Rapid recovery of photosynthetic cell suspension cultures following heterotrophic bleaching

Summary Seven suspension-cultured lines of five different species (Amaranthus powellii Datura innoxia, Glycine max, Gossypium hirsutum, andNicotiana tabacum × Nicotiana glutinosa fusion hybrid), which had been grown under photomixotrophic conditions, were placed under heterotrophic conditions (darkness and media with 3% sucrose or starch) where the chlorophyll levels declined to near zero. After three transfers over a 70-d period, the cells were placed back into photomixotrophic or photoautotrophic conditions where regreening occurred rapidly and continued growth was observed. This rapid adaptation to photosynthetic conditions contrasts with the original initiation process for these cultures, which required many months and an apparent selection since many of the original cells died. Thus, these seven photosynthetic cell suspension cultures appear to be different from the original cultures due possible to genetic or adaptive changes.     

Genetic and transgenic perturbations of carbon reserve production in Arabidopsis seeds reveal metabolic interactions of biochemical pathways

The biosynthesis of seed oil and starch both depend on the supply of carbon from the maternal plant. The biochemical interactions between these two pathways are not fully understood. In the Arabidopsis mutant shrunken seed 1 (sse1)/pex16, a reduced rate of fatty acid synthesis leads to starch accumulation. To further understand the metabolic impact of the decrease in oil synthesis, we compared soluble metabolites in sse1 and wild type (WT) seeds. Sugars, sugar phosphates, alcohols, pyruvate, and many other organic acids accumulated in sse1 seeds as a likely consequence of the reduced carbon demand for lipid synthesis. The enlarged pool size of hexose-P, the metabolites at the crossroad of sugar metabolism, glycolysis, and starch synthesis, was likely a direct cause of the increased flow into starch. Downstream of glycolysis, more carbon entered the TCA cycle as an alternative to the fatty acid pathway, causing the total amount of TCA cycle intermediates to rise while moving the steady state of the cycle away from fumarate. To convert the excess carbon metabolites into starch, we introduced the Escherichia coli starch synthetic enzyme ADP-glucose pyrophosphorylase (AGPase) into sse1 seeds. Expression of AGPase enhanced net starch biosynthesis in the mutant, resulting in starch levels that reached 37% of seed weight. However, further increases above this level were not achieved and most of the carbon intermediates remained high in comparison with the WT, indicating that additional mechanisms limit starch deposition in Arabidopsis seeds.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Expression of the Kidney Bean Phenylalanine-Ammonia Lyase Gene in the Hairy Roots of Astragalus sinicus

Using Agrobacterium rhizogenes, Astragalus sinicus plants were transformed with the kidney bean pal5 gene coding for phenylalanine-ammonia lyase (PAL). The hairy root culture thus obtained manifested enhanced PAL activity and lignin content in the cell walls; in addition, the transformed cells differed from the wild-type ones in several electrophysiological indices. In particular, the diffusion component of the total membrane potential of plasmalemma increased in the pal-transformed roots. The authors presume that the volume density of the protein-related negative charge of the cytoplasm increases in the transformed root cells along with changes in the cytoplasmic pH and pCa²⁺, the extent of coupling of these two indices, and the hydraulic conductivity of plasmodesmata.     

Turnover of Galactans and Other Cell Wall Polysaccharides during Development of Flax Plants

We investigated the synthesis and turnover of cell wall polysaccharides of the flax (Linum usitatissimum L.) plant during development of the phloem fibers. One-month-old flax plants were exposed to a 40-min pulse with 14CO2 followed by 8-h, 24-h, and 1-month periods of chase with ambient CO2, and radioactivity in cell wall sugars was determined in various plant parts. The relative radioactivity of glucose in noncellulosic polysaccharides was the highest compared with all other cell wall sugars immediately after the pulse and decreased substantially during the subsequent chase. The relative radioactivities of the other cell wall sugars changed with differing rates, indicating turnover of specific polysaccharides. Notably, after 1 month of chase there was a marked decrease in the proportional mass and total radioactivity in cell wall galactose, indicating a long-term turnover of the galactans enriched in the fiber-containing tissues. The ratio of radiolabeled xylose to arabinose also increased during the chase, indicating a turnover of arabinose-containing polymers and interconversion to xylose. The pattern of label redistribution differed between organs, indicating that the cell wall turnover processes are tissue- and cell-specific.     

