Homology among 3S and 7S Globulins from Cereals and Pea

The globulins from wheat caryopses were found to consist primarily of protein sedimenting at approximately 3S and 7S. These proteins displayed a molecular weight distribution similar to that of the purified vicilin-like fractions from oat and pea, with variations occurring in the isoelectric points and relative quantities of their major subunits. concanavalin A Sepharose chromatography suggested that the major polypeptides of the wheat (3S + 7S) fraction are glycosylated. Western blot analysis using antioat (3S + 7S) globulin immunoglobulin G revealed the vicilins from pea and the globulin fractions of oat, wheat, barley, rye, corn, and rice to contain immunologically homologous polypeptides. Major groups of polypeptides were shared by all the cereals and pea, including subunits of approximately 75, 50, 40 kilodaltons and 20 to 25 kilodaltons. These results indicate that legume-like 3S and 7S globulins have been conserved and are being expressed in cereals.     

Effect of translocation-hindering procedures on source leaf photosynthesis in cucumber

Three treatments which altered translocation rate were applied to cucumber plants: Girdling of source leaf petiole; removal of all aerial sinks; removal of all source leaves except one. Two different effects were observed, one short-term (during the initial 6 hours), and one long-term (detected after several days).

The short-term effect was observed exclusively in girdled leaves and involved a reduction in ¹⁴CO₂ fixation rate paralleled by an increase in stomatal resistance. The effects were maximal after 3 hours with subsequent recovery. Stomatal closure apparently resulted from the 5 to 10% water deficit temporarily detected in girdled leaves which probably induced the observed temporary increases in abscisic acid content. Kinetin counteracted the effects of girdling.

The long-term effect was detected 3 days after girdling and 3 to 5 days after sink manipulation. An increase or decrease in ¹⁴CO₂ fixation rate was observed when the sink-source ratio was increased or decreased respectively, accompanied by a respective decrease or increase in starch content. Changes in the relative amount of ¹⁴CO₂ incorporated into various photosynthetic products were also observed. Stomatal closure was not involved, and the decrease in CO₂ fixation was not counteracted by kinetin.

     

Nitrate Reductases from Wild-Type and nr(1)-Mutant Soybean (Glycine max [L.] Merr.) Leaves : I. Purification, Kinetics, and Physical Properties

NADH:nitrate reductase (EC 1.6.6.1) and NAD(P)H:nitrate reductase (EC 1.6.6.2) were purified from wild-type soybean (Glycine max [L.] Merr., cv Williams) and nr₁-mutant soybean plants. Purification included Blue Sepharose- and hydroxylapatite-column chromatography using acetone powders from fully expanded unifoliolate leaves as the enzyme source.

Two forms of constitutive nitrate reductase were sequentially eluted with NADPH and NADH from Blue Sepharose loaded with extract from wild-type plants grown on urea as sole nitrogen source. The form eluted with NADPH was designated c₁NR, and the form eluted with NADH was designated c₂NR. Nitrate-grown nr₁ mutant soybean plants yielded a NADH:nitrate reductase (designated iNR) when Blue Sepharose columns were eluted with NADH; NADPH failed to elute any NR form from Blue Sepharose loaded with this extract. Both c₁NR and c₂NR had similar pH optima of 6.5, sedimentation behavior (s_20,w of 5.5-6.0), and electrophoretic mobility. However, c₁NR was more active with NADPH than with NADH, while c₂NR preferred NADH as electron donor. Apparent Michaelis constants for nitrate were 5 millimolar (c₁NR) and 0.19 millimolar (c₂NR). The iNR from the mutant had a pH optimum of 7.5, s_20,w of 7.6, and was less mobile on polyacrylamide gels than c₁NR and c₂NR. The iNR preferred NADH over NADPH and had an apparent Michaelis constant of 0.13 millimolar for nitrate.

Thus, wild-type soybean contains two forms of constitutive nitrate reductase, both differing in their physical properties from nitrate reductases common in higher plants. The inducible nitrate reductase form present in soybeans, however, appears to be similar to most substrateinduced nitrate reductases found in higher plants.

