MAPK和活性氧参与植物抗病防卫反应的信号转导

促分裂原活化蛋白激酶（MAPK）级联途径和活性氧参与调控植物过敏性细胞死亡。本文介绍促分裂原活化蛋白激酶级联途径在植物抗病防卫反应信号转导中的作用研究进展,并对活性氧积累与MAPK之间的关系作了分析。     

拟南芥金属蛋白酶FtSH4通过生长素与活性氧调控叶片衰老

植物金属蛋白酶Ft SH基因家族在拟南芥(Arabidopsis thaliana)中有12个成员,目前各基因的功能还不清楚。该文利用细胞生物学和遗传学方法初步分析了拟南芥FtSH4在叶片衰老中的功能。ftsh4-4突变体叶片中H_2O_2含量及细胞死亡率增加,叶绿素含量降低;此外,突变体中过氧化物酶基因表达上调,过氧化物酶活性增加,出现早衰表型。外源抗氧化剂As A、内源和外源生长素能够通过降低ftsh4-4体内H_2O_2含量、过氧化物酶基因的表达及过氧化物酶活性,恢复ftsh4-4叶片的衰老表型。ftsh4-4突变体中生长素响应因子基因ARF2和ARF7上调表达,外源生长素和抗氧化剂能够降低ARF2和ARF7的表达,并且ARF2突变能够降低ftsh4-4的H_2O_2含量并恢复其早衰表型。以上结果表明,FtSH4基因通过生长素与活性氧在调控植物叶片衰老中起重要作用。     

Correlation between Oxygen Availability, Energy Charge, and Protein Synthesis in Squash Cotyledons Isolated from Germinating Seeds

The influence of O₂ availability on the rate of protein synthesis, the levels of RNA and of adenylates, and the value of the energy charge in squash (Cucurbita maxima) cotyledons isolated from seeds germinated for 15 or 28 hours at different O₂ concentration (3% or 20% O₂) has been investigated.

The rate of protein synthesis is five times lower in cotyledons maintained in 3% O₂ than in those maintained in 20% O₂. Also net RNA synthesis is almost blocked in 3% O₂, while in 20% O₂ it proceeds almost linearly for 48 hours.

The different RNA contents cannot explain the different rates of protein synthesis.

The results of shift experiments (cotyledons shifted from 20% to 3% O₂ or vice versa) show that the rate of protein synthesis is strictly correlated with actual O₂ availability and is largely independent of the one in the previous period. O₂ controls the development of the adenylate pool and particularly the increase of ATP level. Thus, both the adenylate pool and the values of the energy charge ratio are lower in cotyledons grown in 3% than in 20% O₂.

The shifts of O₂ availability induce rapid changes of ATP, ADP, and AMP levels and thus of the values of the energy charge, which are about 0.7 at 3% O₂ and higher than 0.8 at 20% O₂, independent of previous O₂ availability.

The rate of protein synthesis appears to be largely independent of the levels of the single nucleotides and better correlated to the energy charge values.

     

Growth Capacity of Embryo Axes Excised from Dormant and Germinating Horse Chestnut Seeds and Their Response to Exogenous Abscisic Acid

In embryo axes excised from mature horse chestnut (Aesculus hippocastanum L.) seeds, both freshly-fallen and subjected to cold stratification, the ability for growth was studied. While excised axes were kept on water at 28°C for 3 days, their fresh weight and length increased, the polypeptide composition of soluble proteins changed, the content of some heat-stable polypeptides decreased, and the capacity for protein synthesis in vivo retained. All these processes were similar to those in the axes of intact seeds during stratification until radicle protrusion. Growth of excised axes accelerated with the increasing duration of stratification. Cycloheximide (50 mg/l) and -amanitin (7 mg/l) inhibited axis growth, but an inhibitor of ABA synthesis fluridone (5 mg/l) and a natural cytokinin dihydrozeatin (10^–5 M) did not influence the growth rate. The growth capacity of axes excised from dormant and germinating horse chestnut seeds indicates the absence of dormancy in the axes of mature seeds. ABA (10^–5 M) suppressed completely the growth of axes detached from seeds experiencing cold stratification but still not germinating, although protein synthesis was not inhibited. The axes excised from the seeds after radicle emergence were insensitive to ABA and grew actively in its presence. ABA-induced growth inhibition might be related to the suppressed synthesis of minor polypeptides required for growth or to the activated synthesis of some growth-retarding proteins. The conclusion was drawn that the excised axes could be used as a model for studying the processes preceding visible germination of recalcitrant seeds.     

