We have developed a laboratory experiment for the digestion of protein at secondary school. We used trypsin and papain as the protease, and the protein rich substrates ; egg white, milk, powdered skimmed milk, and tofu cake. We stuffed 10g of the substrate suspension into a dialysis membrane bag with 5ml of 1% enzyme solution, and soaked it in 30ml-buffer solution at 37°C. Then we sampled 2ml of the buffer solution every 5 minutes, and the Ninhydrin Reaction of each sample was examined and wes measured using the colorimerty of 570 nm wave length. As a result, we could detect the increase of digested products within 30 minutes not only quantitatively but also visually. We examined further experiments to test the optimum pH and temperature of these enzyme reaction. The optimum pH of each enzyme could be found out, but the optimum temperature could not be measured distinctly. The best result was obtained using the powdered skimmed milk as substrate. Using this substrate we could detect the decreasing step of the substrate as a visual color change from the original white to colorless.

In the present study, we could clarify the best conditions of the medium and regulatory substances for the dedifferentiation of explants (shoot apex and lateral bud), and the redifferentiation of callus induced from them in water cress (Nasturtium ofjicinale R. Br.): 1. The best condition of the dedifferentiation of explants was MS (Murashige and Skoog) solid medium supplemented with 1.0mg/l 2, 4-D (2, 4-dichlorophenoxyacetic acid). 2. The best condition of the redifferentiation of the induced callus was MS solid medium supplemented with 0.01mg/l 2, 4-D and 0.1mg/ l BA (benzyladenine).

After explants of the water cress were cultured during 1-2 weeks on the best conditions for dedifferentiation, good explants of this plant changed wholly into the calli. On the other hand, after the good calli were cultured during 1-2 weeks on the best conditions for redifferentiation, they formed themselves into normal plantlets.

During a short period (approximately 4 weeks), students might learn the basic biotechnology and the totipotency of plant cells by the tissue culture of the water cress.