Vascular differentiation in the shoot apex of Matteuccia struthiopteris
1994
Ma, Y. | Steeves, T.A.
Initial vascular differentiation is generally considered to occur in procambium. In ferns, however, a provascular tissue immediately subjacent to the promeristem has been suggested as an initial stage within which the procambium is subsequently formed. In contrast to this interpretation, a zonation concept applied in ferns recognizes a promeristem consisting of several layers of cells in which no differentiation takes place. This study demonstrates that the shoot apex of Matteuccia struthiopteris has one cell layer of promeristem. Immediately subjacent to the promeristem is the provascular tissue surrounding a central group of pith mother cells. The developmental continuity between the provascular tissue and the mature vascular tissue, and between the pith mother cells and the pith, through transitional stages, indicates that the initial differentiation of vascular tissue and pith takes place in this prestelar tissue. The continuity of vascular differentiation in the area confronting young leaves or incipient leaf positions is interrupted by the formation of leaf gap initials. Developing leaves thus begin to exert influence on the vascular system at the prestelar stage. Small protoxylem elements with helical cell wall thickening, and distinctive protophloem elements are present in the leaf traces, but end abruptly near the junction regions of leaf traces to the meristele.
اظهر المزيد [+] اقل [-]الكلمات المفتاحية الخاصة بالمكنز الزراعي (أجروفوك)
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