Tip growth is a specialized type of polar growth where new cell wall is deposited in a localized region of the cell, the growing tip. These cells show a characteristic zonation, with a high accumulationof secretory vesicles containing cell wall components at the tip, followed by an organelle-enriched a Medicago sativapolygalacturonase gene isolated in our laboratory, specifically expressed during the interaction of this plant with its symbiotic partner Sinorhiz-obium melilotiand which might participate in tip growth processes during symbiosis
