间作对植株生长及养分吸收和根际环境的影响

通过盆栽实验研究了线辣椒和玉米间作对其植株生长、矿质养分吸收、根际环境以及铁载体分泌的影响,以探索间作促进铁、磷等养分吸收利用的可能生理机制.结果表明:(1)与单作相比,间作线辣椒地上部干重降低23.0%,根系干重增加44.2%,玉米地上部和根系的干重分别增加8.7%和22.9%;间作线辣椒根冠比和根系活力分别显著提高86.4%和29.8%;间作线辣椒、玉米叶绿素含量分别显著提高12.6%和7.8%.(2)与单作相比,间作线辣椒的铁、锌、锰含量分别增加1.50倍、1.39倍和1.34%,而间作玉米则无显著变化;间作线辣椒和玉米的钙含量都显著低于相应单作,氮含量没有显著变化,但磷、钾含量显著增加.(3)间作线辣椒和玉米的根际土、非根际土的酸性磷酸酶活性及根系酸性磷酸酶活性都显著高于相应单作,而其根际土和非根际土的pH值无显著变化;间作玉米根系的铁载体分泌比单作减少32.8%,间作线辣椒根系的铁还原酶活性是单作的1.10倍.研究发现,线辣椒/玉米间作能通过影响根际生物学特征和化学过程提高植株的铁、锌、磷和钾养分水平,缓解养分胁迫,是一种很有推广价值的种植模式.     

The Bradyrhizobium japonicum fsrB gene is essential for utilization of structurally diverse ferric siderophores to fulfill its nutritional iron requirement

In Bradyrhizobium japonicum, iron uptake from ferric siderophores involves selective outer membrane proteins and non-selective periplasmic and cytoplasmic membrane components that accommodate numerous structurally diverse siderophores. Free iron traverses the cytoplasmic membrane through the ferrous (Fe²⁺) transporter system FeoAB, but the other non-selective components have not been described. Here, we identify fsrB as an iron-regulated gene required for growth on iron chelates of catecholate- and hydroxymate-type siderophores, but not on inorganic iron. Utilization of the non-physiological iron chelator EDDHA as an iron source was also dependent on fsrB. Uptake activities of ⁵⁵Fe³⁺ bound to ferrioxamine B, ferrichrome or enterobactin were severely diminished in the fsrB mutant compared with the wild type. Growth of the fsrB or feoB strains on ferrichrome were rescued with plasmid-borne E. coli fhuCDB ferrichrome transport genes, suggesting that FsrB activity occurs in the periplasm rather than the cytoplasm. Whole cells of an fsrB mutant are defective in ferric reductase activity. Both whole cells and spheroplasts catalyzed the demetallation of ferric siderophores that were defective in an fsrB mutant. Collectively, the data support a model whereby FsrB is required for reduction of iron and its dissociation from the siderophore in the periplasm, followed by transport of the ferrous ion into the cytoplasm by FeoAB.     

Dissolution of ferric phosphate by alfalfa (Medicago sativa L.) root exudates

Alfalfa (Medicago sativa L.) was grown in hydroponic culture to investigate adaptation to Fe-deficiency. Root exudates released into the nutrient solution from Fe-deficient plants were trapped and condensed on an amberlite XAD-4 resin column. The diethyl ether fraction of these exudates dissolved ferric phosphate remarkably. The dissolving capability was about 62 times higher than that of root exudates obtained from Fe-sufficient plants in complete nutrient solution. The Fe-dissolving compound was separated and identified. It was a new natural compound with molecular formula C₁₄H₁₀O₅ and was identified as 2-(3,5-dihydroxyphenyl)-5,6-dihydroxybenzofuran by means of mass spectrometry and ¹H-nuclear magnetic resonance. This new compound worked as a phytoalexin and inhibited completely the fungal growth of Fusarium oxysporum f. sp. phaseoli.     

Assignments of the paramagnetically shifted heme methyl nuclear magnetic resonance peaks of cyanometmyoglobin by selective deuteration

Three of the four paramagnetically shifted heme methyl nuclear magnetic resonance peaks of cyanometmyoglobin could be assigned by comparing the proton nuclear magnetic resonance spectra of myoglobins reconstituted from selectively deuterated hemes. These spectra indicate that the fourth methyl nuclear magnetic resonance peak has to be looked for outside the region ?9 to ?43 parts per million.     

Protective effect of capsinoid on lipid peroxidation in rat tissues induced by Fe-NTA

The activity of a single IP administration (15 or 30 mg/Kg body weight) of vanillyl nonanoate, a simplified analog of capsiate, on ferric nitrilotriacetate (Fe-NTA)-mediated oxidative damage was investigated. A sub-lethal dose of Fe-NTA (15 mg Fe/Kg body weight) was administered IP to rats; animals were sacrificed, and kidney and plasma were collected 1 h after injection. In response to the Fe-NTA administration, a reduction of the levels of total lipids, total unsaturated fatty acids and cholesterol was observed, accompanied by a rise in the concentrations of malondialdehyde (MDA), conjugated dienes fatty acids hydroperoxides and 7-ketocholesterol in plasma and kidney 1 h after administration. A pre-treatment with synthetic capsiate (SCPT) showed remarkable protective effect on the reduction of the levels of total lipids, total unsaturated fatty acids and cholesterol, and the cellular antioxidant vitamin E, inhibiting the increase of MDA, conjugated dienes fatty acids hydroperoxides and 7-ketocholesterol in the plasma and kidney. The protective effect of SCPT and two analogues (vanillyl alcohol and vanillin) during the linoleic acid and cholesterol oxidation was investigated in in vitro systems, providing evidence of definite structure-activity relationships.     

