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The Effect of Growth Substances and Chemical Carcinogens on Fibrous Roots of Carrot Tissue Grown In vitro

Michael Levine
American Journal of Botany
Vol. 38, No. 2 (Feb., 1951), pp. 132-138
Stable URL: http://www.jstor.org/stable/2437835
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Effect of Growth Substances and Chemical Carcinogens on Fibrous Roots of Carrot Tissue Grown In vitro
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Abstract

Fibrous roots from carrot tissue cultures grown on standard media increase in length, produce secondary roots, but fail to develop buds which form cauline elements. Fibrous roots seeded on media with indole acetic acid (IAA) 5 mg./l. produce hyaline calluses along the length of the root. The length of this root increases little but from the calluses new roots are formed. Coconut milk (CM) incorporated in standard media has little effect on growth of excised fibrous roots. Single, isolated, slow growing calluses are exceptional occurrences on fibrous roots on standard media or media with CM. CM in combination with IAA produces opaque pigmented nodular masses which fuse to cover the upper surface of the cultured excised fibrous root. Microscopic sections of the hyaline tissue masses reveal the dedifferentiation of the root tissue with the formation of primordia surrounded by loose cells, probably epidermal proliferations. Microscopic sections of the nodular callus formed on fibrous roots after CM with IAA had been added show somewhat organized parenchymatous cells with aberrant centers consisting of lignified cells. The chemical carcinogens used in these studies stimulate root growth but produce no calluses. Hyaline calluses separated and planted on standard media differentiate in the absence of IAA. The nodular type of growth when grown on media free of IAA differentiates. When seeded on CM the growth is rapid and abundant but differentiation is retarded and the plantlets formed frequently lack vigor. Tissue calluses differentiate freely on media with the carcinogens used. Indole acetic acid (5 mg./l.) at the concentration used in these studies hastens the formation of cauline initials from excised fibrous roots of the carrot. Their development occurs when the influence of the growth substance becomes attenuated or when freed from the IAA by transfer to media lacking it.

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