Study of Differentiation and Characteristics of Sieve Elements and P-protein Body in Ginkgo biloba

The ultrastructure observation, energy spectrum analyses and study on sieve elements in gingko (Ginkgo biloba. L) root phloem showed: 1) The inside wall had a large retention of small grains with a diameter of 3- 4 μm, and the outside wall membrane structure wrapped P-protein body with a kernel of high electronic density. 2) The growth had the typical process of programmed cell death (PCD), i.e. the cell karyoplasm condensed, chromatins congealed and contracted and gradually agglomerated to the periphery of the nuclear membrane, and accordingly a nuclear of malformation appeared; the endoplasmic reticulum extended and connected and merged mutually, and the shallow part fused with the cell membrane. After packing the cell organelle, the endoplasmic reticulum divided the cell into several combined necrotic corpuscles of different sizes, the cell organelles collapsing with the cell and gathering abundantly in the inside cell wall. There were two kinds of degradation for the mitochondria: One was that the electronic density of the matrix decreased, the ridges died out to be cavitations gradually, and the double-layer membrane broke and ruined; the other was that parts of the territorial structure of the membrane broke, and the substance it contained escaped. 3) The ultrastructure of the course of gingko root phloem developing from cell with protein thin wall into sieve elements might make out that the P-protein body was produced in PCD and developed with retention in the combined necrotic corpuscle. 4) The P-protein had higher contents of S, K, P than the sieve elements wall tissue, and the percentage composition of S was 4.64%, which was more than twice the composition in the cell wall with 2.14 %. According to the observation through transmission electron microscope that showed the P-protein had high electronic density, we might affirm that it was a P-protein body with S, P. The composition of K was 21.62%, 1.52 times that of the cell wall which was 14.23%. The existing of high quantity of P, S, K in P-protein body showed P-protein body was the main cell organelle for nourishment material in phloem, especially for sugar transportation.