Influence of Temperature on Effects of Growth Regulators on Hypocotyl Elongation

Influences of temperature on effects of growth regulator on hypocotyl elongation of cucumber seedling were analized with the use of bromocholine bromide and gibberellic acid under the controlled temperature in phytotron.Seeds of cucumber (Cucumis sativus L. “Santo”) were sown in plastic containers filled with burnt chaff. The bottom of the container was kept being soaked in water to moisten the burnt chaff, and sown seeds were incubated at 25°C. One day after germination, each of the solutions of 5 ×10-3M bromocholine bromide (BCB) and 100 ppm gibberellic acid (GA) which contains 85% of GA3 was sprayed on cotyledons of the cucumber seedlings. At the same time, the hypocotyl unit was marked; the hypocotyl of each seedling was marked with ink at cotyledonary node and at a distance 1 cm below the cotyledonary node. The treated seedlings were cultured at 20°C, 25°C, 30°C and 35°C respectively. The length of the hypocotyl unit was measured every day.The elongation of the hypocotyl unit was inhibited by BCB and was promoted by GA under the temperature conditions of 20°C, 25°C, 30°C and 35°C. At the same time, the elongation of the hypocotyl unit was remarkably affected by temperature. The difference between the length of hypocotyl unit of treated seedlings and that of untreated ones was large at higher temperature and was small at lower temperature. While, the ratio of the length of the hypocotyl unit of the treated seedling to that of untreated seedling indicated that the promotive effect of GA on the hypocotyl elongation is small at 35°C, and also indicated that the inhibitory effect of BCB on the hypocotyl elongation is small at 20°C.These facts suggest that the temperature of envi-ronment should be taken into consideration for the analysis of the effects of the growth regulator.