Lateral quantization of the electronic motion in AlxGa1-xAs/GaAs heterojunctions with a microstructured gate electrode is investigated with static magnetotransport and infrared spectroscopy. In these structures a negative gate bias causes a transition from two-dimensional to quasi-one-dimensional electronic behavior. Spacings of one-dimensional subbands as well as one-dimensional electron densities are derived from quantum oscillations of the magnetoresistance and compared with intersubband resonance energies and electron densities extracted from infrared spectra.