Study on the changes of anatomical structure and endogenous hormones in the pear trees of compact type

Two types of pear trees were studied on morphological characteristics,growth and development characteristics,changes in endogenous hormones in one-year old grafted plantlets and anatomical structure in new shoots of 15-year-old pear tree.The results showed that the shoot tips of compact type contained significantly lower level of ABA,GA3 and higher level of cytokinins(ZR and Z+ZR)than those of common type,only was the level of IAA slightly higher but no significant dif-ference compared with common type existed.In the apex of the new shoots of compact type,there were significantly more wood parenchymatous cells,less vessels and lower level of lignocelluloses and soluble sugar.Two conclusions are firstly put forward: the first is that when the density of lignocelluloses is lower than 1300 ind.mm-2,the density of wood parenchymatous cell is higher than 1700 ind.mm-2,the density of vessels is lower than 270 ind.mm-2 in the xylem of the shoot apex,it can be preliminary identified as compact type.The second is that the short internodes of compact type may be caused by the reduc-tion of gibberellins,and the swelling of shoot apex may be induced by the accumulation of cytokinins.