Does calcium ameliorate the negative effect of NaCl on melon root water transport by regulating aquaporin activity?

The hydraulic conductance ( L ₀) of detached, exuding root systems from melon ( Cucumis melo cv. Amarillo oro) was measured. All plants received a half-strength Hoagland nutrient solution, and plants stressed either solely with NaCl (50 mM) or with NaCl (50 mM) following treatment (2 d) with CaCl₂ (10 mM) were compared with controls and CaCl₂-treated (10 mM) plants. The L ₀ of NaCl-treated plants was markedly decreased when compared to control and CaCl₂-treated plants, but the decrease was smaller when NaCl was added to plants previously treated with CaCl₂. A similar effect was observed when the flux of Ca²⁺ into the xylem and the Ca²⁺ concentration in the plasma membrane of the root cells were determined. In control, CaCl₂- and NaCl + CaCl₂-treated plants, HgCl₂ treatment (50 μM) caused a sharp decline in L ₀ to values similar to those of NaCl-stressed roots, but L ₀ was restored by treatment with 5 mM DTT. However, in NaCl roots only a slight effect of Hg²⁺ and DTT were observed. The effect of all treatments on L ₀ was similar to that on osmotic water permeability ( P _f) of individual protoplasts isolated from roots. The results suggest that NaCl decreased the passage of water through the membrane and roots by reducing the activity of Hg-sensitive water channels. The ameliorative effect of Ca²⁺ on NaCl stress could be related to water-channel function.     

Hair Snares for Noninvasive Sampling of Felids in North America: Do Gray Foxes Affect Success?

Abstract: Hair-snare sampling has become a popular technique to assess distribution and abundance of felids. Using standard hair-snaring protocols, we sampled for margays (Leopardus wiedii) in Mexico and mountain lions (Puma concolor) in California, USA, without success. However, we noted a preponderance of gray fox (Urocyon cinereoargenteus) hair at sampling stations. Our review of recent literature suggests a pattern of failure to detect target felids in hair-snare surveys conducted within the range of the gray fox. We propose, among several alternative explanations, that marking by gray foxes interferes with the tendency of felids to face-rub at sampling stations.     

Enhancement of root hydraulic conductivity by methyl jasmonate and the role of calcium and abscisic acid in this process

The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wild‐type plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.     

Direct and indirect effects of soil structure on the density of an antlion larva in a tropical dry forest

Abstract.  1. We used structural equation models to discriminate direct and indirect effects of soil structure on the abundance of the antlion Myrmeleon crudelis , a neuropteran larva that digs conical pits in soil to capture small arthropods. We proposed that soil structure may modify antlion density indirectly through its influence on tree cover, which in turn directly alters the amount of sun and rain that can reach the forest floor and the amount of litter fall.
2. The proportion of finer soils positively affected antlion density directly, but negatively tree cover. Tree cover positively affected both the amount of leaf litter and antlion density. Leaf litter negatively affected antlion density. The indirect effects of soils varied in strength and sign depending on whether trees are considered shelters against sun and rain, or leaf litter sources. The relative importance of these effects might also vary between years and seasons.
3. Antlions may select patches of finer soils not only because they are easy substrates in which to build pits, but also for their indirect benefit as sites with low leaf litter, illustrating how indirect interactions may affect the local abundance of semi-sedentary insects.     

Methane (CH4) release from littoral wetlands of Boreal lakes during an extended flooding period

Lake littoral zones have a transitional nature and dynamic conditions, which are reflected in their CH₄ emissions. Thus, detailed studies are needed to assess the littoral CH₄ emissions in a regional scale. In this study, CH₄ fluxes were followed during the ice‐free seasons in 1998 and 1999 by using the static chamber method in the littoral zone of two lakes in Finland. An exceptionally high water level in 1998 caused an unusually long inundation in otherwise ephemerally flooded zone. The flooding was normal in year 1999. The factors controlling CH₄ emissions were examined and statistical response functions were constructed. Further, the effect of extended flooding on the littoral CH₄ budged was estimated. The methane flux was primarily regulated by the water level in grass and sedge dominated eulittoral zone, but not in infralittoral reed and water lily stands. Methane emissions in the sedge dominated zone decreased significantly, when the flood was high enough to submerge the venting structures of the plants. Besides water level, sediment temperature determined CH₄ emission. The cumulative CH₄ emissions from the whole littoral wetlands in wet year were 1.1 times (L. Kevätön), or 0.61 and 0.79 times (L. Mekrijärvi) those in dry year. The crucial factor was the discrepancy between the exceptional and the average water level. The extension of inundated area does not necessarily increase CH₄ emissions if the flood reaches infrequently inundated areas, which apparently have low CH₄ production potential. This is the case especially, if the emissions in lower zones simultaneously decrease due to high water level. Our study analyses these complex responses between CH₄ emissions and water level.     

Plasma membrane fluidity and hydraulic conductance in wheat roots: interactions between root temperature and nitrate or phosphate deprivation

The hypothesis was tested that the negative effect of mineral nutrient deprivation (–N and –P) on the hydraulic conductance (L0) of wheat roots may be relieved by increasing the fluidity of plasma membrane (PM) lipids through elevated temperature. An increase in root temperature from 20 to 30°C increased the sap flow, J_v, from the excised roots of nutrient-deprived plants for 4 h, with a corresponding increase in L₀. In the same period, there was a decline in the flux of osmotically active solutes (J_s > to the xylem. As the duration of the period at 30°C increased, it was clear that the differential in L₀ between control and nutrient-deprived roots was maintained, even though L_u was significantly greater than the initial (20 °C) value after 48h. The lipid order parameter, determined by fluorescence polarization of 1, 6 diphenyl- 1, 3, 5-hexatriene (DPH), decreased markedly in two-phase purified PMs in the first 4 h of treatment at 30°C, but thereafter remained steady. The differential between control and nutrient-deprived roots was maintained throughout the 48h period. The correlation between lowered L₀ in nutrient-deprived roots and increased PM lipid ordering remained unchanged in conditions where the overall membrane fluidity was increased by elevated temperature.     

famsphere : a computer program for parental allocation from known genotypic pools

famsphere is a computer program that implements a distance‐based method to allocate families based on microsatellite marker information. It formalizes the exclusion method considering genotyping errors or mutations. Contrary to the standard exclusion method, famsphere provides a way to resolve conflicts in the case of multiple paternities. The information linked to the defined distances is similar to that of the transmission probabilities used in the likelihood approaches. However, in famsphere the information of loci is used as a whole, contrary to the likelihood approaches. famsphere is free software and can be downloaded from http://www.uvigo.es/webs/c03/webc03/XENETICA/XB2/antonio/famsphere/famsphere.htm