Boron re-translocation in tea (Camellia sinensis (L.) O. Kuntze) plants

Boron (B) re-translocation is an important factor determining tolerance to B deficiency in plants. In this work growth, B content of leaves with different ages, B partitioning between soluble and cell wall (CW) fractions, and B re-translocation were investigated in tea (Camellia sinensis (L.) O. Kuntze) plants grown hydroponically without (<2.5 μM) and with adequate (46 μM) B supply. Under B deficiency, the proportion of CW bound B increased in the old leaves but decreased in roots. Contrastingly, the proportion of CW bound B was not influenced by B supply in the young leaves. A continuous reduction of B content was observed in all fully expanded leaves as well as in roots of low B plants. Taken together, these results revealed considerable re-translocation of B from mature to growing leaves. Leaf extract and phloem exudate samples were analyzed and sucrose, glucose, and fructose were detected while xylitol, sorbitol, mannitol, maltose, galactose, cellobiose or rafinose were not found in these samples. In the leaf extracts, concentration of sucrose increased under B deficiency conditions, concentration of glucose decreased, while that of fructose remained unchanged. Our results provide circumstantial evidence for a considerable re-translocation of B in tea plants despite lacking polyol compounds.     

Excessive aluminium accumulation in the pea mutant E107 (brz)

E107 is a pleiotropic mutant of peaPisum sativum cv. ‘Sparkle’, characterized by forming few nodules and developing bronze necrotic spots on older leaves. The mutant accumulates Al and has symptoms typical of Al toxicity. The lateral roots of E107 are fewer (40%) and shorter (50%) than those of its parent. High concentrations of Al accumulate in E107 shoots (1000 mg kg^-1) and roots (3000 mg kg^-1), and three-week old E107 plants extrude 2.5 times more protons than ‘Sparkle’ plants of similar age. Al concentrations of the roots of the mutant and of its parent ‘Sparkle’ are similar for the first two weeks of growth. Thereafter they differ. In 2 week old plants Al continues to accumulate in excessive amounts in E107 primary and lateral roots whereas in ‘Sparkle’ roots, it reaches a plateau. In E107, Al is erratically distributed in the walls of root hairs and epidermal cells in both primary and lateral roots. Some of these cells have also Al in their nucleus.     

茶叶主要化学品质指标和茶树体部分微量元素的钙铝调控效应

以一年生茶树扦插苗为材料,采用水培法研究了添加钙铝对茶叶主要化学品质及茶树钙、铝、锌、铁吸收积累的调控效应.结果表明:(1)适量铝(10或20mg·L-1)有利于提高茶叶茶多酚、咖啡碱、黄酮、可溶性总糖和氨基酸的含量;添加钙可提高上述化学成分的含量,且在高铝浓度(30mg·L-1)下提高的幅度最大.(2)适量的铝可促进茶树对铝和铁的吸收和积累,而高浓度的铝(30mg·L-1)抑制茶树对铝和铁的吸收与积累;添加铝可降低茶树根对钙和锌的吸收,但适量添加铝不影响茎和叶对钙和锌的积累.(3)添加钙可提高茶树体钙的含量,降低铝和锌的吸收与积累,但对铁的吸收与积累没有明显影响.研究表明,铝和钙可调控茶叶化学品质含量和茶树体微量元素的吸收;合理控制茶园土壤铝积累,并适量补充钙可能有利于提高茶叶品质,创建生态高值茶园.     

Localization of aluminium in tea (Camellia sinensis) leaves using low energy X-ray fluorescence spectro-microscopy

Information on localization of Al in tea leaf tissues is required in order to better understand Al tolerance mechanism in this Al-accumulating plant species. Here, we have used low-energy X-ray fluorescence spectro-microscopy (LEXRF) to study localization of Al and other low Z-elements, namely C, O, Mg, Si and P, in fully developed leaves of the tea plant [Camellia sinensis (L.) O. Kuntze]. Plants were grown from seeds for 3?months in a hydroponic solution, and then exposed to 200?μM AlCl₃ for 2?weeks. Epidermal-mesophyll and xylem phloem regions of 20?μm thick cryo-fixed freeze-dried tea-leaf cross-sections were raster scanned with 1.7 and 2.2?keV excitation energies to reach the Al–K and P–K absorption edges. Al was mainly localized in the cell walls of the leaf epidermal cells, while almost no Al signal was obtained from the leaf symplast. The results suggest that the retention of Al in epidermal leaf apoplast represent the main tolerance mechanism to Al in tea plants. In addition LEXRF proved to be a powerful tool for localization of Al in plant tissues, which can help in our understanding of the processes of Al uptake, transport and tolerance in plants.     

