. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Consequences of administration of indoleacetic acid (c) The cells in the region of elongation and early differentiation have a low level of peroxidase activity which may be dramatically increased by preincubation of the tissue with ca. 10~" M lAA. Specifically, in these regions it is the potentially lignified cells of the xylem and phloem which show the marked increase in peroxidase activity, while cortex,
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Consequences of administration of indoleacetic acid (c) The cells in the region of elongation and early differentiation have a low level of peroxidase activity which may be dramatically increased by preincubation of the tissue with ca. 10~" M lAA. Specifically, in these regions it is the potentially lignified cells of the xylem and phloem which show the marked increase in peroxidase activity, while cortex, epidermis, and pith show essentially no peroxidase activity either before or after treatment with lAA. These results conform well with other recent discoveries. It has been demonstrated (Torrey, 1953) that administration of IAA to pea roots results in premature lignification, the occurrence of lignified cells closer to the root apex. It is also clear that lAA may promote the differentiation of xylem strands in a wounded stem of Coletis (Jacobs, 1952). 7-^n. =5: Cofffro/ 10'^ 10'^ 10''^ lAA Concentration Figure 14. The effect of various lAA pretreatments on the subsequent peroxidase activity of successive sections o/Vicia roots. Note the marked effect of lAA on activity in the posterior sections, and the shift of the optimum from young to older tissues. How may the induced formation of peroxidase explain the lignogenic action of lAA? The answer is suggested by the work of Siegel (1955), who has demonstrated clearly that lignin is synthesized in certain plant cells by the action of peroxidase and HgOg on hydroxyphenylpropane precursors such as eugenol. Fortified by this knowledge, Jensen was able to show, in his Vicia roots, that the same cells which are induced to higher peroxidase activity by lAA, have, after such induction, a greatly increased ability to convert eugenol to a lignin-like compound. Thus, it appears that the morpho- genetic action of lAA in promoting lignif
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