Effects of Light Fluence and Wavelength on Expression of the Gene Encoding Cucumber Hydroxypyruvate Reductase

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Abstract
We have investigated the regulation of cucumber (Cucumis sativus) hydroxypyruvate reductase mRNA abundance in response to white-, red-, and far-red-light treatments. Following irradiation of dark-adapted cucumber seedlings with 15 min to 4 h of either white or red light and return to darkness, the mRNA level for the gene encoding hydroxypyruvate reductase (Hpr) in cotyledons peaks in the darkness 16 to 20 h later. The response of the Hpr mRNA level to total fluence of white light depends more directly on irradiation time than on fluence rate. In addition to this time-dependent component, a phytochrome-dependent component is involved in Hpr regulation in dark-adapted green cotyledons as shown by red-light induction and partial far-red-light reversibility. Parallel measurements of mRNA levels for the ribulose bisphosphate carboxylase/oxygenase small subunit and for the chlorophyll a/b-binding protein show that Hpr is the most responsive to short (about 60 min) white- and red-light treatments and that each mRNA has a characteristic pattern of accumulation in dark-adapted cotyledons in response to light.