Water relations of cut roses as influenced by vapor pressure deficits and temperatures

Freshly harvested 'Bridal Pink' roses (Rosa hybrida L.), with their stem ba ses in test tubes containing deionized water, were placed in a glass tank a nd held in a controlled environment room at 14, 20, or 30 degrees C. The va por pressure deficit (VPD) in the tank was maintained at nearly 0 kPa (no V PD: NVPD) or 0.9 kPa (intermediate VPD: IVPD). At all temperatures and VPDs, the fresh weight of cut roses increased initi ally and then decreased; the decrease occurred earlier in IVPD than in NVPD and at higher temperatures. Necks of all flowers placed in IVPD became ben t within 48, 144, and 312 hr of postharvest at 30, 20, and 14 degrees C, re spectively; whereas, bent neck did not develop in NVPD. Irrespective of tem perature, transpiration and water uptake rates of the roses placed in IVPD were markedly higher than those in NVPD. In IVPD, these rates increased ini tially, but decreased after 48, 72, and 96 hr at 30, 20, and 14 degrees C, respectively. Petal water potential gradually decreased during the first 36 hr at 30 degrees C in IVPD, but did not change at 14 degrees C. The osmoti c potential increased with time and was higher at 30 degrees C than at 14 d egrees C. Fructose, glucose, and sucrose were the major sugars in petals. C oncentrations of these sugars decreased during the first 36 hr, the decreas e being greater at 30 degrees C than at 14 degrees C. The contribution of t hese sugars to the petal osmotic potentials was only 10 %. These data indicate that the water relations of cut roses? immediately afte r harvest, was greatly influenced by high VPD by hastening the transpiratio n rate, and subsequently by increasing temperature through rise in the osmo tic potential which was partly attributable to the consumption of respirato ry substrate.