The Effects of Canavanine on Protein and Nucleic Acid Synthesis in Canavanine Resistant and Sensitive Species of Higher Plants

Abstract

The effectiveness of the inhibitor, canavanine, was evaluated by examining its action in Canavalia ensiformis and Glycine max. Isolated roots were grown in culture tubes containing White's medium plus canavanine or arginine. A differential effect of canavanine on the incorporation of precursors of DNA, RNA, and protein was found, which is assumed to be related to the ability of the plant to utilize canavanine in reactions typically involving arginine. Canavanine was not found to affect DNA, RNA, or protein synthesis in Canavalia ensiformis, a plant in which this amino acid is synthesized naturally. In the canavanine sensitive species, Glycine max, of the same subfamily Papilionoideae, canavanine was observed to inhibit strongly DNA, RNA, and protein synthesis. A primary inhibition of the RNA synthesizing system is suggested. The data indicate the canavanine inhibitions are more complex than a simple competition with arginine in protein synthesis.

Effects of Canavanine on Arginine Utilization in Plants with Special Reference to Mitotic Activity

“…The effect of canavanine on arginine utilization was evaluated by measuring the incorporation of L-arginine-Hî nto the TCA-insoluble fractions of excised roots. The treatment concentrations used corresponded to those which produced the greatest inhibitory effects in growth experiments (Weaks and Hunt 1974).…”

“…Assuming that kinetin shortened prophase and lengthened telophase, it was postulated that kinetin functioned by affecting RNA metabolism of the nucleus. Evidence of a primary canavanine inhibition of the RNA synthesizing system in Glycine max has been shown (Weaks and Hunt 1973).…”

“…Excised primary roots of Phaseolus vtdgaris L. were treated with canavanine and arginine while growing in culture tubes using the method of Weaks and Hunt (1973).…”

“…Root tips of P. vulgaris were excised and axenically cultured. The method of Weaks and Hunt (1974) was used, in which roots were placed in an agar medium with the organic substrate separated from the inorganic nutrients. The basal end (about 5 mm) of an excised root tip was inserted into the solid organic medium in a vial.…”

“…It seems likely that as genetic factors giving rise to canavanine evolved in this plant group, other genetic factors providing resistance to the toxic effects of canavanine evolved in parallel within the same plants. A differential effect of canavanine on plant growth has been shown and has been assumed to be related to the ability of the plant to utilize this amino acid in reactions typically involving arginine (Weaks and Hunt 1974). A conversion of canavanine into non-inhibitory products occurs in Neurospora (Teas 1951, Lockhart andGarner 1955).…”