Responses of plant leaf stomatal conductance and photosynthesis to water deficit have been extensively reported; however, little is known concerning the relationships of stomatal density with regard to water status and gas exchange. The responses of stomatal density to leaf water status were determined, and correlation with specific leaf area (SLA) in a photosynthetic study of a perennial grass, Leymus chinensis, subjected to different soil moisture contents. Moderate water deficits had positive effects on stomatal number, but more severe deficits led to a reduction, described in a quadratic parabolic curve. The stomatal size obviously decreased with water deficit, and stomatal density was positively correlated with stomatal conductance (gs), net CO2 assimilation rate (An), and water use efficiency (WUE). A significantly negative correlation of SLA with stomatal density was also observed, suggesting that the balance between leaf area and its matter may be associated with the guard cell number. The present results indicate that high flexibilities in stomatal density and guard cell size will change in response to water status, and this process may be closely associated with photosynthesis and water use efficiency.

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A hydrothermal route to water-stable luminescent carbon dots as nanosensors for pH and temperature, Carbon (2014), doi: http:// dx. AbstractCarbon dots (CDs) as a class of heavy-metal-free fluorescent nanomaterials has drawn increasing attention in recent years due to their high optical absorptivity, chemical stability, biocompatibility, and low toxicity. Herein, we report a facile method to prepare stable CDs by hydrothermal treatment of glucose (glc) in the presence of glutathione (GSH). With this approach, the formation and the surface passivation of CDs are carried out simultaneously, resulting in intrinsic fluorescence emission. The influence of reaction temperature, reaction time and feed ratio of GSH/glc on the photoluminescence property of CDs is studied. The as-prepared CDs are characterized by UV-Vis, photoluminescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscope, from which their structural information and property are interpreted. Owning to their pronounced temperature dependence of the steady-state fluorescence emission spectra and pH-responsive behavior, resultant CDs could work as versatile nanothermometry devices by taking advantage of the temperature sensitivity of their emission intensity, which change considerably over the physiological temperature range (1560 ºC), as well as a sensor for pH.

Drought and high-temperature stresses have been extensively studied; however, little is known about their combined impact on plants. In the present study, we determined the photosynthetic gas exchange, chlorophyll fluorescence, nitrogen level, and lipid peroxidation of the leaves of a perennial grass (Leymus chinensis (Trin.) Tzvel.) subjected to three constant temperatures (23, 29 and 32 degrees C), and five soil-moisture levels (75-80%, 60-65%, 50-55%, 35-40% and 25-30% of field capacity, respectively). High temperature significantly decreased plant biomass, leaf green area, leaf water potential, photosynthetic rate (A), maximal efficiency of PSII photochemistry (F (v)/F (m)), actual PSII efficiency (Phi(PSII)), the activities of nitrate reductase (NR; EC 1.6.6.1) and glutamine synthetase (GS; EC 6.3.1.2), but markedly increased the ratio of leaf area to leaf weight (SLA), endopeptidase (EP; EC 3.4.24.11) activity, and malondialdehyde (MDA) content, especially under severe water stress conditions. The A and F (v)/F (m) were significantly and positively correlated with leaf-soluble protein content, and the activities of NR and GS. However, both photosynthesis parameters were significantly and negatively correlated with EP activity and MDA content (P < 0.05). It is suggested that high temperature, combined with severe soil drought, might reduce the function of PSII, weaken nitrogen anabolism, strengthen protein catabolism, and provoke lipid peroxidation. The results also indicate that severe water stress might exacerbate the adverse effects of high temperature, and their combination might reduce the plant productivity and distribution range of L. chinensis in the future.