Fe^2＋诱发谷粒颖壳中乙烯释放和促进水稻幼苗生长的关系

Ｆｅ２＋ 可诱发水稻（Ｏｒｙｚａ ｓａｔｉｖａ Ｌ．）谷粒颖壳中释放大量乙烯,诱导反应是一个非酶促的化学过程。可能在谷粒颖壳中存在一种非气态的乙烯前体,在Ｆｅ２＋ 的作用下可转化为气态乙烯。Ｆｅ２＋ 促进水稻幼苗的生长可能是通过其诱导乙烯所引起的。因为Ｆｅ２＋ 诱发颖壳中的乙烯释放和它促进幼苗生长在时间上正好同步,当第一次处理后再更新Ｆｅ２＋ 溶液时,不再能诱发乙烯释放,也不再促进幼苗生长;Ｆｅ２＋ 不能刺激萌发糙米的乙烯产生,也不促进其幼苗生长     

渗透胁迫下稻苗中铁催化的膜脂过氧化作用

在－０．７ＭＰａ渗透胁迫下,水稻幼苗体内和Ｈ２Ｏ２大量产生,Ｆｅ２＋积累,膜脂过氧化作用加剧。水稻幼苗体内Ｆｅ２＋含量与膜脂过氧化产物ＭＤＡ含量呈极显著的正相关。外源Ｆｅ２＋、Ｆｅ３＋、Ｈ２Ｏ２、Ｆｅ２＋＋Ｈ２Ｏ２、ＤＤＴＣ均能刺激膜脂过氧化作用,而铁离子的螯合剂ＤＴＰＡ则有缓解作用。ＯＨ的清除剂苯甲酸钠和甘露醇能明显地抑制渗透胁迫下Ｆｅ２＋催化的膜脂过氧化作用。这都表明渗透胁迫下水稻幼苗体内铁诱导的膜脂过氧化作用主要是由于其催化Ｆｅｎｔｏｎ型Ｈａｂｅｒ－Ｗｅｉｓｓ反应形成ＯＨ所致。     

渗透胁迫下稻苗中铁催化的膜脂过氧化作

在－０．７ＭＰａ渗透胁迫下,水和思苗体内Ｏ２↑－．和Ｈ２Ｏ２大量产生,Ｆｅ＾２＋含量与膜脂过氧化产物ＭＤＡ含量呈极显著的正相关。外源Ｆｅ＾２＋、Ｆｅ＾３＋、Ｈ２Ｏ２、Ｆｅ＾２＋＋Ｈ２Ｏ２、ＤＤＴＣ均能刺激膜脂过氧化作用,而铁离子的螯合剂ＤＴＰＡ则有缓解作用。ＯＨ的清除剂苯甲酸钠和甘露醇能明显地抑制渗透胁迫下Ｆｅ＾２＋催化的膜脂过氧化作用。这都表明渗透胁迫下水稻幼苗体内铁诱导的膜脂过氧化作用主要是由     

亚铁离子对水稻萌发后幼苗生长的促进作用

本文最新报道亚铁离子在远高于营养浓度的情况下（０．４４－７．１６ｍｍｏｌ／Ｌ）能显著促进水稻萌发后的幼苗生长,其效果与已报道的促进因子Ｃ２Ｈ４相当．在试验的１９种不同化合物中,发现只有ＦｅＳＯ４对萌发后水稻幼苗生长有显著的促进作用,并证明其有效成分为Ｆｅ（２＋）．这种促进作用在淹水的厌氧条件下和通气条件均能发生,但通气条件下促进程度稍低．水稻不同基因型对Ｆｅ（２＋）的反应无明显差异,可能这种促进作用是水稻适应水田厌氧环境的方式之一．高浓度乙烯（５０—１００ｐｐｍ）的促进作用与亚铁离子的效果相近．这一发现有助于提高水稻在淹水厌氧直播时的出苗率．－－ｓｉｇｎｉｆｉｃａｎｔａｔｌ％ｌｅｖｅｌ;＊－－ｓｉｇｎｉｆｉｃａｎｔａｔ５％ｌｅｖｅｌ;ｕｓ－－ｎｏｔｓｉｇｎｉｆｉｃａｎｔ．２．３ＥｆｆｅｃｔｏｆｖａｒｉｏｕｓＦｅ＋＋ｃｏｎｃｅｎｔｒａｈｏｎｓｏｎｔｈｅｓｅｅｄｌｉｎｇｇｒｏｗｔｈｏｆｒｉｃｅＴｗｏｇｅｎｏｔｙｐｅｓ,ｍｏｄｅｒｎＩＲ５０ａｎｄｔｒａｄｉｔｉｏｎａｌＡＳＤＩ,ｗｅｒｅｕｓｅｄｆｏｒｆｕｒｔｈｅｒｓｔｕｄｙ．Ｆｅ＋＋ｗｉｔｈｃｏｎｃｅｎｔｒａｔｉｏｎｓｆｒｏｍ０．４４ｔｏ７．１６ｍｍｏｌ／Ｌｗ     

