The first line of plant defence responses against pathogens can be induced by the bacterial flg22 and can be dependent on various external and internal factors. Here, we firstly studied the effects of daytime and ethylene (ET) using Never ripe (Nr) mutants in the local and systemic defence responses of intact tomato plants after flg22 treatments. Flg22 was applied in the afternoon and at night and rapid reactions were detected. The production of hydrogen peroxide and nitric oxide was induced by flg22 locally, while superoxide was induced systemically, in wild type plants in the light period, but all remained lower at night and in Nr leaves. Flg22 elevated, locally, the ET, jasmonic acid (JA) and salicylic acid (SA) levels in the light period; these levels did not change significantly at night. Expression of Pathogenesis-related 1 (PR1), Ethylene response factor 1 (ERF1) and Defensin (DEF) showed also daytime- and ET-dependent changes. Enhanced ERF1 and DEF expression and stomatal closure were also observable in systemic leaves of wild type plants in the light. These data demonstrate that early biotic signalling in flg22-treated leaves and distal ones is an ET-dependent process and it is also determined by the time of day and inhibited in the early night phase.

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Plant defense responses against Fusarium infection can be controlled by light. In this study, the effects of nocturnal red light were investigated on glutathione transferases (GSTs) in the leaves of the moderate- and high-Fusarium resistant wheat cultivars, GK Ígéret and GK Arató, respectively. GST activity increased in the light phase during the day, while it decreased after midnight. Since GST activity was lowest at midnight, we examined whether red light application at midnight could prevent the night-time drop in enzyme activity. We found that 15-min-long nocturnal red light application was effective to increase GST activity at dawn. The effects of red light pretreatments on GST expression and activity, as well as the oxidative stress induced by fumonisin B1 (FB1), were investigated. FB1 exposure increased GST activity and the expression of GST genes at dawn but nocturnal red light application in combination with the mycotoxin also increased GST activity and the transcript levels of the selected GSTs in the resistant GK Arató. In addition to its effects on GSTs, it was discovered that, depending on the degree of tolerance, nocturnal red light increased the activity of the major antioxidant enzymes at dawn in both of the chosen wheat genotypes. These decreased FB1’s oxidative stress-causing actions, resulting in lower lipid peroxidation and less cell viability loss when exposed to the mycotoxin. Pretreatment with nocturnal red light enhanced the activity of GST and antioxidant enzymes in wheat plant leaves, contributing to FB1 detoxification and reducing oxidative stress.

Sciences. We thank Mrs. Bécsné for her excellent technical assistance. We are grateful to editor and reviewers for their constructive comments and suggestions to this study.