Alteration of stimulus-specific guard cell calcium oscillations and stomatal closing in Arabidopsis det3 mutant.

Cytosolic calcium oscillations control signaling in animal cells, whereas in plants their importance remains largely unknown. In wild-type Arabidopsis guard cells abscisic acid, oxidative stress, cold, and external calcium elicited cytosolic calcium oscillations of differing amplitudes and frequencies and induced stomatal closure. In guard cells of the V-ATPase mutant det3, external calcium and oxidative stress elicited prolonged calcium increases, which did not oscillate, and stomatal closure was abolished. Conversely, cold and abscisic acid elicited calcium oscillations in det3, and stomatal closure occurred normally. Moreover, in det3 guard cells, experimentally imposing external calcium-induced oscillations rescued stomatal closure. These data provide genetic evidence that stimulus-specific calcium oscillations are necessary for stomatal closure.

Ecology and behavior of the desert burrowing cockroach,Arenivaga sp. (Dictyoptera, Polyphagidae).

Measurements were made of environmental conditions in the microhabitat ofArenivaga sp., and results were correlated with their diurnal migratory behavior. The animals live in sand dunes with less than 1% moisture most of the year. During the day in spring, summer and fall they borrow in the sand at a depth of 20-60 cm, while at night, when surface temperatures have cooled, they borrow within 1-3 cm of the surface. In winter they are rarely found near the surface, remaining active at lower levels during both night and day. Adult males were collected on the surface or at a depth of 20-60 cm, but they were never observed burrowing near the surface at 1-3 cm.The larvae and adult females are photonegative and remain at lower levels during the day, even though daytime temperature and humidity are sometimes favorable near the surface. In the summer, they migrate to the surface about 2 h later after darkness than in spring and fall. Temperature measurements indicated this was probably due to delayed nighttime cooling of the surface in the summer months. By burrowing near the surface the animals can experience cooler nighttime temperatures and water-loss may be reduced during the summer. This behavior may also facilitate disperasal and mating.The cockroaches feed on decaying leaves and the roots of desert shrubs. Since the latter have 35-38% moisture, they are probably the main source of water for these animals.

Antennal chemoreceptors of the desert burrowing cockroach, Arenivaga sp.

The antennae of Arenivaga have six types of chemoreceptor sensilla. Some of these have unusual morphological features which may be adaptations for survival in a dry habitat. The sensory dendrites are well protected by cuticular structures, and in some receptors stimulatory molecules must pass through long channels or through pores filled with strands to reach the sensory cells. Large grooved pegs (possibly pheromone receptors) are numerous on antennae of adult males, and grooved sensilla are described here in detail for the first time. Thin-walled pegs, present in males and females, do not have pore tubules or hollow filaments as observed in many other insects. Rather, they contain structures designated here as pore strands, since they have a dense core rather than a light center as previously described for pore tubules and filaments. These strands do not appear to be evaginations of the dendritic membrane, but are probably formed in association with the cuticular structures of the sensilla.

The role of pore structures in the selective permeability of antennal sensilla of the desert burrowing cockroach, Arenivaga sp.

To obtain information about the chemical composition of pore structures in antennal sensilla, the antennae were exposed to lipid solvents, or they were prepared to show negative-contrast images in electron micrographs. A heavy-metal tracer, lanthanum nitrate, was also used to indicate the permeability of the receptors to water. The grooves of the large grooved peg open into tubular cavities containing electron-opaque material, through which stimulatory molecules must pass to reach the sensory dendrites at the center of the sensillum. The material in these cavities was removed by chloroform or acetone, suggesting a lipid composition. Lanthanum penetrated this receptor only after it had been exposed to acetone or chloroform. Strands at pores of the thin-walled pegs were also removed by the lipid solvents, and the water-soluble tracer failed to penetrate these receptors unless they had been previously exposed to chloroform or acetone. The pore structures appear to be hydrophobic, allowing entry of lipid-soluble substances, while preventing passage of water. The differential action of the solvents on the various types of sensilla suggests that receptor discrimination among different classes of chemical stimuli may be partially determined by the chemical properties of structures at the sensillar pores.

Dominant negative guard cell K+ channel mutants reduce inward-rectifying K+ currents and light-induced stomatal opening in arabidopsis.

Inward-rectifying potassium (K+(in)) channels in guard cells have been suggested to provide a pathway for K+ uptake into guard cells during stomatal opening. To test the proposed role of guard cell K+(in) channels in light-induced stomatal opening, transgenic Arabidopsis plants were generated that expressed dominant negative point mutations in the K+(in) channel subunit KAT1. Patch-clamp analyses with transgenic guard cells from independent lines showed that K+(in) current magnitudes were reduced by approximately 75% compared with vector-transformed controls at -180 mV, which resulted in reduction in light-induced stomatal opening by 38% to 45% compared with vector-transformed controls. Analyses of intracellular K+ content using both sodium hexanitrocobaltate (III) and elemental x-ray microanalyses showed that light-induced K+ uptake was also significantly reduced in guard cells of K+(in) channel depressor lines. These findings support the model that K+(in) channels contribute to K+ uptake during light-induced stomatal opening. Furthermore, transpirational water loss from leaves was reduced in the K+(in) channel depressor lines. Comparisons of guard cell K+(in) current magnitudes among four different transgenic lines with different K+(in) current magnitudes show the range of activities of K+(in) channels required for guard cell K+ uptake during light-induced stomatal opening.