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Inter-Tissue Correlations in Organ Fragments

Organogenetic Capacity of Tissues Excised from Stem Segments of Torenia fournieri Lind Cultured Separately in Vitro

^a Laboratoire du Phytotron, Centre National de la Recherche Scientifique, 91190-Gif-sur-Yvette, France

In order to study the effect of inter-tissue correlations on the organogenetic capacities of various tissues of stem segments of Torenia fournieri Lind, different types of explants were excised and grown separately: epidermis, subepidermal parenchyma, epidermis plus subepidermal parenchyma but devoid of vascular tissue and stem segments devoid of epidermis.

The epidermis, normally capable of bud formation in the context of a stem segment, dies if grown in culture alone; however, it can form buds after callus formation if, after excision, it is replaced on the original stem segment. Subepidermal parenchyma, normally mitotically inactive in the stem segment, forms roots when grown alone and buds and roots when grown with the epidermis. A stem segment devoid of epidermis forms only roots. The histological study showed that, in explants composed of epidermal and a few subepidermal parenchyma layers, buds can arise exclusively from the epidermis or from both epidermal and subepidermal cells, whereas roots are exclusively formed by parenchyma tissue.

The break in correlations among tissues by the culture of each tissue separately seems to "liberate" masked capacities in certain tissues and to repress the expression of capacities in others.