Effects of UV irradiation on barley and tomato leaves: thermoluminescence as a method to screen the impact of UV radiation on crop plants

Abstract

The effect of different UV intensities and irradiation times on barley and tomato leaves was investigated by analysis of thermoluminescence (TL) and chlorophyll (chl) fluorescence measurements. Epifluorescence microscopy was used to estimate the epidermal UV transmittance of leaves. In barley a strong supression of TL emission from the S 2 Q B − (B-band) and the S 2 Q A − (Q-band) charge recombination was observed, increasing with prolonged UV exposure. Primary barley leaves were more sensitive to UV than secondary leaves. In tomato plants a decrease in the B-band only takes place at very high UV intensities and after prolonged exposure times (4 h). The impact of UV in cotyledons was more pronounced than in pinnate leaves of tomato plants. The strong differences in sensitivity to UV in the investigated barley and tomato variety may be due to different concentrations of UV screening pigments in the epidermal layer as demonstrated by epifluorescence measurements. The results show that TL has the same potential to analyse the sensitivity or tolerance of crop plants to UV irradiation as routine fluorescence techniques. Furthermore, TL is directly monitoring the radical pair states of PSII and can distinguish between UV-induced donor and acceptor site-related damage.

Photosystem II reaction centre quenching: mechanisms and physiological role

“…1). A survey of the recent literature indicates that either molecular manipulations of PsbA, the gene encoding D1, or exposure to numerous changes in the external environment has dramatic effects on PSII photochemistry in a broad range of organisms including cyanobacteria (Minagawa et al 1999;Sane et al 2002;Fufezan et al 2007;Cser and Vass 2007), Chlamydomonas (Pocock et al 2007), lichens (Kopecky et al 2005), mosses (Bukhov et al 2001), monocots (barley, rye) (Skotnica et al 2000(Skotnica et al , 2003Gilbert et al 2004;Ivanov et al 2006), dicots (tomato, pea, spinach, Arabidopsis) (Bukhov et al 2001;Sane et al 2003;Gilbert et al 2004;Skotnica et al 2000) and pine trees (Ivanov et al 2001Sveshnikov et al 2006) under controlled and natural field conditions. Based on these data, we suggest that PSII reaction centres can be reversibly interconverted from photochemical energy transducers that convert light into ATP and NADPH to efficient, non-photochemical energy quenchers that protect the photosynthetic apparatus from photodamage.…”