Higher plants have both high-and low-affinity nitrate uptake systems. These systems are generally thought to be genetically distinct. Here, we demonstrate that a well-known low-affinity nitrate uptake mutant of Arabidopsis, chl1 , is also defective in high-affinity nitrate uptake. Two to 3 hr after nitrate induction, uptake activities of various chl1 mutants at 250 M nitrate (a high-affinity concentration) were only 18 to 30% of those of wild-type plants. In these mutants, both the inducible phase and the constitutive phase of high-affinity nitrate uptake activities were reduced, with the inducible phase being severely reduced. Expressing a CHL1 cDNA driven by the cauliflower mosaic virus 35S promoter in a transgenic chl1 plant effectively recovered the defect in high-affinity uptake for the constitutive phase but not for the induced phase, which is consistent with the constitutive level of CHL1 expression in the transgenic plant. Kinetic analysis of nitrate uptake by CHL1 -injected Xenopus oocytes displayed a biphasic pattern with a Michaelis-Menten K m value of ‫ف‬ 50 M for the high-affinity phase and ‫ف‬ 4 mM for the low-affinity phase. These results indicate that in addition to being a low-affinity nitrate transporter, as previously recognized, CHL1 is also involved in both the inducible and constitutive phases of high-affinity nitrate uptake in Arabidopsis. INTRODUCTIONNitrate uptake is a physiological process critical for plant growth. Plants have evolved a host of transport systems to accommodate external nitrate concentration levels that can vary up to 10,000 times (Jackson and Caldwell, 1993), and expression of these systems appears to be tightly regulated (Hoff et al., 1994;Crawford, 1995; Glass and Siddiqi, 1995;Wirén et al., 1997). Early experiments with kinetic measurements have identified at least three nitrate transport systems in higher plants. One operates at high nitrate concentrations (over ‫ف‬ 0.5 mM) and is constitutively expressed. It is usually referred to as the cLATS (for constitutive low-affinity transport system); at ‫ف‬ 0.5 mM nitrate, uptake is performed by two HATS (for high-affinity transport system). One is constitutive (cHATS) and the other is inducible (iHATS) (reviewed in, e.g., Larsson and Ingemarsson, 1989; Glass and Siddiqi, 1995). Extensive efforts have been directed in recent years toward cloning and characterizing the genes that are responsible for these transport systems (reviewed in Crawford and Glass, 1998; Daniel-Vedele et al., 1998). As a result, our knowledge about nitrate transporters of higher plants is rapidly accumulating, and it is now clear that the three-system (cLATS, iHATS, and cHATS) model derived from early physiological studies is overly simplified.For example, cloning and functional characterization of the Arabidopsis nitrate transporter gene CHL1 ( AtNRT1 ) (Tsay et al., 1993; Huang et al., 1996) have shown that CHL1 is responsible for an additional LATS that is nitrate inducible, that is, iLATS, which was not revealed by previous physiological char...

The output enhancement of a green InGaN/GaN quantum-well (QW) light-emitting diode (LED) through the coupling of a QW with localized surface plasmons (LSPs), which are generated on Ag nanostructures on the top of the device, is demonstrated. The suitable Ag nanostructures for generating LSPs of resonance energies around the LED wavelength are formed by controlling the Ag deposition thickness and the post-thermal-annealing condition. With a 20 mA current injected onto the LED, enhancements of up to 150% in electroluminescence peak intensity and of 120% in integrated intensity are observed. By comparing this with a similar result for a blue LED previously published, it is confirmed that surface plasmon coupling for emission enhancement can be more effective for an InGaN/GaN QW of lower crystal quality, which normally corresponds to the emission of a longer wavelength.

Anticancer therapies are often compromised by nonspecific effects and challenged by tumour environments’ inherent physicochemical and biological characteristics. Often, therapeutic effect can be increased by addressing multiple parameters simultaneously. Here we report on exploiting extravasation due to inherent vascular leakiness for the delivery of a pH-sensitive polymer carrier. Tumours’ acidic microenvironment instigates a charge reversal that promotes cellular internalization where endosomes destabilize and gene delivery is achieved. We assess our carrier with an aggressive non-small cell lung carcinoma (NSCLC) in vivo model and achieve >30% transfection efficiency via systemic delivery. Rejuvenation of the p53 apoptotic pathway as well as expression of KillerRed protein for sensitization in photodynamic therapy (PDT) is accomplished. A single administration greatly suppresses tumour growth and extends median animal survival from 28 days in control subjects to 68 days. The carrier has capacity for multiple payloads for greater therapeutic response where inter-individual variability can compromise efficacy.

The authors demonstrate the coupling effects between the quantum well ͑QW͒ and surface plasmon ͑SP͒ generated nearby on the p-type side in an InGaN / GaN single-QW light-emitting diode ͑LED͒. The QW-SP coupling leads to the enhancement of the electroluminescence ͑EL͒ intensity in the LED sample designed for QW-SP coupling and reduced SP energy leakage, when compared to a LED sample of weak QW-SP coupling or significant SP energy loss. In the LED samples of significant QW-SP coupling, the blueshifts of the photoluminescence and EL emission spectra are observed, indicating one of the important features of such a coupling process. The device performance can be improved by using the n-type side for SP generation such that the device resistance can be reduced and the QW-SP coupling effect can be enhanced ͑by further decreasing the distance between the QW and metal͒ because of the higher carrier concentration in the n-type layer.

