IAA-oxidase activity in light grown cucumber hypocotyls treated with helminthosporol

Summary Helminthosporol (H-ol) promoted the growth of light grown cucumber hypocotyls. The IAA-oxidase activity per dry weight of the hypocotyl of H-ol treated materials was less than that of controls. There was an inverse relationship between IAA-oxidase activity and H-ol induced elongation of the hypocotyl. However, when IAA-oxidase activity per plant was compared between H-ol treated materials and controls there was no essential difference. It is concluded that the apparent inhibitory effect of H-ol on IAA-oxidase activity is not directly related to the mechanism of H-ol action.     

Distribution of an Indoleacetic Acid-oxidase-inhibitor in the Storage Root of Daucus carota

Indoleacetic acid (IAA)-oxidase from both secondary phloem and xylem was dependent on 2,4-dichlorophenol for activity, and was enhanced by addition of Mn²⁺. The pH optimum was 6.0 from both tissues. IAA-oxidase and its inhibitors were distributed differently in the secondary phloem and secondary xylem of carrot root. In the phloem a high IAA-oxidase activity was distributed uniformly along the radius but in the xylem a somewhat lower concentration decreased from the cambium. IAA-oxidase inhibitor in the phloem increased exponentially from a very low concentration near the cambium, whereas in the xylem an appreciable concentration was present near the cambium, decreasing linearly with distance from the cambium. Longitudinal gradients in the xylem parallel studies by other workers with the greatest IAA-destroying capacity present in older tissues. In the xylem inhibitor decreased and IAA-oxidase increased from the root apex. In the phloem IAA-oxidase was uniform, whereas the inhibitor increased in older tissue.

The IAA-oxidase inhibitors in phloem and xylem may be different. In the xylem the IAA-oxidase inhibitor may be a lignin precursor present in young cells which disappears as lignification proceeds. In the phloem IAA-oxidase reacting with endogenous IAA appears to form a physiologically active product.

     

Treatment of bean cuttings by chestnut extracts during rooting modifies their IAA-oxidase activity

The IAA-oxidase activity in bean cuttings ( Phaseolus vulgaris L. cv. Contender) treated with extracts from juvenile and adult chestnut ( Castanea sativa Mill.) was studied in the light of the effect of the extracts on the rooting activity of some auxins. Extracts from adult chestnut increased IAA-oxidase activity in bean cuttings. Extracts from juvenile chestnut inhibited IAA-oxidase activity only slightly, but substantially reduced the IAA-oxidase activity of bean cuttings pre-treated with adult chestnut extracts. These findings provide evidence that there is a relationship between the IAA-oxidase system and the effect of chestnut extracts on IAA-induced rhizogenesis in bean cuttings.     

The masking of peroxidase-catalysed oxidation of IAA in Vigna

Partially purified enzyme preparations of extracts of Vigna seedlings exhibited guaiacol-oxidase activity but not IAA-oxidase activity. However, by ageing the enzyme preparations, or by treating them with H₂O₂, it was possible to unmask IAA-oxidase activity. Gel filtration of Vigna extracts on Sepharose yielded separate peaks for IAA-oxidase, guaiacol-oxidase and auxin protectors. The appearance of a separate IAA-oxidase peak reflected the overlap of peroxidase and protector; the apparent difference in the migration rate of IAA-oxidase and guaiacol-oxidase activity proved to be an artifact. The data imply that previous reports of differences between peroxidase and IAA oxidase need to be reinvestigated to rule out the possible effect of contamination by endogenous, high MW auxin protectors. A rapid method for removing most of the auxin protectors and thereby unmasking IAA-oxidase activity is described.     

Indole-3-acetic Acid Oxidase in a Nicotiana Hybrid and its Parental Types

The metabolism of IAA is correlated with tumor formation in the Nicotiana hybrid, N. glauca x langsdorffii. Higher IAA-oxidase activity was found in leaves of hybrid plants than in leaves of parental types. Furthermore, topographical distribution study revealed that young expanding leaves contained more IAA-oxidase activity than older leaves. In hybrid plants, there is a close correlation between IAA-oxidase activity and the ability of a leaf to produce tumors. Leaves which yield the greatest number of injury-induced tumors also yield the highest IAA-oxidase activity. IAA incites callus-like outgrowths in hybrid plants which do not differentiate into a multitude of apices as is the case with spontaneous tumors. The results are interpreted on the basis of a concept that the IAA-oxidase system in plants may function as part of an IAA activating mechanism rather than in the basis of an IAA destroying system.     

