Attia, Z., Dalal, A., and Moshelion, M. (2018). Vascular bundle sheath and mesophyll regulation of leaf water balance in response to chitin. bioRxiv. Doi.org/10.1101/337709
Plants can detect pathogen invasion by sensing pathogen-associated molecular patterns (PAMPs). This sensing process leads to the induction of defense responses. Most PAMP mechanisms of action have been described in the guard cells. Here, we describe the effects of chitin, a PAMP found in fungal cell walls, on the cellular osmotic water permeability (Pf) of the leaf vascular bundle-sheath (BS) and mesophyll cells and its subsequent effect on leaf hydraulic conductance (Kleaf). The BS is a parenchymatic tissue that tightly encases the vascular system. BS cells have been shown to control Kleaf through changes in their Pf, for example, in response to ABA. It was recently reported that, in Arabidopsis, the chitin receptors 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 both BS cells and mesophyll cells exhibit a sharp decrease in Pf in response to chitin treatment. In addition, xylem-fed chitin decreased Kleaf and led to stomatal closure. However, an Atlyk5 mutant showed none of these responses. Complimenting AtLYK5 specifically in the BS cells (using the SCARECROW promoter) and transient expresion in mesophyll cells each resulted in a response to chitin that was similar to that observed in the wild type. These results suggest that BS and mesophyll cells each play a role in the perception of apoplastic chitin and in initiating chitin-triggered immunity.
Golan, A., Hendel, E., Mendez Espitia, G.E., Schwartz, N., and Peleg, Z. (2018). Activation of seminal root primordia during wheat domestication reveals underlying mechanisms of plant resilience. Plant, Cell & Environment. 41 (4):755-766. Doi.org/10.1111/pce.13138
Seminal roots constitute the initial wheat root system and provide the main route for water absorption during early stages of development. Seminal root number (SRN) varies among species. However, the mechanisms through which SRN is controlled and in turn contribute to environmental adaptation are poorly understood. Here, we show that SRN increased upon wheat domestication from 3 to 5 due to the activation of 2 root primordia that are suppressed in wild wheat, a trait controlled by loci expressed in the germinating embryo. Suppression of root primordia did not limit water uptake, indicating that 3 seminal roots is adequate to maintain growth during seedling development. The persistence of roots at their primordial state promoted seedling recovery from water stress through reactivation of suppressed primordia upon rehydration. Our findings suggest that under well‐watered conditions, SRN is not a limiting factor, and excessive number of roots may be costly and maladaptive. Following water stress, lack of substantial root system suppresses growth and rapid recovery of the root system is essential for seedling recovery. This study underscores SRN as key adaptive trait that was reshaped upon domestication. The maintenance of roots at their primordial state during seedling development may be regarded as seedling protective mechanism against water stress.
Cohen, I., Rspaport, T., Tal Berger, R., and Rachmilevitch, S. (2018). The effects of elevated CO2 and nitrogen nutrition on root dynamics. Plant Science. 272:294-300. Doi.org/10.1016/j.plantsci.2018.03.034
Ambient CO2 concentration is currently 400 μmol mol−1, and projections forecast an increase up to 970 μmol mol−1 by century’s end. Elevated CO2 can stimulate C3 plant growth, whereas nitrogen is the main nutrient plants acquire from soils and often limits growth. Plants primarily obtain two nitrogen sources from the soil, ammonium (NH4+) and nitrate (NO3−). At elevated CO2 levels, plant growth and nitrogen metabolism is affected by the nitrogen source. Most research has focused on shoot traits, while neglecting the plants’ hidden half, the root. We studied the effects of elevated CO2 and nitrogen source on hydroponically grown tomato plants, a C3 model and crop plant. Our main objective was to determine how the nitrogen source and elevated CO2 affect root development. Our results indicate they affect development in terms of the size and anatomy of different root orders. Specifically, root xylem development was found sensitive to the nitrogen source, whereas NO3−-supplied plants displayed greater xylem development compared to their NH4+ counterparts, and also to a lesser extent, to elevated CO2, which we found inhibits this development. Additionally, elevated CO2 decreased root respiration in different root orders exclusively in plants supplied with NH4+as the sole nitrogen source.
