Pigeon pea was shown to be more efficient at utilizing iron-bound phosphorus (Fe-P) than several other crop species. This ability is attributed to root exudates, in particular piscidic acid and its p-O-methyl derivative, which release phosphorus from Fe-P by chelating Fe(3+). Pigeon pea is normally intercropped with cereals under low-input conditions in the Indian subcontinent. Although pigeon pea can utilize the relatively insoluble Fe-P, intercropped cereals must rely on the more soluble calcium-bound phosphorus. This finding suggests that cultivation of pigeon pea increases total phosphorus availability in cropping systems with low available phosphorus.

No abstract

Not only Al but also Sr and Ba applications inhibited root growth of rice cultivars under low Ca conditions. As expected, rice cultivars more tolerant of Sr and Ba were also tolerant of Al (japonica > indica). Although Mg application did not affect Sr or Ba toxicity, Mg alleviated Al toxicity to the same level as Ca application. In addition, Ca application decreased the Al content in root tips without displacement. These results suggest that Ca does not have a specific, irreplaceable role in Al toxicity, unlike Sr and Ba toxicities. Alleviation of Al toxicity with increasing concentrations of Ca in rice cultivars is due to increased ionic strength, not due to decreased Al activity. The difference in Al tolerance between indica and japonica cultivars disappears under high ionic strength conditions, suggesting that different electrochemical characteristics of root-tip cells are related to the significant difference in Al tolerance under low ionic strength conditions.

f Longer-and/or branched-chain polyamines are unique polycations found in thermophiles. N 4 -aminopropylspermine is considered a major polyamine in Thermococcus kodakarensis. To determine whether a quaternary branched penta-amine, N 4 -bis(aminopropyl)spermidine, an isomer of N 4 -aminopropylspermine, was also present, acid-extracted cytoplasmic polyamines were analyzed by high-pressure liquid chromatography, gas chromatography (HPLC), and gas chromatography-mass spectrometry. N 4 -bis(aminopropyl)spermidine was an abundant cytoplasmic polyamine in this species. To identify the enzyme that catalyzes N 4 -bis(aminopropyl)spermidine synthesis, the active fraction was concentrated from the cytoplasm and analyzed by linear ion trap-time of flight mass spectrometry with an electrospray ionization instrument after analysis by the MASCOT database. TK0545, TK0548, TK0967, and TK1691 were identified as candidate enzymes, and the corresponding genes were individually cloned and expressed in Escherichia coli. Recombinant forms were purified, and their N 4 -bis(aminopropyl)spermidine synthesis activity was measured. Of the four candidates, TK1691 (BpsA) was found to synthesize N 4 -bis(aminopropyl)spermidine from spermidine via N 4 -aminopropylspermidine. Compared to the wild type, the bpsA-disrupted strain DBP1 grew at 85°C with a slightly longer lag phase but was unable to grow at 93°C. HPLC analysis showed that both N 4 -aminopropylspermidine and N 4 -bis(aminopropyl)spermidine were absent from the DBP1 strain grown at 85°C, demonstrating that the branched-chain polyamine synthesized by BpsA is important for cell growth at 93°C. Sequence comparison to orthologs from various microorganisms indicated that BpsA differed from other known aminopropyltransferases that produce spermidine and spermine. BpsA orthologs were found only in thermophiles, both in archaea and bacteria, but were absent from mesophiles. These findings indicate that BpsA is a novel aminopropyltransferase essential for the synthesis of branched-chain polyamines, enabling thermophiles to grow in high-temperature environments. P olyamines are small, positively charged aliphatic molecules containing more than two amine residues present in almost all living organisms. Putrescine [4], spermidine [34], and spermine [343] are polyamines commonly observed in the cells of various living organisms, from viruses to humans (1-4). Polyamines are important in cell proliferation and cell differentiation (5, 6), as well as contributing to adaptation to various stresses (7). Interestingly, in addition to common polyamines, thermophiles contain two types of unusual polyamines as major polyamines. One type consists of long linear polyamines such as caldopentamine [3333] NH, N,. Because the relative amounts of long/branched-chain polyamines in cells of (hyper)thermophiles were found to increase as growth temperatures increased, these unique polyamines are regarded as supporting the growth of thermophilic microorganisms under high-temperature conditions (18)(19)(20). An in...

The capability to utilize different forms of nitrogen (N) by sorghum (Sorghum bicolor), rice (Oryza sativa), maize (Zea mays), and pearl millet (Pennisetum glaucum) was determined in pot experiments. Seedlings were grown for 21 d without N, or with 500 mg N kg(-1) soil applied as ammonium nitrate, rice bran or a mixture of rice bran and straw. No treatment-dependent changes of root length, surface area, and fractal dimension were observed. Shoot growth and N uptake in maize and pearl millet correlated with the inorganic N (ammonium and nitrate) concentration in the soil, suggesting that these species depend upon inorganic N uptake. On the other hand, shoot growth and N uptake patterns in sorghum and rice indicated that these two species could compensate low inorganic N levels in the organic material treatments by taking up organic N (proteins). Analysis of N uptake rates in solution culture experiments confirmed that sorghum and rice roots have higher capabilities to absorb protein N than maize and pearl millet.