STIGMA SURFACE SECRETIONS OF PENNISETUM AMERICANUM

The stigma of Pennisetum americanum (L.) Leeke is of the dry type. Receptive surfaces of papillae are covered by an extracuticular proteinaceous secretion that has esterase activity. Permeability mapping of an intact stigma indicates that the papillate tips of trichome cells are especially penetrable. Numerous discontinuities of the cuticle probably allow passage of surface secretions and of water for pollen hydration. Comparison of pellicle and intracellular proteins by native polyacrylamide gel electrophoresis and analytical electrofocusing showed them to be different. One particular fraction that had esterase activity was a glycoprotein with a molecular weight of 180,000–200,000 daltons and an isoelectric focusing point of 7.5–8.0. This protein was a major component of the pellicle and may play a nonselective role in pollen capture.