     

Proton transport in isolated vacuoles from corn coleoptiles

Vacuoles were isolated from corn coleoptile protoplasts and ATP-dependent proton transport was measured by quinacrine fluorescence quenching or by the uptake of [¹⁴C]methylamine. Intact vacuoles were judged to be free of a surrounding plasma membrane based on fluorescent staining with fluoroscein-diacetate. Essentially all of the detectable ATP-stimulated methylamine uptake and α-mannosidase activities present in intact protoplasts were recovered in isolated vacuoles. In contrast, the activities of marker enzymes for plasma membranes, Golgi, endoplasmic reticulum, and mitochondria were reduced to 5 to 17% in vacuolar preparations. The characteristics of proton pumping by isolated vacuoles were compared to those of light microsomal membranes possibly derived from the tonoplast. ATP-dependent proton pumping by both isolated vacuoles and light microsomal vesicles was stimulated by Cl⁻, and inhibited by NO₃⁻, carbonyl cyanide-m-chlorophenylhydrazone, N,N′-dicyclohexylcarbodiimide, N-ethylmaleimide, 4,4′-diisothiocyano-2,2′-stilbene disulfonic acid, diethylstilbestrol, and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, but not by vanadate. Both activities also showed substrate specificity for Mg-ATP. Finally, proton transport activities of vacuolar and microsomal fractions exhibited similar profiles after flotation in linear dextran gradients. We conclude that the microsomal proton pump previously characterized in corn coleoptiles (Mettler et al. 1982 Plant Physiol 70: 1738-1742) is derived from the tonoplast.     

Acclimation Processes in the Light-Harvesting System of the Cyanobacterium Anacystis nidulans following a Light Shift from White to Red Light

Cyanobacteria acclimate to changes in light by adjusting the amounts of different cellular compounds, for example the light-harvesting macromolecular complex. Described are the acclimatization responses in the light-harvesting system of the cyanobacterium Anacystis nidulans following a shift from high intensity, white light to low intensity, red light.

The phycocyanin and chlorophyll content and the relative amount of the two linker peptides (33 and 30 kilodaltons) in the phycobilisome were studied. Both the phycocyanin and chlorophyll content per cell increased after the shift, although the phycocyanin increased relatively more. The increase in phycocyanin was biphasic in nature, a fast initial phase and a slower second phase, while the chlorophyll increase was completed in one phase. The phycocyanin and chlorophyll responses to red light were immediate and were completed within 30 and 80 hours for chlorophyll and phycocyanin, respectively. An immediate response was also seen for the two phycobilisome linker peptides. The amount of both of them increased after the shift, although the 33 kilodalton linker peptide increased faster than the 30 kilodalton linker peptide. The increase of the content of the two linker peptides stopped when the phycocyanin increase shifted from the first to the second phase. We believe that the first phase of phycocyanin increase was due mainly to an increase in the phycobilisome size while the second phase was caused only by an increase in the amount of phycobilisomes. The termination of chlorophyll accumulation, which indicates that no further reaction center chlorophyll antennae were formed, occurred parallel to the onset of the second phase of phycocyanin accumulation.

     

Physiological and isotopic aspects of photosynthesis in peperomia

Physiological and isotopic aspects of several Peperomia species were investigated. All but one species had C₃-like stomatal behavior, in that stomata were open during the day and closed during the night. In these species, most atmospheric CO₂ uptake occurred during the day. Concurrent with this stomatal behavior, there were Crassulacean acid metabolism-like acid fluctuations in most species. Carbon and hydrogen isotope ratios of cellulose nitrate from Peperomia reflect their physiological behavior. The δ¹³C values of cellulose nitrate from Peperomia species were similar to values observed in C₃ plants and consistent with the daytime uptake of exogeneous CO₂ via the C₃ photosynthetic pathway. The δD values of cellulose nitrate from Peperomia species approach those of Crassulacean acid metabolism plants. These elevated δD values are caused by fractionations occurring during biochemical reactions and not as a consequence of water relations.     

Changes in carbohydrate composition in wheat and pea seedlings induced by calcium deficiency

Wheat (Triticum aestivum L. cv Jubilar) seedlings were grown for 10 days in hydroponics with or without calcium. In the leaves, Ca deficiency caused the level of ethanol soluble carbohydrate to increase between 2-and 10-fold, enhanced dark respiration and decreased CO₂ fixation capacity. Sucrose was the major carbohydrate to accumulate in wheat roots.     

Hormonal Regulation of the Lectin Biosynthesis in Callus Culture of the Phaseolus vulgaris Plant

Callus cultures established from Phaseolus vulgaris seedlings were used to investigate hormonal influence on lectin biosynthesis. The plant tissue cultures were initiated using defined levels of both a cytokinin (kinetin) and an auxin (2,4-dichlorophenoxyacetic acid) and were then transferred to media containing different amounts of these hormones. The lectin content of each callus culture was determined using an enzyme immunoassay specific for the seed lectin of the P. vulgaris plant. The lectin biosynthesis was directly affected by the levels of auxin and cytokinin in the culture media and no lectin was detected in hormone-free medium. This enabled us to compose culture media yielding a maximal or minimal lectin content of the callus cultures, illustrating the ability to induce an enhancement or suppression of the in vitro lectin biosynthesis. The lectin level of callus tissue during the growth cycle of a culture was, furthermore, related to the cellular growth rate which might indicate an involvement of the lectin in cellular events during rapid cell division.