Zhou, K., Jerszurki, D., Sadka, A., Shlizeman, L., Rachmilevitch, S., and Ephrath, J. (2018). Effect of photoselective netting on root growth and development of young grafted orange trees under semi-arid climate. Scientia Horticulturae. 238:272-280. Doi.org/10.1016/j.scienta.2018.04.054
Photoselective netting is well-known for filtering the intercepted solar radiation, therefore affecting light quality. While its effects on above-ground of plants have been well investigated, the root system was neglected. Here, we evaluated the effects of photoselective netting on root growth and plant development. Minirhizotron and ingrowth cores were applied in a field experiment, performed in a 4-year-old orange orchard grown under three different photoselective net treatments (red, pearl, yellow) and an unnetted control treatment. Our observations confirmed the significant positive effect of photoselective nets on tree physiological performance, by increases of photosynthesis rate and vegetative growth. Trees grown in the pearl plot developed evenly distributed root system along the observation tubes while trees in control, red and yellow plots had a major part of roots concentrated at different depth ranges of 60–80, 100–120, and 120–140 cm, respectively. Photoselective nets showed a strong impact on shoot-root interaction and proved equally successful in promoting rapid establishment of young citrus trees. However, at long-term effect, yellow net might outperform because it could enable plants to develop deeper root systems, which will uptake water and nutrients more efficiently in semi-arid areas with sandy soil.
Gosa, S.C., Lupo, Y., and Moshelion, M. (2018). Quantitative and comparative analysis of whole-plant performance forfunctional physiological traits phenotyping: New tools to support prebreedingand plant stress physiology studies. Plant Science. In Press. Doi.org/10.1016/j.plantsci.2018.05.008
Plants are autotrophic organisms in which there are linear relationships between the rate at which organicbiomass is accumulated and many ambient parameters such as water, nutrients, CO2 and solar radiation. Theselinear relationships are the result of good feedback regulation between a plants sensing of the environment andthe optimization of its performance response. In this review, we suggest that continuous monitoring of the plantphysiological profile in response to changing ambient conditions could be a useful new phenotyping tool, allowingthe characterization and comparison of different levels of functional phenotypes and productivity. Thisfunctional physiological phenotyping (FPP) approach can be integrated into breeding programs, which are facingdifficulties in selecting plants that perform well under abiotic stress. Moreover, high-throughput FPP willincrease the efficiency of the selection of traits that are closely related to environmental interactions (such asplant water status, water-use efficiency, stomatal conductance, etc.) thanks to its high resolution and dynamicmeasurements. One of the important advantages of FPP is, its simplicity and effectiveness and compatibility withexperimental methods that use load-cell lysimeters and ambient sensors. In the future, this platform could helpwith phenotyping of complex physiological traits, beneficial for yield gain to enhance functional breeding approachesand guide in crop modeling.
Pincovici, S., Cochavi, A., Karnieli, A., Ephrath, J., Rachmilevitch, S. (2018). Source-sink relations of sunflower plants as affected by a parasite modifies carbon alocations and leaf traits. Plant Science. 271:100-107. Doi.org/10.1016/j.plantsci.2018.03.022
Sunflower broomrape (Orobanche cumana) is a root holoparasitic plant causing major damage to sunflower (Helianthus annuus L.). Parasite infection initiates source-sink relations between the parasite (sink) and the host (source), allocating carbohydrates, water and nutrients to the parasite. The primary aim of the current study was to explore responses of sunflower to broomrape parasitism, specifically to examine alternations in leaf area, leaf mass per area (LMA), mesophyll structure and root hydraulic conductivity. Leaf changes revealed modifications similar to described previously in shade adapted plants, causing larger and thinner leaves. These traits were accompanied with significantly higher root hydraulics. These changes were caused by carbohydrate depletion due to source-sink relationships between the host and parasite. An Imazapic herbicide (ALS inhibitor) was used for controlling broomrape attachments and by to investigate the plasticity of the traits found. Broomrape infected plants which were treated with Imazapic had leaves similar to non-infected plants, including mesophyll structure and carbon assimilation rates. These results demonstrated source-sink effects of broomrape which cause a low-light-like acclimation behavior which is reversible.
