To date, many rhizosphere microbiome studies and growth chambers systems focus on the impact of plant developmental stage, genotype and soil type on microbial composition and function . On the other hand, predation as a driver in the rhizosphere microbiome remains understudied. For instance, protists are abundant in the soil and are active consumers of bacteria and fungi and play a role in nutrient cycling yet remain an overlooked part of the rhizosphere . Viruses are also pivotal in modulating host communities thereby affecting bio-geochemical cycles but their influence in the rhizosphere is poorly studied . These predatorprey interactions in the rhizosphere deserve in-depth studies which can be facilitated by these specialized growth chambers. Another area worth investigating in the rhizosphere is in anaerobic microbial ecology. At microbially relevant scales, soils primarily exist as aggregates . Aggregation creates conditions different from bulk soil, particularly in terms of oxygen diffusion and water flow resulting in anoxic spaces within aggregates and influences the microbial community . The rhizosphere is also rich in a wide range of compounds which can serve as alternative electron acceptors such as nitrate, iron, sulfate and humic substances in the absence of oxygen .
However,arandanos cultivo most anaerobic studies in the rhizosphere focus only on aqueous environments such as water-logged paddy soils despite biochemical and metatranscriptomic evidence pointing to the possibility of anaerobic respiration in the rhizosphere . To fully understand biogeochemical cycles in the rhizosphere, it is imperative to investigate rhizosphere processes in the micro-scale and to include localized redox conditions as one of the influencing parameters. Microfluidic platforms with its fast prototyping capabilities can be helpful in creating growth chambers designed to stimulate these redox changes. In the study of the rhizosphere microbiome, genetic manipulation strategies are foundational in deep characterization of microbial mechanisms and current manipulation techniques require axenic isolates. However, the uncultivability of a significant portion of soil microorganisms continues to hamper efforts in gaining mechanistic knowledge. Even for culturable isolates, the process of isolation introduces selective pressure and disturbance to the community with inevitable loss of information on spatial interactions. A recent innovation in gene editing technologies using CRISPR-cas systems demonstrated in situ editing of genetically tractable bacteria within a complex community .
Coupled with the use of transparent soil-like substrates , the application of such a technique for the editing of in situ rhizosphere microbiome while preserving spatial and temporal associations would indeed bring invaluable insights. Specialized growth chambers using 3D fabrication and microfluidic technologies are primed to facilitate such innovations. Finally, this review revealed that while similarities exist among the different growth chamber systems, many of these systems are bespoke. This makes it difficult to replicate experiments and determine reproducibility which are important cornerstones of scientific advancement. The complexity of rhizosphere interactions also warrant that computational models are essential to gain a better understanding of system level processes . However, predictive modeling requires data from standardized approaches to be comparable between experiments. Thus, future growth chamber systems and designs are encouraged to follow the open science framework to enable standardization to an extent, such as in the case of EcoFABs . Cerium oxide nanoparticles are widely used in applications such as catalyst automotive industry, glass mirrors, plate glass, and ophthalmic lenses . These NPs are among the 13 engineered nanomaterials in the list of priority for immediate testing by the Organization for Economic Cooperation and Development . However, the environmental release of CeO2 NPs from factories or applications, and their behavior and effects in the environment are not well known yet .
