White lupin (Lupinus albus) is able to adapt to phosphorus deficiency by producing proteoid roots that release a huge amount of organic acids, resulting in mobilization of sparingly soluble soil phosphate in rhizosphere. The mechanisms responsible for the release of organic acids by proteoid root cells, especially the trans-membrane transport processes, have not been elucidated. Because of high cytosolic pH, the release of undissociated organic acids is not probable. In the present study, we focused on H ϩ export by plasma membrane H ϩ ATPase in active proteoid roots. In vivo, rhizosphere acidification of active proteoid roots was vanadate sensitive. Plasma membranes were isolated from proteoid roots and lateral roots from P-deficient and -sufficient plants. In vitro, in comparison with two types of lateral roots and proteoid roots of P-sufficient plants, the following increase of the various parameters was induced in active proteoid roots of P-deficient plants: (a) hydrolytic ATPase activity, (b) V max and K m , (c) H ϩ ATPase enzyme concentration of plasma membrane, (d) H ϩ -pumping activity, (e) pH gradient across the membrane of plasmalemma vesicles, and (f) passive H ϩ permeability of plasma membrane. In addition, lower vanadate sensitivity and more acidic pH optimum were determined for plasma membrane ATPase of active proteoid roots. Our data support the hypothesis that in active proteoid root cells, H ϩ and organic anions are exported separately, and that modification of plasma membrane H ϩ ATPase is essential for enhanced rhizosphere acidification by active proteoid roots.P is one of the most important plant nutrients that significantly affect growth and metabolism. Although the total amount of P in soil may be high, it is often present in unavailable forms such as phytic acid (Richardson, 1994), or Ca, Fe, and Al phosphates (Holford, 1997). Low availability of P is a major constraint for crop production in many low-input systems of agriculture worldwide, especially in the highly weathered soils of the humid tropics and subtropics, in many sandy soils of the semiarid tropics, and in calcareous soils of the temperate regions, where crop productivity is severely compromised through lack of available P (Raghothama, 1999). Also, after application of P to the soil the recovery of applied P by crop plants in a growing season is very low, because in the soil more than 80% of the P becomes immobile and unavailable for plant uptake due to adsorption on Al or Fe oxides/hydroxides, precipitation with Ca, or conversion to organic forms (Holford, 1997).Higher plants have developed various strategies of acquiring sparingly soluble nutrients from soil. In response to P deficiency, various species from different families develop so-called proteoid roots. These are bottlebrush-like clusters of rootlets of limited growth with an average length of 0.5 to 1 cm. The rootlets are closely arranged along lateral roots and are usually covered with long and dense root hairs (Purnell, 1960; Dinkelaker et al., 1995;Watt and Evans...

inhibitors (BNIs). The chemical structure was analyzed which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH 4 + in the root environment and the stimulatory effect of NH 4 + lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED 50 0.2 μM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED 50 100 μM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay. Conclusions There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.

The bioavailability of phosphorus (P) in sediments from West Lake and Lake Tai (China) and Lough Erne (Northern Ireland) was evaluated using total P (TP), water soluble P (WSP), readily desorbable P (RDP), algal available P (AAP) and Olsen-P. The results indicated that the TP content, the amounts of phosphorus extracted by each method and their proportions to TP varied widely between sediments of the three lakes. TP and chemical extractable phosphorus in the sediments of Lough Erne were considerably higher than those of the two lakes in China. Although TP in the West Lake sediments was similar to that of Lake Tai, the extractable phosphorus data suggested that the bioavailability of P in West Lake sediments was higher than that in sediments from Lake Tai. Nevertheless, the rank order of extraction e ciency was the same in all lakes and the amount extracted was in the sequence AAP b Olsen-P b WSP b RDP. There was a good correlation between extracted and TP in all the methods examined. Ó

MicroRNAs (miRNAs) are a newly discovered class of non-protein-coding small RNAs with roughly 22 nucleotidelong. Increasing evidence has shown that miRNAs play multiple roles in biological processes, including development, cell proliferation and apoptosis and stress responses. In this research, several approaches were combined to make computational prediction of potential miRNAs and their targets in Brassica napus. We used previously known miRNAs from Arabidopsis, rice and other plant species against both expressed sequence tags (EST) and genomic survey sequence (GSS) databases to search for potential miRNAs in B. napus. A total of 21 potential miRNAs were detected following a range of strict filtering criteria. Using these potential miRNA sequences, we could further blast the mRNA database and found 67 potential targets in this species. According to the mRNA target information provided by NCBI (http:// www.ncbi.nlm.nih.gov/), most of the target mRNAs appeared to be involved in plant growth, development and stress responses. To validate the prediction of miRNAs in B. napus, we performed a RT-PCR based assay of mature miRNA expression. Five miRNAs were identified in response to auxin, cadmium stress and phosphate starvation. So far, little is known about experimental or computational identification of miRNA in B. napus species. To improve efficiency for blast search, we developed an implementation (miRNAassist) that can identify homologs of miRNAs and their targets, with high sensitivity and specificity. The program is allowed to be run on Windows Operation System platform. miRNAassist is freely available if required.

MicroRNAs (miRNAs) have emerged as a class of gene expression regulators that play crucial roles in many biological processes. Recently, several reports have revealed that micoRNAs participate in regulation of symbiotic interaction between plants and nitrogen-fixing rhizobia bacteria. However, the role of miRNAs in another type of plant-microbe interaction, arbuscular mycorrhizal (AM) symbiosis, has not been documented. We carried out a microarray screen and poly(A)-tailed reverse transcriptase-polymerase chain reaction (RT-PCR) validation for miRNA expression in tomato (Solanum lycopersicum) under varying phosphate (Pi) availability and AM symbiosis conditions. In roots, miRNA158, miRNA862-3p, miRNA319, miRNA394 and miR399 were differentially regulated under three different treatments, Pi sufficient (+P ), Pi deficient (-P) and AM symbiosis (+M ). In leaves, up to 14 miRNAs were up- or down-regulated under either or both of the Pi treatments and AM symbiosis, of which miR158, miR319 and miR399 were responsive to the treatments in both roots and leaves. We detected that miR395, miR779.1, miR840 and miR867 in leaves were specifically responsive to AM symbiosis, which is independent of Pi availability, whereas miR398 in leaves and miR399 in both roots and leaves were Pi starvation induced. Furthermore, miR158 in roots as well as miR837-3p in leaves were responsive to both Pi deprivation and AM colonization. In contrast, miR862-3p in roots was responsive to Pi nutrition, but not to AM symbiosis. Moreover, the group of miRNA consisting miR319 and miR394 in roots and miR158, miR169g*, miR172, miR172b*, miR319, miR771 and miR775 in leaves were up- and down-regulated by Pi starvation, respectively. The data suggest that altered expression of distinct groups of miRNA is an essential component of Pi starvation-induced responses and AM symbiosis.