Removal of root apices enables study of direct toxic effects of aluminum on rice (Oryza sativa L.) leaf cells

Root growth inhibition is a well-known symptom of aluminum (Al) toxicity in intact plants, mainly because the mechanisms of Al exclusion or resistance that operate outside the root endodermis prevent the ascent of this metal from roots into shoots. This work presents a new method to better understand the direct effects of this metal on rice leaves. For this, Al-sensitive and tolerant rice genotypes, having had their root apices removed, were incubated in AlCl₃ solutions to evaluate unblocked metal ascension toward the leaf cells. To avoid regrowth and closing of roots, apices were removed daily and also verified for a lack of tyloses production and consequent obstruction in tracheal elements. Thus, seedlings of both cultivars, which were root apex-free, accumulated differentially high amounts of Al in the leaves, highlighting the importance of mechanisms of Al exclusion or resistance in roots of intact plants. Also, Al moved freely toward leaf cells, clearly inducing necrosis-like mesophyll alterations in both genotypes. Added ultrastructural analyses revealed significant cytoplasmatic damage, mainly in chloroplasts. These results suggest that differential responses to Al sensitivity/tolerance preserved in roots between the genotypes studied are also expressed in leaves. Therefore, this method allowed for development of a possible biological model suitable for investigating the direct effect of Al on cells and, alternatively, other compounds in plant leaf cell physiology.     

氮磷肥对茶树锌硒等中微量元素吸收与分配的影响

锌（Zn）和硒（Se）及其他中微量元素（铝Al,钙Ca,铁Fe,铜Cu,锰Mn）是茶叶品质的重要指标,但茶树吸收Zn、Se能力及氮（N）磷（P）肥影响中微量元素吸收与分配的过程尚不清楚。以红壤丘陵区福鼎大白茶树为研究对象,开展Zn+Se、Zn+Se+N、Zn+Se+P、Zn+Se+N+P和对照共5种处理3次重复随机化区组试验,处理第3年春季分茶叶、成熟叶、吸收根、运输根和储藏根采集植物样品,测定其元素含量。结果表明,茶树地上和地下器官Zn和Se及其他中微量元素对N、P、Zn、Se添加的响应具分异性。与对照相比,茶树地上和地下器官Zn和Se含量均显著增加,与Zn+Se相比,施N和/或P肥仅显著提高茶叶和成熟叶Se含量（P<0.05）;与对照相比,施肥处理均显著提高吸收根和运输根Al、Fe含量以及储藏根Cu含量;运输根Mn含量表现为Zn+Se+N、Zn+Se+P、Zn+Se+N+P显著高于对照,储藏根Mn含量为Zn+Se+N+P显著高于其他处理;茶树各器官Ca含量对施肥处理无显著响应。此外,茶叶和成熟叶的Zn含量与吸收根显著正相关,而Se含量则与储藏根显著正相关。茶树具有吸收和积累Zn和Se的能力,而施N、P肥有助于提高茶叶Se含量,研究结果为红壤丘陵区培育高品质锌硒茶及营建生态高值茶园提供了依据。     

Exogenous nitric oxide enhances cadmium tolerance of rice by increasing pectin and hemicellulose contents in root cell wall

To study the mechanisms of exogenous NO contribution to alleviate the cadmium (Cd) toxicity in rice (Oryza sativa), rice plantlets subjected to 0.2-mM CdCl₂ exposure were treated with different concentrations of sodium nitroprusside (SNP, a NO donor), and Cd toxicity was evaluated by the decreases in plant length, biomass production and chlorophyll content. The results indicated that 0.1 mM SNP alleviated Cd toxicity most obviously. Atomic absorption spectrometry and fluorescence localization showed that treatment with 0.1 mM SNP decreased Cd accumulation in both cell walls and soluble fraction of leaves, although treatment with 0.1 mM SNP increased Cd accumulation in the cell wall of rice roots obviously. Treatment with 0.1 mM SNP in nutrient solution had little effect on the transpiration rate of rice leaves, but this treatment increased pectin and hemicellulose content and decreased cellulose content significantly in the cell walls of rice roots. Based on these results, we conclude that decreased distribution of Cd in the soluble fraction of leaves and roots and increased distribution of Cd in the cell walls of roots are responsible for the NO-induced increase of Cd tolerance in rice. It seems that exogenous NO enhances Cd tolerance of rice by increasing pectin and hemicellulose content in the cell wall of roots, increasing Cd accumulation in root cell wall and decreasing Cd accumulation in soluble fraction of leaves.     

