Inhibition of Tyrosine Aminotransferase by β-N-Oxalyl-l-α,β-Diaminopropionic Acid, the Lathyrus sativus Neurotoxin

Abstract: Species differences in susceptibility are a unique feature associated with the neurotoxicity of β-N-oxalyl-l -α,β-diaminopropionic acid (l -ODAP), the Lathyrus sativus neurotoxin, and the excitotoxic mechanism proposed for its mechanism of toxicity does not account for this feature. The present study examines whether neurotoxicity of l -ODAP is the result of an interference in the metabolism of any amino acid and if it could form the basis to explain the species differences in susceptibility. Thus, Wistar rats and BALB/c (white) mice, which are normally resistant to l -ODAP, became susceptible to it following pretreatment with tyrosine (or phenylalanine), exhibiting typical neurotoxic symptoms. C57BL/6J (black) mice were, however, normally susceptible to l -ODAP without any pretreatment with tyrosine. Among the various enzymes associated with tyrosine metabolism examined, the activity of only tyrosine aminotransferase (TAT) was inhibited specifically by l -ODAP. The inhibition was noncompetitive with respect to tyrosine (K_i = 2.0 ± 0.1 mM) and uncompetitive with respect to α-ketoglutarate (K_i = 8.4 ± 1.5 mM). The inhibition of TAT was also reflected in a marked decrease in the rate of oxidation of tyrosine by liver slices, an increase in tyrosine levels of liver, and also a twofold increase in the dopa and dopamine contents of brain in l -ODAP-injected black mice. The dopa and dopamine contents in the brain of only l -ODAP-injected white mice did not show any change, whereas levels of these compounds were much higher in tyrosine-pretreated animals. Also, the radioactivity associated with tyrosine, dopa, and dopamine arising from [¹⁴C]tyrosine was twofold higher in both liver and brain of l -ODAP-treated black mice. Thus, a transient increase in tyrosine levels following the inhibition of hepatic TAT by l -ODAP and its increased availability for the enhanced synthesis of dopa and dopamine and other likely metabolites (toxic?) resulting therefrom could be the mechanism of neurotoxicity and may even underlie the species differences in susceptibility to this neurotoxin.     

山黧豆幼苗对干旱胁迫的生理响应

用PEG6000模拟干旱对山黧豆进行胁迫。结果发现，胁迫初期（0~48 h），突然的水分亏缺使气孔导度（Sc）和蒸腾速率（Tr）迅速下降，而净光合速率（Pn）和水分有效利用率（WUE）基本维持稳定。胁迫后期（48~108 h），上述四个光合指标均不同程度地向对照水平恢复；脯氨酸和相对电导率（REC）受胁迫强度影响较小，但与胁迫时间呈明显正相关，分别在48和60 h增幅最大，而且当REC上升至对照的50%左右时，脯氨酸含量已达对照的14倍之多。由此认为，山黧豆可能主要通过迅速减小Sc和Tr以及大量而急剧的积累脯氨酸来减轻干旱所造成的伤害。     

Pyramiding QTL for multiple lateral branching in cucumber using inbred backcross lines

Multiple lateral branching (MLB) is a quantitatively inherited trait associated with yield in cucumber (Cucumis sativus L.; 2n = 2x = 14). Although quantitative trait loci (QTL) have been identified for MLB and QTL-marker associations have been verified by marker-assisted selection, the individual effects of these QTL have not been characterized. To test the effects of pyramiding QTL for MLB, molecular genotyping was utilized to create two sets (standard- and little-leaf types) of inbred backcross (IBC) lines possessing various numbers of QTL that promote branching. These IBC lines were evaluated for lateral branch number in two Wisconsin environments at three plant densities. Highly significant differences in the number of primary lateral branches were detected between spacings, leaf types, and lines, but not between locations. Lateral branch number decreased at higher plant densities in all genotypes, while genotype by environment and QTL by environment interactions were marginally non-significant. As the number of QTL increased among IBC lines, the number of branches did not generally change in the little-leaf lines, but decreased in the standard-leaf lines, demonstrating an epistatic effect related to genetic background during lateral branch development. The genomic location with the greatest effect on MLB was confirmed as the QTL that was previously mapped near the little-leaf locus (ll), while the addition of one specific QTL consistently decreased the number of lateral branches in standard-leaf lines. Although pyramiding QTL for MLB did not uniformly increase the number of lateral branches, pyramiding QTL in IBC lines allowed further characterization of individual QTL involved in MLB. Our results, coupled with those of previous studies indicate that lateral branch development in cucumber is determined by growing environment (i.e., plant spacing), genetic background, and QTL composition.     

Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

Effects of Application Strategies of Fumigant and Nonfumigant Nematicides on Cantaloupe Grown in Deep Sand Soils in Florida

A 2-year study was conducted in which three treatment tactics of oxamyl (at planting application, application every 2 weeks, and rescue applications, as determined by crop symptoms) were compared to fumigant treatments with methyl bromide, 1,3-dichloropropene (1,3-D), and 1,3-D plus chloropicrin for management of Meloidogyne spp. In 2002, treatments that included 1,3-D produced higher yields as determined both by number and weight of marketable fruit. All treatment tactics relying solely on oxamyl, at planting, scheduled treatments, and rescue, were not different from untreated controls for both marketable yield and number of fruit. Gall ratings in 2002 were lowest for 1,3-D at the 112-liters/ha rate, followed by 1,3-D at 84 liters/ha with and without oxamyl. All treatments of oxamyl, except when combined with 1,3-D, had gall ratings not different from untreated plots. In 2004, treatments of methyl bromide and 1,3-D plus chloropicrin had the highest total number of both marketable fruit and highest marketable yields. All treatment strategies relying solely on oxamyl had yields equivalent to the untreated controls. Mean root-gall ratings were lowest for methyl bromide plus chloropicrin and 1,3-D plus chloropicrin treatments. Root-gall ratings for all treatment tactics relying solely on oxamyl were not different from untreated controls.     