Effect of cold stress in the rhizosphere on the activity of antioxidant enzymes in the tissues of Pinus sylvestris

The activities of lipase, peroxidase, IAA-oxidase, superoxide dismutase, and catalase have been comparatively studied in the needles, inner bark of stem and roots of 10-year-old self-sawn Pinus sylvestris trees in Central Siberia under natural conditions and in experiment imitating the effect of permafrost. It is shown that a decrease in the rhizosphere temperature for self-sawn Pinus sylvestris causes not only a change in the morphogenesis of the sprouts of the current year and reduction of the annual ring but also a shift of the natural dynamics of antioxidant enzyme activity to a later time. Before soil thawing, the activity of antioxidant enzymes on the experimental plot weakened thus implying the enhancement of the oxidative stress, while the growth of buds and sprouts is hindered during this period because of the high activity of IAA-oxidase. An active part in the elimination of the oxidative stress consequences belongs to the conjugated pair of antioxidant enzymes superoxide dismutase—catalase.     

Indoleacetic acid oxidase activity in main stem homogenates of flax genotrophs and genotypes

The IAA-oxidase and peroxidase capabilities along the length of the main stem tissues of two flax genotrophs L and S and two flax genotypes R and M were examined in vitro. Stem gradients for peroxidase activity increased basipetally in all plant types, as did IAA-oxidase activity gradients at non-rate-limiting concentrations of Mn²⁺. Correlations between peroxidase activity and non-rate-limited IAA-oxidase activity supported the contention of dual activities on the same molecule. At rate-limiting concentrations of Mn²⁺, IAA-oxidase activity did not correlate with peroxidase activity. Plant type differences were detected in rate-limited IAA-oxidase activity. This activity was higher in the stem region immediately above the cotyledons (axillary buds) of the more branched types, L and R, than in the sparsely branched types, S and M.     

Simple phenolic glycosides as potential regulators of the IAA-oxidase system

The effect of phenols and simple phenolic glycosides on the activity of IAA-oxidase isolated from gherkin seedlings was studied in experimentsin vitro. Phenol stimulated the enzyme system activity, eugenol and quinol were proven as inhibitors. Simple phenolic glycosides (arbutin, gein and phenol glucoside) influenced IAA-oxidase activity only if β-glycosidase was present: rree phenols released from their bound form increased or decreased the IAA level. The potential fegulatory effect of simple phenolic glycosides on the IAA level in plants has been discussed; this effect is thought to be mediated by free phenols and by influence on the IAA-oxidase system.     

Histochemical IAA-oxidase localization in the shoot of wheat

A histochemical method for the determination of IAA-oxidase has been used in sections of various aerial parts of winter wheat plants. High IAA-oxidase activity was localized in the cell walls of sclerenchyma near the periphery of the stem, in the vascular bundle sheath of sclerenchyma and in xylem, both in the stem and in the leaf. The cell wall—bound IAA-oxidase activity therefore appeared in lignifying tissues. The staining was very weak or absent in the cell walls of parenchyma tissues and phloem. The positive reaction of the cytosol at the bulbous ends of guard cells and in the leaf primordia is presumed to be due to cytosolic IAA-oxidase. These results are discussed in relation to peroxidase localization and to our previousin vitro studies.     

Peroxidase and IAA-oxidase in crude and partially purified enzyme extracts of growing and differentiating root cells

Crude enzyme extracts from the zones of division, elongation and differentiation of cells of primary maize (Zea mays) root show peroxidase activity but lack IAA-oxidase activity. After partial purification of the extracts by gel filtration on Sephadex G-25, the specific peroxidase activity increases almost twice and a high IAA-oxidase activity appears. The partial purification of the enzyme extracts does not change the electrophoretic pattern of the peroxidase isoenzymes, but significantly improves the separation and the visualization of isoenzymes with IAA-oxidase activity. The data obtained were interpreted in connection with the different modifying effect of the low molecular compounds (mainly phenolics) on the activity and the isoenzyme patterns of the peroxidase and the IAA-oxidase.     

