VARIATION IN NECTAR SUGAR COMPOSITION AT THE INTRAPLANT LEVEL IN IPOMOPSIS LONGIFLORA

The nectar sugar composition of individual flowers from single plants in both greenhouse and field populations was determined by High-Performance Liquid Chromatography (HPLC). Intraplant variability in nectar sugar composition of greenhouse-grown plants was significantly greater than can be attributed to the analytical methodology. Individual greenhouse-grown plants had significantly different sugar compositions, suggesting genetic differences. Under field conditions the situation was complex. Variation among flowers from single plants in field populations was significantly greater than that of plants under greenhouse conditions. Unprotected flowers of some field populations were more variable at the intraplant level than others. Field experiments showed that, in untreated (open-visited) flowers, the percent sucrose relative to other sugars declined significantly and coefficients of variability increased significantly with flower age. However, nectars never exposed to the natural environment did not change significantly with flower age. Further, within single plants it was found that percent sucrose in nectars varied in a small but significant way during the growing season. The data suggest that, in this species, both intrinsic and extrinsic factors affect nectar sugar composition and it is desirable to obtain samples from numerous flowers to accurately characterize the nectar sugar composition of an individual under field conditions.