Abstract
Summary The effects of cold-hardening (5 °C) and non-hardening (20 °C) temperatures on the greening of etiolated seedlings under intermittent light conditions was examined in winter rye (Secale cereale L. cv. Muskateer). Development at 5 °C resulted in 2-fold higher levels of chlorophyll a and a 3-fold higher chlorophyll a fluorescence emission at 725 nm than leaves developed at 20 °C. Exposure of etiolated seedlings to low intensity (1 OWE — m-z . s-1), intermittent light at 20 °C resulted in the formation of higher levels of the trans-A3-hexadecenoic acid content associated with phosphatidylglycerol compared to exposure of etiolated seedlings to intermittent light at 5 °C. Subsequent exposure of seedlings grown either at 20 °C or 5 °C in intermittent light to continuous light (200 /,E — m-z . s-') caused a decrease in the ratio of chlorophyll a, b from between 7-10 to about 3.0 with the concomitant appearance of light harvesting complex II. However, in vitro data indicate that the oligomeric form of light harvesting complex II predominates at 20 °C (oligomer , monomer = 1.64) whereas the monomeric form predominates at 5 °C (oligomer, monomer = 0.42). Also, at 20 °C a maximum ratio of oligomer, monomer of 1.6-1.7 was attained after only 24 h of continuous illumination in seedlings initially exposed to 48 cycles of intermittent light. In contrast, 72 h at 20 °C was required to attain the same ratio in etiolated seedlings that had not been exposed to intermittent light. We conclude that low, intermittent light can induce the accumulation of high levels of trans-A3-hexadecenoic acid in the absence of light harvesting complex II. The prior accumulation of trans-A3-hexadecenoic acid enhances the stabilization of the oligomeric form of light harvesting complex II. This is consistent with a sequential process for the accumulation of trans-A3-hexadecenoic acid and the stabilization of light harvesting complex II in its in vitro oligomeric form.
Published Version
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