Studies on the Germination of Pine Pollen (Pinus mugo) in vitro. III. Inhibition by D‐Mannose and Deoxyhexoses

D‐Mannose, 2‐deoxy‐D‐glucose, 6‐deoxy‐D‐galactose, and 2‐deoxy‐D‐galactose inhibit germination of pine pollen (Pinus mugo Turra) probably competitively with a metabolizable sugar. Inhibition by D‐mannose, 2‐deoxy‐D‐glucose, or 6‐deoxy‐D‐galactose is reversed by transfer of pollen to sucrose medium, if the inhibitors was added before tube growth has started. In contrast, inhibition by 2‐deoxy‐D‐galactose is irreversible except after very short exposures to the inhibitor, in which case the transfer results in reduced growth and germination. Incubation with 2‐deoxy‐D‐glucose, 6‐deoxy‐n‐galactose, or 2‐deoxy‐D‐galactose after tube growth has started, results in irreversible inhibition of growth. If D‐mannose is used, growth is resumed if the pollen are transferred to sucrose medium. Addition of D‐mannose or lowering of the temperature prior to incubation with the deoxyhexoses protected against the irreversible growth inhibition. Uptake of oxygen and 32P‐labelled phosphate is reduced upon addition of either of the inhibitors.