Polymyxin B Enhances Formation of a New Pigment,a Peptide–Ferropyrimine Complex,in Serratia marcescens

We previously isolated a Serratia marcescens O5: HI Z-54 strain which produces a new reddish-violet pigment, a peptide- ferropyrimine complex. This study showed that polymyxin B enhances the formation of the pigment about threefold. This occurs because polymyxin B in the medium causes the formation of an iron-polymyxin B complex which imposes a low iron stress on the bacteria and, in turn, enhances pigment production. This shows that polymyxin B is both a membrane-disrupting and ionophoric antibiotic.     

Uptake and distribution of calcium, magnesium and potassium in cucumber of different age

Uptake and distribution of Ca⁺, Mg²⁺ and K²⁺ were investigated in plants of cucumber ( Cucumis sativus L. var. Cila) which had been cultivated for 12, 19, 32, or 53 days in complete nutrient solution with 1.0 m M Ca²⁺, 2.0 m M Mg²⁺ and 2.0 m M K⁺. The ⁺ concentration was about the same in roots and shoots, while the Ca²⁺ and Mg²⁺ concentrations were low in roots compared to shoots. The K⁺ concentration decreased with increasing leaf age, while the Ca²⁺ and Mg²⁺ concentrations increased, except in older plants with flowers and fruits, where an increased concentration was found in the youngest leaves. This is discussed in connection with increased indoleacetic acid (IAA) synthesis in the shoot. Excision of leaves at different levels from 21-day-old plants, followed by uptake for 24 h from the nutrient solution on days 22 and 23, resulted in no immediate reduction in Ca²⁺ (⁴⁵Ca) uptake. Transport of Ca²⁺ increased to leaves above and below the excision point and total Ca²⁺ uptake remained at the same level as for the intact plant. It is suggested that regulation of Ca²⁺ uptake is primarily achieved in the root while the distribution in the shoot is regulated by the accessability of negative binding sites.     

Phosphorus uptake and translocation in salt-stressed melon plants

Melon seedlings (Cucumis melo L. cv.Galia) were grown hydroponically to study the effect of salinity (80 mmol/LNaCl) on phosphate (Pi) uptake and translocation at two levels of Pi (25 μmol/L and 1 mmol/L). Net uptake rates of Pi were determined by depletionof the medium and by plant content. Salinity decreased Pi uptake at low Pi (high affinity uptake mechanism), 25 μmol/L, although no specific competitive inhibition of Pi uptake by Cl⁻ was observed. When plants were grown with high Pi (1 mmol/L), the uptake of Pi through the low affinity system was increased by 80 mmol/L NaCl. Salinity also reduced the phosphorus flux, as Pi, through the xylem. It is hypothesised that high levels of NaCl decrease the mobility of Pi stored in vacuoles, and as a result, inhibit export from this storage compartment to other parts of the plant.     

Effects of exogenous salicylic acid on manganese toxicity, element contents and antioxidative system in cucumber

The effects of salicylic acid (SA) on manganese (Mn) toxicity in cucumber plants (Cucumis sativus L.) were studied by investigating the symptoms, plant growth, lipid peroxidation, antioxidative enzymes and antioxidants. Excess Mn caused serious chlorosis and inhibited the growth of cucumber plants, and dramatically increased accumulation of Mn in both shoots and roots, furthermore, inhibited the absorption of Ca, Mg and Zn. Addition of SA decreased the transport of Mn from roots to shoots, alleviated the inhibition of Ca, Mg and Zn absorption induced by excess Mn, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in cucumber leaves exposed to excess Mn, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances (TBARS). Addition of SA significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes showed different changes, addition of SA inhibited catalase (CAT) and ascorbate peroxidase (APX) activities, while increased activities of superoxide dismutase (SOD), peroxidase (POD), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) in cucumber leaves exposed to excess Mn. As important antioxidants, ascorbate and glutathione contents in cucumber leaves exposed to excess Mn were significantly increased by SA treatment.     

Effect of temperature on the growth of individual cucumber fruits

In order to study the effect of temperature on the growth of individual fruits in cucumber (cucumis sativus L. cv. Corona), fruits were grown at 17. 5. 20,25 and 30°C continuously or the fruit temperature was changed from 17. 5 to 27.5°C or vice versa. Fruit development appeared to be closely related to the temperature sum. When the growth of a fruit was not constrained by assimilate supply, a decrease in growing period with increasing temperature was more than compensated for by a strong increase in growth rate, resulting in an increase in final fruit weight. However, when the growth of a fruit was constrained by assimilate supply, the increase in growth rate with increasing temperature was small and did not compensate for the decrease in growing period, resulting in a decrease in final fruit weight. Determinations of cell number and size showed that the effect of temperature on fruit growth was due to effects on cell expansion rather than on cell division. When growth was not constrained by assimilate supply. However, when assimilate supply did constrain fruit growth the number of cells per fruit decreased with increasing temperature, while the effect on cell size was negligible. In all stages of fruit development, the growth rate of a cucumber fruit responded within one day to a change in temperature. It was not irreversibly impaired by a low temperature (17. 5°C) during the early development of a fruit. A high temperature treatment (27. 5°C), however, had a great effect on the growth rate of a fruit after the temperature treatment had terminated. At all stages of fruit development (even before anthesis) a period of four days at 27. 5°C resulted in a pronounced stimulation of the growth rate afterwards at 17. 5°C.