Crystal structure of the catalytic domain of MMP-16/MT3-MMP: characterization of MT-MMP specific features

Membrane-type matrix metalloproteinases (MT-MMPs) have attracted strong attention, because four of them can activate a key player in the tumor scenario, proMMP-2/progelatinase A. In addition to this indirect effect on the cellular environment, these MT-MMPs degrade extracellular matrix proteins, and their overproduction is associated with tumor growth. We have solved the structure of the catalytic domain (cd) of MT3-MMP/MMP-16 in complex with the hydroxamic acid inhibitor batimastat. CdMT3-MMP exhibits a classical MMP-fold with similarity to MT1-MMP. Nevertheless, it also shows unique properties such as a modified MT-specific loop and a closed S1' specificity pocket, which might help to design specific inhibitors. Some MT-MMP-specific features, derived from the crystal structures of MT-1-MMP determined previously and MT3-MMP, and revealed in recent mutagenesis experiments, explain the impaired interaction of the MT-MMPs with TIMP-1. Docking experiments with proMMP-2 show some exposed loops including the MT-loop of cdMT3-MMP involved in the interaction with the proMMP-2 prodomain in the activation encounter complex. This model might help to understand the experimentally proven importance of the MT-loop for the activation of proMMP-2.     

Effects of various inhibitors on in vivo reduction by Plantago lanceolata L. roots

Roots of Plantago lanceolata L. showed an iron stress-induced increase in the rates of electron transport to the extracytoplasmatic acceptors FeEDTA and ferricyanide. No significant changes in the reduction of hexachloroiridate were observed with respect to the iron-nutritional status of the plants. The reduction activity of iron-deficient roots was inhibited by the translation inhibitor cycloheximide (CHM) and the amino acid analog p-fluorophenylalanine (FPA). In both cases, the reduction of FeEDTA and ferricyanide was affected to a different extent, providing evidence for enzyme heterogeneity. Resupply of FeEDTA to iron-deficient plants resulted in a qualitatively similar pattern of decrease in FeEDTA and ferricyanide reduction rates, although a longer time period was required for the decrease of the redox activity by iron resupply compared to the effect of inhibitors of protein synthesis.Inhibitors of the plasma membrane (PM)-bound H⁺-ATPase decreased the FeEDTA reduction activity of iron-deficient plants. In contrast, the reduction of ferricyanide and hexachloroiridate was not inhibited. Oxidation of ferrocyanide occurs in both iron-deficient and iron-sufficient plants at comparable rates. The reaction was decreased by the H⁺-ATPase inhibitor orthovanadate.The results are interpreted in terms of a simultaneous action of distinct redox systems in iron-deficient roots. The role of proton extrusion in the regulation of iron stress-induced electron transport is discussed.     

Transfer cell formation in sugar beet roots induced by latent Fe deficiency

Leaves of Fe deficient sugar beets precultured in complete nutrient solution with Fe(III)EDTA remained green during the first 6 days of –Fe treatment when grown in a small nutrient solution volume (0.5 L/plant). After 3 days of –Fe treatment, roots placed in agar showed enhanced H⁺ release and ferric reduction at the tips of young laterals where short root hairs and transfer cells had developed. However, the H⁺ release was too weak to cause a pH decrease of the bulk nutrient solution. Nevertheless, the Fe stress response reactions probably lead to mobilization of Fe from the apoplasmic pool so that chlorosis development was prevented. Slight chlorosis symptoms appeared only after 4 more days of Fe deficiency and the pH of the bulk nutrient solution decreased to pH 4.5 simultaneously with renewed transfer cell formation and subsequent rapid regreening. In the 10 times higher volume of 5 L-Fe solution/plant, laterals with root hairs and transfer cells also showed localized acidification of the agar system. However, the protons released were so diluted that no pH decrease of the bulk solution was measurable. Instead, the leaves showed continuously increasing chlorosis with degenerated chloroplast ultrastructure. It is concluded that root hairs and transfer cells are not only formed under severe chlorosis but, instead, they seem to be an integral part of the adaptive response to latent Fe deficiency.     

Iron reductase systems on the plant plasma membrane—A review

Higher plant roots, leaf mesophyll tissue, protoplasts as well as green algae are able to reduce extra-cellular ferricyanide and ferric chelates. In roots of dicotyledonous and nongraminaceous, monocotyledonous plants, the rate of ferric reduction is increased by iron deficiency. This reduction is an obligatory prerequisite for iron uptake and is mediated by redox systems localized on the plasma membrane. Plasma membrane-bound iron reductase systems catalyze the transmembrane electron transport from cytosolic reduced pyridine nucleotides to extracellular iron compounds. Natural and synthetic ferric complexes can act as electron acceptors.This paper gives an overview about the present knowledge on iron reductase systems at the plant plasma membrane with special emphasis on biochemical characteristics and localisation.