The Structure And Development Of Secondary Phloem In Pseudolarix Amabilis And Comparison With Abies Nephrolepis

Pseudolarix amabilis is one of the most famous endemic trees in China. It was noted thatsticky substances (SSs) were exuded from the bark of P. amabilis right after the bark wasinjured. This paper mainly focused on the structure and cell development of Secretory Cell (SC)in P. amabilis. SCs in the secondary phloem of P. amabilis and Abies.nephrolepis, fiber-sclereidin the secondary phloem of Larix gmelini were studied, and also confirmed if other6species(expect Cathaya argyrophylla) of Pinaceae had SC or not. Beside that, the development of P.amabilis’s periderm and seasonal change of callose were studied. The following conclusionswere got:1. SSs were produced from SCs and stained by both ruthenium red and nile blue. It wassuggested that SSs were the compound of polysaccharide and acid resin. A large number of SCswas also observed in the secondary phloem of A.nephrlepis. The chemical components of SSsin P. amabilis and A.nephrolepis were similar. Observing the cross sections of7species ofPinaceae, there were a few SCs in the secondary phloem of Keteleeria fortunei andPseudotsuga sinensis, however, no SCs were found in other5species.2. SC was developed from the phloem parenchymal cell. The shape of SC was differentbetween different species: the average length and diameter of P. amabilis’s SC were1533.74μmand257.51μm, while the average length and diameter of A. nephrolepis’s SC were419.40μmand165.56μm. The amount of SC was also different in different species: the number of SC perunit phloem area in P. amabilis was9.28, while in A. nephrolepis was23.15.3. SCs were distributed in P. amabilis’s nonconducting phloem. The number of SC thatcontained SSs per unit area of secondary phloem was high in April23to July14and decreasedin August15to next April1. It reached to the lowest on April1. It was evident that SCsproduced more SSs in the growing than dormant season.4. The size of fiber-sclereid and SC were similar, while fiber-sclereid was a kind ofsclerenchyma cell, the content of lignin and cellulose in fiber-sclereid’s cell wall was high.Fiber-sclereid was distributed in the non-conducting phloem, and had no regular arrangement.The average length and diameter of Larix gmelini’s fiber-sclereid were1278.27μmand104.74μm.5. There were two kinds of cell arrangement in P. Amabilis s secondary phloem. In theconducting phloem: phloem parenchymal cell and sieve cell band arranged alternatively. In thenonconducting phloem: phloem parenchymal cell--sieve cell without SC (crushed)--phloemparenchymal cell--sieve cell with SC--phloem parenchymal cell, or phloem parenchymalcell--sieve cell with SC--phloem parenchymal cell--sieve cell with SC--phloem parenchymalcell. The sclereid distributed in the nonconducting phloem.6. The new phellogen of P. amabilis was formed between May15and May31, it produced5-8layers of phellem cells and3-4layers of phelloderm cells. The new formed periderm was composed of6-8layers of phloem parenchymal cells, sieve cells and SCs, which finally becamea part of rhytidome.7. Callose distributed widely in P. amabilis’s secondary phloem, but it mainly distributedin the nonconducting phloem. The distribution of callose was closely related to conductingfunction of sieve cell. In the conducting phloem: when the conducting function of sieve cell wasstrong (growing season), there had more callose deposited in the sieve area; when theconducting function of sieve cell was weak (dormant season), there had less callose depositedin the sieve area. In the nonconducting phloem: there had more callose deposited in the dormantseason than growing season. When completely into the dormant season (February), bothconducting and nonconducting phloem had plenty of callose deposited.