Roots are the main channel for water and nutrient uptake in plants. Optimization of root architecture provides a viable strategy to improve nutrient and water uptake efficiency and maintain crop productivity under water-limiting and nutrient-poor conditions. We know little, however, about the genetic control of root development in wheat, a crop supplying 20% of global calorie and protein intake. To improve our understanding of the genetic control of seminal root development in wheat, we conducted a high-throughput screen for variation in seminal root number using an exome-sequenced mutant population derived from the hexaploid wheat cultivar Cadenza. The screen identified seven independent mutants with homozygous and stably altered seminal root number phenotypes. One mutant, Cadenza0900, displays a recessive extra seminal root number phenotype, while six mutants (Cadenza0062, Cadenza0369, Cadenza0393, Cadenza0465, Cadenza0818 and Cadenza1273) show lower seminal root number phenotypes most likely originating from defects in the formation and activation of seminal root primordia. Segregation analysis in F 2 populations suggest that the phenotype of Cadenza0900 is controlled by multiple loci whereas the Cadenza0062 phenotype fits a 3:1 mutant:wild-type segregation ratio characteristic of dominant single gene action. This work highlights the potential to use the sequenced wheat mutant population as a forward genetic resource to uncover novel variation in agronomic traits, such as seminal root architecture.

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The reduction of acridine at the dropping-mercury electrode has been studied over the pH range 0-14.I n aqueous solution, complex anomalous polarograms are obtained. In solutions containing upwards of 60% alcohol, the anomalies disappear, leaving two one-electron reduction steps which are thermodynamically irreversible, and for which diffusion currents are proportional to acridine concentrations in the range 10-9-1W~. The anomalies in aqueous solutions may be satisfactorily explained on BrdiEka's theory as due to adsorption of acridine, mainly in the semiquinone reduced state, on the mercury electrode. Supporting evidence for adsorption has been obtained from a cathode-ray oscillographic study of the current-time relation during the formation of a mercury drop at the electrode. Acridine is found to undergo a two-step electroreduction, both in aqueous and alcoholic solutions, with the formation of an intermediate semiquinone radical, the apparently great stability of which is attributed to resonance.

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All four dyes are reducible in aqueous solution a t the dropping mercury electrode, giving polarograms distorted by dye adsorption on the mercury. When adsorption effects are eliminated by addition of ethanol, normal polarograms result, exhibiting two well-separated one-electron steps which indicate the formation a t the first step of a semiquinone free radical of apparently very great stability. For all but malachite-green, which was not studied in sufficient detail to establish the point, the half-wave potential of the first reduction step is independent of pH in the biologically important region around pH 7, so that, as with the more strongly antibacterial aminoacridines (J., 1951, 2638), semiquinone formation involves the uptake of one electron and no proton. Equations are derived which represent satisfactorily the observed variation of half-wave potential with pH.PREVIOUS work on the polarographic reduction of acridine (J., 1951, 27) and several aminoacridines (I., 1951, 2638) has shown that, while all these compounds give two widely separated one-electron reduction steps, indicating the formation of a semiquinone free radical of exceptionally great apparent stability, the more strongly antibacterial of them alone have a horizontal portion of the El-pH curve ( E , = half-wave or effective standard redox potential of first step) extending over the biologically important pH region around 7. This horizontal section indicates that the formation of semiquinone involves the uptake of a single electron but no proton, a matter of significance in connection with a theory of the mechanism of these antibacterials (Kaye, J . Pharm. Phannacol., 1950, 2, 902).I n order t o find whether the antibacterial triphenylmethane dyes crystal-violet, brilliant-green, and malachite-green, and the bacteriostatic diphenylmethane dye auramine behave similarly t o the active aminoacridines, we have investigated their polarographic reduction. We are not aware of any previous comprehensive polarographic studies of these dyes, although Linnell and Stenlake ( J . Pharm. Pharmacol., 1949, I , 314) confirmed polarographically the identity of a derivative of brilliant-green. EXPERIMENTALCrystal-violet and brilliant-green of medicinal purity, and commercial malachite-green and auramine, were purified by recrystallisation from water ; for the first two, prolonged standing of the solutions was necessary. All other materials, apparatus, and technique were as previously described (J., 1951, 27). The temperature of all experiments was 25", all polarograms were corrected for residual current, and electrode potentials are relative to the saturated calomel electrode standard. RESULTS AND DISCUSSIONCrystal-violet.-In aqueous solution this dye is electro-reducible at the dropping mercury electrode, giving two-step reduction waves (Fig. 1) which are distorted, especially at the second step. The distortions were associated with anomalous galvanometer * (2)