Organic Acids, Lipids and Sterols

Abstract

The organic acids are a poorly assayed group of pollen constituents. These key metabolic intermediates vary with respect to development, species, and prior handling of the samples. Initial assays of acid content were made by titrating alcohol extracts with base. Kressling (1891) reported that an extract of 5 gms of Pinus sylvestris pollen contained 1.76 equivalents of acid (H⁺). By salt formation and a specific color reaction he determined that the principle acid in the extract was tartaric, with malic and acetic acids also present. Assay of an alcohol extract of 100 mg samples of Pinus ponderosa, P. echinata, P. lambertiana and P. radiata showed that viable pollen stored 15 years contained about 1.65 equivalents of acid per 5 gms. Non-viable pollen, stored the same length of time but at higher relative humidity than the viable samples, contained 20% less organic acids (Stanley and Poostchi, 1962). Quince pollen with 20% viability also contained 20% less total organic acid than a variety with 40% viability (Džamič and Pejkić, 1970). This suggests that high levels of organic acids, as well as levels of complex carbohydrates, are associated with germination capacity of pollen.