Strobach, E., Bel, G. (2017). Quantifying Uncertainties in an Ensembke of Decadal Climate Predictions. Journal of Geophysical Research. 122:13,191-13,200. Doi:10.1002/2017JD027249
Meaningful climate predictions must be accompanied by their corresponding range of uncertainty. Quantifying the uncertainties is nontrivial, and different methods have been suggested and used in the past. Here we propose a method that does not rely on any assumptions regarding the distribution of the ensemble member predictions. The method is tested using the Coupled Model Intercomparison Project Phase 5 1981–2010 decadal predictions and is shown to perform better than two other methods considered here. The improved estimate of the uncertainties is of great importance both for practical use and for better assessing the significance of the effects seen in theoretical studies.
Raij, I., Šimůnek, J., Ben-Gal, A. and Lazarovitch, N.(2016). Water flow and multicomponent solute transport in drip irrigated lysimeters. Water Resour. Res., 52. Doi:10.1002/2016WR018930.
Controlled experiments and modeling are crucial components in the evaluation of the fate of water and solutes in environmental and agricultural research. Lysimeters are commonly used to determine water and solute balances and assist in making sustainable decisions with respect to soil reclamation, fertilization, or irrigation with low-quality water. While models are cost-effective tools for estimating and preventing environmental damage by agricultural activities, their value is highly dependent on the accuracy of their parameterization, often determined by calibration. The main objective of this study was to use measured major ion concentrations collected from drip-irrigated lysimeters to calibrate the variably saturated water flow model HYDRUS (2D/3D) coupled with the reactive transport model UNSATCHEM. Irrigation alternated between desalinated and brackish waters. Lysimeter drainage and soil solution samples were collected for chemical analysis and used to calibrate the model. A second objective was to demonstrate the potential use of the calibrated model to evaluate lower boundary design options of lysimeters with respect to leaching fractions determined using drainage water fluxes, chloride concentrations, and overall salinity of drainage water, and exchangeable sodium percentage (ESP) in the profile. The model showed that, in the long term, leaching fractions calculated with electrical conductivity values would be affected by the lower boundary condition pressure head, while those calculated with chloride concentrations and water fluxes would not be affected. In addition, clear dissimilarities in ESP profiles were found between lysimeters with different lower boundary conditions, suggesting a potential influence on hydraulic conductivities and flow patterns.
M. Kwame, Sherman, T., Lazarovitch N., Fait, A. and Rachmilevitch, S. (2017). A
bell pepper cultivar tolerant to chilling enhanced nitrogen allocation and
stress-related metabolite accumulation in the roots in response to low root
zone temperature. Physiologia Plantarum 161:196-210. Doi:0.1111/ppl.12584.
Two bell pepper (Capsicum annuum) cultivars, differing in their responseto chilling, were exposed to three levels of root-zone temperatures. Gasexchange, shoot and root phenology, and the pattern of change of the centralmetabolites and secondary metabolites caffeate and benzoate in the leavesand roots were profiled. Low root-zone temperature significantly inhibitedgaseous exchange, with a greater effect on the sensitive commercial pepperhybrid (Canon) than on the new hybrid bred to enhance abiotic stress tolerance(S103). The latter was less affected by the treatment with respect to plantheight, shoot dry mass, root maximum length, root projected area, numberof root tips and root dry mass. More carbon was allocated to the leavesof S103 than nitrogen at 17∘C, while in the roots at 17∘C, more nitrogenwas allocated and the ratio between C/N decreased. Metabolite profilingshowed greater increase in the root than in the leaves. Leaf response betweenthe two cultivars differed significantly. The roots accumulated stress-relatedmetabolites including -aminobutyric acid (GABA), proline, galactinol andraffinose and at chilling (7∘C) resulted in an increase of sugars in both cultivars.Our results suggest that the enhanced tolerance of S103 to root cold stress,reflected in the relative maintenance of shoot and root growth, is likely linkedto a more effective regulation of photosynthesis facilitated by the induction ofstress-related metabolism.
