Materials and Methods

Preparation，Culture，and Light Treatment of Potato Tuber Discs.Centennial and Katahdin，two varieties of potato tubers supplied by the United States Department of Agriculture were used in this study.The tubers were peeled and sterilized with Amphyl（National Laboratories，Lehn and Fink Industrial Products Division of Sterling Drug Inc.，New Jersey）.Discs（10×2 mm2）were made with a sterile cork borer and a gel slicer.These discs，after washing in sterile water，were placed on 1%agar plates in sterile Petri dishes（9 cm），40 discs per dish.The discs were illuminated at room temperature by fluorescent tubes with intensity of 3,000 lux.

Chlorophyll and RuBPCase Determination.Chl was determined according to Arnon［2］.RuBPCase was detected with a Model E analytical ultracentrifuge，as previously described［9］.Schlieren pictures were taken at 44,770 rpm，10 min after attaining this speed.An Ouchterlony double diffusion test was employed to determine the RuBPCase specifically.The antiserum was prepared against RuBPCase from tobacco［15］.

Light-Driven Protein Synthesis in Chloroplasts.Ten g of green potato tuber discs which had been exposed to white light for 7 d were homogenized in a Waring Blendor with cold isolation buffer（sucrose 0.35 mol/L，Hepes-NaCl 25 mmol/L，EDTA 2 mmol/L，isoascorbateNa 2 mmol/L，pH 7.6）and filtered through 2 layers of Miracloth.The resultant filtrate was centrifuged at 30g for 1 min to remove starch granules，and the supernatant was then centrifuged at 2,500 g for 1 min.The pellet was resuspended in 1 ml of KCl suspension（KCl 0.2 mol/L，Tricine-KOH 66 mmol/L，MgCl2 6.6 mmol/L）.The chloroplast suspension was transferred to a Petri dish（3 cm in diameter）and incubated with［35S］methionine（10 μCi）at room temperature under white light（4，000 lux）.During a 2 h incubation，the incorporation of［35S］methionine into proteins was measured.After the 2 h incubation the radioactive polypeptides were separated on an SDS-polyacrylamide gradient gel（8%—15%），followed by fluorography as described by Blair and Ellis［4］.(https://www.daowen.com)

O2 Evolution Assay.The ability of chloroplasts from potato tuber discs to evolve O2 was measured in the Hill reaction according to the procedure of Marsho et al.［12］.The incubation system consisted of ferricyanide 1.7 mmol/L，methylamine 3 mmol/L，glyceraldehyde 10 mmol/L，and chloroplasts corresponding to 15 μg of ChI in a total volume of 0.6 ml.The reaction was initiated by irradiation with red light（22.4 mW/cm2）.The O2 evolution was measured and recorded with a polarograph.