Previous studies have shown that CeO2 NPs are stable in soil at pH values of 7 to 9 . This suggests CeO2 NPs will remain in soil for a long time. In addition, reports from recent investigations have shown a wide variety of plant responses after exposure toCeO2 NPs. For instance, Schwabe found that CeO2 NP treatments did not reduced the growth in pumpkin and wheat. However, Ma et al. reported that, at 2000 mg/L, nano-CeO2 reduced root elongation in lettuce . Van Hoecke et al. found that CeO2 NPs, at concentrations as low as 2.6 and 5.4 mg/L, produced chronic toxicity to the unicellular alga Pseudokirchneriella subcapitata. Previous results from our research group have shown that CeO2 NPs at 2000 mg/L reduced corn and tomato germination by 30% and cucumber germination by 20% . In a more recent study, we demonstrated that CeO2 NPs are taken up and stored without change in maize roots . This previous study also revealed that the uptake of CeO2 NPs by corn plants was affected by soil organic matter content and alginate surface coating . Alginates are naturally occurring polysaccharides that have been used to stabilize NPs for several applications . This suggests that excess of alginate can be released into the environment together with NPs, with unknown consequences for edible plants. Thus, more studies are needed to better understand the impact of CeO2 NPs in plants, in environments where excess alginates could be present. On the other hand, studies have shown that carbon-based nanoparticles such as single walled carbon nanotubes triggered reactive oxygen species generation in Arabidopsis and rice . In addition, multiwall carbon nanotubes have been found to induce gene expression of heat shock protein 90 in tomato leaves and roots . However, there are no reports on the effect of CeO2 NPs on heat shock protein expresion in plants. For example, at concentration higher than 89 µmol/L, cerium affected the foliar chlorophyll content, nitrate reductase activity, shoot root length and relative yield in cowpea plants . The authors suggested the effects could be produced by the substitution of Mg2+ by Ce in chlorophyll synthesis. It has also been suggested that, due to their similar chemical characteristics, Eu, a REE, may compete with Ca for organic ligands . These studies suggest that REE elements can have serious impacts on the uptake of nutritional elements in food crops. However, to the authors’ knowledge the impact of REE NPs on the uptake of nutritional elements by plants has yet to be reported. The purposes of this work were to determine the effects of alginate on: the transport of Ce within corn plants treated with CeO2 NPs, the uptake and transport of micro and macro nutrients, the chlorophyll content, and the expression of stress related heat shock protein 70. Maize was selected for this study because it is a crop widely cultivated throughout the world for direct and indirect consumption. In addition, 40% of the corn world’s harvest is produced in the United States . In this study, corn plants were grown in soil spiked with CeO2 NPs with various alginate concentrations for one month.
After harvest, the concentration of Ce and many nutrient elements were determined by ICP-OES in the root and shoots tissues. Cyclopentenone oxylipins regulate diverse biological processes. In animals, prostaglandins formed by cylcooxygenases have hormone-like effects that sustain homeostatic functions and mediate pathogen interactions, including inflammation responses.Plant cyclopentenones also have important roles in signaling and defense. While distinct functions for various cyclopentenones have been elucidated,maceteros grandes reciclados the vast majority of plant studies have focused on the 13-lipoxygenase product 12-oxo-phytodienoic acid and its derivatives, collectively termed jasmonates. A vast number of physiological and genetic analyses have demonstrated diverse roles for jasmonates including developmental processes and inducible defenses against biotic threats.In maize , genetic evidence highlights roles for jasmonic acid in defense against biotic threats, senescence, and developmental processes that control male sex determination.As an essential jasmonate precursor, 12-OPDA can trigger development and defense signaling distinct from JA itself or its bio-active amino acid conjugate -7-iso-jasmonoyl-L-isoleucine.During physiological stress in Arabidopsis, free 12-OPDA binds cyclophilin 20–3 to promote the formation of a cysteine synthase complex leading to elevated glutathione levels and cellular redox homeostasis.In general, 12-OPDA signaling is consistent with a role in cell protection and inhibition of cell death.In addition to the 13-LOX jasmonate pathway, 9-LOX genes also function in plant development and plant-biotic interactions. Specific 9-LOXs have been shown to influence cell death, root growth,senescence,and to promote either susceptibility or resistance to pathogens and pests in host-species interactions. Despite evidence linking 9-LOX genes to important biological roles, many of the specific metabolites that promote these functions have remained elusive. 10- oxo-11-phytoenoic acid and 10-oxo-11,15-phytodienoic acid have been long considered candidates for biologically active compounds given their similarity to jasmonates .First isolated from potato , 10-OPEA and 10-OPDA were identified as products of 9-allene oxide synthase enzymes and subsequent nonenzymatic cyclization, resulting in racemic mixtures of low yield stereoisomers.In contrast, our empirical findings in maize silks and a concurrent study done in maize roots showed that cis-10-OPEA synthesis in maize is consistent with full enzymatic biosynthesis, yielding predominantly – 10-OPEA as a result of an as-yet unidentified enzyme with novel 9-AOC activity.
