. Auxins and plant growth. Auxin; Plant growth promoting substances. Developmental Effects of Auxins 103 As in the auxin control ot growth, a dualism is exerted in the auxin control oi organ differentiation. A relatively high concentration ol auxin, physiologically speaking, can bring about dedifferentiation instead ot ditlerentiation of cells. Auxin applications to plants will sometimes cause large areas of differentiated parenchyma, pericycle, or endodermis tissues to dedifferentiate into callus. Again, under cer- tain circumstances auxin levels can exert a control over the redif- ferentiati
. Auxins and plant growth. Auxin; Plant growth promoting substances. Developmental Effects of Auxins 103 As in the auxin control ot growth, a dualism is exerted in the auxin control oi organ differentiation. A relatively high concentration ol auxin, physiologically speaking, can bring about dedifferentiation instead ot ditlerentiation of cells. Auxin applications to plants will sometimes cause large areas of differentiated parenchyma, pericycle, or endodermis tissues to dedifferentiate into callus. Again, under cer- tain circumstances auxin levels can exert a control over the redif- ferentiation of these callus tissues and meristems, giving rise to roots, buds, or flowers. Carrying the feature of dualism still further, we know of comse that the appearance of a given organ may be promoted by one range of auxin concentrations and inhibited by higher con- centrations. in z> _j < o 10- . • Auxin Added. l No Auxin 12 16 20 MG/L CONG. OF ADENOSINE Fig. 47. The effect of adenosine on the gifmth of tobacco stem calkis in ihe presence and absence of auxin, najilithaleneacetic acid (Skoog and Tsui, 1948). Before discussing the interaction of auxins with other plant con- stituents in the control of organ differentiation, it might be well to mention a graphic case to emphasize how sharply auxin action may be altered by other plant constituents present. Skoog and Tsui (1948) have shown that applications of auxin alone to cultures of excised tobacco stems will inhibit growth of the stem sections. When applied in conjunction with adenosine the same auxin applications will stimu- late growth (figure 47). This interaction lays a cornerstone for the understanding of the interactions of other compounds with auxin. It. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Leopold, A. Carl (Aldo Carl),
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