Eitaro Miwa

Remodeling of the Major Light-Harvesting Antenna Protein of PSII Protects the Young Leaves of Barley (Hordeum vulgare L.) from Photoinhibition under Prolonged Iron Deficiency

Because of the high demand for iron of the photosynthetic apparatus in thylakoid membranes, iron deficiency primarily affects the electron transfer between the two photosystems (PSI and PSII), resulting in photooxidative damage in plants. However, in barley, PSII is protected against photoinhibition, and the plant survives even with a low iron content in its chlorotic leaves. In this study, we report an adaptation mechanism of the photosynthetic apparatus in barley to iron deficiency, which is concomitant with the remodeling of a PSII antenna system. Transcriptome analysis revealed that long-term iron deficiency induced the expression of two genes of the major light-harvesting Chl a/b-binding protein of PSII (LHCII), namely HvLhcb1.11 and HvLhcb1.12. Chl fluorescence analysis of the wild type and Lhcb1-less chlorina mutants clearly showed that non-photochemical quenching (NPQ) of the wild type was increased by approximately 200% by iron deficiency, whereas NPQ of chlorina mutants did not change significantly under iron deficiency. The mutant showed severe photodamage in young leaves under prolonged iron deficiency, suggesting that the HvLhcb1 protein is essential for both thermal dissipation and photoprotection in iron-deficient barley. Analysis of thylakoid protein complexes revealed that the proportion of the monomeric form of Lhcb1 significantly increased in barley grown under iron-deficient conditions. We hypothesize that alteration of the HvLhcb1 subpopulations modifies the organization of LHCII in the thylakoid membranes, which is a key step for thermal dissipation to compensate for excess excitation energy and thereby protect the photosystems from serious damage in iron-deficient barley leaves.

Difference in the distribution and speciation of cellular nickel between nickel‐tolerant and non‐tolerant Nicotiana tabacum L. cv. BY‐2 cells

To evaluate Ni dynamics at the subcellular level, the distribution and speciation of Ni were determined in wild-type (WT) and Ni-tolerant (NIT) tobacco BY-2 cell lines. When exposed to low but toxic levels of Ni, NIT cells were found to contain 2.5-fold more Ni (14% of whole-cell Ni values) in their cell walls than WT cells (6% of whole-cell Ni values). In addition to higher levels of Ni in the apoplast, a higher proportion (94%) of symplastic Ni was localized in the vacuoles of NIT cells than in the vacuoles of WT cells (81%). The concentration of cytosolic Ni in the NIT cells was significantly lower (18 nmol g(-1) FW) than that in the WT cells (85 nmol g(-1) FW). In silico simulation showed that 95% of vacuolar Ni was in the form of Ni-citrate complexes, and that free Ni(2+) was virtually absent in the NIT cells. On the other hand, the amount of free metal ions was markedly increased in WT cells because free citrate was depleted by chelation of Ni. A protoplast viability assay using BCECF-AM further demonstrated that the main mechanism that confers strong Ni tolerance was present in the symplast as opposed to the cell wall.

Allocation of Fe and ferric chelate reductase activities in mesophyll cells of barley and sorghum under Fe-deficient conditions

Although the photosynthetic apparatus requires large amounts of Fe, the adaptive mechanisms of mesophyll cells for Fe acquisition under Fe-deficient conditions are unknown. Barley and sorghum, which are tolerant and susceptible to Fe deficiency, respectively, have similar Fe and chlorophyll contents in their leaves. However, the Fe-deficient barley photosynthetic apparatus was functional while that of sorghum was not. We show that barley preferentially allocates Fe to thylakoid membranes under Fe-deficient conditions. On the other hand, in sorghum, the proportion of leaf Fe allocated to thylakoids was not altered by Fe deficiency. The relationship between the maintenance of photosynthesis and light-dependent ferric chelate reductase activity on plasma membranes and chloroplast envelopes is also discussed.

STUDIES ON CONTROLLED POTASSIUM FERTILIZERS : I. Relative Effectiveness of Various Hardly Soluble Potassium Compounds as Source of Slow-release

Abstract Relative effectiveness of various hardly soluble K materials as sources of slow availability for plants was compared by uptake of K in Brassica seedlings grown in quartz sand-nutrient medium with occasional leaching, and by the release pattern of K. Material characteristics exert a great influence on K availability. Water solubility is not a dominant factor for controlling the availability of K to the plants, but particle sizes and the reaction of K in fertilizers with nutrient ions in the medium play a significant role in the release pattern of K. Moreover, the plant roots have an ability to accelerate K release from such hardly soluble aources as fused potassium phosphate, KMgPO4, and K2CaP2O7. According to the results obtained, that is, total dry matter production, pattern of K uptake through four successive croppings and loss of K by leaching the examined materials appear to be divided into the following three groups: a) Materials having a high degree of slow availability-KMgPO4 (+3 mesh), fu...

Base to Tip and Long-Distance Transport of Sodium in the Root of Common Reed [Phragmites australis (Cav.) Trin. ex Steud.] at Steady State Under Constant High-Salt Conditions

We analyzed the directions and rates of translocation of sodium ions (Na(+)) within tissues of a salt-tolerant plant, common reed [Phragmites australis (Cav.) Trin. ex Steud.], and a salt-sensitive plant, rice (Oryza sativa L.), under constant high-salt conditions using radioactive (22)Na tracer and a positron-emitting tracer imaging system (PETIS). First, the test plants were incubated in a nutrient solution containing 50 mM NaCl and a trace level of (22)Na for 24 h (feeding step). Then the original solution was replaced with a fresh solution containing 50 mM NaCl but no (22)Na, in which the test plants remained for >48 h (chase step). Non-invasive dynamic visualization of (22)Na distribution in the test plants was conducted during feeding and chase steps with PETIS. Our results revealed that (22)Na was absorbed in the roots of common reed, but not transported to the upper shoot beyond the shoot base. During the chase step, a basal to distal movement of (22)Na was detected within the root tissue over >5 cm with a velocity of approximately 0.5 cm h(-1). On the other hand, (22)Na that was absorbed in the roots of rice was continuously translocated to and accumulated in the whole shoot. We concluded that the basal roots and the shoot base of common reed have constitutive functions of Na(+) exclusion only in the direction of root tips, even under constant high-salt conditions. This function apparently may contribute to the low Na(+) concentration in the upper shoot and high salt tolerance of common reed.