豌豆Sparkle及其单基因突变体E107的铁锰吸收及转移效率

用豌豆Ｓｐａｒｋｌｅ及其单基因突变体Ｅ１０７进行的水培的试验表明,－Ｆｅ和＋Ｆｅ处理的Ｅ１０７幼苗以及－Ｆｅ处理的Ｓｐａｒｋｌｅ幼苗均表现出根系Ｈ＋分泌量大、根系Ｆｅ（Ⅲ）还原力强等特点,其中尤以＋Ｆｅ处理的Ｅ１０７最为突出;而十Ｆｅ处理的Ｓｐａｒｋｌｅ则无以上特点。与Ｓｐａｒｋｌｅ相比,Ｅ１０７各处理的地上部Ｆｅ、Ｍｎ合量均很高,但根部含量则相反。与Ｓｐｅｋｌｅ相比,Ｅ１０７—Ｆｅ处理表现为Ｆｅ高效,即使在＋Ｆｅ处理下,Ｅ１０７仍表现出－Ｆｅ条件下的根系生理特性,活化并还原了根际大量Ｆｅ（Ⅲ）和Ｍｎ,因而它对Ｆｅ、Ｍｎ具有较高的吸收效率,但是这些元素并不在根系中贮存,而是源源不断地运输到地上部,并在叶片中累积乃至使叶片中毒坏死,充分表现了Ｅ１０７单基因突变体对Ｆｅ、Ｍｎ也具有较高的转移效率。     

根表铁氧化物胶膜对水稻吸收Zn的影响

采用营养液培养方法研究了水稻根表形成的铁氧化物胶膜对水稻吸收Ｚｎ的影响．结果表明,在有Ｆｅ２＋的嫌气环境中,由于根际氧化作用水稻根表会形成红色的铁氧化物胶膜,根表的铁氧化物胶膜影响水稻对Ｚｎ的吸收．铁膜数量较少时,由于对Ｚｎ的富集作用有限,其对水稻Ｚｎ的吸收虽有促进作用,但不明显．随着根表铁膜数量的增加,这种促进作用也相应增加,并且在铁膜数量增加到一定值时,对水稻吸收Ｚｎ的促进作用达到最大．而后,随着铁膜数量的进一步增加,铁膜反而阻碍水稻对Ｚｎ的吸收,成为水稻吸收Ｚｎ的障碍层．在此过程中,水稻的根分泌物,特别是其中的植物铁载体对覆有铁膜水稻根系吸收Ｚｎ有促进作用．这种促进作用随铁膜数量的增加而逐渐减弱．因此,根表铁氧化物胶膜对水稻吸收Ｚｎ并不总是起促进作用,其作用的方向和程度取决于铁膜的数量．     

辐射及活性氧对DNA的损伤以及芥子碱的保护作用

在Ｘ射线照射下,小牛胸腺ＤＮＡ的碱基损伤及链断裂随着剂量升高而增加,其损伤主要集中于链断裂;活性氧可以引起ＤＮＡ损伤,Ｈ２Ｏ２仅造成少量伤害,当在含有Ｈ２Ｏ２的体系中加入微量的Ｃｕ＾２＋、Ｆｅ＾２＋时损伤急剧增加,这是由反应产生的．ＯＨ所致,Ｃｕ＾２＋的致损伤效果明显高于Ｆｅ＾２＋。ＯＨ清除剂芥子碱具有很强的抗辐射及抗氧化作用,且对ＤＮＡ无伤害。这说明ＯＨ在ＤＮＡ的氧化损伤中起重要作用。     

