バラ切り花の吸水，蒸散および水ポテンシャルの変化に及ぼす光周期の影響

Abstract

Freshly harvested 'Bridal Pink' roses (Rosa hybrida Hort.) were held in deionized water and placed in a room at 20°C under continuous dark, light, or a 12-hr photoperiod. Cut flower weight, water uptake, transpiration, petal water potential, and bud opening stage were measured at 4-hr intervals. Under continuous dark conditions, water uptake and transpiration rates were slow, ranging around 1 g·100 gfw-1·hr-1. Because transpiration did not exceed the water uptake throughout the three-day experimental period, a steady increase in fresh weight resulted. Petal water potential ranged around -0.2 MPa, decreased slightly (becoming more negative) after 7 : 00. Under continuous light, water uptake and transpiration rates changed cyclically with increases between 7 : 00 and 19 : 00. Transpiration rate began to exceed the water uptake at 7 : 00a11 : 00 on Day 3 ; concurrently, fresh weight, which had been increasing began to decrease. Petal water potential decreased between 7 : 00 and 19 : 00 and increased from 19 : 00. But the tendency for water potential was to gradually decline with time. Although bud opening stage was advanced early in the morning under both dark and light conditions, it proceeded faster under latter. Diurnal periodicity was detected in some parameters obtained under the light conditions by using Fourier analysis. Fluctuations in the water uptake and transpiration rates closely corresponded to diurnal periodicity under a 12-hr photoperiod, being elevated in the light and depressed in the dark. These diurnal changes in water uptake and transpiration were greatest during the third and fourth light periods. Transpiration exceeded water uptake in the fourth light period and thereafter. Thus, fresh weight initially increased but decreased in the light and increased again in the dark. But the tendency for fresh weight was to gradually decline with time. Petal water potential decreased in the light and increased in the dark, but the recovery in the dark became insufficient so that the petals finally wilted completely. Bud opening stage advanced immediately after the beginning of light periods except for Day 1 and 2 during which it lagged.