A role of cotyledons and sucrose in the differentiation of primary phloem fibers in hypocotyls of sunflower seedlings
Sucrose treatment of the hypocotyls of derooted 7-day-old sunflower seedlings stimulated growth of hypocotyls as measured by dry weight. The fresh weight of the hypocotyls was unaffected. Stimulatory effect of sucrose was much greater in the presence of the cotyledons than in their absence. Cotyledons also influenced the differentiation of primary phloem fibers in the hypocotyls of seedlings, although when cotyledons were removed, induction of some phloem fiber differentiation was possible by sucrose treatment alone. In the presence of the cotyledons, sucrose in the concentrations of 0.025 and 0.05 M greatly enhanced primary phloem fiber differentiation and secondary cell wall thickening. Stimulation of dry weight of the hypocotyls by sucrose treatment in the presence of the cotyledons may be due to enhanced secondary cell wall thickening.