Abstract: The anatomical characterization is the basis of physiological function of plants, so it is necessary to analyze heterosis performance and to reveal anatomical mechanism of heterosis. Anatomical characterization of the functional leaf in stem and vascular bundles of sympodial leaf stalk and boll stalk during flowering stage was investigated using three transgenic Bt pest-resistant cotton hybrids Nankang 3, Lumianyan 15, Xiangzamian 3, and their parents. The result showed that there were significant differences between hybrid and its parents in distribution of vascular bundles in the leaf nervures of the functional leaf (the fourth from top) in main stem. Three types of vascular bundles, three-offshoot, two-offshoot and no-offshoot were observed in leaf nervures of all tested materials. These were three-offshoot type in 3 hybrids and one of their parents, implying that the three-offshoot type was inherited dominantly. There were differences in the number of vessels, area of a vessel, area of all vascular bundles, area ratio of vascular to transection, leaf thickness, palisade tissue length, and palisade tissue width with different parents and hybrids. The total area of vascular bundles of functional leaf nervures in three hybrids were 0.72–0.77. The ratio of palisade tissue to spongy tissue of all hybrids was 1.12–1.15, suggesting that there existed transgressive or mid-parent heterosis in all hybrids. The total area of stomata per unit leaf area was a useful index for characteristic of stoma. There were transgressive heterosis in total area of stomata per unit leaf area on down leaf surface for three hybrids, but no heterosis on upper surface. There were negative correlation between two sides of leaf in the total area of stomata per unit leaf area (mm² cm-²) of three hybrids, and significant negative correlation between stoma frequency and stama length (R²=0.5087), and positive correlation between stoma frequency and total area of stomata per unit leaf area (R²=0.5943) for upper surface of leaf but not significant for down surface of leaf. Moreover, there was significant positive correlation between leaf stalk of fruit branch and boll stalk in the number of vessel and area of a vessel, it demonstrated that the leaves on fruit branch have more contribution to the boll development than functional leaves in stem (R₁²=0.4791*, R₂²=0.4702*).

Key words: Transgenic Bt, G. hirsutum L., Vascular bundle, Heterosis, Stoma