Peroxidase and IAA Oxidase Activity and Isoenzyme Patterns in Cucumber Plants, as Affected by Sex Expression and Ethephon

Peroxidase and IAA-oxidase activity, electrophoretic patterns of total proteins and isoenzymes and the effect of Ethephon (= Ethrel, 2-chloroethane phosphonic acid) on these patterns were compared in extracts of monoecious and gynoecious cucumber plants. The activity of both peroxidase and IAA oxidase was greater in gynoecious than in monoecious plants. Ethephon treatments given at the 2-leaf stage increased peroxidase activity, especially in monoecious plants, and decreased IAA-oxidase activity. Ethephon treatment did not affect total protein or isoenzyme patterns, but increased band intensity, especially that of one band in monoecious plant extracts. No differences between monoecious and gynoecious plants were found in total protein, peroxidase and IAA-oxidase isoenzyme patterns. Peroxidase and IAA-oxidase activity sites on the gel were similar.     

Higher flower bud formation in haploid tobacco is connected with higher peroxidase/IAA-oxidase activity,lower IAA content and ethylene production

Haploid tobacco plants (cv. Samsun) form inflorescences with a larger number of flowers than diploid plants. Leaves of haploid plants were shown to have lower free IAA level (by 40 %), higher peroxidase (by 160 %) and IAA-oxidase (by 70 %) activities and produce less ethylene (by 25 %) than leaves of corresponding diploid plants. The increase of peroxidase activity in haploids was due to the increase in the activity of the cathodic isozyme which is known to have high IAA-oxidase activity. It is proposed that higher peroxidase/IAA-oxidase activity in haploid plants may take part in IAA catabolism, at least duringin vitro culture of haploid explants. Lowered IAA level and ethylene production may then be directly correlated with a larger number of flower buds; as a higher IAA level is generally considered to act as a background inhibitor of flowering.     

Properties of the Ribosome-Bound Peroxidase/IAA-oxidase of Cabbage Roots

The ribosomal fraction of cabbage roots contains IAA-oxidase and peroxidase activity. EDTA dissociates these enzymes from the ribosomal RNA. The IAA-oxidase of intact ribosomes shows allosteric, whereas that of EDTA disintegrated shows conventional kinetics. Gel electrophoresis separated three peroxidases from the ribosomal RNA.     

Influence of Substrate and Tissue Manganese on the IAA-Oxidase System in Cotton

Tissue manganese was found to influence the indoleacetic acid (IAA) system of cotton over a wide range of concentrations. The cofactor and inhibitor activities of the IAA-oxidase system were affected as the concentration of manganese in the tissue was varied. Maximum inhibitor activity was found in leaf extracts from the plants grown in 0.5 mg/l manganese (Hoagland's level). The inhibitor activity decreased in the leaf extracts of plants grown at concentrations of manganese either higher or lower than 0.5 mg/l. Abnormally high IAA-oxidase activity was found in the leaves of plants grown in deficient levels of manganese (<0.0005, 0.005 mg/l) and the extracts from plants in the <0.0005 mg/l Mn treatment showed IAA-oxidase cofactor activity.     

Levels of Indol-3yl-acetic acid (IAA), IAA-oxidase and Peroxidase in Developing Cucumber Seedlings

The level of indol-3yl-acetic acid (IAA) in the cotyledons of cucumber seedlings increases in the period 4 to 11 days after germination. In hypocotyls and roots the IAA level decreases. IAA-oxidase activity of homogenates of cotyledons, hypocotyls and roots decreases with age. The soluble fraction of all three organs contains an IAA-oxidase, which may be allosteric. It is suggested that this IAA oxidase limits the upper level of IAA in the cell. The cell wall fraction of the three organs contains IAA-oxidases with conventional kinetics. The function of this IAA oxidase is probably to degrade exogenous IAA.     

