大豆幼苗之Stringent-like反應

Stringent-Like Response in Soybean Seedlings

The meristematic hook portion of soybean seedlings from 0 to 0.5 cm below cotyledons were excised and incubated in phosphate buffer (1 mM, pH 6.0) or various culture media, such as B5, MS, ER, and White, and in addition of either yeast extract or coconut milk or casein hydrolysate for 12 hours at 28°C. Then polyribosomal level (as protein synthetic activity) in the tissues and the RNA polymerase activity in the isolated nuclei were examined. Comparison was made on the efficiency of various medium to maintain the polyribosomal level and the RNA polymerase I activity in the excised hook tissues. Our results indicated that the B5 medium plus yeast extract was the most effective for the maintenance of both polyribosomal level and RNA polymerase I activity. At the end of 12 hours incubation period, RNA polymerase I activity was increased 40% (51% of its original activity) and polyribosomal level was increased 50% (79% of its original level). For examination of the relationship between protein synthesis and rRNA synthesis in excised root tips, 8H-leucine or 8H-uridine was used. There was a positive relationship between the protein synthetic activity and the total RNA synthetic activity. The total RNA synthesis decreased rapidly and reached very low level within 4 hours of incubation in phosphate buffer. The majority of this decrease was due to the cessation of rRNA synthesis based on use of the base analogue, 5-fluorouracil, for inhibition of rRNA synthesis. At end of s ix hours incubation RNA polymerase I activity decrea5ed to only 16% of its original activity and protein synthesis was also decreased to 10% of its original level in the excised root tips. From these results of this experiment a stringent-like response was operative in meristematic regions of higher plant.