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Date palm Phoenix dactylifera is a desert crop well adapted to survive and produce fruits under extreme drought and heat. How are palms under such harsh environmental conditions able to limit transpirational water loss?, Here, we analysed the cuticular waxes, stomata structure and function, and molecular biology of guard cells from P. dactylifera., To understand the stomatal response to the water stress phytohormone of the desert plant, we cloned the major elements necessary for guard cell fast abscisic acid ( ABA) signalling and reconstituted this ABA signalosome in Xenopus oocytes. The Phoenix SLAC1-type anion channel is regulated by ABA kinase Pd OST1. Energy-dispersive X-ray analysis ( EDXA) demonstrated that date palm guard cells release chloride during stomatal closure. However, in Cl− medium, Pd OST1 did not activate the desert plant anion channel Pd SLAC1 per se. Only when nitrate was present at the extracellular face of the anion channel did the OST1-gated Pd SLAC1 open, thus enabling chloride release. In the presence of nitrate, ABA enhanced and accelerated stomatal closure., Our findings indicate that, in date palm, the guard cell osmotic motor driving stomatal closure uses nitrate as the signal to open the major anion channel SLAC1. This initiates guard cell depolarization and the release of anions together with potassium. [ABSTRACT FROM AUTHOR]

• The initial contact between Blumeria graminis f.sp. hordei and its host barley ( Hordeum vulgare) takes place on epicuticular waxes at the surfaces of aerial plant organs. Here, the extent to which chemical composition, crystal structure and hydrophobicity of cuticular waxes affect fungal prepenetration processes was explored. • The leaf surface properties of barley eceriferum ( cer) wax mutants were characterized in detail. Barley leaves and artificial surfaces were used to investigate the early events of fungal infection. • Even after epicuticular waxes had been stripped away, cer mutant leaf surfaces did not affect fungal prepenetration properties. Removal of total leaf cuticular waxes, however, resulted in a 20% reduction in conidial germination and differentiation. Two major components of barley leaf wax, hexacosanol and hexacosanal, differed considerably in their ability to effectively trigger conidial differentiation on glass surfaces. While hexacosanol, attaining a maximum hydrophobicity with contact angles of no more than 80, proved to be noninductive, hexacosanal significantly stimulated differentiation in c. 50% of B. graminis conidia, but only at contact angles > 80. • These results, together with an observed inductive effect of highly hydrophobic, wax-free artificial surfaces, provide new insights into the interplay of physical and chemical surface cues involved in triggering prepenetration processes in B. graminis. [ABSTRACT FROM AUTHOR]

Epicuticular wax tubules were reconstituted in vitro by recrystallizing nonacosan-10-ol from the soluble cuticular lipids of Picea pungens Engelm, on a glass support. Fumigation of these preparations for 100 h with dry O3 (1.8%), SO2 (100%) or for 1500 h with NO2 (0.1%) did not change their composition or crystal habit. Exposure of reconstituted wax tubules to 1% of dry NO2 yielded planar crystals of nonacosan-10-one after 100 h. Further exposure (264 h) resulted in the complete degradation of aggregates and the formation of nonadecanoic and eicosanoic acids. The same oxidation steps and the accompanying changes of crystal shapes could be induced by fumigation of nonacosan-10-ol tubules with 100% of dry NO2 for 0.25-1 h and for 2 h, respectively. The oxidation of nonacosan-10-ol depended on the doses applied. At ambient concentrations, equivalent doses would accumulate only over thousands of years. Oxidative transformations alone can therefore not account for the in vivo degradation of wax tubules on conifer needles. [ABSTRACT FROM AUTHOR]

Epicuticular wax tubules were reconstituted in vitro by recrystallizing nonacosan-10-ol from the soluble cuticular lipids of Picea pungens Engelm. on a glass support. Fumigation of these preparations for 100 h with dry O 3 (1.8 %), SO 2 (100%) or for 1500 h with NO 2 (0.1 %) did not change their composition or crystal habit. Exposure of reconstituted wax tubules to 1 % of dry NO 2 yielded planar crystals of nonacosan-10-one after 100 h. Further exposure (264 h) resulted in the complete degradation of aggregates and the formation of nonadecanoic and eicosanoic acids. The same oxidation steps and the accompanying changes of crystal shapes could be induced by fumigation of nonacosan-10-ol tubules with 100% of dry NO 2 for 0.25-1 hand for 2 h, respectively. The oxidation of nonacosan-10-ol depended on the doses applied. At ambient concentrations, equivalent doses would accumulate only over thousands of years. Oxidative transformations alone can therefore not account for the in vivo degradation of wax tubules on conifer needles.