M.K., Sherman, T., Ephrath, J.E., Fait, A., Rachmilevitch, S. and Lazarovitch
N. (2017). Grafting as a method to increase the tolerance response of bell
pepper to extreme temperatures. Vadose Zone Journal.
Fluctuations of winter and summer and day and night temperatures stronglyinfluence shoot and root growth, as well as the whole plant tolerance toextreme soil temperatures. We compared the response of a commercialpepper (Capsicum annuum L.) hybrid (Romance, Rijk Zwaan) to a range ofsoil temperatures when grafted to a new rootstock hybrid (S101, Syngenta),self-grafted, or ungrafted. The new rootstock hybrid was bred for enhancingabiotic stress tolerance. Plants were grown during winter and summer seasonsin a plastic greenhouse with natural ventilation. Minirhizotron cameras andin-growth cores were used to investigate grafted bell pepper root dynamicsand root and shoot interactions in response to extreme (low and high airand soil) temperatures. Soil and air temperatures were measured throughoutthe experiment. The variations of the grafted peppers and the ungraftedaboveground biomass exposed to low and high temperatures during winterand summer were higher in the Romance grafted on the S101 rootstock thanin the self-grafted and ungrafted Romance. The plot of rootstock S101 accumulatedCl, and the rootstock efficiently allocated C into the leaves, stems,and roots and N into the leaves, stems, and fruits. These traits of rootstock S101can be used to improve the tolerance of other pepper cultivars to low andhigh soil temperatures, which could lengthen the pepper growin.
A., Šimůnek, J., Aidoo, M.K., Seidel, S. and Lazarovitch, N. (2017).
Implementation and application of a root growth module in HYDRUS. Vadose Zone
A root growth module was adapted and implemented into the HYDRUSsoftware packages to model root growth as a function of different environmentalstresses. The model assumes that various environmental factors,as well as soil hydraulic properties, can influence root development undersuboptimal conditions. The implementation of growth and stress functions inthe HYDRUS software opens the opportunity to derive parameters of thesefunctions from laboratory or field experimental data using inverse modeling.One of the most important environmental factors influencing root growth issoil temperature. The effects of temperature in the root growth module wasthe first part of the newly developed HYDRUS add-on to be validated bycomparing modeling results with measured rooting depths in an aeroponicexperimental system with bell pepper (Capsicum annuum L.). The experimentwas conducted at root zone temperatures of 7, 17, and 27°C. Inverseoptimization was used to estimate a single set of parameters that was foundto well reproduce measured time series of rooting depths for all temperaturetreatments. A sensitivity analysis showed that parameters such as the maximumrooting depth and cardinal temperatures had only a small impact onthe model output and can thus be specified using values from the literaturewithout significantly increasing prediction uncertainties. On the other hand,parameters that define the growth rate or the shape of the temperaturestress function had a high influence. The root growth module that considerstemperature stress only slightly increased the complexity of the standardHYDRUS models.
J., Tripler, E., Peng, X., and Lazarovitch, N. (2017). A wireless device for
continuous frond elongation measurement. Computers and
electronics in agriculture. 140:1-7.
