The continuing rise in atmospheric [CO2] is predicted to have diverse and dramatic effects on the productivity of agriculture, plant ecosystems and gas exchange. Stomatal pores in the epidermis provide gates for the exchange of CO2 and water between plants and the atmosphere, processes vital to plant life. Increased [CO2] has been shown to enhance anion channel activity proposed to mediate efflux of osmoregulatory anions (Cl- and malate(2-)) from guard cells during stomatal closure. However, the genes encoding anion efflux channels in plant plasma membranes remain unknown. Here we report the isolation of an Arabidopsis gene, SLAC1 (SLOW ANION CHANNEL-ASSOCIATED 1, At1g12480), which mediates CO2 sensitivity in regulation of plant gas exchange. The SLAC1 protein is a distant homologue of bacterial and fungal C4-dicarboxylate transporters, and is localized specifically to the plasma membrane of guard cells. It belongs to a protein family that in Arabidopsis consists of four structurally related members that are common in their plasma membrane localization, but show distinct tissue-specific expression patterns. The loss-of-function mutation in SLAC1 was accompanied by an over-accumulation of the osmoregulatory anions in guard cell protoplasts. Guard-cell-specific expression of SLAC1 or its family members resulted in restoration of the wild-type stomatal responses, including CO2 sensitivity, and also in the dissipation of the over-accumulated anions. These results suggest that SLAC1-family proteins have an evolutionarily conserved function that is required for the maintenance of organic/inorganic anion homeostasis on the cellular level.

No abstract

The present study experimentally demonstrated that solid H 2 O is formed through the surface reaction OH + H 2 at 10 K. This is the first experimental evidence of solid H 2 O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H 2 O formation through the reaction OH + H 2 is about one order of magnitude more effective than HDO formation through the reaction OH + D 2 . This significant isotope effect results from differences in the effective mass of each reaction, indicating that the reactions proceed through quantum tunneling.

No abstract

In molecular clouds at temperatures as low as 10 K, all species except hydrogen and helium should be locked in the heterogeneous ice on dust grain surfaces.Nevertheless, astronomical observations have detected over 150 different species in the gas phase in these clouds. The mechanism by which molecules are released from the dust surface below thermal desorption temperatures to be detectable in the gas phase is crucial for understanding the chemical evolution in such cold clouds. Chemical desorption, caused by the excess energy of an exothermic reaction, was first proposed as a key molecular release mechanism almost 50 years ago 1 . Chemical desorption can, in principle, take place at any temperature, even below the thermal desorption temperature. Therefore, astrochemical net-work models commonly include this process 2,3 . Although there have been a few previous experimental efforts 4-6 , no infrared measurement of the surface (which has a strong advantage to quantify chemical desorption) has been performed. Here, we report the first infrared in situ measurement of chemical desorption during the reactions H + H 2 S → HS + H 2 (reaction 1) and HS + H → H 2 S (reaction 2), whichare key to interstellar sulphur chemistry 2,3 . The present study clearly demonstrates that chemical desorption is a more efficient process for releasing H 2 S into the gas