Root hairs of Arabidopsis play significant roles in the absorption of water and several minerals, secretion of acid phosphatases and organic acids, and anchoring of roots.
The micronutrient zinc is essential for all living organisms, but it is toxic at high concentrations. Here, to understand the effects of excess zinc on plant cells, we performed an iTRAQ (for ...isobaric tags for relative and absolute quantification)-based quantitative proteomics approach to analyze microsomal proteins from Arabidopsis (Arabidopsis thaliana) roots. Our approach was sensitive enough to identify 521 proteins, including several membrane proteins. Among them, IRT1, an iron and zinc transporter, and FRO2, a ferric-chela te reductase, increased greatly in response to excess zinc. The expression of these two genes has been previously reported to increase under iron-deficient conditions. Indeed, the concentration of iron was significantly decreased in roots and shoots under excess zinc. Also, seven subunits of the vacuolar H
+
-ATPase (V-ATPase), a proton pump on the tonoplast and endosóme, were identified, and three of them decreased significantly in response to excess zinc. In addition, excess zinc in the wild type decreased V-ATPase activity and length of roots and cells to levels comparable to those of the untreated de-etiolated3-1 mutant, which bears a mutation in V-ATPase subunit Interestingly, excess zinc led to the formation of branched and abnormally shaped root hairs, a phenotype that correlates with decreased levels of proteins of several root hair-defective mutants. Our results point out mechanisms of growth defects caused by excess zinc in which cross talk between iron and zinc homeostasis and V-ATPase activity might play a central role.
Aims This study reveals the accumulation properties of Co from viewpoints of the analogy with Ni and also the variation of the other essential micro elements in the Co accumulator tree, Clethra ...barbinervis. Methods Seedlings of C. barbinervis were grown in single and mixed treatments in the rhizosphere containing Co, Ni, or both at three different concentrations (5, 50, and 500 μM). In roots, stems, and leaves, the concentrations of Cu, Fe, Mn, and Zn, together with Co and Ni, were determined. Results Biomass was reduced in plants treated with 500 μM Ni, but not when treated with Co. The Co concentration in leaves was higher than those in other tissues, and the maximum Co accumulation in leaves was 2012 μg g−1. Accumulation of Co competed with Zn transport and stimulated Cu transport. Conclusion Our results indicate that C. barbinervis is a Co hyperaccumulator and is more tolerant to Co than to Ni. The Co hyperaccumulation capacity is likely achieved by Zn transport systems involved in root to shoot translocation, and Co accumulation has some competitive and facilitative interactions with the other heavy metals.
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CsCl solution was applied to the foliage of Japanese cedar (
Cryptomeria japonica
) and Konara oak (
Quercus serrata
) under field conditions to investigate whether radiocesium could be ...translocated from the foliage to other parts through senescence of foliage, and whether this differs between tree species.
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Cs was translocated to nearby foliage in both species, whereas translocation to the base of the branches was observed in Konara oak, but not in Japanese cedar. These results suggest that the translocation of radiocesium towards woody branches might be more prominent in Konara oak than in Japanese cedar through senescence of foliage.
Bark-wood translocation has been suggested as an important route for the contamination of trees via radiocesium in the initial stage of deposition. In this study, we investigated the cesium ...absorption through bark of mature Konara oak (Quercus serrata). Stable Cs (
133
Cs) was applied onto the bark at 1.2 m, and then after 8 weeks, the
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Cs concentration was determined in the outer bark, inner bark, sapwood, and heartwood of stem disks at several heights, as well as in the current-year leaves and branches from the tree tops. At the height of 1.2 m, the
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Cs concentration was significant higher in the sapwood of the treated trees than in those of the control trees. However, no difference was found in the
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Cs concentration in the heartwood of the treated and control trees not only in the wood above and below 1.2 m but also at 1.2 m. There was no significant difference in the
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Cs concentration of the current-year leaves and branches of the treated and control trees. Our results suggest that Cs absorption through bark may occur even in the dormant period of tree and the absorption is probably independent of cambial activities.
Key message
The accumulation and tolerance mechanisms for Co are clearly different from those for Ni in the leaves of
C. barbinervis
in terms of both the distribution and speciation.
Clethra ...barbinervis
is a Co-hyperaccumulating tree and also accumulates Ni at high concentrations. The mechanism and role of accumulation in tree physiology remains unclear. The aim of this study was to determine the localization and speciation of Co and Ni in the leaves of
C. barbinervis
to reveal the mechanisms behind its tolerance to high concentrations of these elements.
C. barbinervis
seedlings were grown for 3 years under treatments with Co or Ni in the rhizosphere. X-ray fluorescence (XRF) and X-ray absorption near edge structure (XANES) analyses were then used to evaluate the distribution and chemical states of Co, Ni, and S in the adaxial leaf epidermis. In addition, the treated leaves were cut into several parts according to the XRF imaging results on Co or Ni, and the concentrations of elements, sulfate, and organic acids were determined in each part by chemical analyses. XRF images showed that Co was present at the tip of the leaf at a high concentration, whereas Ni was mainly distributed around the leaf edge. Results of chemical analyses on leaf parts containing Co or Ni indicated that sulfate acts as a counter ion for Co and that Ni combined with succinic and/or oxalic acid. In addition, XANES analysis showed that sulfate tended to be reduced and glutathione was generated in the tip of the leaf. Our results indicate that
C. barbinervis
distinguishes Co and Ni and translocates them to different parts of the leaf.