Together, these results suggest pathway diversity in 9-cyclopentenone formation between dicot and monocot species. In a recent study, we initiated the functional characterization of 10-OPEA, 10-OPDA and derived C14 and C12 metabolites, collectively termed death acids.10-OPEA is inducible at the local site of pathogen and insect attack and has antimicrobial and herbivore growth inhibitor activity. The capacity of 10-OPEA as a plant defense signal/metabolite is similar to 12-OPDA, yet it demonstrates specificity, with only 60%overlap in the co-expression of over 5000 genes differentially expressed in response to these 2 conceptually related oxylipins. One distinction from 12-OPDA activity is the weak ability of 10-OPEA to promote accumulation of transcripts coding for protease inhibitors. Furthermore, exogenous 10-OPEA application strongly induces cysteine protease activation and programmed cell death, as evidenced by immunoblot protease labeling, lesion development, ion leakage, and DNA fragmentation.Collectively these results suggest that 9- and 13-LOXderived cyclopentenones can have distinct and separate functions, despite their structural similarities. To further elucidate and contrast the established roles of 12-OPDA in insect related defense responses, and the more specific role of 10-OPEA in fungal-infected tissues, we examined the induction of 9-LOX and 13-LOX derived cyclopentenones in additional maize tissues under varied stress conditions. To explore 9- and 13-LOX derived cyclopentenone production in maize in response to pathogen and insect attack, we first infected the inner-whorl leaf tissue and developing upper node and internode stem tissue with Cochliobolus heterostrophus and measured 10-OPEA, 10- OPDA, and 12-OPDA over a 3 day time course. At 24 h post inoculation, 10-OPEA concentrations in inner-whorl leaf tissues were significantly higher than 10-OPDA or 12-OPDA and remained higher over the duration of the time course . Similar results were observed in node/internode stem tissues, collectively indicating a bias toward 10-OPEA production in both leaf and developing node/internode tissues. Previous work has routinely demonstrated that all of these metabolites are near or at the limits of detection in healthy untreated control tissues.To mimic insect feeding, regurgitant from Spodoptera frugiperda was applied to fully expanded maize leaves. Basal levels of 12-OPDA were signifi- cantly higher than 10-OPEA and 10-OPDA with 3- and 10- fold differences, respectively . By 1 h post treatment, FAW-R had elicited a strong 13-LOX response with 12-OPDA levels exceeding 10-OPEA and 10-OPDA production by >65 fold, demonstrating a strong preference for the jasmonate pathway in response to herbivory on mature leaves. Both insect feeding and pathogen attack can occur on diverse maize organs and cause the damage-induced collapse of cells. To build upon our previous results showing abundant levels of 9-LOX cyclopentenones in the silks13 and to better understand the capacity of different organs to produce 10-OPEA and 12-OPDA, hydroponic root and silk tissues were crush damaged and metabolites were measured over a time course. Both hydroponic roots and silks displayed a rapid induction of 10-OPEA upon damage, producing approximately 3 and 40ug/ g FW within 20 min, respectively, and sustaining high levels for at least 120 min . Both 10-OPDA and 12- OPDA were at least 2-fold less than 10-OPEA in response to crush-damage and remained significantly lower throughout both time courses. Together, these results demonstrate that 10- OPEA is the predominant LOX-derived cyclopentenone in silks and roots in response to cell damage. The maize scutellum is an important developmental organ in early maize ontogeny, acting to absorb, store, and transfernutrients from the endosperm to the growing seedling while preventing microbial infections.