紫罗兰离体叶冷处理后转暖期乙烯和ACC的产生及CO_2的作用

火焰紫罗兰离体叶片在0℃下产生的伤害乙烯,只有当叶片从0℃移到20℃时才释放出来,释放高峰在转暖后四小时。低温直接刺激叶片ACC的合成。这两者的变化与叶片受冷伤害的程度相关。CO_2匮乏抑制冷伤害乙烯释放和ACC形成,这种抑制解除后,此过程又可恢复,照光不影响这种抑制。     

光谱技术研究固氮酶铁硫簇的理化特性

Ｎ－甲基甲酰胺碱度是提取高质量固氮酶铁钼辅基的关键因素之一。过量的亚甲蓝能氧化并分解铁钼铺基为含双钼铁硫簇［Ｍｏ２Ｆｅ＾２＋Ｆｅ５＾３＋Ｓ６］＾－和铁硫簇（［Ｆｅ＾２＋Ｆｅ５＾３＋Ｓ６］＾－。固氮酶铁钼铺基和［Ｍｏ２Ｆｅ＾２＋Ｆｅ５＾３＋Ｓ６］＾－在紫外可见光谱区中均无特征吸收峰,而［Ｆｅ＾２＋Ｆｅ５＾３＋Ｓ６］＾－在３２０ｎｍ处却呈弱吸收峰。棕色固氮菌固氮酶和该菌的突变菌株ＵＷ４５固氮酶（缺铁钼     

脂肪酸对盐胁迫大麦幼苗液泡膜微囊膜脂组分及功能的影响

用１００ｍｍｏｌ／ＬＮａＣｌ处理大麦（ＨｏｒｄｅｕｍｖｕｌｇａｒｅＬ．）幼苗２ｄ,根系液泡膜微囊膜脂不饱和度上升,并不随外源脂肪酸的饱和度而改变。外源硬脂酸和亚油酸降低大麦幼苗对Ｎａ＋的吸收及其向地上部的运输,增加Ｋ＋的吸收和向地上部的运输,降低根系的电解质渗漏率。增加液泡膜磷脂、糖脂结合半乳糖含量及Ｈ＋ＡＴＰａｓｅ和Ｈ＋ＰＰａｓｅ（焦磷酸酶）活性,与它们调节大麦对离子的吸收、分配的结果相一致,硬脂酸和亚油酸均有一定程度的缓解盐害的效应,亚油酸的效应大于硬脂酸     

Iron toxicity and stress-induced ethylene production in rice leaves

The relationship among iron toxicity, bronzing symptom, and stress-induced ethylene production (SEP) was investigated in detached rice (Oryza sativa L.) leaves during the vegetative-ripening stage and in whole plants during the vegetative stage. When Fe²⁺ (200 mg L^-1) was applied to the detached leaf through a transpiration stream, SEP was higher in the first leaf than in the second and third leaves from the top and maximal around the panicle primordia initiation stage. The genotype difference in SEP was more pronounced in the second and third leaves than in the first leaf. Bronzing intensity increased as SEP increased; iron concentration increase during treatment in the tissue did not correlate with bronzing intensity or with SEP among the 16 genotypes tested. When the roots of an intact plant were exposed to 300 mg L^-1 of Fe²⁺ in culture solution little stress-induced ethylene was produced. By partially or totally derooting the plant, however, stress-induced ethylene was evoked, indicating that roots reduced the Fe²⁺ uptake so that little stress ethylene is produced in the intact plant. Leaf tissue tolerance for Fe²⁺ may contribute to genotype differences in iron toxicity tolerance of rice plants when roots are injured during transplanting or exposed to toxic substances in the soil.     

