Isoprene emission aids recovery of photosynthetic performance in transgenic Nicotiana tabacum following high intensity acute UV-B exposure

• The emission of isoprene by plants under thermal and drought stress is widely considered to have a protective function.
• The effect of UV-B radiation on the emission of isoprene and what role this may play in the mitigation of stress is unclear.
• We exposed isoprene emitting (IE) and non-emitting (NE) transgenic tobacco to high intensity UV-B radiation.
• Isoprene emission did not mitigate the negative effects of UV-B but did enhance the recovery of photosynthesis post-exposure.
• The enhanced recovery of photosynthesis in IE plants was associated with increased anti-oxidant cycling and activity.

Isoprene emission by terrestrial plants is believed to play a role in mitigating the effects of abiotic stress on photosynthesis. Ultraviolet-B light (UV-B) induces damage to the photosynthetic apparatus of plants, but the role of isoprene in UV-B tolerance is poorly understood. To investigate this putative protective role, we exposed non-emitting (NE) control and transgenic isoprene emitting (IE) Nicotiana tabacum (tobacco) plants to high intensity UV-B exposure. Methanol emissions increased with UV-B intensity, indicating oxidative damage. However, isoprene emission was unaffected during exposure to UV-B radiation, but declined in the 48 h following UV-B treatment at the highest UV-B intensities of 9 and 15 W m−2. Photosynthesis and the performance of photosystem II (PSII) declined to similar extents in IE and NE plants following UV-B exposure, suggesting that isoprene emission did not ameliorate the immediate impact of UV-B on photosynthesis. However, after the stress, photosynthesis and PSII recovered in IE plants, which maintained isoprene formation, but not in NE plants. Recovery of IE plants was also associated with elevated antioxidant levels and cycling; suggesting that both isoprene formation and antioxidant systems contributed to reinstating the integrity and functionality of cellular membranes and photosynthesis following exposure to excessive levels of UV-B radiation.