Genesis And Differentation Of Primary Thickening Meristem In Shoot Apex Of Sugarcane

Observed from the longitudinal section in shoot apex of sugarcane, the primary thicking meristem (PTM) originated from promeristem of the shoot apex, and the primary meristem consisted of protodem, ground meristem, primary thicking meristem and procambial bundles.The PTM usually existed in the bases of leaf primordium and young leaves in elongation zone of the shoot apex, its cells divided predominantly in periclinal planes and were arranged perpendicular to the stem surface (anticlinal). From the base of the 3rd young leaf to that of the 5th one, there was a increasing tendency in cell files of the PTM, and the cells of the PTM rapidly divided and less differentiated. From the base of the 6th to 7th leaf, more parenchymas and procambia bundles developed from the PTM. Approximately from the base of 8th leaf, there was a basipetally decreasing tendency in cell files of the PTM, and its cells slowly divided, most of the PTM cells differentiated into parenchynas and procambia bundles until the mature zone. The cells increased in quantity and enlarged in volume made the stem diameter thicker.Most of the procambium bundles came from the PTM. The differentiating process of xylem, protophloem sieve element and some cells' natural degeneration or death were similar to the programmed cell death.The cell division indexes of PTM in six varieties(YT86/368, YT91/976, GT11, ROC16, CP80-1827, NL8) with different stem diameter were higher than those of the apical meristem, but both of them showed similar curves.In addition, the cell division indexes were positively correlated with the stem diameter.Studies on three sugarcane varieties(YT86/368,GT11,NL8)showed that the total areas of PTM, the density and the quantity of procambial bundles-vascular bundles were positively correlated with the stem diameter, those of YT86/368>those of GT11 >those of NL8. The PTM. area of the fifth leaf base> that of the fourth one > that of the third one, thedensity and the quantity of procambial bundles-vascular bundles in the stems coincided with the 6th-11th leaves were that : the outer layer>the middle one > the inner one in each variety.Treatments of combinations of densities of IAA/6-BA showed stimulating effects on the differentiation of vessels, and made the diameters of vessels enlarged and the parenchyma cells traversely wider in GT92/126 and GT96/24; the different hormone density ratios had different stimulating effects on them; The different hormone combinations showed the inhibitions on the differentiations of procambial bundles in the two varieties.