一氧化氮对渗透胁迫下小麦种子萌发及其活性氧代谢的影响

一氧化氮供体硝普钠(Sodium nitroprusside,SNP)能明显地促进渗透胁迫下小麦(Triticum aestivum L.)种子萌发、胚根和胚芽伸长,提高萌发过程中淀粉酶和内肽酶的活力,加速贮藏物质的降解：胁迫解除后,仍能使种子维持较高的活力。此外,SNP还能显著诱导渗透胁迫下CAT、APX活力的上升和脯氨酸含量积累,抑制LOX活力,从而提高渗透胁迫下小麦种子萌发过程中抗氧化能力。进一步研究还发现,SNP诱导切胚半粒小麦种子萌发早期(6h)的淀粉酶活力上升可能与GA3无直接关系。     

一氧化氮对渗透胁迫下小麦种子萌发及其活性氧代谢的影响

一氧化氮供体硝普钠(Sodium nitroprusside,SNP)能明显地促进渗透胁迫下小麦(Triticum aestivum L.)种子萌发、胚根和胚芽伸长,提高萌发过程中淀粉酶和内肽酶的活力,加速贮藏物质的降解;胁迫解除后,仍能使种子维持较高的活力.此外,SNP还能显著诱导渗透胁迫下CAT、APX活力的上升和脯氨酸含量积累,抑制LOX活力,从而提高渗透胁迫下小麦种子萌发过程中抗氧化能力.进一步研究还发现,SNP诱导切胚半粒小麦种子萌发早期(6h)的淀粉酶活力上升可能与GA3无直接关系.     

Interactions between Abscisic Acid, Gibberellins and Cytokinins in Grand Rapids Lettuce Seeds Germination

Experiments with Grand Rapids lettuce seeds (Lactuca sativa L.) maintained in darkness or irradiated with red light have shown that the inhibition of germination induced by low concentrations of ABA (2, 4, 6 μM) could be overcome by gibberellins (GA₃ or GA₄). The same results were obtained, although to a lesser extent, under the influence of two out of the four cytokinins tested (K and BAP) for seeds maintained in darkness. To suppress the block induced by higher concentrations of ABA (for example 8 μM), it was necessary to apply a cytokinin (K, BAP, Z or 2iP) and a gibberellin (GA₄ or GA₃) simultaneously, or a cytokinin following a red light treatment. Experiments conducted in darkness in which ABA (8 μM) was applied together with a cytokinin (BAP) and a gibberellin (GA₄) showed that the gibberellin and the cytokinin played similar roles towards each other and towards ABA.     

Exogenous Abscisic Acid Modulates Reactive Oxygen Metabolism and Related Gene Expression in Platycladus orientalis under H2O2-Induced Stress

Russian Journal of Plant Physiology - Abscisic acid (ABA) is a plant hormone that regulates tolerance to abiotic stress. In this study, we evaluated the effect of exogenous different concentrations...     

Interplay Between Abscisic Acid and Jasmonic Acid and its Role in Water-oxidative Stress in Wild-type, ABA-deficient, JA-deficient, and Ascorbate-deficient Arabidopsis Plants

The interplay between jasmonic acid (JA) and abscisic acid (ABA) in plant responses to water stress and in water-stress-enhanced oxidative stress was investigated in Arabidopsis thaliana plants subjected to water stress by water deprivation. For this purpose a drought assay was conducted using Arabidopsis mutants impaired in ABA (aba2), JA (aos), and ascorbate (vtc1) biosynthesis. Our results show an interaction between ABA and JA during their biosynthesis. Moreover, the coordinated action of ABA and JA protected wild-type, aba2, and aos plants from the effects of stress. However, this effect was not observed in the vtc1 mutant, which showed a distinct decrease in the F _v/F _m ratio, concomitant with a marked fall in relative water content (RWC), despite high endogenous concentrations of JA and ABA. This finding indicates the relevance of ascorbate metabolism in plant acclimation to stress. Despite the interaction between the two phytohormones, drought-associated stomatal closure is regulated mainly by ABA and weakly by JA, whereas JA plays a role in the formation of antioxidants regulating ascorbate and glutathione metabolism. A time course analysis revealed the relevance of plant age and stress duration in the responses of the mutants compared to wild-type plants. Here we discuss the relationship between ABA, JA, ascorbate, and glutathione in plants under water stress.     

Crosstalk between Nitrite,Myoglobin and Reactive Oxygen Species to Regulate Vasodilation under Hypoxia

The systemic response to decreasing oxygen levels is hypoxic vasodilation. While this mechanism has been known for more than a century, the underlying cellular events have remained incompletely understood. Nitrite signaling is critically involved in vessel relaxation under hypoxia. This can be attributed to the presence of myoglobin in the vessel wall together with other potential nitrite reductases, which generate nitric oxide, one of the most potent vasodilatory signaling molecules. Questions remain relating to the precise concentration of nitrite and the exact dose-response relations between nitrite and myoglobin under hypoxia. It is furthermore unclear whether regulatory mechanisms exist which balance this interaction. Nitrite tissue levels were similar across all species investigated. We then investigated the exact fractional myoglobin desaturation in an ex vivo approach when gassing with 1% oxygen. Within a short time frame myoglobin desaturated to 58±12%. Given that myoglobin significantly contributes to nitrite reduction under hypoxia, dose-response experiments using physiological to pharmacological nitrite concentrations were conducted. Along all concentrations, abrogation of myoglobin in mice impaired vasodilation. As reactive oxygen species may counteract the vasodilatory response, we used superoxide dismutase and its mimic tempol as well as catalase and ebselen to reduce the levels of reactive oxygen species during hypoxic vasodilation. Incubation of tempol in conjunction with catalase alone and catalase/ebselen increased the vasodilatory response to nitrite. Our study shows that modest hypoxia leads to a significant nitrite-dependent vessel relaxation. This requires the presence of vascular myoglobin for both physiological and pharmacological nitrite levels. Reactive oxygen species, in turn, modulate this vasodilation response.