Micronutrient status of the rice plant

Summary Soil solution Zn, Cu, Mn and Fe concentrations which were monitored throughout the growing season were found to be representative for flooded rice culture. Plant Zn, Cu, Mn and Fe contents of top, middle and bottom leaves as well as whole plants were also measured periodically throughout the growing season. These data were found to be within reported ranges for rice plants grown on flooded soils. Simple regression analyses were performed between plant micronutrient contents for each plant part sampled and the corresponding soil solution values. Results showed that the most promising portions of the rice plant to sample for accurate assessment of plant response to changes in soil solution micronutrient concentration as a function of time are as follows: (a) for Zn, bottom leaf; (b) for Cu, top or bottom leaf, whole plant; (c) for Mn, top leaf and (d) for Fe, bottom leaf or whole plant. re]19750915     

Maintaining elevated Fe2+ concentration in solution culture for the development of a rapid and repeatable screening technique for iron toxicity tolerance in rice (Oryza sativa L.)

Background and aims

Iron toxicity decreases rice (Oryza sativa) grain yield especially in acid soils after flooding. Our aim was to establish a high-throughput screening technique using nutrient solution culture for identifying Fe-toxicity-tolerant genotypes.

Methods

Varying levels of Fe, pH, and chelators in Yoshida nutrient solution culture were tested to maintain sufficient Fe²⁺ concentration over time to optimize the severity of Fe toxicity stress for distinguishing between a tolerant (Azucena) and sensitive (IR64) genotype. The optimized solution was tested on 20 diverse genotypes in the greenhouse, with measurement of leaf bronzing scores and plant growth characteristics at the seedling stage. The same 20 genotypes were grown to maturity in a field with natural Fe toxicity stress, with measurement of seedling-stage leaf bronzing scores and grain yield to determine their inter-relationship.

Results

Optimized nutrient solution conditions were 300 mg L^?1 Fe supplied as Fe²⁺ at pH 4.0 with a 1:2 molar ratio of Fe:EDTA, which maintained sufficient Fe²⁺ stress over 5 days. The highest correlation of nutrient solution phenotypic data with field grain yield was found with leaf bronzing scores at 4 weeks, with a Pearson r of 0.628 for simple association and a Spearman corrected r of 0.610 for rank association (P?<?0.01) using 20 diverse rice genotypes with proven Fe toxicity tolerance reaction. The Leaf bronzing scores at 4 weeks in nutrient culture solution were also found highly correlated with LBS under natural field stress after 8 weeks that had highest correlation with grain yield under stress.

Conclusion

This culture solution-based standardized screening technique can be used in plant breeding programs as a high-throughput technique to identify genotypes tolerant to Fe toxicity.     

Hydraulic and Chemical Responses of Citrus Seedlings to Drought and Osmotic Stress

In this work we investigated the function of abscisic acid (ABA) as a long-distance chemical signal communicating water shortage from the root to the shoot in citrus plants. Experiments indicated that stomatal conductance, transpiration rates, and leaf water potential decline progressively with drought. ABA content in roots, leaves, and xylem sap was also increased by the drought stress treatment three- to sevenfold. The addition of norflurazon, an inhibitor of ABA biosynthesis, significantly decreased the intensity of the responses and reduced ABA content in roots and xylem fluid, but not in leaves. Polyethylene glycol (PEG)-induced osmotic stress caused similar effects and, in general, was counteracted only by norflurazon at the lowest concentration (10%). Partial defoliation was able to diminish only leaf ABA content (22.5%) at the highest PEG concentration (30%), probably through a reduction of the active sites of biosynthesis. At least under moderate drought (3–6 days without irrigation), mechanisms other than leaf ABA concentration were required to explain stomatal closure in response to limited soil water supply. Measurements of xylem sap pH revealed a progressive alkalinization through the drought condition (6.4 vs. 7.1), that was not counteracted with the addition of norflurazon. Moreover, in vitro treatment of detached leaves with buffers iso-osmotically adjusted at pH 7.1 significantly decreased stomatal conductance (more than 30%) as much as 70% when supplemented with ABA. Taken together, our results suggest that increased pH generated in drought-stressed roots is transmitted by the xylem sap to the leaves, triggering reductions in shoot water loss. The parallel rise in ABA concentration may act synergistically with pH alkalinization in xylem sap, with an initial response generated from the roots and further promotion by the stressed leaves.     

Do Polyamines Participate in the Long-Distance Translocation of Stress Signals in Plants?

