Starch-iodine staining patterns in petals of cut roses

Abstract

The starch distribution pattern and decline in starch content of Sonia rose petals were examined by starch-iodine staining. Flowers were harvested and held in 150 mg/L of sodium dichloroisocyanurate (DICA) or 150 mg DICA/L + 2% (w/v) sucrose, or were left on the plant. Starch was degraded initially from the outer margins of petals, then from the interveinal area nearest the petal margins, and finally towards the petal bases. Starch was first lost from the outermost petal and then sequentially towards the innermost petals. The rate of starch degradation was slowest in flowers left on the plant, intermediate in flowers harvested and kept in DICA + sucrose, and most rapid in flowers harvested and held in DICA. Preharvest treatments applied in an attempt to vary starch deposition (i.e. shading, leaf removal, and leaf removal with girdling) did not alter the normal starch-iodine staining pattern, reduce starch concentrations, or reduce vase life. However, flower pigmentation was less intense, abnormal flower development occurred, and dry weight and starch contents were reduced, suggesting that carbohydrate supply to the developing bud was affected. Thus, starch-iodine staining of cleared petals of mature Sonia roses was not useful for identifying flowers that developed under conditions of restricted carbon supply. In petals of flowers that had been harvested and held in cool storage (0-3¦C) for 7 days, starch was degraded evenly from all parts across the petal. This diffuse pattern of starch degradation was sufficiently distinctive that it may prove a useful test for determining whether flowers have been cool-stored.