Modification of the cytokinin promotion of deoxyisoflavone synthesis in soybean tissue

Plant secondary metabolism in altered gravity

Plans by the space program to use plants for food supply and environmental regeneration have led to an examination of how plants grow in microgravity. Because secondary metabolic compounds are so important in determining the nutritional and flavor characteristics of plants-as well as making plants more resistant to biotic and abiotic stresses-their responses to altered gravity are now being studied. These experiments are technically challenging because temperature, humidity, atmospheric composition, light, and water status must be maintained around the plant while simultaneously altering the g-load, either in the free-fall of orbital spacecraft or on a centrifuge rotor. In general, plants have shown increased accumulation of small secondary metabolites in microgravity (<10(-3) g), while these have decreased in hypergravity (>1-g). Gravity-related changes in the plant environment as well as mechanical loading effects account for these responses.

Do some plant responses to cytokinins involve the cyanide-resistant respiratory pathway?

A disengagement of the cyanide-resistant, alternative respiratory pathway in soybean (Glycine max (L.) Merr.) callus tissue was observed prior to the start of deoxyisoflavone production stimulated by addition of the cytokinin benzyladenine. To test whether this loss of alternativepathway activity was part of the response to cytokinin, inhibitors of the alternative pathway were assayed for their ability to elicit cytokinin-like responses. Salicylhydroxamic acid (SHAM) was found to produce a deoxyisoflavone difference spectrum similar to that observed following treatment of the callus tissue with benzyladenine, while propyl gallate (PG) was without effect. Both SHAM and PG were further tested for cytokinin-like activity in other bioassays. In two anti-senescence bioassays using leaf tissue (of Avena sativa L. and Xanthium pensylvanicum Wallr.) and in the Cucumis sativus L. bioassay which measures stimulation of weight gain by excised cotyledons, both SHAM and PG were effective "cytokinins" at 1 mM and 0.1 mM, respectively. In two other bioassays (betacyanin formation in Amaranthus caudatus L. seedlings and the soybean-callus celldivision assay), SHAM appeared to be toxic. These results substantiate the suggestion that effects on the alternative pathway may play a role in some cytokinin responses and further raise the question of what should be considered a true cytokinin response.

Cytokinin inhibition of respiration by cells and mitochondria of soybean, Glycine max (L.) Merrill

Cells of a soybean tissue strain, suspended in an aerated liquid medium, caused disappearance of p-coumaric acid from the medium and oxidation of guaiacol, benzidine, pyrogallol, L-dihydroxyphenylalanine and L-epinephrine. Both the disappearance and the oxidations were inhibited by 6-benzylaminopurine (BAP) at a concentration of 0.5 mM. BAP at other concentrations either promoted or inhibited oxidation of epinephrine in precisely the pattern reported earlier for the disappearance of coumarate; therefore, the disappearance of coumarate probably involves its oxidation. The effectiveness of other cytokinins in inhibiting the oxidation was studied.At 0.5 mM, and perhaps even at 0.5 μM, some of the several cytokinins tested inhibited oxygen consumption by the soybean cells. This inhibition, which did not require any of the above metabolizable compounds, was especially marked in the presence of cyanide, azide or Antimycin A, and was detectable in 10 min or less. Either Antimycin A or salicylhydroxamic acid alone promoted O2 consumption but together they were quite inhibitory. The soybean cells apparently have an alternate respiratory pathway and cytokinins may influence its operation.Several cytokinins at 0.5 mM, and perhaps at 0.5 μM, also inhibited oxygen consumption by mitochondrial preparations from the soybean cells, the inhibition being evident in about 20 s. The consumption required a substrate such as malate, succinate or NADH. Cytokinins and related compounds varied in effectiveness as follows: BAP and 6-isopentenyla-minopurine ≥ 9-tetrahydropyranyl-BAP > kinetin, ribosyl-isopentenylaminopurine, 9-methyl-BAP and 9-methoxymethyl-BAP > 6,6-dimethylaminopurine and zeatin (slight activity) > 6-methylaminopurine, nicotinamide and adenine (ineffective). To a great extent this order parallels the order of effectiveness of the compounds in causing cell division. Mitochondria, therefore, may contain a site for an important cytokinin action.