Increased contribution of N-methyl-D-aspartate receptors to synaptic transmission inCA1 area of the rat hippocampus after short-term episodes of hypoxia/aglycemia

Effect of hypoxia/aglycemia episodes on excitatory postsynaptic currents (EPSC) evoked in pyramidal neurons of the rat hippocampalCA1 area by electrical stimulation of Schaffer collaterals was studied using voltage-clamp and intracellular perfusion techniques. By 60–80 min after a 10-min-long hypoxia/aglycemia episode, the EPSC amplitude increased and the EPSC decay was considerably slowed down, if compared with control. In contrast to control conditions, under which EPSC decay kinetics did not depend on the stimulus strength, hypoxia/aglycemia was followed by slowing down of the EPSC decay when stimulus intensity increased. The stimulus-dependent posthypoxic “slow” EPSC component was depressed both by D-(−)-2-amino-5-phosphonovaleric acid, an NMDA receptor blocker, and by 6-cyano-7-nitroquinoline-2,3-dion, a non-NMDA receptor blocker, which suggested possible polysynaptic origin of the above EPSC component. We suggest that short-term hypoxia/aglycemia transforms into an active state the NMDA receptors in the synapses of excitatory reccurrent collaterals of theCA1 hippocampal area, which had not functioned before. An increase in the intracellular calcium concentration from 1.5 to 5.0 mM resulted in the effect similar to that produced by hypoxia/aglycemia, which suggests that calcium channels play an important role in the mechanisms responsible for hypoxia-related activation of “silent” NMDA receptors.     

Modification of isoflavones in soybean seeds via expression of multiple phenolic biosynthetic genes

To modify the level and composition of isoflavones, the important bioactive constituents of soybean seeds, soybean was transformed via co-bombardment of embryogenic cultures with three DNA cassettes containing the CHS6-chalcone synthase and IFS2-isoflavone synthase genes, and a fragment of PAL5-phenylalanine ammonia-lyase gene, all in sense orientation under the lectin promoter mixed with the selectable marker gene, HPT (hygromycin phosphotransferase) under the 35S promoter. Four of six fertile lines produced integrated all four genes.Isoflavone levels were lower in T1 mature seeds of 5 of the 6 lines compared to the control. Transgene segregation was found in one selected line, with formation of additional sublines with different transgene composition found also in the homozygous plants. Decreased isoflavone concentrations (by about 70%) were found in T4 homozygous seeds of the two lines studied in detail here. The embryo axes accumulated most of the glycitein and contained a higher isoflavone concentration than the cotyledons. Expression of transgenes driven by the lectin promoter reduced the isoflavone concentration only in the cotyledons and not in embryo axes, indicating that this promoter is preferably active in cotyledons.     

Antioxidant-caused changes in the permeability of proton-gated ion channels for sodium and calcium

Using a patch-clamp technique in the whole-cell configuration, we studied the effect of an exogenous antioxidant, dithiothreitol (DTT), on transmembrane currents in isolated cells obtained from the rat spinal ganglia. We demonstrated that this antioxidant (DTT) is capable of modulating the proton-gated current. In most neurons, proton-gated currents increased in the presence of the antioxidant. Since proton-gated receptor-channel complexes of sensory neurons are involved in different processes of signalling and transmission of sensory information in the peripheral nervous system, we hypothesize that the influences mediated by alterations of the concentrations of antioxidants participate in the formation of the state of algesia under normal physiological conditions and of that of hyperalgesia in pathological states. In addition, oxidative stress, which causes a shift in the balance of concentrations of antioxidants, accompanies numerous abnormal pathophysiological states, in particular diabetes, ischemia, and inflammation. Since proton-gated channels are permeable for calcium ions, an antioxidant-induced increase in calcium signalling can be significantly important for a number of biochemical processes occurring in tissues. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 193–197, May–June, 2006.     

Stimulation of root development on buckwheat thin cell-layer explants by pectic fragments from pea stem cell walls

Buckwheat (Fagopyrum esculentum Moench.) thin cell-layers (TCLs) cultured individually in a liquid medium were used to test the root-inducing activity of pectic polysaccharides with a degree of polymerization (DP) of 20–25, isolated from pea (Pisum sativum L.) stem cell walls. These pectic fragments induced more rapid root formation on the explants in comparison with untreated controls. This pectic fragment treatment also promoted root growth as measured by both fresh and dry weights and about doubled the number of roots formed. This buckwheat TCL system is proposed as a new bioassay for oligosaccharins due to its sensitivity, reproducibility and ease of preparation.     

Porphyrin-proteinoid complexes as models of prebiotic photosensitizers

Photochemical activity as well as some spectral properties of various porphyrins and their model complexes with proteinoids were studied. Photochemical activity increased from the less advanced biosynthetic chlorophyll precursors to the more advanced compounds. The significant increase was detected as a result of the formation of complexes of phytol-containing porphyrins with proteinoids, which brings about the disaggregation of the pigment clusters formed in the aqueous environment. Hemin is photochemically inactive, either alone or in complex with proteinoid. Although hemoproteinoid was demonstrated to be able to catalyse photochemical electron transfer, its activity is about 20 times lower when compared with the chlorophyll a-proteinoid complex. Experimental results are discussed in context of the early evolution of photosynthesis.