| Browning of potato tuber (Solanum tuberusm L.) when damaged is caused by Polyphenol Oxidase (PPO), which could change the colour and tasty of potato product. It is important to study the dynamics of PPO activity in various tissue and organs at different development stage of the varieties that suitable for processing so that we could clone the PPO gene and use the reverse genetic techniques to develop an anti browning potato variety. The main results in this paper are described as below:1) The activities of the PPO in different tissue and organ at the main development stages of 5 varieties including "Gannongshu No1", "Gannongshu No2", "Shapedy", "Snowden" and "Norvalley" were measured using spectrophotometer. Patterns of the PPO activities in leaf, creeping stem, tuber and pollen have been found. The activity of PPO in leaf showed as low, high and low from flower-bud to tuber -rapidly-developing stages and it reached highest at stage of tuber expansion [31.12 0.01 ΔOD.min-1]]. In tuber, PPO activities showed high, low and high. It reached to highest at tuber initiation stage (60.60(0.01 ΔOD.min-1). PPO showed as the same trend of its activity in pollen as in leaf and it reached to the highest at flower season [129.80 (0.01 ΔOD.min-1)]. The PPO activity in different tissue and organ appeared different at the same development stage (between 25th of June and 24th of July). The trend was: anther >stem> flower bud and pedal>leaf. The highest activity in anther was 68.30 (0.01 ΔOD.min-1). The activity did not keep the same level even in different parts of the same tissue. For example, PPO in epidermal tissue of the tuber showed the highest activity but the lowest in inner tissue.2) The PPO activities of in vitro plants, callus induced from stem explants, tuber and tuber buds were tested under conditions of different temperature and pH. When pH was between 5.0~5.5, the PPO activity showed higher levels in tuber buds [94.20(0.01ΔOD.min-1)] and in the callus [20.40(0.01ΔOD.min-1)] than in the other tissues. The in vitro plants reached its highest PPO when pH was 8.0. The in vitro plants of the five varieties showed different PPO activities under different temperatures. "GANNONGSHU No1" and 'Atlantic" reached to highest between 18 and 25℃, It's up to 16.80 and 37.20(0.01ΔOD.min-1) respectively , but "Shapedy" and "Snowden" reached the highest at 5℃. The potato tubers in storage had the highest PPO activity at 25℃.3) The efficiency of inhibition to PPO in leaf, stem and tuber of potato was tested by using browning inhibitors such as Vitamin C, AgNO3, L-cysteine, boric acid, citric acid and sodium bisulfite. The activity of PPO in stem was reduced more than it was in leaf and tuber. The L-cysteine and citric acid inhibited PPO more effectively in tuber than in leaf, but vitamin C, AgNO3, boric acid and sodium bisulfite appeared more effective to prevent browning of leave than to other organs. The optimum concentration of different inhibitors for controlling browning of different tissue and organs has been selected. 4) According to the sequence of potato PPO gene (POT32) published from Genbank, two pairs of primers were designed. Two fragments of PCR products, 1840 bp and 476 bp, were amplified from genomic DNA of "GANNONGSHU No1" using these primers, and then they were inserted into PMD-18T plasmid. Two construct PMDPPOqc and PMDPPOty were produced. Sequencing results showed that the 1840 bp fragment had 98% homology to that of POT32 and the fragment of 476 bp was 100% homologue to PPO gene. These two fragments were inserted into a binary vector PC3 with invert orientation to produce two antisense constructs named as PC3-ASPPOqc and PC3-ASPPOty. They were then introduced into Agrobacterium strain EHA105 respectively.5) Agorbacterium mediated transformations were conducted for the four varieties "Atlantic, "GANNONGSHU No1", "GAN DAN HUA No 9", and Norvalley using EHA105/PC3-ASPPOqc and EHA105/PC3-ASPPOty. Various explants have been tried. When leaf discs were...
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