EFFECT OF EXOGENOUS GROWTH REGULATORS ON PATTERN OF XYLOGENESIS IN YOUNG SHOOTS OF LEUCAENA LEUCOCEPHALA

摘要

The effect of exogenous application of growth regulators (IAA, NAA, GA3 and BAP) on xylogenesis has been investigated in actively growing shoots of Leucaena leucocephala by anatomical methods. Auxins are (both IAA and NAA) found to be the key regulators of differentiation of narrow lumen vessels and tracheids. These elements were derived not only from fusiform cambial cells, but also from axial parenchyma through transdiffer-entiation. The exogenous feeding of GA3 induced differentiation of gelatinous fibres, deformed vessels, elongated thin walled fibres and a high fibre/vessel ratio. BAP application decreased the cambial activity and cell differentiation process resulting in development of thick walled fibres and vessel elements, and also delayedlignification of cell walls. The application of combination of hormones showed both synergistic and antagonistic nature of interaction among different hormones. Combination of GA3 and auxins induced cambial cell division and relatively fast differentiation of xylem, while increasing concentrations of GA3 over auxins induced differentiation of gelatinous fibres. The combination of high concentration of BAP either with auxins or with GA3 slowed down cambial activity and xylem differentiation. Moderate concentrations of BAP and GA3 induced gelatinous fibres with thick gelatinous layer indicating the synergistic effect of both hormones.