Nectar Production in Abutilon III. Sugar Secretion

Abstract

Analysis of Abutilon nectaries shows that the sugar content of the nectary rises sharply as nectar secretion begins. Nectar secretion on the plant occurs at a steady rate of 2-5 mg total sugar per flower. hour for 36-48 hr. A total of about 100 mg sugar per flower is secreted, and this is about seven times the maximum sugar content of the nectary at any time. Secretion of sugar in nectar by isolated nectaries floating on 0--0· 4M sucrose solution is in two phases. During phase I the rate is independent of concentration of sucrose in the external medium, but the rate is decreased by increasing the osmotic pressure of the medium with mannitol. In phase II the rate of secretion of sugar depends on the concentration of sucrose in the external medium and is independent of increase in osmotic pressure with mannitol. The rate is zero on water and reaches a maximum on about O· 4M sucrose. Secretion is reduced in both phases on media of sucrose concentration