Role of IAA-oxidase in the formation of ethylene from 1-aminocyclopropane-1-carboxylic acid

The IAA-oxidase system of olive tree (Olea europea) in the presence of its substrate, IAA, and cofactors, DCP and Mn², forms ethylene from 1-aminocyclopropane-l-carboxylic acid (ACC) bound as a Schiffs base to pyridoxal phosphate. Similarly, olive leaf discs upon incubation with ACC liberate considerable amounts of ethylene. The results suggest that this IAA-oxidase system may be the one active in the last step in the biosynthesis of ethylene from methionine.     

Effect of manganese toxicity on the indoleacetic Acid oxidase system of cotton

The effect of substrate manganese on tissue manganese levels and activity of the indoleacetic acid (IAA)-oxidase system of cotton (Gossypium hirsutum, L.) was investigated. A sand culture technique was used with 1, 3, 9, 27 and 81 mg manganese (MnSO₄) per liter nutrient solution applied in various experiments.

The following relationships held for both long-term (126 days) and short-term (12-14 days) exposures to manganese treatment: A) There was a direct relationship between substrate and tissue manganese. B) Only the 81 mg/liter Mn plants exhibited severe manganese toxicity symptoms. C) At the toxic level of manganese an increased IAA-oxidase activity and decreased IAA-oxidase inhibitor activity was observed. There was a direct relationship between degree of enzyme response and severity of visible symptoms. D) With the manganese toxicity plants, but none of the other treatments, extracts of the young leaves contained as much IAA-oxidase activity as extracts of much older leaves. E) Crude extracts from the plants grown with 81 mg manganese per liter solution, in contrast to those of other treatments, destroyed IAA without addition of MnCl₂ to the assay medium.

A hypothesis is advanced stating that manganese toxicity symptoms in cotton are expressions of auxin deficiency caused by IAA-oxidase activity increased by the abnormal tissue levels of manganese.

     

Relationship of IAA-oxidase Activity to Gibberellinand IAA-induced Elongation of Light-grown Cucumber Seedlings

The growth and IAA-oxidase activity of light-grown cucumber seedlings (cv. Aonagajibae) were investigated in response to GA₃ and IAA. Both GA₃ and IAA induced significant elongation of the hypocotyl. The fresh and dry weights of the hypocotyl increased due to GA₃ or IAA treatment, whereas no significant change was observed in the cotyledons of GA₃-treated seedlings as compared with the controls. The fresh and dry weights of IAA-treated cotyledons were both lower than those of controls. Treatment with GA₃ or IAA resulted in retardation of IAA-oxidase activity in the hypocotyl and cotyledons. The degree of retardation was less in the cotyledons than in the hypocotyl. An inverse relationship was recognized between GA₃- or IAA-induced elongation and IAA-oxidase activity in the hypocotyl. The auxin-mediated mechanism for gibberellin action was discussed.     

Variations de quelques aclivités enzymatiques (peroxydase, catalase, AIA-oxydase) et de la teneur en polyphénols au cours de la germination de I'Orge. Influence de la kinétine

Peroxidase catalase, IAA-oxidase and polyphenol content of growing barley coleoptile. Effect of kinetin. - Kinetin strongly inhibits root and coleoptile growth of germinating barley in the dark. Treated coleoptiles become senescent before the untreated ones. Soluble proteins content, peroxidase, catalase and IAA-oxidase activity were greatly increased in treated coleoptiles while the level of polyphenols was reduced. These biochemical effects joined with the other property of kinetin to diminish α-amylase synthesis in the endosperm are discussed in relation to growth and in connection with the classic view of a cytokinin retarded senescence.     

高压静电场对银杏愈伤组织生长的影响

银杏愈伤组织经１ ．０ｋＶ／ ｃｍ 强度的高压静电处理后, 愈伤组织生长速率提高, 超氧物歧化酶（ＳＯＤ） 活性和蛋白质及糖含量增加,过氧化物酶（ＰＯＤ） 和吲哚乙酸（ＩＡＡ） 氧化酶活性下降。实验表明,正高压静电场促进银杏愈伤组织细胞的生长,与ＨＶＥＦ 影响体内ＳＯＤ、ＰＯＤ 和ＩＡＡ 氧化酶活性以及蛋白质和糖含量的变化相关