Changes and Growth Effect of pH in Pollen Tube Culture.

pH 5.9 is optimal for tobacco pollen tube growth in suspension culture. Little pH changes of sugar-mineral medium result from the release of surface-linked compounds from pollen grains. Germination and pollen tube growth bring about a progressive medium acidification resulting in total growth inhibition. An increase of the buffering capacity of the culture medium enhances pollen tube growth. When the pH was kept near the optimum by 25 mM MES-KOH buffer, pollen tubes grew for 4 days and in the presence of casein hydrolysate they reached a length of up to about 4 cm. The growth related acidification of the medium is independent of the presence of mineral cations and is not due to the hydration of respiratory CO(2). It is suggested that it is brought about by proton secretion from pollen tubes.