Accumulation and ethylene-dependent translocation of free polyamines was studied in various organs, the phloem and xylem exudates of common ice plants (Mesembryanthemum crystallinum L.). Under normal conditions (23–25°C), spermidine predominated among polyamines. Cadaverine was found in old leaves, stems, and, in large quantities, in roots. The heat shock treatment (HS; 47°C, 2 h) of intact plant shoots induced intense evolution of ethylene from leaves but reduced the leaf content of polyamines. Under these conditions, the concentration of polyamines in roots, particularly of cadaverine, increased many times. The HS treatment of roots (40°C, 2 h) induced translocation of cadaverine to stems and putrescine to leaves. An enhanced polyamine content after HS treatment was also found in the xylem and phloem exudates. The exposure of detached leaves to ethylene led to a reduction in their putrescine and spermidine and accumulation of cadaverine, which implies the ethylene-dependent formation of cadaverine and a possible relation between the HS-induced translocation of this diamine to roots and the transient ethylene evolution by leaves. To validate this hypothesis, we compared the ethylene evolution rate and interorgan partitioning of cadaverine and other polyamines for two lines of Arabidopsis thaliana: the wild type (Col-0) and ein4 mutant with impaired ethylene reception. In plants grown in light at 20–21°C, the rate of ethylene evolution by rosetted leaves was higher in the mutant than in the wild type. The content of putrescine and spermidine was reduced in mutant leaves, whereas cadaverine concentration increased almost threefold compared with the wild type. In roots, cadaverine was found only in the wild type and not in the mutant line. Our data indicate the ethylene-dependent formation of cadaverine in leaves and possible involvement of cadaverine and ethylene in the long-distance translocation of stress (HS) signal in plants.     

Does high bicarbonate supply to roots change availability of iron in the leaf apoplast?

The role of the leaf apoplast in iron (Fe) uptake into the leaf symplast is insufficiently understood, particularly in relation to the supposed inactivation of Fe in leaves caused by elevated bicarbonate in calcareous soils. It has been supposed that high bicarbonate supply to roots increases the pH of the leaf apoplast which decreases the physiological availability of Fe in leaf tissues. The study reported here has been carried out with sunflower plants grown in nutrient solution and with grapevine plants grown on calcareous soil under field conditions. The data obtained clearly show that the pH of the leaf apoplastic fluid was not affected by high bicarbonate supply in the root medium (nutrient solution and field experiments). The concentrations of total, symplastic and apoplastic Fe were decreased in chlorotic leaves of both sunflower (nutrient solution experiment) and grapevine plants in which leaf expansion was slightly inhibited (field experiment). However, in grapevine showing severe inhibition of leaf growth, total Fe concentration in chlorotic leaves was the same or even higher than in green ones, indicative to the so-called `chlorosis paradox'. The findings do not support the hypothesis of Fe inactivation in the leaf apoplast as the cause of Fe deficiency chlorosis since no increase was found in the relative amount of apoplastic Fe (% of total leaf Fe) either in the leaves of sunflower or grapevine plants. It is concluded that high bicarbonate concentration in the soil solution does not decrease Fe availability in the leaf apoplast.     

Whole Plant and Leaf Steady State Gas Exchange during Ethylene Exposure in Xanthium strumarium L

The effects of ethylene evolved from ethephon on leaf and whole plant photosynthesis in Xanthium strumarium L. were examined. Ethylene-induced epinasty reduced light interception by the leaves of ethephon treated plants by up to 60%. Gas exchange values of individual, attached leaves under identical assay conditions were not inhibited even after 36 hours of ethylene exposure, although treated leaves required a longer induction period to achieve steady state photosynthesis. The speed of translocation of recently fixed ¹¹C-assimilate movement was not seriously impaired following ethephon treatment; however, a greater proportion of the assimilate was partitioned downward toward the roots. Within 24 hours of ethephon treatment, the whole plant net carbon exchange rate expressed on a per plant basis or a leaf area basis had dropped by 35%. The apparent inhibition of net carbon exchange rate was reversed by physically repositioning the leaves with respect to the light source. Ethylene exposure also inhibited expansion of young leaves which was partially reversed when the leaves were repositioned. The data indicated that ethylene indirectly affected net C gain and plant growth through modification of light interception and altered sink demand without directly inhibiting leaf photosynthesis.     

