Auxin-like compounds act as protectors against UV-B irradiation in garden pea plants

Pretreatment with the original auxin physiological analogues 1-[2-chloroethoxycarbonylmethyl]-4-naphthalenesulfonic acid calcium salt (TA-12) and 1-[2-dimethylaminoethoxicarbonylmethyl]naphthalene chlormethylate (TA-14) and subsequent UV-B irradiation (180 min at λₘₐₓ 312 nm for 6.6 kJ·m⁻²) of pea plants (Pisum sativum L.) was investigated to assess if foliar application of these compounds has ability to attenuate the negative effects caused by UV-B stress. UV-B treatment increased malondialdehyde (MDA) and proline levels as well as superoxide dismutase, catalase and guaiacol peroxidase activities, but decreased hydrogen peroxide, low-molecular thiols, total phenolics and total soluble protein contents. The pre-treatment with TA compounds decreased the oxidative stress provoked by UV-B radiation detected by lower level of MDA, increased the content of thiols and UV-absorbing compounds and had favourable effect on H₂O₂ content and enzymatic activities. Exogenous application of auxin-like compounds on pea plantlets successfully counteracted UV-B induced oxidative stress via activation of ROS detoxifying enzymes and non-enzymatic antioxidants.