced PSII activity and chlorophyll content.
• γ-irradiation limited photosynthetic capacity under high light flux but not low light irradiance.
• Antioxidant enzyme APX and antioxidants ( AsA and GSH) were involved in the protection of Z. latifolia plant against oxidative stress induced by γ-irradiation.

The aim of the present work was to investigate the photosynthetic performance and antioxidant enzyme activities in response to γ-irradiation of an aquatic plant Zizania latifolia. The Z. latifolia seedlings at 6-leaf stage were exposed to 25, 50 and 100 Gy of γ rays from a 60Co source. The growth parameters, chlorophyll contents, photosynthetic gas exchange, chlorophyll fluorescence, malondialdehyde (MDA) content, antioxidant enzyme activities and antioxidant contents were examined at 1–5 weeks post-irradiation (WPI). The results showed that plant height, leaf number and tiller (branch close to ground) number were significantly suppressed by 50 and 100 Gy irradiation at 5, 3–5 and 4–5 WPI, respectively, but they were not significantly different from control by 25 Gy irradiation. Chlorophyll a, chlorophyll b, and total chlorophyll contents were also found to be significantly decreased by irradiation. The net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr) generally declined in a dose-dependent manner. As for the chlorophyll fluorescence parameters, maximum quantum efficiency of PSII photochemistry (Fv/Fm), actual photochemical efficiency of PSII (ΦPSII) and photochemical quenching (qP) were observed to be significantly decreased compared to the control at 3 WPI, while non-photochemical quenching (NPQ) significantly increased by 100 Gy. γ-irradiation induced substantial increase in MDA content, ascorbate peroxidase (APX) activity, reduced ascorbate (AsA) content and reduced glutathione (GSH) content, suggesting a protective mechanism of Z. latifolia plant against oxidative stress when exposed to γ-irradiation.

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