Extremely low frequency weak magnetic fields enhance resistance of NN tobacco plants to tobacco mosaic virus and elicit stress-related biochemical activities.

Increasing evidence has accumulated concerning the biological effects of extremely low frequency magnetic fields (ELF-MFs) in different plant models. In the present study, effects of ELF-MFs in tobacco plants reacting to tobacco mosaic virus (TMV) with a hypersensitive response (HR) were evaluated. Plants were exposed for 8 or 24 h (either before or after TMV inoculation) to a static MF, at either -17 or 13 microT, combined with a 10 Hz sinusoidal MF with different intensities (25.6 or 28.9 microT). The working variables were the area and number of hypersensitive lesions in leaves. Following ELF-MFs exposure, an increased resistance was detected, particularly after an 8-h treatment, as shown by the decrease in lesion area and number. Moreover, two enzyme activities involved in resistance mechanisms were analyzed: ornithine decarboxylase (ODC) and phenylalanine ammonia-lyase (PAL). Uninoculated leaves previously exposed to ELF-MFs in general showed a significant increase relative to controls in ODC and PAL activities, in particular for 13 microT static MF plus 28.9 microT, 10 Hz sinusoidal MF (24 h) treatment. In conclusion, ELF-MFs seem to influence the HR of tobacco to TMV, as shown by the increased resistance and changes in ODC and PAL activities, indicating the reliability of the present plant model in the study of bioelectromagnetic interactions.

Responses of anthocyanin-producing and non-producing cells of Glehnia littoralis to radical generators.

The responses of anthocyanin-producing (violet) and non-producing (white) cells of Glehnia littoralis to radical generators were compared. Cell growth, anthocyanin content, phenylalanine ammonia-lyase (PAL) activity and furanocoumarin production were determined after treatment with H(2)O(2), 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), X-ray and yeast extract, independently. AAPH and H(2)O(2) repressed the growth of both violet and white cells, but violet cells grew better than white cells. On the other hand, the anthocyanin content in violet cells decreased. Neither X-ray nor yeast extract affected cell growth or pigment production. Treatment with H(2)O(2), yeast extract, and X-ray, but not AAPH, induced PAL activity and furanocoumarin production in white cell cultures, whereas violet cell cultures did not produce furanocoumarin following any of the treatment employed.

Effect of gamma-irradiation on phenolic compounds and phenylalanine ammonia-lyase activity during storage in relation to peel injury from peel of Citrus clementina hort. Ex. tanaka.

The influence of gamma-irradiation on the content of phenolic compounds was evaluated on Moroccan Citrus fruits (Citrus clementina Hort. ex. Tanaka) treated at a mean dose of 0.3 kGy and stored for 49 days at 3 degrees C. The results show that irradiation has enhanced the synthesis of total phenolic compounds and is correlated with phenylalanine ammonia-lyase activity (PAL) during storage. Accumulation of phenolic compounds in cells is demonstrated and may be explained by the enhancement of PAL activity. HPLC/UV (diode array detector) analysis demonstrated that hesperidin was the major flavanone and nobiletin and heptamethoxyflavone were the major polymethoxylated flavones. Hesperidin is also the major phenolic compound in clementines. Irradiation stimulates the biosynthesis of hesperidin after 14 days of storage, corresponding to the maximum of PAL activity. p-Coumaric acid was also identified, and its content was particularly high in irradiated fruits after 49 days of storage. Accumulation of flavonoids and p-coumaric acid could be related to a better resistance. The percentage of losses due to peel injury "pitting" during storage was between 1 and 5% after 49 days of storage. The connections between irradiation, enzyme activity, phenolic content, and peel injury are briefly discussed.

Effect of gamma-irradiation on phenylalanine ammonia-lyase activity, total phenolic content, and respiration of mushrooms (Agaricus bisporus).

Ionizing treatments were applied at 0.5 kGy, 1.5 kGy, and 2.5 kGy to edible mature mushrooms (Agaricus bisporus, albidus) in order to assess the effect of the gamma-irradiation on some biochemical parameters. Irradiation at doses of 1.5 kGy and 2.5 kGy reduced significantly (p < or = 0.05) the rate of respiration of the mushrooms, compared to that of samples irradiated at 0.5 kGy and nonirradiated control samples (C). Ionizing treatments increased significantly (p < or = 0.05) the phenylalanine ammonia-lyase (PAL) activity and total phenols concentration between days 1 and 4. From days 3-4, to the end of the storage period (day 12), both PAL activity and total phenols in the irradiated samples (I) collapsed to lower values. In contrast, the activity of polyphenol oxidase (PPO) increased until days 7, 9, and 12 for samples treated at 0.5, 1, and 2 kGy, respectively. Color measurements showed a loss of whiteness (L value) during storage. After day 4, however, the effectiveness of gamma-irradiation became apparent, and highest L values were obtained for I only.

Properties of L-phenylalanine ammonia-lyase and turnover rate in etiolated and far-red illuminated seedlings of radish.

1. L-Phenylalanine ammonia-lyase (EC 4.3.1.5) was purified from radish cotyledons. The adsorption of the enzyme on L-phenylalanine-Sepharose 4B was nonspecific; the present data disprove the conclusions reached previously (Blondel, J.D., Huault, C., Faye, L., Rollin, P. and Cohen, P. (1973) FEBS Lett. 36, 239-244). 2. The apparent molecular weight of the enzyme fluctuated according to pH and ionic strength. A mean value of 290 000 was determined for the 'native' form. The activation energy was 54.4 kJ/mol. L- and D-phenylalanine protected the lyase from sodium borohydride denaturation. 3. Two Michaelis constants, KHm = 1.5 x 10(-5) M and KLm = 9.5 x 10(-5) M, were determined. The Hill coefficient value (h) was 0.48. This coefficient was 0.6 for cinnamate inhibition. These results suggest that phenylalanine ammonia-lyase in radish cotyledons is regulated by a negative cooperativity mechanism. 4. The phytochrome-mediated increase in phenylalanine ammonia-lyase activity was investigated by density labelling with 2H2O followed by isopycnic centrifugation in KBr gradients. An apparent half-life of 3.5 h was found for both the enzyme extracted from etiolated or far-red irradiated cotyledons. 5. Provided that phytochrome does not control the availability of labelled amino acids for protein synthesis, the present results are consistent with a far-red light-induced increase in the rate of synthesis of the lyase in radish cotyledons.