Do low-ethylene-producing transgenic canola (Brassica napus) plants expressing the ACC deaminase gene differ from wild-type plants in response to UVB radiation?

Abstract

Few studies have considered ethylene involvement in plant responses to ultraviolet-B (UVB) radiation. We studied the responses to UVB radiation of one wild-type (WT, ‘Westar’) canola (Brassica napus L.) with normal ethylene evolution and two transgenic (C1, C2) lines with lower ethylene evolution. Canola plants were grown under biologically effective levels of UVB (UVBBE) radiation: 0.03 (low), 4.88 (medium), and 9.78 (high) kJ·m–2·d–1 in controlled-environment growth chambers. The growth and physiological parameters of the plants were measured. Of the two transgenic lines, C1 demonstrated higher ethylene evolution than C2 but lower than WT. The lowest aboveground and belowground biomass was found with exposure to high UVB radiation. WT produced more biomass than C2. Net CO2 assimilation and transpiration did not vary among plant lines or UVB treatments. Water-use efficiency was lower under high UVB radiation than under low UVB. The quantum yield of photosystem II was higher for C2 than for either WT or C1. WT did not differ from transgenic plants in respect to photosynthetic pigments and UV-screening compounds. Photosynthetic pigment concentration decreased, but concentration of UV-screening compounds, thickness of epicuticular wax, and the rate of root hydraulic conductance were increased by exposure to UVB radiation. While there appears to be a lack of ethylene involvement in some of the measured physiological parameters, the transgenic plants exhibited differential sensitivity to UVB in a few key measured parameters.