Growth rate is one of the indicators for a plant’s physiological condition. Date palms are characterized byhigh frond elongation rates, which are mainly subjected to drought and salinity stresses. Thus, continuousmeasurement of these rates can provide real-time growth information, for assessing water statuswithin the soil-plant-atmosphere continuum of cultivated date palms. This study introduces a noveldevice, the Palmeter, which continuously measures real-time date palm frond elongation. ThePalmeter was calibrated in the laboratory and tested in a date palm orchard with a measurement resolutionof 0.52 mm. A field test indicated that the Palmeter could wirelessly transmit acquired data to asignal receiver over a distance of 100 m with a success rate of more than 98%, facilitating the establishmentof wireless sensor networks in date palm orchards. Neither temperature nor wind affected thePalmeter measurement within the orchard. The temporal patterns of the frond elongation measuredby the Palmeter were found to be sensitive to various cultivation treatments, such as fruit load regimes,applied within a field study. Additionally, a six-volt power supply is recommended in order to reduce thePalmeter’s power consumption. The feasibility and robustness of the Palmeter system guaranteed theaccurate measurement of the frond elongation under harsh field conditions. Therefore, the Palmetercan be potentially applied to measure the frond elongation of date palms and perhaps other palms, suchas oil palms and coconut palms, for irrigation scheduling and cultivation management in large orchards.
Raij, I., Ben-Gal, A., Lazarovitch, N. (2018). Soil and
irrigation heterogeneity effects on drainage amount and concentration. in
lysimeters: a numerical study. Agricultural water management. 195:1-10. Doi.org/10.1016/j.agwat.2017.09.012
Water and solute fluxes measured
from lysimeters located in the field can be used to estimate evapotranspiration,
for irrigation scheduling and in solute leaching management. System-imposed heterogeneities are expected to affect
the variability of the measured fluxes, and therefore the uncertainty of data
obtained using lysimeters. In this study, local heterogeneities in soil
hydraulic conductivity and dripper discharge rate were studied and their effect
on drainage amount and concentration assessed. Three-dimensional simulations
were performed with HYDRUS (2D/3D) with 100 simulations per treatment. The
effect of three levels of soil and irrigation heterogeneities was studied for
lysimeters of two different sizes (1 m2 and 0.5 m2).
Additionally, three leaching fraction levels and water uptake reduction due to
solute stress were evaluated. Coefficient of variations of the drainage amount
and solute concentrations were evaluated for the different scenarios.
Irrigation heterogeneity caused higher variability in drainage amount while
soil heterogeneity caused higher variability in drainage concentration. The
larger the lysimeter, or the higher the leaching fraction, the lower the variability
for both drainage
concentration and amount. Combined soil and irrigation heterogeneities produced
no synergistic effect, suggesting that the variability measured in lysimeters
was governed by the factor that caused the highest variability. When water uptake reduction due to salinity was
considered, the same trends were observed. The results from this study can help
to decide if to use either drainage concentration or amount values, for saline
water irrigation management using lysimeters, according to the soil or
irrigation heterogeneity levels.
Reem Brenholtz G, Tamir-Ariel D, Okon Y, Burdman S. 2017. Carotenoid production and phenotypic variation in Azospirillumbrasilense. Research in Microbiology 168:493-501.
We assessed the occurrence of phenotypic variation in Azospirillum brasilensestrains Sp7, Cd, Sp245, Az39 and phv2 during growth in rich media, screening for variants altered in colony pigmentation or extracellular polysaccharide (EPS) production. Previous studies showed that EPS-overproducing variants of Sp7 appear frequently following starvation or growth in minimal medium. In contrast, no such variants were detected during growth in rich media in the tested strains except for few variants of phv2. Regarding alteration in colony pigmentation (from pink to white in strain Cd and from white to pink in the others), strain Sp7 showed a relatively high frequency of variation (0.009–0.026%). Strain Cd showed a lower frequency of alteration in pigmentation (0–0.008%), and this type of variation was not detected in the other strains. In A. brasilense, carotenoid synthesis is controlled by two RpoEsigma factors and their cognate ChrR anti-sigma factors, the latter acting as negative regulators of carotenoid synthesis. Here, all tested (n = 28) pink variants of Sp7 carried mutations in one of the anti-sigma factor genes, chrR1. Our findings indicate that, in A. brasilense, phenotypic variation is strain- and environment-dependent and support the central role of ChrR1 in regulation of carotenoid production.
Rapaport T., Hochberg U., Cochavi A., Karnieli A., Rachmilevitch S. 2017. The potential of the spectral ‘water balance index’ (WABI) forcrop irrigation scheduling. New Phytologist. Doi: 10.1111/nph.14718.
