The relationship between relative water content (R.W.C.) and water potential (ψtotal) of Gerbera petals was studied when cut inflorescences aged in a vase. The regression of sap osmotic potential (ψosm), matric potential (ψm) and pressure potential (ψpress) on R.W.C. appeared to be the same for young and old inflorescences. Computing ψpressas the difference between ψtotalmeasured with a pressure chamber and ψosm+ ψmgave erroneous results for old cut inflorescences because of the increasing leakage of ions from petal cells. As there existed a correlation between ψpressand the bending of petals (B) caused by a small weight, it was possible to obtain time courses of ψpressby measuring B. Time courses of ψosmand ψpressof petals were completely different when inflorescences aged on the plant as compared to ageing in a vase. For inflorescences ageing in a vase without stem plugging, ψosmincreased during the first 6 days, followed by a decrease, and ψpressdecreased during the entire vase period. When inflorescences were left on the plant, ψosmwas steady during the first 6 days and increased thereafter, whereas ψpresswas steady until day 6 and then decreased. A hypothesis to explain the difference between inflorescences in the vase and on the plant is given. © 1979.
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