Figure 4.

GA Is the Specific Signal for Fiber Differentiation.

Tobacco plants were decapitated and deleafed.

(A) After maintaining the plants for 2 weeks with lanolin applied to the apical cut end, they were treated with GA₃, NAA, and the combination of the two hormones. Vessels (hollow cells with a higher lumen–to–cell wall ratio compared with fibers) are mainly detected subsequent to NAA application, while fibers form in response to GA₃ treatment. Dots indicate the area in the beginning of the xylem phenotype induced by the respective treatments. Curved line indicates the area of the undifferentiated region.

(B) Plants were treated as in (A) with the exception of an apical leaf that was kept intact. Cross sections were performed at the bottom of the leaf’s petiole. F, fibers; UR, undifferentiated region; V, vessels. Bars = 55 μm.

[See online article for color version of this figure.]