Materials and Methods
Brassica napus Linn.var.“Victory”was used as experimental material.During the blooming period，flowers were marked every five days.After definite time intervals，buds，flowers，and siliques of different ages were collected and made into acetone powders for subsequent estimation of the enzyme activities.
Preparation of acetone powder.The procedure for preparing acetone powder essentially followed the method of Hageman and Arnon［7］.Fresh siliques（10 g）were cut to pieces with a stainless steel scissors in a glass motar.After the addition of 15 ml of a mixture of EDTA（0.03 mol/L）and phosphate（1.1 mol/L）buffer，pH 8.2，the tissue was ground until homogenized，and transferred to a 500 ml beaker.Cold acetone（-15°to-20℃，100 ml）was then added slowly with stirring，and the slurry was filtered immediately by suction in a Büchner funnel.The precipitate was washed with 40 ml cold acetone for three times，left in the air about 1 hour until free from acetone odour，and dried in vacuo for 12 hour over P2 O5.The dry povrder was then stored in a bottleat-15℃.
Enzyme extract.Acetone powder extracts were prepared by grinding the powder in a glass motar with a mixture of EDTA（0.001，5 mol/L）and phosphate（0.01 mol/L）buffer，pH 7.2（25 ml buffer solution for 10g of fresh tissues）.The slurry was filtered through four layets of cheese-cloth，and the resulting filtrate was centrifuged in the cold at 10，000×g for 5 to 10 min.The filtrate is designated as enzyme extract.
Assay of enzymes.G-6-P DH and 6-PG DH were determined spectrophotometrically by measuring the reduction of NADP at 340 mμm with a Beckman DU spectrophotometer.
R-5-P conversion enzymes were determined by following the disappearance of R-5-P with time of incubation at 30℃.
Phosphoglucoisomerase was measured by the method of Slein［8］，F-6-P formed from G-6-P was determined by the resorcinol method of Roe［9］.
Phosphofructokinase was detected by determining the quantity of phosphotriose formed with the endogenous aldolase from F-6-P and ATP.
Aldolase activity was estimated by the procedure of Sibley and Lehninger［10］，the phosphotriose formed was determined by dinitrophenyl hydrazine reaction in alkaline medium.(https://www.daowen.com)
Phosphoglyceraldehyde dehydrogenase activity was determined by the method of Black and Humphreys［11］，in which the NADH2 formed was measured spectrophotometrically at 340 mμm with a Hitachi EPU-2A spectrophotometer.
Phosphoglyceric kinase activity was determined by the method of Axelrod and Bandurski［12］，the 1，3-diphosphoglycerate formed is trapped by hydroxylamine.
Enzymes involved in the conversion of 3-PGA into pyruvic acid were detected by determining the pyruvic acid formed from 3-PGA with the method modified by Kachmar and Boyer［13］.
Measurement of respiration.Seeds of different developmental stages were placed in weighing bottles containing iodoacetamide（0.05 mol/L）or sodium fluoride（0.1 mol/L）and infiltrated under reduced pressure for about 2hr in a desiccator.Oxygen uptake was measured with the conventional Warburg apparatus at 30℃，at pH 5.0，without exogenous substrate.
Separation and purification of the inhibitor.Extract of acetone powder of rape buds was boiled for 5 min in a water bath.After removal of the precipitated proteins by centrifugation，the supernatant was further fractionated by paper chromatography or paper electrophoresis.In some experiments the supernatant was washed several times with chloroform or benzene to remove lipid impurity before being subjected to chromatography or electrophoresis.
Paper chromatography.Samples（5 ml）were applied to a 20 cm×17.5 cm sheet of Whatman No.1 filter paper and developed by the descending technique with acetone：formic acid：water（20∶10∶65）for 24 hour at 25℃.After drying，the paper was cut equally into four sections from the starting line to the solvent front.Including the original region there were all together five sections，designated as 0，1，2，3，4 respectively.Each section was extracted with 5 ml redistilled water and the inhibitory effect on G-6-P DH or 6-PG DH was estimated.
Paper electrophoresis.A sample（0.5 ml）was applied to a 2 cm×36 cm strip of filter paper held horizontally with ends dipped into borate buffer（pH 9）.A potential of 400 V was applied for four hours at room temperature.At the end of electrophoresis，the paper was allowed to dry in air and cut into several sections according to colour.After extraction by 4 ml of redistilled water，the inhibitory effect of each section was estimated as above.
