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Ionising radiation may have different effects on plant metabolism, growth and reproduction, depending on radiation dose, plant species, developmental stage and physiological traits. In this study, exposure of dwarf bean plants to different doses of X-rays (0.3, 10, 50, 100 Gy) was investigated with a multidisciplinary approach consisting of morphological, ecophysiological and biochemical analysis. Both mature and young leaves still growing during the X-rays exposure were compared with non-irradiated control leaves. In particular, leaf expansion, leaf anatomy and functional traits, as well as photosynthetic pigment content and Rubisco expression were analysed. Moreover, the activity of poly(ADP-ribose) polymerase (PARP) was also measured as an indicator of radiation-induced DNA damage. Our data showed that leaf growth is affected by high levels of radiation and demonstrate that mature leaves are more radio-resistant than young leaves, which experience severe dose-dependent changes in leaf functional traits. In particular, young leaves exhibited a reduction of area and an increase in specific mass and dry matter content, as well as a decline in Rubisco activity. Moreover, they showed elevated PARP activity and an increase in phenolic compounds in wall cells if compared with mature leaves. Both of these strategies have been interpreted as a way to help developing leaves withstand irradiation.

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