Biochemie und Physiologie der Pflanzen最新文献

Carbon dioxide evolved by CAM plants (Aloe vera, Neoregelia sp. Sansevieria guineensis) in light (δ13C = 0.8 ± 1.8%) was significantly enriched in ¹³C relative to that in dark (δ13C = -13.0 ± 1.4%). The changes in S 13C values of CO2 with light intensity revealed curves similar to those of photosynthetic rate versus light. The ratio of the amount of collected CO₂ C_c over the amount of malic acid consumed (C_m) declined sharply from low light to about 95 µmol m⁻² s⁻¹. Thereafter, this decline tended to be slow. The δ¹³C values of CO₂ evolved versus the corresponding C_c/C_m were linearly correlated, showing different slopes for each species, which is consistent with the expectations of the model established in this study. The yields of carbon dioxide for each malic acid decarboxylated evaluated from the model equation, termed N, were 3.0, 1.5, and 1.3 for S. guineensis, A. vera, Neoregelia sp., respectively.

Maximum activities of phosphofructokinase (PFK), PPi: fructose-6-phosphate 1-phosphotransferase (PFP) and fructose- 1,6-bisphosphatase (FBPase) were determined in desalted extracts from gluconeogenic and non-gluconeogenic tissues from seedlings of peanut, safflower, black gram, green gram, radish and buckwheat. FBPase activity was high only in gluconeogenic tissues, but PFP activity was distributed at significant levels in all tissues examined. PFP activity was always higher than PFK activity. In normal and γ-irradiated peanut cotyledons, the changing pattern of activity of FBPase after germination, but not that of PFP, resembled the changing pattern of gluconeogenic capacity, as estimated by the incorporation of [2-¹⁴C]glycerol to sugars. The minor role of PFP in gluconeogenesis in germinating fatty seeds is discussed.

Polyamines can be considered as a new class of plant growth regulators. However to be considered as hormones, they have to respond to the translocatability criterion in the whole plant. The results presented here show that a small droplet (10 µl) of ¹⁴C-putrescine supplied to a source leaf is redistributed to the whole plant. Long-distance transport occurs mainly towards young growing organs (apex, roots, stolons, tubers). Bidirectional translocation, which is also found is a result of interactions between the attractive strengths of different sinks. Heat girdling of shoots induces a strong inhibition of transport which suggests transport via the phloem. Other data, such as non labeling of mature leaves, normally fed by xylem flux and the higher content (4 to 10 times) of endogenous PA_s in phloem exudate compared with xylem exudate confirm this conclusion. After a 3 h period of transport, separation of labelled compounds by thin layer chromatography shows that the radioactivity supplied as ¹⁴C-putrescine is found as putrescine (from 64% to 82%), spermidine (from 14% to 28%) and spermine (3%) depending on the organ. This indicates that there is no important degradation of putrescine before it reaches the transport pathway.

Calcium ions serve as a second messenger in the transduction of environmental and hormonal signals to the responsive elements of cell metabolism. Effects of Al on the cell Ca²⁺ homeostasis remain to be elucidated. Short-term net ⁴⁵Ca²⁺ uptake by Amaranthus tricolor protoplasts was measured in media prepared to test the influence of various buffers, pH values, Ca²⁺ and Al concentrations. A modified GEOCHEM program was used to calculate activities of Ca²⁺ and all monomeric Al species. Net ⁴⁵Ca²⁺ uptake was smaller at pH 4.5 compared to uptake at pH 5.5 and increased linearly with an increase in Ca²⁺ activity in the uptake media from 0.23 to 2.0 mM. Aluminium caused a significant decrease in net ⁴⁵Ca²⁺ uptake. This Al-related decrease was less expressed at higher Ca²⁺ activities. Summed activities of monomeric Al species (Al³⁺ and hydroxy-Al) were significantly related to the reduction of net ⁴⁵Ca²⁺ uptake. The equilibrium constant (Ki) of the reversible association of the Ca²⁺ membrane-transporter and monomeric Al species was calculated from Dixon plots to be equivalent to 4 and 30 micromolar activity of total monomeric Al for uptake media with pH values of 4.5 and 5.5, respectively. It is suggested that the primary Al effects are generally exerted through reducing inward Ca²⁺ fluxes across the plasma membrane.

Proteins of healthy pea plants (Pisum sativum L. cv. Nadja) and of plants infected with red clover mottle virus were examined by one- and two-dimensional electrophoresis.

Silver-stained 2-D slab gels revealed more than ten additional protein spots with markedly changed intensity in the extracts from infected plants as compared to extracts from uninfected plants. Two of these spots corresponded to virus proteins (about 38 and 21 kDa).

A sensitive and comparatively simple spectrophotometric method for the assay of meso-diaminopimelic acid decarboxylase is presented. It is based upon the coupled reaction of the decarboxylase with pea diamine oxidase and horseradish peroxidase.L-Lysine, a product of meso-diaminopimelic acid decarboxylase is oxidized by pea diamine oxidase and the hydrogen peroxide generated is estimated as the red colour (quinoneimine dye) formed on the peroxidative oxidation of the mixture of 3,5-dichloro-2-hydroxybenzenesulfonate and 4-aminoantipyrine. The method was compared with the result by a high performance liquid chromatography assay.

Ethionine markedly inhibits the replication of potato virus X (PVX) after infiltration into leaf disks of Nicotiana tabacum L. “Samsun”. P-fluorophenylalanine and 5-methyl-DL-tryptophane inhibit this replication less effectively and only at phytotoxic concentrations. Methionine strongly reduces the inhibitory activity of ethionine in the replication of PVX. In leaf disks with synchronized virus infection, the time-response course of ethionine inhibition indicates that a late event is inhibited. Short time after the beginning of ethionine inhibition decline virus protein was detected by ELISA. Contrary to leaf disks, in intact tobacco plants PVX replication is inhibited by ethionine sprays only in very high and phytotoxic doses. However, low doses of ethionine increase synergistically the inhibitory activity of 5-azadihydrouracil.