Hyperspectral sensing can detect slight changes in plant physiology, and may offer a faster and nondestructive alternative for water status monitoring. This premise was tested in the current study using a narrow-band ‘water balance index’ (WABI), which is based on independent changes in leaf water content (1500 nm) and the efficiency of the nonphotochemical quenching (NPQ) photo-protective mechanism (531 nm).
The hydraulic, photo-protective and spectral behaviors of five important crops – grapevine, corn, tomato, pea and sunflower – were evaluated under water deficit conditions in order to associate the differences in stress physiology with WABI suitability.
Rapid alterations in both leaf water content and NPQ were observed in grapevine, pea and sunflower, and were effectively captured by WABI. Apart from water status monitoring, the index was also successful in scheduling the irrigation of a vineyard, despite phenological and environmental variability. Conversely, corn and tomato displayed a relatively strict stomatal regime and/or mild NPQ responses and were, thus, unsuitable for WABI-based monitoring.
WABI shows great potential for irrigation scheduling of various crops, and has a clear advantage over spectral models that focus on either of the above mentioned physiological mechanisms.
Dalal A., Attia Z. and Menachem M. 2017. To Produce or to Survive: How
Plastic Is Your Crop Stress
Physiology? frontiers in Plant Science. Doi: 10.3389/fpls.2017.02067.
Abiotic stress causes major crop losses and is considered a greater challenge than
biotic stress. Comparisons of the number of published articles and patents regarding
these different types of stresses, and the number of commercially released crops
designed to tolerate different types of stresses, revealed a huge gap in the benchto-field
transfer rate of abiotic stress-tolerant crops, as compared to crops designed
to tolerate biotic stress. These differences underscore the complexity of abiotic
stress-response mechanisms. Here, we suggest that breeding programs favoring yieldrelated
quantitative physiological traits (QPTs; e.g., photosynthesis rate or stomatal
conductance) have canalized those QPTs at their highest levels. This has affected the
sensitivity of those QPTs to changing environmental conditions and those traits have
become less plastic. We also suggest that breeding pressure has had an asymmetric
impact on different QPTs, depending on their sensitivity to environmental conditions
and their interactions with other QPTs. We demonstrate this asymmetric impact on the
regulation of whole-plant water balance, showing how plastic membrane water content,
stomatal conductance and leaf hydraulic conductance interact to canalize whole-organ
water content. We suggest that a QPT’s plasticity is itself an important trait and that
understanding this plasticity may help us to develop yield-optimized crops.
Nir I., Shohat H., Panziel I., Olszewski N.E., Aharoni A. and Weiss D. 2017. The Tomato DELLA Protein PROCERA Acts in Guard Cells to Promote Stomatal Closure. Plant Cell. Doi: https://doi.org/10.1105/tpc.17.00542.
Plants employ stomatal closure and reduced growth to avoid water deficiency damage. Reduced levels of the growth-promoting hormone gibberellin (GA) lead to increased tolerance to water deficit, but the underlying mechanism is unknown. Here, we show that the tomato (Solanum lycopersicum) DELLA protein PROCERA (PRO), a negative regulator of GA signaling, acts in guard cells to promote stomatal closure and reduce water loss in response to water deficiency by increasing abscisic acid (ABA) sensitivity. The loss-of-function pro mutant exhibited increased stomatal conductance and rapid wilting under water-deficit stress. Transgenic tomato overexpressing constitutively active stable DELLA proteins (S-della) displayed the opposite phenotype. The effects of S-della on stomatal aperture and water loss were strongly suppressed in the ABA-deficient mutant sitiens (sit), indicating that these effects of S-della are ABA-dependent. While DELLA had no effect on ABA levels, guard cell ABA responsiveness was increased in S-della and reduced in pro plants compared to wild type. Expressing S-della under the control of a guard-cell-specific promoter was sufficient to increase stomatal sensitivity to ABA and to reduce water loss under water-deficit stress but had no effect on leaf size. This result indicates that DELLA promotes stomatal closure independently of its effect on growth.