Key message
Glucose was a key substance as an energy source in the root growth promotion by Al, and ABA may relate to metabolism involved with its process.
Generally, excess aluminum (Al) ions in ...soil solution are toxic to many cultivated plant species, but beneficial effects of Al for plant growth have been reported. Previously, we reported stimulation of root growth and nitrate reductase (NR) activity by Al. In this study, we focused on sugars, such as sucrose, glucose, and fructose, as energy sources and also signaling substances to regulate root growth. To understand the mechanism of root growth stimulation by Al, we investigated the change in concentration of sugars and phytohormones, and the activity of NR in roots using
Quercus serrata
seedlings. Ten-week-old
Q. serrata
seedlings were hydroponically cultured with nutrient solution containing 2.5 mM Al (pH 4.0) or 3.25 mM calcium (Ca) (pH 4.0) for 3 and 15 days. The growth of first lateral root and NR activity was stimulated for 3 and 15 days of Al treatment. The concentration of starch and sucrose decreased, while the concentration of glucose increased in the Al-treated roots. The concentration of abscisic acid (ABA) in Al-treated roots increased gradually throughout the experiment. From the present study, the mechanism of root growth promotion by Al involves a complex signaling network. We suggest that glucose is a key substance as an energy source and a signaling substance to promote root growth induced by Al and ABA may relate to nitrogen (N) and carbon (C) metabolism involved with the signaling network to promote root growth induced by Al.
The vacuolar Zn(2+)/H(+) antiporter of Arabidopsis thaliana, AtMTP1, has a long cytosolic histidine-rich loop. A mutated AtMTP1 in which the first half of the loop (His-half) was deleted exhibited a ...11-fold higher transport velocity in yeast cells. Transgenic lines overexpressing the His-half-deleted AtMTP1 in the loss-of-function mutant were evaluated for growth and metal content in the presence of various zinc concentrations. These overexpressing lines (35S-AtMTP1 and 35S-His-half lines) showed high tolerance to excess concentrations of zinc at 150 µM, as did the wild type, compared with the loss-of-function line. The His-half AtMTP1 transported cobalt in a heterologous expression assay in yeast, but the cumulative amount of cobalt in 35S-His-half plants was not increased. Moreover, the accumulation of calcium and iron was not changed in plants. Under zinc-deficient conditions, growth of 35S-His-half lines was markedly suppressed. Under the same conditions, the 35S-His-half lines accumulated larger amounts of zinc in roots and smaller amounts of zinc in shoots compared with the other lines, suggesting an abnormal accumulation of zinc in the roots of 35S-His-half lines. As a result, the shoots may exhibit zinc deficiency. Taken together, these results suggest that the His-loop acts as a sensor of cytosolic zinc to maintain an essential level in the cytosol and that the dysfunction of the loop results in an uncontrolled accumulation of zinc in the vacuoles of root cells.
Gamblea innovans is a Cd- and Zn-accumulating deciduous tree widely distributed in the secondary forests of Japan. We aimed to understand the characteristics of Cd and Zn accumulation in G. innovans ...in order to effectively utilize the species for phytoremediation. To accomplish that, we studied the relationship between secondary metabolite concentrations and the accumulation and distributions of Cd and Zn in G. innovans leaves and basal stems using micro-X ray fluorescence (µ-XRF). Our results showed a negative correlation between Zn leaf concentrations and polyphenol/2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. This finding might be related to stress or the manifestation of a mechanism for tolerance to Cd and Zn accumulation. In addition, we observed that Cd accumulated primarily in the apoplastic region of surface tissues such as bark and the epidermis of leaves, whereas Zn accumulated in both apoplastic and symplastic regions. Thus, it might be possible that G. innovans can distinguish between Cd and Zn and control their translocation.
Clethra barbinervis Sieb. et Zucc. accumulates Nickel (Ni) and Cobalt (Co) at high concentrations., We hypothesized that C. barbinervis cannot distinguish between Ni and Co because of the similar ...chemical properties of these two elements. To confirm this hypothesis and understand the role of these elements in C. barbinervis, we conducted a hydroponic split-root experiment using Ni and Co solutions. We found that the bioconcentration factor (BCF; metal concentration of each tissue/metal concentrations of each treatment solution) of Ni and Co did not significantly differ in the roots, but the BCF for Co was higher than that for Ni in the leaves. The leaves of C. barbinervis accumulated Ni or Co at high concentrations. We also found the simultaneous accumulation of Ni and Co by the multiple heavy metal treatments (Ni and Co) at high concentrations similar to those for the single treatments (Ni or Co). Elevated sulfur concentrations occurred in the roots and leaves of Co-treated seedlings but not in Ni. This result indicates that S was related to Co accumulation in the leaves. These results suggest that C. barbinervis distinguishes between Ni and Co during transport and accumulation in the leaves but not during root uptake.
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