Fluorescence imaging and chlorophyll fluorescence to evaluate the role of EDU in UV-B protection in cucumber

摘要

A fluorescence imaging system and chlorophyll fluorescence emissions were used to evaluate whether EDU, N-$LB@2-(2-oxo-1- imidazolidinyl) ethyl$RB@-N'-phenylurea, provided protection against ultraviolet-B (UV-B) irradiation (290 - 320 nm) in cucumber (Cucumis sativus L.) leaves. Plants were grown in growth chambers illuminated for 14 h per day with 400 W high pressure sodium and metal halide lamps. Photosynthetically active radiation (PAR) for 1 hr at the beginning and end of each cycle was provided at 270 $mu@mol m$+$MIN@2$/ s$+$MIN@1$/ PAR; during the other 12 hr of the photoperiod, the plants received 840 $mu@mol m$+$MIN@2$/ s$+$MIN@1$/ PAR. Beginning on the twelfth day, the plants were exposed to UV-B radiation (0.2 & 18.0 kJ m$+$MIN@2$/d$+$MIN@1$/) for 2 days at 8 h per day centered in the photoperiod. Rapidly acquired (less than 1 s), high spatial resolution (less than 1 mm$+2$/) images were obtained for whole adaxial leaf surfaces using a fluorescence imaging system. The steady-state fluorescence images were acquired in four spectral regions: blue (F450 nm), green (F550 nm), red (F680 nm), and far-red (F740 nm). Fluorescence emission spectra for leaf pigments extracted in dimethyl sulfoxide (DMSO) were obtained by excitation at 280 and 380 nm (280EX 300 - 530 nm; 380EX 400 - 800 nm). Both UV-B and EDU induced stress responses in cucumber leaves that altered the fluorescence emissions obtained from extracts. In the fluorescence images only UV-B induced stress responses were observed but this damage was detected before it was visually apparent. There was no evidence that EDU afforded protection against UV-B irradiation. Use of fluorescence imaging may provide an early stress detection capability for helping to assess damage to the photosynthetic apparatus of plants.