Fe deficiency induces phosphorylation and translocation of Lhcb1 in barley thylakoid membranes

HvLhcb1 a major light‐harvesting chlorophyll a/b‐binding protein in barley, is a critical player in sustainable growth under Fe deficiency. Here, we demonstrate that Fe deficiency induces phosphorylation of HvLhcb1 proteins leading to their migration from grana stacks to stroma thylakoid membranes. HvLhcb1 remained phosphorylated even in the dark and apparently independently of state transition, which represents a mechanism for short‐term acclimation. Our data suggest that the constitutive phosphorylation‐triggered translocation of HvLhcb1 under Fe deficiency contributes to optimization of the excitation balance between photosystem II and photosystem I, the latter of which is a main target of Fe deficiency.

Modulation of macronutrient metabolism in barley leaves under iron-deficient condition

Iron (Fe) deficiency primarily damages photosystems. A large proportion of the reducing equivalents in mesophyll cells are dependent on the photosynthetic apparatus in the chloroplasts; thus, Fe deficiency profoundly affects nitrogen (N) and sulfur (S) assimilation. Microarray data suggested that nutrient metabolisms concerning the assimilation and re-utilization of essential elements were modulated in barley under Fe-deficient condition. We compared the concentrations of the major essential elements between Fe-deficient barley leaves and Fe-deficient rice leaves. The Fe-deficient barley and rice plants had the same Fe and chlorophyll concentrations, but growth was reduced more in Fe-deficient rice than in Fe-deficient barley. The accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase protein and nitrite reductase, sulfite reductase, and ferredoxin-dependent glutamate synthase mRNAs was reasonably decreased in the chlorotic young leaves of Fe-deficient barley. , , , , and Ca2+ concentrations were altered to a larger extent in Fe-deficient rice leaves than in Fe-deficient barley leaves, even in the non-chlorotic old leaves. In this paper, we discuss the adaptation of macronutrient metabolism to Fe deficiency in barley leaves.

Growth injury induced by high pH in rice and tomato

Abstract An extremely high pH, above 10, can occur in sodic soils and even in saline soils after heavy rainfall. The indirect and adverse effects on plant growth that are induced by a high soil pH have been well clarified and include nutritional disorders such as P, Fe and Zn deficiencies and NH3 and HCO3 − toxicities. However, studies of the growth injuries induced by the high pH itself are quite limited. We conducted studies to clarify the effect of a high pH on the growth of rice and tomato using a solution culture system developed to eliminate nutrient deficiencies and NH3 and HCO3 − toxicities. Although the P, Fe and Zn contents in the shoots were at a sufficiently high level, growth of the tomato and rice was markedly reduced by the high pH conditions (at pH 10 and 11). Our results show the existence of growth injuries in higher plants, induced by a pH above 10. Inhibition of root elongation might be the primary growth disturbance induced by the direct adverse effect of the high pH.

Studies on controlled potassium fertilizers: II. Evaluation of Potassium Silicates as Slow-release Sources of Potassium*

Abstract Three K silicates having SiO2/K2O ratios of 4, 5, and 6 were compared with single and split applications of KCI, (KPO3)n, and sulfur-coated KCI (SCK-34) for their availability to four cuttings of common bermudagrass. At the rate of 200 mg of K/pot, all silicates applied in fine particles gave the same pattern of yield and K uptake as readily soluble KCl; however, less response to these finely sized K silicates at applications from 200 to 500 mg of K/pot suggests that they supply K more slowly than do soluble sources. K2O.6SiO2, when granulated in the size of 0.41-1.2 or 1.65-2.36 rom gave typical yieiJ and K uptake patterns of slowrelease sources similar to those for SCK-34 at both rates of application. (KPO3) n supplied K in the same pattern as KCl and no effect of granulation was observed. A better balanced K supply through the whole period and the production of forage of more stable mineral composition is expected by the use of these slow-release K sources.

Detoxification of cadmium (Cd) by a novel Cd-associated and Cd-induced molecule in the stem of common reed

Common reed (Phragmites australis) is a phytoremediator tolerant to heavy metals. In this study, we found that 70% of the cadmium (Cd) found in the stem of common reed exists in a soluble form, with more than half of the soluble Cd in the 10- to 50-kDa fraction. Based on an enzyme degradation assay, the major component of the Cd-associated molecule is assumed to be an amylopectin-like α-glucan. This molecule may associate with Cd via the carboxyl group, rather than the thiol group. The conditions required for the disengagement of Cd from the 10- to 50-kDa fraction indicated that disulfide bonds and other intramolecular interactions may contribute to maintaining the proper conformation of the molecule and to stabilizing its association with Cd. Accumulation of the Cd-associated molecule was induced by Cd stress, and the molecule was found to be also associated with Cu and Fe. Thus, we have identified a novel mechanism of Cd-pooling, namely, the association of Cd with an α-glucan-like molecule in reed stem.