Thioglucoside glucohydrolase (myrosinase), TGG1, is a strikingly abundant protein in Arabidopsis guard cells. We investigated responses of tgg1-3, tgg2-1 and tgg1-3 tgg2-1 mutants to abscisic acid (ABA) and methyl jasmonate (MeJA) to clarify whether two myrosinases, TGG1 and TGG2, function during stomatal closure. ABA, MeJA and H(2)O(2) induced stomatal closure in wild type, tgg1-3 and tgg2-1, but failed to induce stomatal closure in tgg1-3 tgg2-1. All mutants and wild type showed Ca(2+)-induced stomatal closure and ABA-induced reactive oxygen species (ROS)production. A model is discussed in which two myrosinases redundantly function downstream of ROS production and upstream of cytosolic Ca(2+) elevation in ABA and MeJA signaling in guard cells.

The dynamics of polyphosphate with respect to toal phosphorus and orthophosphate levels in an arbuscular mycorrhizal association were investigated to clarify the role of polyphosphate in the symbiotic phospharus-translocation.Lotus japonicus was inoculated with Glomus sp. HR1 and grown in a two- compartment culture system in which hyphal and mycorrhizal compartments were separated by nylon mesh bags. Extraradical hyphae and mycorrhizal roots were collected from the hyphal and mycorrhizal compartments, respectively, at one h interval after phosphate application to the hyphal compartment, and polyphosphate, total phosphorus and orthophosphate levels were determined. Total phosphorus and polyphosphate levels in hyphae in the hyphal compartment increased and decreased synchronously after phosphate application, while orthophosphate levels remained constant at lower levels. The level of polyphosphate reached 64% of total phosphorus 5 h after phosphate application. Decreases in polyphosphate in hyphae in the hyphal compartment were concurrent with increases in polyphosphate in the mycorrhizal roots + hyphae in the mycorrhizal compartment. The present study demonstrated that the potential capacity of arbuscular mycorrhizal fungal cell for polyphosphate accumulation was much larger than those reported previously and suggested that polyphosphate plays a central role in the mediation of long-distance phosphorus-translocation through hyphae

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Proliferating cell nuclear antigen (PCNA) is post-translationally modified in yeast and animal cells. Major studies carried out in the last decade have focused on the role of sumoylated and ubiquitinated PCNA. Using different approaches, an interaction between plant PCNA and SUMO both in vivo and in bacteria has been demonstrated for the first time. In addition, identical sumoylation patterns for both AtPCNA1 and 2 were observed in bacteria. The plant PCNA sumoylation pattern has been shown to differ significantly from that of Saccharomyces cerevisiae. This result contrasts with a common opinion based on previous structural analysis of yeast, human, and plant PCNAs, which treats PCNA as a highly conserved protein even between species. Analyses of AtPCNA post-translational modifications using different SUMO proteins (SUMO1, 2, 3, and 5) revealed similar modification patterns for each tested SUMO protein. Potential target lysine residues that might be sumoylated in vivo were identified on the basis of in bacteria AtPCNA mutational analyses. Taken together, these results clearly show that plant PCNA is post-translationally modified in bacteria and may be sumoylated in a plant cell at various sites. These data open up important new perspectives for further detailed studies on the role of PCNA sumoylation in plant cells.

Arbuscular mycorrhizal (AM) fungi benefit their host plants by supplying phosphate obtained from the soil. Polyphosphate is thought to act as the key intermediate in this process, but little is currently understood about how polyphosphate is synthesized or translocated within arbuscular mycorrhizas. Glomus sp. strain HR1 was grown with marigold in a mesh bag compartment system, and extraradical hyphae were harvested and fractionated by density gradient centrifugation. Using this approach, three distinct layers were obtained: layers 1 and 2 were composed of amorphous and membranous materials, together with mitochondria, lipid bodies, and electron-opaque bodies, and layer 3 was composed mainly of partially broken hyphae and fragmented cell walls. The polyphosphate kinase/luciferase system, a highly sensitive polyphosphate detection method, enabled the detection of polyphosphate-synthesizing activity in layer 2 in the presence of ATP. This activity was inhibited by vanadate but not by bafilomycin A 1 or a protonophore, suggesting that ATP may not energize the reaction through H ؉ -ATPase but may act as a direct substrate in the reaction. This report represents the first demonstration that AM fungi possess polyphosphate-synthesizing activity that is localized in the organelle fraction and not in the cytosol or at the plasma membrane.Arbuscular mycorrhizal (AM) fungi are obligate biotrophs that form symbiotic associations with most land plants (29). These fungi promote the growth of host plants via enhanced uptake of phosphate (P i ) and thus play important roles in the terrestrial phosphorus cycle. In the symbiotic phase, AM fungi take up P i from soil through an extensive network of extraradical hyphae and rapidly accumulate inorganic polyphosphate (polyP). This accumulation was as rapid as that for a polyPhyperaccumulating bacterium found in activated sludge (6). PolyP is a linear polymer of three to hundreds of molecules of P i linked by high-energy phosphoanhydride bonds and has been found across all classes of organisms (19). Although polyP is considered to play a central role in long-distance translocation of P i in AM fungal associations (4, 10, 30, 31), the translocation mechanism, metabolism, and dynamics in the fungi have not been elucidated due to the difficulty in obtaining sufficient fungal material for analysis.Many enzymes/genes involved in polyP synthesis/metabolism have been identified and characterized in prokaryotes (19). For instance, exopolyphosphatase hydrolyzes the terminal highenergy bonds of polyP, and polyphosphate glucokinase (PPGK) transfers the terminal P i residue to glucose. Polyphosphate kinase 1 (PPK1) is responsible both for polyP synthesis, using ATP as a phosphoryl donor, and for the reverse ATPgenerating reaction. This enzyme is bound to the plasma membrane (18) and has been found in a wide range of bacteria (17). Unlike the case for prokaryotes, knowledge of polyP synthesis/ metabolism in eukaryotes remains limited. The first eukaryotic PPK genes, DdPPK1 (32) and DdPPK2 (14), we...

The fresh weight of Casuarina equisetifolia seedlings decreased slightly with elevation of NaCl concentration in the culture solution. Na + concentration in the shoots gradually increased with increasing NaCl concentration in the culture solution and with increasing duration of the treatment. The Na + level reached 150 mmol L −1 in seedlings treated with 500 mmol L −1 NaCl for 6 weeks. The proline content of the shoots increased with increasing NaCl concentration in the culture solution and reached 13.5 µmol g −1 fresh weight in the seedlings treated with 500 mmol L −1 NaCl for 6 weeks. The Na + concentration and proline content in the roots also increased with NaCl treatment, but the level was considerably lower than that recorded in the shoots. A highly positive correlation between Na + concentration and proline content was observed in the shoots. These results strongly suggest that C. equisetifolia plants, which are highly tolerant to salt stress, primarily synthesize proline as a major compatible solute to adjust the osmotic pressure when Na + accumulates in the cells, and maintain cell homeostasis under salt-stress conditions.

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