Polyamine oxidase from water hyacinth: purification and properties

Polyamine oxidase was purified to homogeneity from leaves of water hyacinth by the criterion of sodium dodecyl sulfate gel electrophoresis (SDS disc PAGE). The enzyme showed a high specificity for spermidine and spermine (K_m values 28 micromolar and 20 micromolar, respectively). The optimal pH of the enzyme for both spermidine and spermine was 6.5. The molecular weight of the enzyme estimated by Sephadex G-200 gel filtration was 87,000, while SDS disc PAGE gave a single band at the molecular weight of 60,000. Octamethylenediamine and quinacrine were strong inhibitors of the enzyme, but p-chloromercuribenzoate was without effect. A prosthetic group in the enzyme was identified as flavin adenine dinucleotide.     

Salinity stress induced tissue-specific proteins in barley seedlings

Protein changes induced by salinity stress were investigated in two barley cultivars, California Mariout, a salt-tolerant variety and Prato, a salt-sensitive variety. Rapidly growing young barley seedlings were exposed to NaCl and the newly synthesized proteins were resolved on two dimensional polyacrylamide gels following isoelectric focusing or nonequilibrium pH gradient gel electrophoresis in the first dimension. Salinity induces distinct protein changes in root and shoot tissues. In roots, the salinity effects are identical in both cultivars. First, salinity modulates the synthesis of two different sets of proteins, one of which is elevated, and the other, depressed. Second, six new proteins are induced all of which are low in molecular weight, 24 to 27 kilodaltons, with an isoelectric point range of 6.1 to 7.6. In contrast to roots, salinity induces cultivar-specific shoot proteins. Five new shoot proteins are induced whose molecular weights and isoelectric points fall within the range of 20 to 24 kilodaltons and 6.3 to 7.2, respectively. Three of the newly induced proteins are unique to Prato. In addition, salinity inhibits the synthesis of a majority of shoot proteins. The new proteins produced in roots and shoots are unique to each tissue and their induction is apparently regulated coordinately during salinity stress.     

Light and acetate regulate a mitochondrial malate dehydrogenase

A malate dehydrogenase was purified from the unicellular green alga Chlorogonium elongatum Dangeard. The enzyme was localized in the mitochondria by immunogold electron microscopy and was found to be present on the cristae. The concentration of the enzyme is regulated by acetate and light. In cells cultured heterotrophically with acetate as carbon source the activity and the concentration of the enzyme is 5- to 6-fold higher than in autotrophic cells. In mixotrophically cultured cells (light and acetate) the enzyme level attains only half of the value of that in heterotrophic cells. Acetate induces an increase of the enzyme concentration while light has an inhibitory effect on this process.     

Tissue specificity of tobacco peroxidase isozymes and their induction by wounding and tobacco mosaic virus infection

Peroxidases (EC 1.11.1.7) have been implicated in the responses of plants to physical stress and to pathogens, as well as in a variety of cellular processes including cell wall biosynthesis. Tissue samples from leaf, root, pith, and callus of Nicotiana tabacum were assayed for specific peroxidase isozymes by analytical isoelectric focusing. Each tissue type was found to exhibit a unique isozyme fingerprint. Root tissue expressed all of the detectable peroxidase isozymes in the tobacco plant, whereas each of the other tissues examined expressed a different subset of these isozymes. In an effort to determine which peroxidase isozymes from Nicotiana tabacum are involved in cell wall biosynthesis or other normal cellular functions and which respond to stress, plants were subjected to either wounding or infection with tobacco mosaic virus. Wounding the plant triggered the expression of several cationic isozymes in the leaf and both cationic and anionic isozymes in pith tissue. Maximum enzyme activity was detected at 72 hours after wounding, and cycloheximide treatment prevented this induction. Infection of tobacco with tobacco mosaic virus induced two moderately anionic isozymes in the leaves in which virus was applied and also systemically induced in leaves which were not inoculated with virus.     

Influence of leaf age on photosynthesis, enzyme activity, and metabolite levels in wheat

The rate of photosynthesis under high light (1000 micromole quanta per square meter per second) and at 25°C was measured during development of the third leaf on wheat plants and compared with the activity of several photosynthetic enzymes and the level of metabolites. The rate of photosynthesis reached a maximum the 7th day after leaf emergence and declined thereafter. There was a high and significant correlation between the rate of photosynthesis per leaf area and the activities of the enzymes ribulose 5-phosphate kinase (r = 0.91), ribulose 1,5-bisphosphate (RuBP) carboxylase (r = 0.94), 3-phosphoglycerate (PGA) kinase (r = 0.82), and fructose 1,6-bisphosphatase (r = 0.80) per leaf area. There was not a significant correlation of photosynthesis rate with chlorophyll content. The rate of photosynthesis was strongly correlated with the level of PGA (r = 0.85) and inversely correlated with the level of triose phosphate (dihydroxyacetone phosphate and glyceraldehyde 3-phosphate) (r = 0.92). RuBP levels did not change much during leaf development; therefore photosynthesis rate was not correlated with the level of RuBP. The rate of photosynthesis was at a maximum when the ratio of PGA/triose phosphate was high, and when the ratio of RuBP/PGA was low. Although several enzymes change in parallel with leaf development, the metabolite changes suggest the greatest degree of control may be through RuBP carboxylase. The sucrose content of the leaf was highest under high rates of photosynthesis. There was no evidence that later in leaf development, photosynthesis (measured under high light and at 25°C) was limited by utilization of photosynthate.