Effect of Silver Thiosulfate Solution (STS) Having Different Ratios of AgNO₃ and Na₂S₂O₃•5H₂O on Ag Absorption and Distribution, and Vase Life of Cut Carnations

Abstract

Cut carnation flower stems were immersed in solutions of silver thiosulfate (STS) having Ag to thiosulfate ratios of 1 : 1, 1 : 2, 1 : 4, 1 : 8, 1 : 16 and 1 : 32. The solutions were prepared by mixing AgNO₃ and Na₂S₂O₃•5H₂O to give a final Ag⁺ concentration of 1 mM or 0.2 mM. Ag chelate in the solutions with high ratios of thiosulfate to Ag, i. e. 1 : 8 to 1 : 32, was quite stable, whereas at ratios of 1 : 1 to 1 : 4, it was not.
1. Ag was detected in the flower head by atomic absorption analysis after cut carnations were treated with the solutions at ratios from 1 : 2 to 1 : 32. It was not detectable in the flower head when treated with AgNO₃ solution alone (1 : 0). All or most of Ag was located in the lower stem when stems were treated with solutions having a ratio of 1 : 0 or 1 : 1.
2. The amount of Ag translocated to the carnation flower head was closely associated with vase life. Treatment of cut flowers with solutions at the ratios of 1 : 4 to 1 : 32 doubled the vase life compared with flowers treated with deionized water. The solutions with ratios of 1 : 4 to 1 : 32 were equally effective in prolonging vase life. Treatment with the solutions with ratios of 1 : 0 to 1 : 2 extended vase life only slightly.
3. Injury to upper leaves increased proportionally with the increase in Ag accumulation and with the increasing ratios of thiosulfate to Ag. Leaf injury symptoms appeared when stems were immersed in 1 mM Ag solutions.
Thus, to extend the vase life of carnations we recommend the use of a 1 : 8 molar ratio of AgNO₃ to Na₂S₂O₃•5H₂O in the STS solution.