Effect of partial rootzone drying on the concentration of zeatin-type cytokinins in tomato (Solanum lycopersicum L.) xylem sap and leaves

Decreased cytokinin (CK) export from roots in drying soil might provide a root-to-shoot signal impacting on shoot physiology. Although several studies show that soil drying decreases the CK concentration of xylem sap collected from the roots, it is not known whether this alters xylem CK concentration ([CK(xyl)]) in the leaves and bulk leaf CK concentration. Tomato (Solanum lycopersicum L.) plants were grown with roots split between two soil columns. During experiments, water was applied to both columns (well-watered; WW) or one (partial rootzone drying; PRD) column. Irrigation of WW plants aimed to replace transpirational losses every day, while PRD plants received half this amount. Xylem sap was collected by pressurizing detached leaves using a Scholander pressure chamber, and zeatin-type CKs were immunoassayed using specific antibodies raised against zeatin riboside after separating their different forms (free zeatin, its riboside, and nucleotide) by thin-layer chromatography. PRD decreased the whole plant transpiration rate by 22% and leaf water potential by 0.08 MPa, and increased xylem abscisic acid (ABA) concentration 2.5-fold. Although PRD caused no detectable change in [CK(xyl)], it decreased the CK concentration of fully expanded leaves by 46%. That [CK(xyl)] was maintained and not increased while transpiration decreased suggests that loading of CK into the xylem was also decreased as the soil dried. That leaf CK concentration did not decline proportionally with CK delivery suggests that other mechanisms such as CK metabolism influence leaf CK status of PRD plants. The causes and consequences of decreased shoot CK status are discussed.     

Jasmonic acid is involved in the water-stress-induced betaine accumulation in pear leaves

Jasmonic acid (JA) is known to be involved in the response of plants to environmental stresses such as drought, and betaine (glycinebetaine) is an osmopretectant accumulated in plants under environmental stresses including drought. However, it remains currently unclear whether JA is involved in the water‐stress‐induced betaine accumulation in plant leaves. The present experiment, performed with the whole pear plant (Pyrus bretschneideri Redh. cv. Suli), revealed that the exogenously applied JA induced a significant increase of the betaine level in the pear leaves when the plants were not yet stressed by drought, and when the plants were subjected to water stress, the ‘JA plus drought’ treatment induced a significant higher betaine level than did the drought treatment alone. Meanwhile, the ‘JA plus drought’ treatment induced higher levels of betaine aldehyde dehydrogenase (BADH, E C 1.2.1.8) and activities in the leaves than did the drought treatment alone. These results obtained in the whole plant experiments were supported by the results of detached leaf experiments. In detached leaves JA induced significant increases in betaine levels, BADH activities and BADH protein amounts in a time‐ and concentration‐dependent manner. These data demonstrate that JA is involved in the drought‐induced betaine accumulation in pear leaves.     

Ozone suppresses soil drying- and abscisic acid (ABA)-induced stomatal closure via an ethylene-dependent mechanism

Elevated atmospheric ozone concentrations (70 ppb) reduced the sensitivity of stomatal closure to abscisic acid (ABA) in Leontodon hispidus after at least 24 h exposure (1) when detached leaves were fed ABA, and (2) when intact plants were sprayed or injected with ABA. They also reduced the sensitivity of stomatal closure to soil drying around the roots. Such effects could already be occurring under current northern hemisphere peak ambient ozone concentrations. Leaves detached from plants which had been exposed to elevated ozone concentrations generated higher concentrations of ethylene, although leaf tissue ABA concentrations were unaffected. When intact plants were pretreated with the ethylene receptor binding antagonist 1-methylcyclopropene, the stomatal response to both applied ABA and soil drying was fully restored in the presence of elevated ozone. Implications of ethylene's antagonism of the stomatal response to ABA under oxidative stress are discussed. We suggest that this may be one mechanism whereby elevated ozone induces visible injury in sensitive species. We emphasize that drought linked to climate change and tropospheric ozone pollution, are both escalating problems. Ozone will exacerbate the deleterious effects of drought on the many plant species including valuable crops that respond to this pollutant by emitting more ethylene.