Water relations and keeping-quality of cut gerbera flowers. IV. Internal water relations of ageing petal-tissue

Abstract

The relationship between relative water content (R.W.C.) and water potential ( ψ total) of Gerbera petals was studied when cut inflorescences aged in a vase. The regression of sap osmotic potential ( ψ osm), matric potential ( ψ m) and pressure potential ( ψ press) on R.W.C. appeared to be the same for young and old inflorescences. Computing ψ press as the difference between ψ total measured with a pressure chamber and ψ osm + ψ m gave erroneous results for old cut inflorescences because of the increasing leakage of ions from petal cells. As there existed a correlation between ψ press and the bending of petals ( B) caused by a small weight, it was possible to obtain time courses of ψ press by measuring B. Time courses of ψ osm and ψ press of 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, ψ osm increased during the first 6 days, followed by a decrease, and ψ press decreased during the entire vase period. When inflorescences were left on the plant, ψ osm was steady during the first 6 days and increased thereafter, whereas ψ press was steady until day 6 and then decreased. A hypothesis to explain the difference between inflorescences in the vase and on the plant is given.