ABA is therefore necessary for the stomatal closure we observe in esb1-1. Te elevated ABA concentration we observe in leaves of esb1-1 compared to wild-type supports this conclusion. We also used the esb1-1sgn3-3 double mutant to test if SGN3 is involved in initiating this leaf ABA response. In leaves of the esb1-1sgn3-3 double mutant the elevated expression of a set of ABA signalling and response genes observed in esb1-1 is reduced to below that of wild-type . Further, the reduced stomatal aperture of esb1-1 is also recovered to wild-type levels in this double mutant . SGN3is therefore necessary for the ABA-dependent stomatal closure in response to the defective endodermal diffusion barrier in esb1-1. This raises the question of what links detection of a break in the endodermal diffusion barrier with ABA-driven closure of stomates in the leaf? Removal of endodermal suberin in esb1-1 expressing CDEF1 revealed a significant reduction in ABA-regulated gene expression, and a tendency to increasing stomatal aperture towards wild-type . Thus, increased suberin deposition in the endodermis of the esb1-1 root appears to play a partial role in the ABA controlled reduction in leaf transpiration. We have ruled out a role of local ABA signalling in controlling enhanced suberin deposition at the endodermis in esb1-1 . Using a similar strategy of expressing abi1 in the endodermis, in this case using the SCARECROW promoter , primarily active in the endodermis, we also show that in esb1-1 ABA signalling at the endodermis is not promoting stomatal closure or enhanced ABA signalling in leaves . We note that pSCR is also active in bundle sheath cell, and so ABA-signalling in these cells is also not involved in promoting stomatal closure in esb1-1. Furthermore,blueberry packaging containers enhanced ABA signalling in the endodermis is also not responsible for the initiation of the long-distance response of stomatal closure in leaves, and again it is more likely that suppression of ABA signalling is playing a role.
This can be seen in the fact that expression of abi1 in the endodermis, blocking ABA signalling, mimics the efect of esb1-1 on Lpr and stomatal aperture closure . However, these possibilities remain to be further explored. In contrast to these root-based or long-distance effects, the closure of stomata in leaves in response to a root-based CIFs/SGN3 derived signal is mediated by ABA locally in the leaves. We also note that the long distance signal connecting CIFs/SGN3 in roots with reduced leaf transpiration is currently unknown. Interestingly, a root-derived peptide has been recently identified as involved in long-distance signalling. In response to drought stress, CLE25 move from root to shoot and induces ABA accu-mulation in leaves and stomatal closure. Casparian strips have been suggested to play a critical role in forming a barrier to apoplastic diffusion to limit uncontrolled uptake and back fow of solutes from roots reviewed in . However, most Casparian strip mutants only appear to show fairly subtle phenotypic effects, and this has been a source of continued puzzlement. Here, we show that sensing damage to Casparian strips via leakage of the vasculature-derived CIF peptides from the stele into the cortex triggers a mechanism that inactivates aquaporins, promotes enhanced deposition of suberin limiting solute leakage in roots, and reduces transpiration in leaves, which all contribute to increasing solute concentration in the xylem . The overall outcome of this integrated response is a rebalancing of solute and water uptake and leakage. These physiological compensation mechanisms mitigate the loss of Casparian strip integrity, allowing relatively normal growth and development. A key part of this compensation mechanism is the ability of esb1-1 to limit water loss by the shoot by reducing stomatal aperture, in an ABA-dependent manner. This is clearly established by our observation that the esb1-1aba1 double mutant has severely reduced growth and seed production compared to either of the single mutants, and these growth defects can be partially supressed by the exogenous application of ABA .
The mechanisms we have identified are triggered by the loss of Casparian strips integrity. Such an event can occur during biotic stress including root nematodes infestation, and also during developmental processes such as lateral root emergence where Casparian strips are remodelled, suberin deposition occurs, and aquaporin expression is suppressed. Here, we describe novel outputs of the CIFs/SGN3 surveillance system that couple sensing of the integrity of the Casparian strip-based apoplastic diffusion barrier at the endodermis with pathways that regulate both solute leakage and hydraulic conductivity in the root . Long distance signals then connect these root-based responses with compensatory mechanisms in leaves which are mediated by local ABA signalling . Our dis-coveries provide a new framework which integrates our emerging understanding of the molecular development of the Casparian strip and suberin diffusion barriers with two of the major physiological functions required for plant survival – solute and water uptake.In recent years, California has tightened rules for reporting diversions of water for agriculture and other uses. One key challenge has been establishing workable standards for the collection of reliable data on relatively small and remote diversions — such as those for far-flung farms and ranches. Under new legislation, a certification program run by UC Cooperative Extension is helping to solve that problem. The State Water Resources Control Board views ac-curate diversion reporting as a key element of sound water management. “It’s incredibly important to monitor how much water comes into and goes out of the system,” says Kyle Ochenduszko, chief of water rights enforcement at the water board. Diversion reports are fed into a state database and support the orderly allocation of water resources by, for instance, enabling the board’s Division of Water Rights to inform water users when new requests to appropriate water might affect their own supply. Since 1966, the California Water Code has required diverters of surface water, with certain exceptions, to report their diversions to the water board. But in part because the water board lacked fining authority for many years, compliance was poor. In 2009, Senate Bill 8 gave the water board the authority to fine non-compliant diverters an initial $1,000, plus $500 for each additional day of failing to report.
