NECTAR SECRETION IN EXCISED FLOWERS: IV. SELECTIVE TRANSPORT OF SUCROSE IN THE PRESENCE OF OTHER SOLUTES

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Abstract
Various structurally diverse compounds appear in the nectar of excised flowers of snapdragon (Antirrhinum majus) when added to the culture solution. Quantitative analyses of individual nectar constituents were made to obtain information on the interrelations of movement of sucrose, which is the major solute in snapdragon nectar, other solutes that normally are present only in very small amounts or absent, and water. Nectar yields were altered experimentally either by changing the concentration of sucrose in the culture solution or by adding indoleacetic acid (IAA) to it. A representative of each of three different groups of compounds was tested in combination with sucrose. There was a common pattern of variation in yield, differing from that of sucrose, for sodium chloride, urea, and xylose. Sucrose promoted nectar flow and its yield in nectar was depressed by IAA, whereas the other solutes did not promote nectar flow and their yields were insensitive to IAA. Nectar concentrations of the other solutes were not affected by the concentration of sucrose in the culture solution, but their yields were increased proportionately to the sucrose-induced increase in nectar volume. The results are interpreted as indicating a selective transport of sucrose, an indirect influence of sucrose on yield of other solutes through its effect on water movement, and independence of water and solute movement at some stage in the production of nectar in excised snapdragon flowers.