Growth promoters and the synthesis of protein in plant mitochondria: Part I — Effect of kinetin on the incorporation of amino acids into mitochondrial protein

The Role of Phytohormones (Cytokinins) in Chloroplast Development

Abstract: Summary The possible role of phytohormones in light-dependent plastogenesis is reviewed particularly in respect to the influence of cytokinins in this plant-specific differentiation process. The following aspects of cytokinin action in chloroplast formation are considered in detail: Ultrastructure and replication of chloroplasts, chlorophyll accumulation, plastid enzyme synthesis and activity, nucleic acid and protein biosynthesis. Some remarks are made about the importance of the physiological state of the responding tissue. Possible modes of action on the cellular and molecular levels are discussed in relation to plastogenesis. In conclusion, the results available at present are not sufficient for the unequivocal demonstration of a primary or direct phytohormone action in plastogenesis. Although indications are presented that the promotion of chloroplast development by cytokinins is closely connected with a stimulation of the gene expression program for plastogenesis, in particular with enhanced translation of plastid proteins, other sites of hormone action cannot be excluded and are discussed in the last part of the review.

The binding of kinetin to plant ribosomes.

Abstract: The synthetic cytokinins kinetin and 6-benzylaminopurine exhibit equilibrium-type binding to purified chinese-cabbage leaf ribosomes. At 23mum and 4 degrees C one molecule of kinetin and 1.34 molecules of 6-benzylaminopurine are bound per ribosome. Adenine and adenine derivatives that are inactive as cytokinins showed much less affinity for ribosomes. Pretreatment of ribosomes with 0.5m-ammonium chloride or Triton X-100 did not decrease the extent of cytokinin binding. Binding appeared to be to the 83S ribosome species. A positive correlation between the extent of binding and the biological effect of various cytokinin analogues was demonstrated. These results are discussed in terms of cytokinin control of growth processes at the ribosomal level.

Molecular effects of hormone treatment on tissue.

Abstract: Exogenous application of hormones is one of the most common methods in research into the mode of action of such substances. The rationale behind such approaches is based mainly on the idea of replacement of the endogenous, naturally occurring hormone by an exogenous hormone, the level of which may be controlled and its effect monitored. This is fairly easily accomplished in animal systems, where the gland synthesizing a particular hormone can be dissected out and the target tissue monitored after application of the exogenous hormone via the blood stream. This is rarely easy and often impossible to achieve with plant material because in most instances any given hormone may be produced in more than one location within the plant. Furthermore, the same organ or cell which produces the hormone may also be the target.

Molecular and subcellular aspects of hormone action.

Abstract: Throughout this chapter the terms hormone and growth regulator will be used interchangeably. The designation “hormone” was originally restricted by definition to compounds that are produced naturally and exert their action in tissues or cellular localities removed from the point of synthesis. Both terms are, however, widely used in the current literature on plant growth regulation and development to cover both natural and synthetic compounds.

Comparison of the effects of cytokinins on enzyme development in different cell compartments of the shoot organs of rye seedlings

Abstract: Variation in cytokinin supply has different effects on protein formation and enzyme development in primary leaves and coleoptiles of rye seedlings. The accumulation of enzyme activities, localized in different cell compartments of the leaves, responds with different sensivities. (1) In developing primary leaves of dark-grown rye seedlings total protein content and the activities of several enzymes are decreased by lowering the cytokinin supply by excision of the roots. Higher activities are again restored by application of kinetin to plants previously deprived of their roots. However, the activities of the photosynthetic enzymes so far investigated, and of the microbody enzymes, glycolate oxidase and hydroxypyruvate reductase, show a much more marked response to changes in the cytokinin level than either the total protein content or the activities of glucose-6-phosphate dehydrogenase or of the mitochondrial enzymes fumarase and cytochrome c oxidase. (2) In the coleoptiles of rye seedlings, light drastically enhances the breakdown of total protein and the decrease of all enzyme activities measured. By contrast to the behavior of primary leaves, total protein formation and the accumulation of all enzyme activities measured are strikingly prolonged after root excision which was expected to result in a lowered cytokinin supply. Subsequent addition of kinetin enhances the decay of protein and most of the enzyme activities determined and thus, in a similar way to the effect of light, seems to promote the senescence of the coleoptiles.

The mechanism of action of plant growth substances: the role of nuclear RNA in growth substance action.

Abstract: Indoleacetic acid, gibberellic acid or kinetin stimulate the synthesis and release of nuclear RNA. The presence of the nuclei is essential for the growth substance-induced promotion of RNA synthesis. The induced stimulation is abolished by actinomycin D but can be restored partially or completely by relatively higher concentrations of the growth substances.

The mechanism of action of plant growth substances: Growth substance stimulation of amino acid incorporation into nuclear protein

Abstract: Aluxin-induced stimulation of amino acid incorporation into protein of pea internodes is localised largely in the nucleus soon after auxin application. Low concentrations of auxin, kinetin and gibberellic acid also promote the incorporation of amino acids into the protein of free nuclei of coconut milk. The auxin-induced stimulation is abolished by actinomycin D but can be restored considerably by higher concentrations of the growth substances. Puromycin also retards the auxin-induced stimulation of amino acid incorporation into nuclear protein but the inhibition cannot be reversed by higher concentrations of auxin.

Investigation of purinelike compounds in immature maize kernels, germinating barley seeds, and yeast☆

Abstract: The purinelike compounds in immature maize kernels, germinating barley seeds, and baker's yeast were extracted with ethanol and separated by precipitation with cuprous oxide, chromatography on Dowex I and paper chromatography in n-butanol: acetic acid:water (4:1:5). The purines were located on the paper chromatograms with silver nitrate-bromophenol blue. The ultraviolet spectra of eluates in water and in 0.01 N NaOH were determined. The eluates were also examined for kinetinlike activity by testing their ability to retard the degradation of chlorophyll in the cells of leaf tissue. Nine purinelike compounds were detected in maize, ten in barley, and four in yeast. Guanosine, guanine, adenosine, and adenine were tentatively identified in maize; guanosine, guanine, adenosine, adenine, xanthine, and hypoxanthine in barley; and xanthine, hypoxanthine, and adenine in yeast. Other compounds that showed purinelike ultraviolet spectra could not be identified. The unknown purinelike compounds of Rf values of 0.06, 0.75, and 0.81 from maize and 0.06 from barley retarded the breakdown of chlorophyll of wheat or barley leaves floated on their solution. All other compounds from maize, barley or yeast were inactive in this assay. It is suggested that several kinins occur naturally in plants. Since kinetin and naturally occurring kinins were effective in maintaining the detached green leaves turgid and green but were ineffective in preserving the turgidity of the detached albino leaves; therefore, chloroplast are in some way involved in the response of detached leaves to kinins.