The growth of kinetin‐requiring soybean callus was inhibited by the purine analogs 2,6‐diaminopnrine, 8‐azaguanine and 8‐azaadenine. The purine analog 6‐mercaptopnrine and the antibiotic puromycin were not effective as inhibitors at the concentrations employed. Reversal of the inhibition was attempted by raising the kinetin concentration. Kinetin did not reverse the inhibition due to 2,6‐dianiinopurine but it did lessen to some extent the inhibition due to 8‐azagnanine. It is suggested the kinetin affects RNA metabolism.
Exogenously applied 8‐14C‐kinetin is rapidly taken up by seeds of lettuce (Lactuca sativa L. cv. Grand Rapids). Radioactive metabolites were extracted and purified by solvent fractionation, column and paper chromatography. The primary metabolite was identified as the 9‐riboside‐5′‐monophosphate. As germination proceeds, some kinetin is released from this bound storage form, giving a maximum level of free kinetin at 12 hours after imbibition. After this time the concentration of ribotide increases while the concentration of free base decreases. Other metabolites are the 9‐riboside, AMP and IMP. It is suggested that a required amount of free base cytokinin is necessary by 12 hours after imbibition. This concentration of free cytokinin may act as a physiological trigger for later events during germination.
The activities of N6‐benzyladenine (BA) and its 9‐substituted methyl, methoxymethyl, tetrahydropyranyl, cyclopentyl, and cyclohexyl analogs were determined for the promotion of lettuce seed (Lactuca sativa L. cv. Grand Rapids) germination. Cytokinin concentrations used were 10−4, 10−5, 10−6 and 10−7M. All seeds were incubated under total dark conditions at 28 ± 1°C. After 48 h the percentage of germination was recorded. A comparison of means based on Duncan's Multiple Range Test allowed for a ranking of cytokinin activities for the promotion of lettuce seed germination. The activities were: BA = 9‐tetrahydropyranyl BA > 9‐methyl BA > 9‐methoxymethyl BA > 9‐cyclopentyl BA > 9‐cyclohexyl BA. The results were significant at the 95% confidence level as determined by analysis of variance. In order to study the metabolism of a cytokinin, lettuce seeds were incubated with 9‐methyl‐BA‐methylene‐14C. The labeled cytokinin was prepared by refluxing benzylamine hydrochloride (methylene‐14C) with an equal molar ratio of 6‐chloro‐9‐methylpurine. Final cytokinin concentration was 10−5M. Incubation periods were 2, 4, 8, 12, 16 and 20 h at 28 ± 1°C under total dark conditions. At the end of the various time periods the seeds were extracted with 70 percent methanol. The resulting extracts were purified and radioactive metabolites identified by solvent fractionation, Sephadex LH‐20 column chromatography, and paper chromatography. Co‐chromatography with authentic standards in the appropriate solvent system revealed that the metabolites were 9‐methyl BA, N6‐benzyladenosine‐5′‐monophosphate, and N6‐benzyladenosine. The results lend support to the theory that the cytokinin ribonucleotide serves as a storage form which is converted to the active ribonucleoside as needed during lettuce seed germination.
The effect of auxins, cytokinins, gibberellins and phenolics on the incorporation of uridine and thymidine into the nucleic acids of human leukocytes was examined. Both the stimulation and inhibition of the incorporation of the precursors was noted. The auxins consistently promoted the incorporation of uridine.
Summarv. RNA prepared from fractions of chloroplasts and mitochondria sedimented at rates characteristic of ribosomal RNA. A predominance of the 18S species was frequently observed in preparations from chloroplasts from romaine lettuce and enidive. The usual distribuition, a preponderance of the 28S species, was observed in stuidies on tomato and spinach chloroplasts and mitochondria from mulshroom iand cauiliflower. Comparisons of the base composition of RNA from organelles with their cytoplasmic ribosomal couinterparts revealed that the 18S component from romaine lettuice chloroplast was different. A marginally significant difference was observed in the 28S particle from muishroom mitochondria preparations whereas distinct differences, reflected in all the bases, wvere seen when the 18S component of cauiliflower mitochondria preparations was compared with cytoplasmic RNA. The ability of isolated mitochondria from variouis sources to incorporate labelled amino acids into protein has been amply docuimented (6,18,21 In this paper we report techniqtues for the isolation of the 18S and 28S species of ribosomal ribontucleic acids from chloroplasts and from mitochondria. In adldition, a comparison of the base composition of the cytoplasmic ribonuicleic acid components with those from chloroplasts aindl from mitochond(ria is given. Materials and Methods
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