Calcium modifies Cd effect on runner bean plants

The effect of different Ca concentrations in the growth medium on the toxicity of 25 μM CdSO₄ was studied in runner bean plants (var. Pi kny Ja ) at two different growth stages of primary leaves. In young plants growing in a medium with low level of Ca a treatment with Cd for 12 days resulted in Ca accumulation in roots, a strong reduction of the leaf area, a decreased monogalactosyl diacylglycerol/digalactosyl diacylglycerol ratio and efficiency of the photosynthetic apparatus. In leaves of older plants growing under the same conditions, and surviving Cd treatment, a high accumulation of Ca but a low one of Cd, chlorosis of leaves, a decrease of the ratio monogalactosyl diacylglycerol/digalactosyl diacylglycerol and photosynthetic activity were shown. At a high level of Ca in the nutrient medium plant roots showed a remarkably high specificity to accumulate Cd but the toxic effect of the metal on plant growth parameters and content of pigments was decreased. No changes were observed in the level of galactolipids, but changes in fluorescence quenching were recorded. Calcium deficit enhanced the effect of Cd toxicity, including primary photochemistry, whereas excess Ca reduced toxic effects, while it is increasing the nonphotochemical quenching of excitation energy.     

Effect of cadmium ion excess over cell structure and functioning of Zea mays and Hordeum vulgare

Zea mays (maize) and Hordeum vulgare (barley) plants were analyzed in order to study the variation in response to Cadmium (Cd) toxicity based on development of leaf symptoms, effect in dry matter production, Cd uptake, lipid peroxidation and effect on cell ultrastructure in leaves and roots. Cd accumulation in roots of Z. mays and H. vulgare was 18–50 times higher than in the aerial parts. Malondialdehyde (MDA) content was more affected in the roots of both Z. mays and H. vulgare than in shoots (60 and 56–51 and 40%, respectively). At ultrastructural level, in Cd treated seedlings, a decline in the vacuolar content of barley roots cells and maize leaf cells was observed. Results corroborate that these gramineous crops can uptake and accumulate substantial amounts of Cd especially in roots. Therefore, H. vulgare and Z. mays could have a phytostabilization potential and thereafter could be tested in phytoremediation technologies.     

模拟酸雨和铝调控对茶叶主要化学品质与铝积累的影响

为研究模拟酸雨和铝(Al)对茶叶主要化学品质与Al积累的影响及其交互作用,采用3个酸度水平(pH 3.0、4.0、5.0)和4种Al浓度水平(0、10、20、30 mg L-1),用溶液培养法研究茶叶的主要化学指标和Al含量的异同.结果表明,在模拟酸雨下,茶叶的茶多酚和咖啡碱含量随酸度增加先增加后下降,氨基酸、儿茶素和...     

High Aluminum Resistance in Buckwheat : II. Oxalic Acid Detoxifies Aluminum Internally

Buckwheat (Fagopyrum esculentum Moench. cv Jianxi), which shows high Al resistance, accumulates Al in the leaves. The internal detoxification mechanism was studied by purifying and identifying Al complexes in the leaves and roots. About 90% of Al accumulated in the leaves was found in the cell sap, in which the dominant organic acid was oxalic acid. Purification of the Al complex in the cell sap of leaves by molecular-sieve chromatography resulted in a complex with a ratio of Al to oxalic acid of 1:3. A ¹³C-nuclear magnetic resonance study of the purified cell sap revealed only one signal at a chemical shift 164.4 ppm, which was assigned to the Al-chelated carboxylic group of oxalic acid. A ²⁷Al-nuclear magnetic resonance analysis revealed one major signal at the chemical shift of 16.0 to 17.0 ppm, with a minor signal at the chemical shift of 11.0 to 12 ppm in both the intact roots and their cell sap, which is consistent with the Al-oxalate complexes at 1:3 and 1:2 ratios, respectively. The purified cell sap was not phytotoxic to root elongation in corn (Zea mays). All of these results indicate that Al tolerance in the roots and leaves of buckwheat is achieved by the formation of a nonphytotoxic Al-oxalate (1:3) complex.     