Cytokinin modification of metabolism of p-coumaric acid by a cell suspension of soybean (Glycine max (L.) Merrill)

Cells of a soybean tissue strain suspended in an aerated liquid medium caused the disappearance of p-coumaric acid from the medium. The rate of disappearance was modified by cytokinins. When the coumarate and the cytokinin were added to the medium simultaneously, disappearance was increased if the cytokinin was used in the concentration range from 0.05 to 50 μM; higher concentrations inhibited the disappearance. If, however, the cytokinin was added at the beginning of the shaking period (for aeration) and the coumarate added 1 h later, the results were more complex. With this procedure, cytokinins at concentrations from 0.0005 to about 1 μM inhibited, at 50 μM they promoted, and at higher concentrations they inhibited the coumarate disappearance. The promotion was elicited by zeatin, ribosylzeatin, kinetin, 6-benzylaminopurine (BAP), by BAP substituted at the 9-position by methyl, methoxymethyl, cyclohexyl or tetrahydropyran-2-yl groups, by adenine with the amino group substituted by methyl, dimethyl, n-propyl, n-pentyl or n-hexyl groups, by 1,3-diphenylurea and nicotinamide, all at about 50 μM. Adenine and benzimidazole were not effective. The promotion was detected in as little as 12 min. The delayed inhibitory effect required the presence of the cytokinin during the 1 h of shaking before the coumarate was added. This effect was elicited by zeatin, ribosylzeatin, kinetin, BAP, the aforementioned 9-substituted-BAP compounds, 9-glucosyl-BAP, 7-glucosyl-BAP, and 6-isopentenylaminopurine and its ribonucleoside. It was not caused by adenine, cis-ribosylzeatin, diphenylurea, benzimidazole, 6-methylaminopurine, 6,6-dimethylaminopurine or nicotinamide. The chemical specificity for this effect was much the same as that known for promotion of cell division in the soybean tissue.

Biochemical Studies on Development of Mitochondria in Pea Cotyledons during the Early Stage of Germination: Effects of Antibiotics on the Development

l-Leucine-U-(14)C was incorporated into mitochondrial protein in pea (Pisum sativum var. Alaska) cotyledons during the imbibing stages. Incorporation was almost completely inhibited by cycloheximide but not by chloramphenicol. Both antibiotics did not affect increases in mitochondrial activities and components of the cotyledons during imbibition. Therefore, mitochondrial development seems to be achieved by a transfer of protein pre-existing in the cytoplasm into the mitochondria rather than by de novo synthesis of mitochondrial protein. Cycloheximide stimulated an increase in bile saltsoluble protein of mitochondria in imbibing pea cotyledons. The recovery of cytochrome oxidase activity after sucrose density gradient centrifugation was enhanced, and the morphological properties of mitochondria were altered by cycloheximide.

Effects of cytokinins on the respiration of soybean callus tissue

A technique which incorporates a brief blending step to disperse callus tissue into small clumps of cells was developed, and the effects of cytokinins on respiration of soybean (Glycine max [L.] Merrill var. Acme) callus tissue prepared in this way were studied. Adenine alone did not affect respiration, but kinetin and zeatin showed effects correlating with their reported effects on growth of this tissue; after about 3 hours both hormones promoted respiration at concentrations which promote growth, while kinetin, but not zeatin, also exhibited inhibition at higher concentrations. Studies with 2,4-dinitrophenol led to the suggestion that although the respiration of this tissue is largely under the control of ATP levels, kinetin does not exert its control on respiration through effects on ATP levels or oxidative phosphorylation during the monitoring period. Further inhibitor and substrate studies provided evidence that the promotion of respiration by kinetin results from an increase in substrate entering the tricarboxylic acid cycle, perhaps by an effect on pyruvate metabolism.The inhibition of respiration by high concentrations of kinetin is partially due to effects on oxidative phosphorylation or ATP utilization, but 70% of the inhibition cannot be attributed to this.