Proteolytic activity in the stem cambial region of Pinus sylvestris L. - A contribution to the specific differentiation of secondary xylem and phloem

Proteolytic activity was studied in the differentiating xylem and phloem of Scots pine (Pinus sylvestris L.) to determine the specificity of xylem and phloem differentiation. The activity of autolytic proteases was demonstrated in the differentiating xylem during spring, summer and autumn and it was not detectable during winter. It was initiated with the onset of cambial activity in spring and unchanged during subsequent stages of xylem differentiation. The same proteolytic activity was not detectable in the extract of fresh phloem tissue. It could be detected in phloem after removal of the inhibitor found in the extract. The same pH optimum was determined for proteases extracted from xylem and phloem. However, their identity remains uncertain because of different electrophoretic mobility. On the other hand the presence of protease inhibitor in phloem tissue can be an important factor im determining the specificity of xylem an phloem differentiation.