A combination of five mechanisms confers a high tolerance for aluminum to a wild species of Poaceae,Andropogon virginicus L.

How can high tolerance against aluminum (Al) toxicity be obtained in plants? To address this question, tolerant mechanisms were characterized in a highly Al tolerant wild species of Poaceae, Andropogon virginicus L. A. virginicus showed an Al-stress-induced synthesis and secretion of citrate and malate in roots. This mechanism may help to suppress an increase of toxic Al ions in the root region. Microscopic observation of the morin-stained leaves indicated that the Al transferred to shoots was specifically accumulated in the trichomes and spikes of the leaves and that some portion of the accumulated Al was furthermore secreted as sap from the tips of trichomes. Al-induced synthesis of poly-phenolic compounds including anthocyanin also occurred in roots as a long term response to Al toxicity and anthocyanin production did not co-localize with either Al accumulation, nitric oxide (NO) production or lipid peroxides production in the roots. It was suggested that oxidative damage caused by Al stress was suppressed in these areas where anthocyanin was localized. Moreover, induction of NO production occurred in roots within 24 h of Al treatment. Our results suggested that NO could not efficiently ameliorate the Al-dependent nuclei deformation and DNA fragmentation, but could function as a trigger to stimulate anti-peroxidation enzymes under Al stress. Collectively the results suggested that A. virginicus manifests its high Al tolerance by a unique combination of effective mechanisms.     

Absence of aluminium compromises root integrity,reduces leaf hydration and Rubisco performance in Qualea grandiflora,an Al-accumulating species

• Aluminium (Al) is toxic to most plants. Nevertheless, some species accumulate Al without showing toxicity symptoms. Previous studies have evidenced Al in chloroplasts of Al-accumulating species from the Cerrado vegetation in South America. We ask whether Al increases carbon assimilation through enhanced apparent efficiency of Rubisco.
• Seedlings of the Al-accumulator Qualea grandiflora (Vochysiaceae) were grown in nutrient solution with 0, 740, and 1480 μm Al. Growth parameters, relative leaf water content, Al concentration in organs, gas exchange and apparent carboxylation efficiency (measured from A/Ci curves) were evaluated for 60 days.
• Plants without Al showed no root growth, necrotic roots, low gas exchange rates, and decreased apparent carboxylation efficiency. Al-treated plants, however, showed new white roots and increased root biomass leading to higher leaf hydration, and apparent carboxylation efficiency was higher in these plants. Increased Al available in the nutrient solution increased Al accumulation in plant organs.
• Absence of Al compromised root integrity in Q. grandiflora, thus limiting leaf hydration. No positive direct effect of Al on Rubisco was evidenced in Al-treated plants.

     

Old leaves accumulate more heavy metals than other parts of the desert shrub Calotropis procera at a traffic-polluted site as assessed by two analytical techniques

Abstract

Calotropis procera is a perennial big shrub that has the potential to accumulate high concentrations of heavy metals. Metal sequestration in old organs has been considered as a mechanism for plant survival in polluted soils. The aim of the present study was to assess the role of the old leaves as a sink for HMs accumulation in C. procera. Two instruments were used: atomic absorption spectroscopy (AAS) and X-ray fluorescence (XRF) microscopy. Soil and plant samples were collected from around one of the worst congested traffic areas in the United Arab Emirates (UAE). Samples from roots, stem, and green and old leaves were prepared and analyzed by both instruments. Calotropis procera was able to concentrate Fe, Mn, Sr, and Zn in the roots, but their translocation to stem and green leaves was low. Old leaves had greater ability to accumulate significantly higher concentrations of different metals, especially Fe and Sr, than other parts of the plants, indicating that C. procera uses these metabolically less-active leaves as sinks for heavy metals. Fe and Sr attained higher bioconcentration and accumulation values, compared to Zn and Mn. There were significant positive correlations between XRF and AAS for all elements in the different organs.     

Retention and allocation of <Superscript>14</Superscript>C assimilates by maintenance leaves and harvest index of tea (<Emphasis Type="Italic">Camellia sinensis</Emphasis> L.)