Even so, SB 8 did not stipulate precisely how diversions were to be monitored. Rather, it required diverters to measure their diversions using the “best available technologies and best professional practices,” unless they could demonstrate that such technologies and practices were not locally cost-effective. That is, the requirement left wide latitude for interpretation. So things remained until 2015 — when Senate Bill 88 became law. This piece of legislation, passed amid a historically severe drought, directed the water board to draw up emergency regulations regarding water diversions. The regulations, once completed, required diverters of at least 100 acre-feet of water per year to hire an engineer or appropriately licensed contractor to install all monitoring devices. Now the requirements were clear. But the provision mandating installation by an engineer or contractor prompted an outcry from many smaller diverters, particularly those in remote areas of the state. For most diverters near sizable towns — Redding, say — complying with the regulations was manage-able, with expenses limited to the cost of a monitoring device and the services of an installer. But diverters in remote parts of Modoc County, for example, were looking at bigger bills, says Kirk Wilbur of the California Cattlemen’s Association. For such diverters, compliance might require importing an engineer or contractor from far away,blueberry packaging boxes which would entail significant travel expenses. If a site lacked electricity, as many do, the costs would pile higher . So how to reconcile the interests of the state’s diverters with those of the state? How best to balance the public and the private good? The answer, it turned out, was to empower diverters to install their own monitoring devices — with UCCE playing the empowering role. The idea originated with the Shasta County Cattlemen’s Association. It gained the support of the statewide Cattlemen’s Association. It took shape as proposed legislation in 2017 and was shepherded through the Legislature by Assemblyman Frank Bigelow . It breezed through both chambers with no votes in opposition — not even in committee. “All parties realized,” says Assemblyman Bigelow, “that Assembly Bill 589 would cut compliance costs and, as a result, increase compliance rates — which benefited both the regulators and the regulated community.” Essentially, AB 589 allows water diverters to in-stall their own monitoring devices if they successfully complete a monitoring workshop offered by UCCE. Further, it directed UCCE to develop the workshop in coordination with the water board. Khaled Bali, an irrigation water management specialist at the Kearney Agricultural Research and Extension Center, took the lead in drafting the coursework. “Then we met with the [water] board and got feedback,” Bali says. “We made changes until they said, ‘This looks good.’” Attendees at the workshops, which last three and a half hours, gain a solid foundation in the basic principles of diversion monitoring.
They learn how to monitor flows passing through a ditch, over a weir or through a pipe — or gathering in a pond. They learn how to build or install measuring devices appropriate for each type of diversion and how to calibrate those devices to comply with the state’s accuracy requirements. They learn how to navigate the water board’s rather detailed reporting system. Equipment for monitoring flows through open ditches might be limited to a tape measure, a timing device and a floating object. Installing a monitoring device for a diversion routed over a weir — a simple dam with an edge or notch that allows overflow — re-quires a bit more equipment. But once the installation is complete, the diverter need only read a staff gauge that shows the height of the water spilling over the weir’s crest . Diversions flowing through pipes must be outfitted with flow meters. Diversions feeding into a pond or reservoir can be monitored by tracking the depth of the water with a staff gauge, float or pressure transducer . So far, UCCE has offered the course in about 15 lo-cations, from Yreka to Bakersfield. According to Shasta County UCCE County Director Larry Forero — who teaches the $25 course along with Bali, Tehama County UCCE Advisor Allan Fulton and UC Davis–based UCCE Specialist Daniele Zaccaria — about 1,000 people had earned certificates of completion by early October. Even farmers and ranchers who divert less than 100 acre-feet per year are attending. “I’ve been floored,” says Wilbur, “by the number of diverters who have attended the course even though they aren’t required to — they want to better understand the regulations and make sure they’re doing the right thing.” It probably helps that the registration fee is a fraction of the cost of importing a faraway engineer. Due to their increasing use in a wide variety of beneficial industrial and consumer applications, ranging from use as a fuel catalyst, to chemical and mechanical planarization media, there have been increasing concerns about the potential environmental health and safety aspects of manufactured ceria nanomaterials.1,2 Ce is among the most abundant of the rare earth elements making up approximately 0.0046% of the Earth’s crust by weight .3 For example, Ce concentration in soils range from 2 to 150 mg kg−1 . 4 In Europe, the median concentrations of Ce were 48.2 mg kg−1 in soils, 66.6 mg kg−1 in sediment and 55 ng l−1 in water . There are many naturally occurring Ce containing minerals include rhabdophane, allanite, cerite, cerianite, samarskite, zircon, monazite and bastnasite.The existence of naturally occur-ring ceria nanoparticles is also likely and may play a key rolein controlling dissolved Ce concentrations,6 but precisely how the properties of naturally occurring ceria nanoparticles com-pare to manufactured ceria nanomaterials is unclear. There is concern that nanoceria, due to its small particle size and enhanced reactivity by design, may present unique hazards to ecological receptor species. Of critical importance are the redox properties of ceria which enables it to transition between CeIJIII and Ce, which are the key to understanding its potential toxicity.While there has been somewhat extensive investigation into the mammalian toxicity of ceria ,based on the present review, there has been considerably less effort invested into investigation of the environmental fate and effects of nanoceria. In this critical review, we discuss the likely points of environmental release along product life-cycles and resulting environmental exposure to nanoceria, methods of detection in the environment, fate and transport, as well as the available toxicity literature for ecological receptor species.