Remo Reggiani

Anaerobic accumulation of 4-aminobutyrate in rice seedlings; Causes and significance

Accumulation of 4-aminobutyrate is induced by anoxia in rice seedlings. The induction of 4-aminobutyrate accumulation in aerobic conditions by treatments with exogenous 4-aminobutyrate, Gabaculine and glutamate is well tolerated by the seedlings. The inhibition of protein synthesis in aerobic and anaerobic conditions by cycloheximide shows that this process competes with glutamate decarboxylase for glutamic acid. The sensitivity of the anaerobic 4- aminobutyrate accumulation to azaserine indicates that glutamate synthase is important in maintaining glutamate availability. The different tolerance to anoxia and protein metabolism of shoot and root of rice suggests that the causes leading to 4-aminobutyrate accumulation in these tissues are different. It is suggested that ammonia reassimilation in root plays an important role in the synthesis of 4-aminobutyrate.

PRELIMINARY EVIDENCE FOR INVOLVEMENT OF GTP-BINDING PROTEIN(S) IN AUXIN SIGNAL TRANSDUCTION IN RICE (ORYZA SATIVA L.) COLEOPTILE

Summary The relationship between auxin-binding sites and guanine nucleotide binding in membranes from rice coleoptile was studied.The natural auxin, indole-3-acetic acid (IAA), increased the rate of [ 35 S]GTP-γS association to vesicles.This effect was specific for active auxin analogs and for guanine nucleotides; its intensity was correlated with the level of membrane auxin binding site activity.GTP-γS caused a decrease in membrane auxin binding activity.These data suggest that GTP-binding protein(s) is involved in auxin signal transduction in rice coleoptile.

Expression of the Enzymes of Nitrate Reduction during the Anaerobic Germination of Rice

During the anaerobic germination of rice (Oryza sativa L.), nitrate is translocated from the caryopsis and assimilated into the coleoptile (R. Reggiani, M. Mattana, N. Aurisano, A. Bertani [1993] Plant Cell Physiol 34: 379–383). Using antibodies against nitrate and nitrite reductases, proteins with the expected molecular mass were recognized by western blot analysis in extracts from 8-d-old rice coleoptiles. Both enzymes are de novo synthesized in 6- to 8-d-old seedlings, as shown by immunoprecipitation of radiolabeled proteins from young plants grown in the presence of [35S]methio-nine. The anaerobic synthesis of both enzymes was enhanced by the addition of 5 mM KNO3. The effect of exogenous nitrate on the expression of the corresponding genes in anaerobic rice coleoptiles was revealed by the analysis of their transcripts. The importance of the expression of these enzymes during the anaerobic development of rice seedlings is discussed.

Influence of K+ Ions on Polyamine Level in Wheat Seedlings

Summary Incubation of 3-day-old seedlings of Triticum aestivum L. cv. Marinat with KCl concentrations equal or higher than 15 mM, showed a decrease in the polyamine titer which was especially marked with the level of putrescine. The effects of different cations and anions were compared and it was established that the K + ion was the most effective in depressing the polyamine level. Moreover the presence of K + ions inhibited the incorporation of label from 14 C-arginine into putrescine and stimulated the conversion of 14 C-putrescine to spermidine and other compounds. The modulation of polyamine metabolism by K + is discussed in relation to the ion balance.

Plasmalemma ATPase in rice coleoptiles; stimulation by putrescine and polyamines

Abstract A vanadate-sensitive plasma membrane ATPase from aerobic and anaerobic rice coleoptiles is activated by putrescine and polyamines. Calcium ions cannot replace the effect of putrescine and polyamines on ATPase activity. The maximal activation by putrescine occurs between 3 and 5 mM, concentrations found in plant tissues subjected to environmental stresses and in rice coleoptiles during anaerobic germination.

