Abstract
The shoot-tips of Cattleyas cultured on a solid medium turned brown, and eventually died. To reduce browning of tissue, the browning reaction of Cattleya was studied using the powder of freeze-dried leaves and partially purified polyphenoloxidases. In addition, the shoot-tips were cultured under condition where the browning of Cattleya tissue powder was reduced.
1. The spectrometric absorbance maximum of the browning substance was at 285nm.
2. Cattleya polyphenoloxidases had a pH optimum of 6.5 and the activity was greatly inhibited at a lower pH. Furthermore polyphenoloxidase activity or browning was inhibited with potassium cyanide, ascorbic acid, cysteine, thiourea and in a stationary condition.
3. The browning of shoot-tips was most effectively inhibited in a liquid medium in a stationary condition. The inhibitors had no effect or little effect on the browning on a solid medium.
4. Boiled ethanol extracts of Cattleya tissue were oxidised by cattleya polyphenoloxidases, and the major component of substrates were extracted with ethylacetate from acidic aqueous solution.
