Showing papers in "Plant and Cell Physiology in 1979"

Novel inhibitors of ethylene production in higher plants

Abstract: Thcir potency is thus sirnilar to that of aminoethoxyvinylglycine (50% inhibition at 2 \"M), the most potent inhibitor of ethylcne production hitherto known. Methienine partially alleviated inhibition ef ethylene production by a-aminooxy-acetic acid. The results are in agreement with the postulatod involvement ofpyridexal phosphate in ethylene biosynthesis.

Growth and cell wall changes in azuki bean epicotyls I. Changes in wall polysaccharides during intact growth

Abstract: o) was the shortest in the upper region (0-30 mm below the apex) of the epicotyl, where vigorous endogenous growth took place, and became longer toward the basal region, which was mature and not growing. In the upper region of the epicotyl, a lower percentage of a-cellulose and a higher percentage of pectic substances than in the lower region were found. The percentage of hemicellulose content was almost constant over the whole epicotyl. Major components of noncellulosic neutral sugars in the cell wall were galactose and xylose. The percentage of the galactose content to the noncellulosic polysaccharide was highest in the upper region and lowest in the basal region of the epicotyl, and a clearly negative correlation between the galactose composition and the T o value was obtained. On the contrary, the percentage of die xylose content was highest in the basal region and lowest in die upper region, and a clearly positive correlation between die xylose composition and the To value was obtained. During die endogenous growth of die intact epicotyl, all die neutral sugars, particularly galactose, increased in die upper region, whereas in die middle and basal regions, only xylose increased. Similar changes in sugar compositions were observed during IAA-induced elongation of die segment excised from various regions of die epicotyl.

Growth and cell wall changes in azuki bean epicotyls II. Changes in wall polysaccharides during auxininduced growth of excised segments

Abstract: Changes in cell wall polysaccharides and mechanical properties of the cell wall were examined during IAA-induced elongation growth of excised azuki bean epicotyl segments under different growth conditions. Sucrose promoted IAA-induced cell elongation, but had very little effect on IAA-induced cell wall loosening. In the absence of sucrose, the amount of galactose in the cell wall decreased during the incubation period. IAA enhanced the decrease in the galactose level. In the presence of sucrose, on the other hand, IAA induced increases in the amounts of cellulose, galactose and xylose in noncellulosic polysaccharides. These IAA-induced increases were not observed in the presence of mannitol at concentrations higher than 0.1 M, although cell wall loosening was induced by IAA even in the presence of 0.2 M mannitol.

Control of cocklebur seed germination by nitrogenous compounds : Nitrite, nitrate, hydroxylamine, thiourea, azide and cyanide

Abstract: Germination of non-dormant upper cocklebur (Xanthium pinsylvanicum Wallr.) seeds was stimulated by not only CS(NH2)2 but also NH2OH, KCN and NaN3. This stimulation was not via the enhancement of aerobic C2H4 production. NH2OH, KCN and NaN3 in certain concentrations promoted the initial growth of axial and/or cotyledonary parts, but the degree of growth promotion by NH2OH, NaN3 and KCN was slight compared with that by CS(NH2)2. As in the case of CS(NH2)2, however, the germinationstimulating effect of NH2OH disappeared rapidly as the preceding imbibition period was prolonged. In contrast, KCN and NaN3 were still effective in stimulating the germination of aged seeds maintained on a water substratum, as previously seen with anaerobiosis. Anaerobic induction was enhanced not only by NaN3 and KCN but also by NH2OH, KNO3, KNO2 CO(NH2)2 and CS(NH2)2 applied during the anaerobic treatment, but without causing an increase in anaerobic production of C2H4. Furthermore, KCN and NaN3, given prior to the anaerobic treatment acted additively with anaerobic induction. The germination-stimulating actions of nitrogenous compounds are discussed in comparison with those of C2H4 and anaerobiosis.

Auxin-induced changes in the molecular weight of hemicellulosic polysaccharides of the Avena coleoptile cell wall

Abstract: The average molecular weight of the water soluble hemicelluloses (hemicellulose B) of the Avena coleoptile cell wall was determined by gel permeation chromatography (GPC) and viscometry. Analysis of the neutral sugar composition of henucellulose B eluted from a GPC column (Sepharose 4B) indicated that it consists of /J-glucan with a high molecular weight and arabinoxylan with a low molecular weight. A kinetic study of the effect of auxin on the molecular distribution of henucellulose B demonstrated that auxin decreased the /?-glucan content of the hemicellulose as early as the first hour incubation, but not the arabinoxylan content, when it stimulated the extension of the coleoptile segments. Calculation of the weight-average molecular weight from the chromatograms suggested that auxin decreased the molecular weight of hemicellulose B; this was also confirmed by viscometry. Thus, auxin may cause cell wall loosening, leading to cell extension, through its effect on /?-glucan degradation or through the decrease in the molecular weight of hemicellulose B.

Differences in cold lability of pyruvate, Pi dikinase among C4 species

Abstract: The cold lability of pyruvate, Pi dikinase in crude leaf extracts was studied in a number of C4 plants. The survey included C4 monocots and dicots and species representingthe three C4 subgroups: NADP-malic enzyme, NAD-malic enzyme, and PEP-carboxykinase types. In some species (e.g., Digitaria sanguinalis, Sorghum bicolor and Echinochloa crus-galli), the enzyme was very sensitive to cold treatment (half life of about 8 min at 0°C and 10 to 15 min at 10°C). In other species (Panicum miliaceum, Panicum maximum and Panicum texanum), the enzyme was very cold tolerant (retention of 60 to 85% activity after 60 min at 0°C and 90% activity after 60 min at 10°C). Among the plants examined, the most cold sensitive pyruvate,Pi dikinase was found among species of the NADP-malic enzyme subgroup.

Stimulation of dark CO2 fixation by ammonia in isolated mesophyll cells of Papaver somniferum L.

Abstract: Addition of 2 mM arrmonium ion to isolated mesophyll cells of Papaver somniferum resulted in a 3-fold or greater increase in their rate of dark 14c fixation~ while even 0.1 mM NH4+ nearly doubled that rate. The most rapid increase in the labeling of a metabolite occurred is aspartate~ and was accompanied by a decrease .in the steady-state level of labeled phosphoenolpyruvate. No change in labeled pyruvate level occurred, and alanine labeling declined. Ammonium ion addition had no effect on the respiratory rate of these cells in the dark. + We conclude that NH4 stimulates phosphoenolpyruvate carboxylation in this system, but has no detectable effect on the pyruvate kinase reaction in the dark.. Our results are compared with earlier findings and the possible regulatory function of ammonia is discussed.