Vascular bundle sheath and mesophyll cells modulate leaf water balance in response to chitin

Plants can detect pathogen invasion by sensing microbe‐associated molecular patterns (MAMPs). This sensing process leads to the induction of defense responses. Numerous MAMP mechanisms of action have been described in and outside the guard cells. Here, we describe the effects of chitin, a MAMP found in fungal cell walls and insects, on the cellular osmotic water permeability (P_f) of the leaf vascular bundle‐sheath (BS) and mesophyll cells (MCs), and its subsequent effect on leaf hydraulic conductance (K_leaf). BS is a parenchymatic tissue that tightly encases the vascular system. BS cells (BSCs) have been shown to influence K_leaf through changes in their P_f, for example, after sensing the abiotic stress response‐regulating hormone abscisic acid. It was recently reported that, in Arabidopsis, the chitin receptors‐like kinases, chitin elicitor receptor kinase 1 (CERK1) and LYSINE MOTIF RECEPTOR KINASE 5 (LYK5) are highly expressed in the BS as well as the neighboring mesophyll. Therefore, we studied the possible impact of chitin on these cells. Our results revealed that BSCs and MCs exhibit a sharp decrease in P_f in response to chitin treatment. In addition, xylem‐fed chitin decreased K_leaf and led to stomatal closure. However, Atlyk5 mutant showed none of these responses. Complementing AtLYK5 in the BSCs (using the SCARECROW promoter) resulted in the response to chitin that was similar to that observed in the wild‐type. These results suggest that BS play a role in the perception of apoplastic chitin and in initiating chitin‐triggered immunity.     

Dual processes and an invariance result for exchangeable models in population genetics

By means of a representation as interactive particle systems, dual processes are constructed for a large class of exchangeable models in population genetics. It is shown that as the population size becomes large these dual processes tend in distribution to a particularly tractable limiting dual process. Properties of the models are analyzed using the duality relationship and approximate expressions are obtained for various quantities. Diffusion approximations follow easily from the invariance result.     

Growth at elevated carbon dioxide concentration reduces hydraulic conductance in alfalfa and soybean

Hydraulic conductances of alfalfa and soybean plants grown in controlled environment chambers at the current ambient carbon dioxide concentration and at twice the current ambient concentration were determined from measurements of transpiration rate and leaf and stem water potentials in the growth conditions. Growth at elevated carbon dioxide concentration reduced both transpiration rate and hydraulic conductance from the soil to the leaf in both species. Hydraulic conductance from the soil to the base of the stem was also lower at elevated carbon dioxide in soybean, but not alfalfa. These measurements identified the stem to leaf hydraulic pathway as a major target of the carbon dioxide effect in both species. The conductance of excised stem segments was much less in plants grown at elevated carbon dioxide in soybeans.     

Potential of Soil and Groundwater Contamination Due to Mine Subsidence Under a Landfill

Results of a study to evaluate the effects of mine subsidence on the integrity of a clay liner and potential for soil and groundwater contamination below a previously mined landfill are presented. The results show that for the existing site conditions, surface subsidence features are expected to be similar to subsidence troughs, and the site has minimal potential of being contaminated due to deep-sited subsidence in the mine. To further reduce potential for soil and groundwater contamination at the site, it is recommended that the minimum thickness of the compacted clay liner be 4?ft instead of the 2 to 3?ft generally used. Discussion is presented indicating that further study is required to develop an adequate design procedure to determine the effects of nonuniform settlement of foundation soils or refuse on the hydraulic conductivity of landfill clay barriers.     

The Effects of Hydraulic Dredging to Control Oyster Drills on Benthic Macrofauna of Oyster Grounds in Delaware Bay,New Jersey

This study describes the extent and nature of the effects of hydraulic dredging to control oyster drills (Urosalpinx cinerea and Eupleura caudata, Family Muricidae, Order Neogastropoda) on benthic macrofauna and sediments of the oyster grounds in Delaware Bay, New Jersey. The immediate effects of hydraulic dredging were reductions in numbers of species as well as in total numbers of animals on the three oyster grounds selected. However, oyster drills were most affected. Benthic populations have recovered three to ten months after dredging. The sediments of the dredged grounds can be described as muddy sands. Immediately after dredging, additional mud was brought up from subsurface layers which reduced the median grain size on Ground 154 test plot. On Ground 515 test plot, however, there was a slight loss in the mud which increased the median grain size.     

外源凹凸棒土添加对半干旱矿区复垦土壤水分涵养功能的影响

大规模的采矿作业已对我国半干旱区植被生态造成很大破坏,矿区植被亟待恢复,以解决半干旱矿区日益恶化的生态环境问题。如何改良土壤、有效储存和利用降水是半干旱矿区复垦土地植被恢复的首要问题。本研究针对半干旱矿区复垦土地水分涵养功能不足的问题,提出利用凹凸棒土和当地砂土组配作为新覆土材料,并研究了外源凹凸棒土添加对神木矿区复垦土壤入渗、排水和储水能力的影响。结果表明: 随着凹凸棒土含量的增加,土壤的累积入渗量减少4.8%～37.4%,入渗率减少6.4%～46.3%,湿润锋推进速度减小9.8%～116.9%,饱和导水率减小14.3%～59.5%,24 h和72 h排水量分别减少0.3%～4.3%和0.3%～2.5%,土壤最大储水量增加1.6%～22.4%。外源凹凸棒土的作用效果在添加量为150 t·hm^-2时基本已达到最大,结合经济成本的最佳用量在30～150 t·hm^-2。本研究结果系统揭示了凹凸棒土对半干旱矿区土壤减渗保水的作用机理,证明其可以作为半干旱矿区复垦土壤改良的有效材料,为半干旱矿区土地复垦和植被恢复提供参考。     

The relationship between wound-induced proteinase inhibitors and hydraulic signals in tomato seedlings

Localized wounding is known to induce systemic proteinase inhibitors (PI) in seedlings of tomato (Lycopersicon esculentum L.). Inhibitors of elastase (EC 3.4.21.36) were shown here to be among those systemically induced by wounding, and a simple rapid assay for PI based on elastase was developed. Using this assay, the nature of the systemic signalling system (‘PIIF’) was investigated. Hydraulic signals were shown to be induced in tomato by localized wounds. These signals travelled throughout the plant well within the lag time before appearance of systemic wound-induced PI. A number of correlations were drawn between the occurrence of the hydraulic signals and induction of systemic PI, suggesting that hydraulic signals might be the PIIF, or a component of it. It was shown that systemic hydraulic signals could be triggered, without significant wounding, by excision of a single leaflet through the submerged petiole. These hydraulic signals were similar in both kinetics and magnitude to those induced by localized wounding. However, they did not induce systemic PI. In addition, it was shown that systemic events almost as rapid as wound-induced hydraulic signals could be induced without wounding, under certain environmental conditions. This indicates that rapid hydraulic signals do not provide a specific signal of wounding. These findings demonstrate that hydraulic signals per se are not the PIIF.