Biochemie und Physiologie der Pflanzen最新文献

Dry matter allocation is a very good indicator of conditions of both the mineral nutrition of plants and the photosynthetic conditions in vivo. We determined the response of dry matter accumulation and shoot/root ratio of rape seedlings (Brassica napus L.) to different levels of sucrose supply and nitrogen deficiency in vitro. The dry weight of roots and shoots increased significantly with increasing concentration of sugar in the medium from 0 % to 9 % (w/v) but shoot/ root ratio decreased. Nitrogen deficiency caused a further decrease in the shoot/root ratio. The results show that exogenous sugar supply can induce a similar shift in partitioning of dry matter as favourable photosynthetic conditions and that the response to exogenous sugar is influenced by nitrogen deficiency.

The cellular nitrite reductase activity in response to different nitrogen sources has been studied in the cyanobiont Nostoc ANTH isolated from the liverwort Anthoceros. De novo protein synthesis of nitrite reductase occurred even in the absence of added nitrogen source, although enzyme activity was higher when nitrite or nitrate served as the sole nitrogen source. In tungstate-treated cells, nitrate did not show any positive effect on nitrite reductase activity, suggesting that the stimulatory effect was not due to nitrate itself but it requires its reduction to nitrite. Thus, nitrite may be the actual inducer in this case. Ammonium-grown cells showed reduced level of nitrite reductase activity. The nitrite reductase activity was freed from ammonium repression by L-methionine-DL-sulphoximine (MSX), an irreversible inhibitor of glutamine synthetase (GS). Thus ammonium metabolism through GS is required for the ammonium repression of nitrite reductase to occur.

Addition of gallic and chlorogenic acid to the reaction mixture caused a marked inhibition of starch-iodine reaction. This inhibition, however, could be partially alleviated by enhancing the level of iodine-potassium iodide reagent (IKI) in the reaction mixture. It is likely that these phenolics deplete the iodine from the system which could account for inhibition of reaction. IKI addition to the solution of gallic and chlorogenic acid induced a change in the absorption spectra of the respective phenolic compound causing a shift in the absorption peaks. Such a change may be ascribed to a complex being formed between the tested compounds and iodine.

An electrical potential difference appears across an intact Chenopodium rubrum L. (Sel. 184) plant, with marked transients induced by light on-off. A study of this potential and the transients was made by means of two electrodes in contact with the bathing solution and the cotyledon of a six-day-old plantlet. We varied the light intensity and wavelength, and worked with green and photobleached (SANDOZ 9789 pretreated) plants. Light intensities below 1.4 W m⁻²2 of white light did not produce any appreciable transients, the amplitude of change of potential difference then increasing to a maximum ≈ 20 W m⁻², where it stayed constant upto light intensities above 100 W m⁻². A maximum in response was obtained at 644 nm and wavelengths>700 nm did not cause any transients. No transients could be observed with bleached or DCMU treated plants. Thus while the participation of the photosynthetic process in the light-induced transients is unequivocal, the participation of a phytochrome coupled component could not be ascertained.

Protoanemonin, a lactone present in Ranunculaceae plants, at subinhibitory concentration (19 μg ml⁻¹) caused deep morphogenetic anomalies on the yeast Rhodotorula glutinis. The cell wall was strongly thickened, the nuclei were lobed and irregular in shape, and consistent deposits of calcium aggregates were scattered in the mitochondrial matrix as proved by the cation-precipitating K-pyroantimonate test. The ultrastructural results confirm that the antifungal activity of the protoanemonin is related to the interaction of the compound with cytoplasmic microtubules.

The amount and the redox status of pyridine nucleotides as well as OZ gas exchange and delayed fluorescence in spruce seedlings were examined after prolonged exposure to methyl viologen (25–200 ppm). During a period of 24 h, methyl viologen induced a significant decrease of NADPH + H⁺ compared with the control, resulting in a marked decrease of ARC (anabolic reduction charge: [NADPH + H⁺]/[NADPH + H+ + NADP⁺]). Later on, the ARC of treated samples remained on a constant level at least until 72 h, though the total content of phosphorylated pyridine nucleotides decreased. The CRC (catabolic reduction charge: [NADH + H⁺]/[NADH + H⁺ + NAD⁺]) of treated seedlings was lowered only transiently. This indicates that reducing equivalents contribute to the detoxification of reactive oxygen species only initially during methyl viologen application. The decrease of functions — photosynthesis, respiration — supports the view that after prolonged treatment the progressive damage of cell components rather than the availability of reducing equivalents limits the capacity of the plant tissue to detoxify methyl viologen-induced reactive oxygen species.