ABA induces 4-aminobutyrate accumulation in wheat seedlings

Abstract Accumulation of amino acids and 4-aminobutyrate is induced by ABA treatment in wheat roots. The accumulation of amino acids as well as a decrease in pr

Evaluation of Camelina sativa (L.) Crantz meal as an alternative protein source in ruminant rations

BACKGROUND Camelina sativa (CS) is an oilseed crop used for biofuel production. By-products from oil extraction are high in protein and can be used in ruminant rations; more information about their nutritive value is required also considering the antinutrional factor content of the by-products. The aim of this study was to evaluate the nutritive value of CS meal genotypes in comparison with canola. RESULTS Ten CS genotypes and one canola cultivar were evaluated. Meals were obtained from seeds after solvent oil extraction. CS average crude protein (CP) content (g kg⁻¹ dry matter) was 457. Numerical differences in lysine and sulfur amino acid content were observed among CS genotypes. Glucosinolate (mmol kg⁻¹) content was higher for CS (23.1) than canola (7.2). Sinapine content (g kg⁻¹) was lower for CS (2.79) than for canola (4.32). Differences were observed among CS genotypes for rumen undegraded protein (RUP). Average RUP (g kg⁻¹ CP) was 316 for CS and 275 for canola. CONCLUSIONS CS meal has potential for use in ruminant rations as a high-quality protein source. In vivo studies are needed to compare CS with other protein sources used in cattle rations. Implementation of breeding programs for improved meal quality is recommend.

Changes in polyamine metabolism in seedlings of three wheat (Triticum aestivum L.) cultivars differing in salt sensitivity

Abstract Germination is a developmental stage extremely sensitive to salinity. We studied the effects of three regimes of salinity (50, 100 and 150 mM NaCl) on polyamine (PA) metabolism during the germination seeds of three wheat ( Triticum aestivum L.) cultivars. These genotypes exhibited inhibition of germination by salt, in the following order: Ardenica > Agimi > Dajti. The presence of salt decreased the putrescine (Put) level, especially in roots. On the contrary, the levels of spermidine (Spd) and spermine (Spm) were increased by salt with a greater effect in shoot. A positive correlation with the growth inhibition of the three cultivars was observed for the level of Spd and Spm and, even better, for the PA/diamine ratio. Feeding experiments with [ 14 C]Put showed that, in the presence if 150 mM NaCl, Ardenica tissues synthesize more PAs than Dajti tissues. The effect of salinity on PA metabolism and the use of PAs as a makers of salt sensitivity in wheat seedlings are discussed.

Nitrate assimilation during the anaerobic germination of rice: expression of ferredoxin-dependent glutamate synthase

Ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) is the last enzyme involved in the pathway of nitrate assimilation in higher plants. This paper describes the synthesis and expression of the enzyme in anaerobic coleoptiles of rice (Oryza sativa L.) and its regulation by exogenous nitrate. The activity of Fd-GOGAT was strongly inhibited by cycloheximide between 4 and 9 d of anaerobic germination. The addition of nitrate slightly increased, in the first 5 h, the specific activity of Fd-GOGAT as well as the amount of a 160-kDa protein specifically immunoprecipitated with anti-Fd-GOGAT serum. Northern blot analysis, performed with a specific riboprobe, showed the presence of mRNA of the expected size and the inductive effect of nitrate. The role of Fd-GOGAT is discussed in relation to the anaerobic assimilation of nitrate by rice coleoptiles.

Expression of glutamine synthetase during the anaerobic germination of Oryza sativa L.

Glutamine synthetase (GS; EC.6.3.1.2.) occurs as cytosolic (GS1) and plastidic (GS2) polypeptides. This paper describes the expression of GS isoenzymes in coleoptile during the anaerobic germination of rice (Oryza sativa L.) and the influence of exogenous nitrate on this. By immunoprecipitation with anti-GS serum, two polypeptides of 41- and 44-kDa were detected of which the former was predominant. After fractionation by ion-exchange chromatography, the 41 and 44 kDa bands were identified as GS1 and GS2, respectively. Northern blot analysis with specific probes showed the presence of mRNA for cytosolic GS but not for the plastidic form. The presence of exogenous nitrate did not alter the activity and expression of GS in the coleoptile. The role of GS during the anaerobic germination of rice seems to induce the re-assimilation of ammonia rather than the assimilation of nitrate.