Novel Light-Regulated Chloroplast Thylakoid Membrane Protein

A 64 kilodalton chloroplast membrane polypeptide was dependent on growth irradiance with 10-fold greater quantities of the protein present in barley (Hordeum vulgare) grown under 500 micromoles of photons per square meter per second compared with growth at 50 micromoles per square meter per second. The concentration of the protein was sensitive to changes in irradiance, with a slow time course for the response (days) similar to other reported light acclimation processes. The polypeptide also was observed in maize (Zea mays), oats (Avena sativa), and wheat (Triticum aestivum), but not in soybean (Glycine max Merr). The 64 kilodalton polypeptide did not correspond to any thylakoid membrane protein with an assigned function, so its structural or regulatory role is not known.