An apparatus was designed that permitted acetylene reduction (N2 fixation) by root nodules to be ineasured in situ simultaneously with net photosynthesis, dark respiration, and transpiration of the shoot in soybean plants (Glycine max [L.] Merr. var. Beeson). Tests showed that acetylene reduction was linear with time for at least a hours, except for the first 30 to 60 minutes. Endogenous ethylene production did not affect the measurements. Successive determinations of acetylene reduction could be made without apparent aftereffects onl the plant.This apparatus was used to investigate the effects of soil flooding and desiccation on acetylene reduction under conditions where soil, nodule, and leaf water potentials could be measured. No acety-lene reduction was detectable in flooded soil or in soil desiccated to a water potential of -19.5 bars. Between these extremes, acetylene reduction displayed a sharp optimum. Removing the soil eliminated the inhibitory effects of flooding, suggesting that rates of gas exchange were restricted between the nodules and thie atnosphere at soil water potentials above -2 bars.As the soil desiccated further, acetylene reduction decreased, and the decrease was correlated with decreases in photosvnthesis and transpiration. Although dark respiration was inhibited, it was not affected to thie extent that acetylene reduction, photosynthesis, or transpiration were. Consequently, it was concluded that photosynthesis, transpiration, or some direct effect on the nodules other than that caused by respiration were most likely to account for the inhibition of acetylene reduction at soil water potentials below -2 bars. (11,13,22,29,30). Generally, plant moisture status was not determined, but in those cases where soil water potential was measured, one study showed a decrease (22) whereas the other showed an enhancement (13) in acetylene reduction (N2 fixation) at low soil water potentials. Sprent (29) observed a decrease in acetylene reduction and nodule respiration when detached nodules lost 20 % of their fresh weight during drying in air. In intact soybean, acetylene reduction decreased at soil water contents below "field capacity" (30), and Sprent suggested that direct effects of low water potentials on the nodules may account for the decrease in activity for acetylene reduction, probably because of an inhibition of nodule respiration (11,29,30).Nitrogen fixation depends on a number of factors which must be supplied either by the host plant or by the soil. Photosynthates are required in order for nodule respiration to supply the reductant and ATP necessary for the reduction of N2, and for the carbon chains that combine with NH3 before it is exported by the nodules (3, 12). Since the amino acid products of N2 fixation move to the shoot in the transpiration stream (26-28), transpiration may be required, particularly since the accumulation of NH3 in the nodules might cause a repression of the synthesis of nitrogenase, as it does in free-living organisms (10, 25). In addition to water from...

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We report the synthesis and characterization of alloyed Sn–Pb methylammonium mixed-halide perovskites (CH3NH3Sn y Pb1–y I3–x Cl x ) to extend light harvesting toward the near-infrared region for carbon-based mesoscopic solar cells free of organic hole-transport layers. The proportions of Sn in perovskites are well-controlled by mixing tin chloride (SnCl2) and lead iodide (PbI2) in varied stoichiometric ratios (y = 0–1). SnCl2 plays a key role in modifying the lattice structure of the perovskite, showing anomalous optical and optoelectronic properties; upon increasing the concentration of SnCl2, the variation of the band gap and band energy differed from those of the SnI2 precursor. The CH3NH3Sn y Pb1–y I3–x Cl x devices showed enhanced photovoltaic performance upon increasing the proportion of SnCl2 until y = 0.75, consistent with the corresponding potential energy levels. The photovoltaic performance was further improved upon adding 30 mol % tin fluoride (SnF2) with device configuration FTO/TiO2/Al2O3/NiO/C, producing the best power conversion efficiency, 5.13%, with great reproducibility and intrinsic stability.

The role of photosynthesis and transpiration in the desiccation-induced inhibition of acetylene reduction (nitrogen fixation) was investigated in soybean (Glycine max [L.] Merr. var. Beeson) using an apparatus that permitted simultaneous measurements of acetylene reduction, net photosynthesis, and transpiration. The inhibition of acetylene reduction caused by low water potentials and their aftereffects could be reproduced by depriving shoots of atmospheric C02 even though the soil remained at water potentials that should have favored rapid acetylene reduction. The inhibition of acetylene reduction at low water potentials could be partially reversed by exposing the shoots to high C02 concentrations. When transpiration was varied independently of photosynthesis and dark respiration in plants having high water potentials, no effects on acetylene reduction could be observed. There was no correlation between transpiration and acetylene reduction in the C02 experiments. Therefore, the correlation that was observed between transpiration and acetylene reduction during desiccation was fortuitous. We conclude that the inhibition of shoot photosynthesis accounted for the inhibition of nodule acetylene reduction at low water potentials.