P-proteins (phloem proteins) and their conformational changes in the functional and non-functional sieve elements in secondary phloem of Armeniaca vulgaris Lam. (Rosaceae) were examined with an electron microscope. Scattered throughout the cell, the fibrillar components of p-protein in active sieve elements were much denser sieve plate surfaces. P-proteins in inactive sieve elements, different from those of active ones, were observed to appear as disordered, short, thread-like fibrils with fern-like crystalline structure.

P-proteins (phloem proteins) and their conformational changes in the functional and non-functional sieve elements in secondary phloem of Armeniaca vulgaris Lam. (Rosaceae) were examined with an electron microscope. Scattered throughout the cell, the fibrillar components of p-protein in active sieve elements were much denser sieve plate surfaces. P-proteins in inactive sieve elements, different from those of active ones, were observed to appear as disordered, short, thread-like fibrils with fern-like crystalline structure.