Partitioning of ¹⁴C-labelled photosynthates to various parts of un-pruned tea clones TV1 and TV25 was assessed in vivo by exposing maintenance leaves to ¹⁴CO₂ at monthly intervals throughout the year. The plants from shoot apex to root tip were divided into twelve components to assess the allocation and retention of ¹⁴C-photosynthates by the maintenance foliage. Out of the total photosynthates produced by the maintenance leaves, only 11.08 % was allocated to the commercially useful harvestable two and a bud shoots which is accepted as the harvest index of tea. The photosynthetically active maintenance leaves retained 19.05 % while 24.56 % was distributed to the branches. The bottom and the top parts of the trunk utilized 7.44 and 7.21 %, respectively. The thick roots at the base of the trunk, medium sized roots, pencil size roots, and feeder roots imported 7.28, 7.72, 7.65, and 8.01 % of ¹⁴C assimilates, respectively. Except retention by leaves, all the plant parts of vigorous clone TV25 required higher percentage of assimilates than TV1. The mean quantities of net photosynthates utilized by the stem and the roots were 69.37 and 30.63 %, respectively.     

Boron supply alleviates Al-induced inhibition of root elongation and physiological characteristics in rapeseed (Brassica napus L.)

Aluminum (Al) toxicity is one of the major problems affecting crop production. Boron (B) is an essential micronutrient for higher plants. In the present study, we investigated the alleviation of Al-induced inhibition of root growth and physiological characteristics by B in rapeseed. The rapeseeds were grown in different Al concentrations (0 and 300?μM), and for every concentration, two B treatments (2.5 and 25?µM as H₃BO₃) were applied. The results showed that Al toxicity under low B drastically inhibited root growth. The supply of B improved root length, photosynthesis, root activity, total chlorophyll by 60.15%, 104.7%, 102%, and 106.3%, respectively under Al toxicity. This further resulted in improvement of peroxidase, catalase, and ascorbate peroxidase activities while decreasing malondialdehyde, H₂O_2, and Al contents in roots and leaves. It might be supposed that B alleviates Al toxicity by less mobilization of Al in plant parts and through improving antioxidant enzyme activities.     

Characterization of an ascorbate peroxidase in plastids of tobacco BY-2 cells

In higher plants, ascorbate peroxidase (APX; EC 1.11.1.11), the major H₂O₂-scavenging enzyme, occurs in several distinct isoenzymes that are localized in cytosol and various cell organelles. Here, we have purified and characterized an APX from the soluble fraction of plastids of non-photosynthetic tobacco BY-2 cells. The plastidic APX was a monomer with a molecular weight of 34 000. The enzymatic properties of the plastidic APX, including the rapid inactivation by H₂O₂ in ascorbate-depleted medium, were highly comparable with those of the chloroplastic stromal APX of spinach and tea leaves. However, the other chloroplastic APX isoenzyme, the thylakoid-membrane bound APX, was not detected in the plastids of the BY-2 cells. The N-terminal amino acid sequence of the plastidic APX was completely identical with the deduced amino acid sequence of a previously identified cDNA sequence of tobacco chloroplastic APX. When a green fluorescence protein gene tagged with the chloroplast-targeting signal sequence of APX was expressed in the BY-2 cells, the fluorescence protein exclusively localized into plastids, and not into mitochondria. We conclude that plastidic APX in non-photosynthetic tissues is the same as the chloroplastic APX that occurs in leaves.     

The Accumulation and Subcellular Distribution of Arsenic and Antimony in Four Fern Plants

In the present study, Pteris cretica ‘Albo-Lineata’ (PC), Pteris fauriei (PF), Humata tyermanii Moore (HT), and Pteris ensiformis Burm (PE), were selected to explore additional plant materials for the phytoremediation of As and Sb co-contamination. To some extent, the addition of As and Sb enhanced the growth of HT, PE, and PF. Conversely, the addition of As and Sb negatively affected the growth of PC and was accompanied with the accumulation of high levels of As and Sb in the roots. The highest concentration of Sb was recorded as 6405 mg kg^?1 in the roots of PC, and that for As was 337 mg kg^?1 in the rhizome of PF. To some degree, As and Sb stimulated the uptake of each other in these ferns. Arsenic was mainly stored in the cytoplasmic supernatant (CS) fraction, followed by the cell wall (CW) fraction. In contrast, Sb was mainly found in the CW fraction and, to a lesser extent, in the CS fraction, suggesting that the cell wall and cytosol play different roles in As and Sb accumulation by fern plants. This study demonstrated that these fern plants show a good application potential in the phytoremediation of As and Sb co-contaminated environments.