Kinetics of fenugreek peroxidase isoenzymes

Peroxidase from fenugreek seedlings was separated into 6 isoenzymes; 4 on CM-cellulose and 2 on DEAE-cellulose. The kinetics of these peroxidase isoenzymes with regard to o-dianisidine and catechol are described.     

Influence of boron deficiency on 3H indole-3yl-acetic acid uptake and efflux in cell cultures of Daucus carota L.

³H-IAA net uptake and efflux was measured in carrot cell suspensions after two and five days in either boron (B) sufficient or B deficient media. Contrary to earlier observations with substances such as phosphate, glucose and potassium (or Rb⁺), ³H-label uptake from IAA over a 3 h period did not differ significantly after two days of treatment. After five days of B deficiency, cells accumulated higher ³H-activity than those receiving B. Total ³H-efflux from deficient and sufficient cells did not differ significantly but B deficient cells released more water soluble (pH 3.0) ³H, and less methanol soluble ³H activity, which may be due to a higher IAA oxidase activity. Correspondingly, we found an elevated peroxidase (POD) activity in B deficient cell cultures which was 54% higher after two days of deficieny and which increased further threefold after five days. Similar changes have been found in the amount of POD activity released to the nutrient solution with even more pronounced differences after two days. Thus, B deficient cells released less authentic ³H-IAA (1.7% vs. 3.1% related to total ³H efflux), as determined by HPLC separation.     

The determination of sensitivity parameters for auxin-induced H+-efflux from Avena coleoptile segments

Abstract A method is described for the measurement of auxin-induced H⁺-efflux from small populations of Avena coleoptile segments. The method allows the simultaneous investigation of the kinetics of rapid auxin responses over a wide concentration range. IAA promoted linear rates of H⁺-efflux and the change in amplitude of response occurred mainly over a low, narrow concentration range (10–50 μmol m^-3). The sigmoidal curve of best-fit to each set of dose-response data was determined using non-linear regression techniques, allowing the objective determination of characteristic tissue sensitivity parameters (R_MIN, R_MAX, K_D and p). The sensitivity parameters for the auxin-type herbicide fluroxypyr are also presented as well as IAA parameters determined in the presence of abscisic acid and the ‘antiauxin’ PCIB. The interpretation of the parameter values and the potential use of sensitivity parameter analysis for the evaluation of theories concerning plant hormone action and interaction is discussed.     

Enzymatically generated electronically excited molecules induce transformation of 4-thiouridine to uridine

Oxidation of 4-thiouridine-5'-monophosphate in t-RNA, from E. coli, by singlet oxygen generated via self-sensitization, photosensitization or by energy transfer from bioenergized systems yields uridine-5'-monophosphate. Studies with absorption, fluorescence and circular dichroism techniques showed similar interactions between singlet oxygen and the nucleotide in t-RNA generated by either optical or enzymatic systems. Protection by histidine and an enhancement of the photodegradation in the presence of D2O corroborates the important role of singlet oxygen in these processes.     

Hormonal Status in Wheat and Rice Seedlings under Anoxia

A comparative analysis of the effects of anoxia on growth, fresh weight gain, and phytohormones in wheat (Triticum aestivum L.) and rice (Oryza sativa L.) seedlings was performed. In both plant species, a total cessation of root growth occurred during the initial hours of anoxia. In an anaerobic environment, the fresh weight of wheat seedlings decreased. An increase in the shoot length and weight under the stress conditions was found only in rice seedlings. During the initial hours of anoxia, the level of free ABA in wheat and rice tissues increased manifold, and the accumulation of a free ABA form occurred at the expense of the hydrolysis of its bound forms. The IAA content in plant tissues also increased. In wheat, the accumulation of IAA was short, but in rice, a high hormone level was retained during the entire experiment, and, as a result, its concentration exceeded that of ABA. A level of cytokinins in the tissues of both plant species was affected by anoxia to a lesser extent than that of other phytohormones. This level somewhat decreased under anoxia similarly to the level in darkness under aeration. It is suggested that IAA accumulation in hypoxia-tolerant rice seedlings under anoxia favors maintenance of shoot growth and simultaneous inhibition of root growth. At the same time, in the hypoxia-sensitive wheat, an increase in the ABA level resulted in growth cessation.     

Iaa oxidase and polyphenol oxidase activities of peanut peroxidase isozymes

Four anionic isozymes (A₁, A₂, A₄ and A₅) from peanut cells in suspension medium possessed IAA oxidase and polyphenol oxidase activities. The specific activities of each of the enzymes differed among the 4 isozymes. The pH optima established in these assays for peroxidase was acidic, for IAA oxidase neutral and for polyphenol oxidase alkaline. All 4 isozymes had different K_m and V_max for the enzyme activities of peroxidase and polyphenol oxidase. The sigmoid kinetics from the IAA oxidase assays for the isozymes probably indicates an allosteric nature.     

富贵竹提取液中几种成分的初步研究

在富贵竹枝条基部提取液中，ＩＡＡ含量和酚类物质含量显著地高于中部和上部提取液的含量；中部提取液中的可溶性糖含量和蛋白质含量最高．     

Phytohormones in algae

In various algal taxa, essentially all known phytohormones were detected in concentrations comparable with their content in higher plants. The occurrence of diverse free and conjugated hormone forms substantiates the functioning of the complex system of metabolism and activity regulation of these compounds. In most cases, the spectrum of biological activities of algal hormones corresponds to the functions of higher plant hormones. Some physiological and biochemical processes in algal cells and tissues are under the control of several phytohormones. All these facts permit a consideration of the algal hormonal system as a full-value regulatory system.     

Low-order fine roots of Picea asperata have different physiological mechanisms in response to seasonal freeze and freeze–thaw of soil

• Seasonal soil freezing (F) and freeze–thaw cycles (FTCs) are common natural phenomena in high latitude or altitude areas of the world, and seriously affect plant physiological processes. However, studies on the effect of soil F and FTCs on fine roots are less common, especially in subalpine coniferous forests of western Sichuan, China.
• We set up a controlled experiment in growth chambers to explore the effects of F and FTCs on low-order fine roots of Picea asperata and differential responses of first-order roots and the first three root orders (1st, 2nd and 3rd order roots combined as a unit).
• Soil F and FTCs resulted in serious damage to cell membranes and root vitality of low-order fine roots, accompanied by increased MDA content and O₂·⁻ production. FTCs had a stronger effect than F treatment. In turn, low-order fine roots are the unit that responds to cold stress. These roots had increased unsaturated fatty acid contents, antioxidant enzyme activities, osmolytes and plant hormones contents when acclimation to cold stress. The first-order roots were more sensitive to cold stress than the combined first three root orders for several processes (e.g. antioxidant enzymes, osmolytes and hormones) because of their specific structure and physiological activity.
• This study explains physiological differences in responses of fine roots of different root orders to seasonal soil freezing, which will improve the understanding of fine root heterogeneity and support agriculture and forest management.