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Stomata are pores on the leaf surface, which are formed by a pair of curved, tubular guard cells; an increase in turgor pressure deforms the guard cells, resulting in the opening of the stomata. Recent studies employed numerical simulations, based on experimental data, to analyze the effects of various structural, chemical, and mechanical features of the guard cells on the stomatal opening characteristics; these studies all support the well-known qualitative observation that the mechanical anisotropy of the guard cells plays a critical role in stomatal opening. Here, we propose a computationally based analytical model that quantitatively establishes the relations between the degree of anisotropy of the guard cell, the bio-composite constituents of the cell wall, and the aperture and area of stomatal opening. The model introduces two non-dimensional key parameters that dominate the guard cell deformations-the inflation driving force and the anisotropy ratio-and it serves as a generic framework that is not limited to specific plant species. The modeling predictions are in line with a wide range of previous experimental studies, and its analytical formulation sheds new light on the relations between the structure, mechanics, and function of stomata. Moreover, the model provides an analytical tool to back-calculate the elastic characteristics of the matrix that composes the guard cell walls, which, to the best of our knowledge, cannot be probed by direct nano-mechanical experiments; indeed, the estimations of our model are in good agreement with recently published results of independent numerical optimization schemes. The emerging insights from the stomatal structure-mechanics \"design guidelines\" may promote the development of miniature, yet complex, multiscale composite actuation mechanisms for future engineering platforms.

Trichomes play a key role in both heavy metal tolerance and herbivory defense, and both stressors have been shown to induce increased trichome density. However, the combined effect of these stressors on trichome density in general, and specifically on metal-hyperaccumulating plants, has yet to be examined. The aim of this study was to test the effect of cadmium availability and herbivory on leaf trichome density and herbivore deterrence in the metal hyperaccumulator Helianthus annuus. To test this, H. Annuus plants were grown in control pots or pots inoculated with 10 mg/kg cadmium and were subjected to either no herbivory or simulated herbivory using mechanical damage and foliar jasmonic acid application. Herbivore deterrence was tested in a feeding assay using Spodoptera littoralis caterpillars. Interestingly, while the trichome density of H. annuus increased by 79% or 53.5% under high cadmium availability or simulated herbivory, respectively, it decreased by 26% when the stressors were combined. Furthermore, regardless of cadmium availability, simulated herbivory induced a 40% increase in deterrence of S. littoralis. These findings suggest that the combination of metal availability and herbivory might present excessive stress to hyperaccumulators. Moreover, they suggest that the risk of metal bioaccumulation in phytoremediation can be reduced by simulated herbivory.

To enhance the distribution of their seeds, plants often utilize hygroscopic deformations that actuate dispersal mechanisms. Such movements are based on desiccation-induced shrinkage of tissues in predefined directions. The basic hygroscopic deformations are typically actuated by a bi-layer configuration, in which shrinking of an active tissue layer is resisted by a stiff layer, generating a set of basic movements including bending, coiling, and twisting. In this study, we investigate a new type of functionally graded hygroscopic movement in the fruit (capsule) of sesame ( L.). Microscopic observations of the capsules showed that the inner stiff endocarp layer is built of a bilayer of transverse (i.e., circumferential) and longitudinal fiber cells with the layers positioned in a semi-circle, one inside the other. The outer mesocarp layer is made of soft parenchyma cells. The thickness of the fibrous layers and of the mesocarp exhibits a graded architecture, with gradual changes in their thickness around the capsule circumference. The cellulose microfibrils in the fiber cell walls are lying parallel to the cell long axis, rendering them stiff. The outer mesocarp layer contracted by 300% as it dried. Removal of this outer layer inhibited the opening movement, indicating that it is the active tissue. A biomechanical hygro-elastic model based on the relative thicknesses of the layers successfully simulated the opening curvature. Our findings suggest that the sesame capsules possess a functionally graded architecture, which promotes a non-uniform double-curvature hygroscopic bending movement. In contrast to other hygroscopic organs described in the literature, the sesame capsule actuating and resisting tissues are not uniform throughout the device, but changing gradually. This newly described mechanism can be exploited in bio-inspired designs of novel actuating platforms.

The bark fulfils several essential functions in vascular plants and yields a wealth of raw materials, but the understanding of bark structure and function strongly lags behind our knowledge with respect to other plant tissues. The recent technological advances in sampling and preparation of barks for anatomical studies, along with the establishment of an agreed bark terminology, paved the way for more bark anatomical research. Whilst datasets reveal bark’s taxonomic and functional diversity in various ecosystems, a better understanding of the bark can advance the understanding of plants’ physiological and environmental challenges and solutions. We propose a set of priorities for understanding and further developing bark anatomical studies, including periderm structure in woody plants, phloem phenology, methods in bark anatomy research, bark functional ecology, relationships between bark macroscopic appearance, and its microscopic structure and discuss how to achieve these ambitious goals.

Societal Impact Statement Crop diversification is considered key to ensuring agricultural sustainability and food security. Tef (Eragrostis tef (Zucc.) Trotter) is a cereal crop grown mainly in Ethiopia, where it thrives in a wide range of environments, including stress‐prone habitats. It is considered a promising new crop and is gaining popularity in cultivation and in research worldwide. Lodging, the greatest factor limiting tef productivity and its wide adoption, was targeted in this study. The results highlight the central role of root traits in tef lodging, thus paving the way to reducing lodging and improving tef productivity, crop diversification, and food security. Summary Lodging is the most prominent yield‐restricting problem in tef (Eragrostis tef (Zucc.) Trotter) cultivation, responsible for 30%–50% yield loss. A significant advance in lodging resistance has been achieved in various cereals by reducing plant height. In this study, we investigated the role of crown root morphology and anatomy, rather than plant height, in tef lodging. Twenty‐eight tef lines, representing a wide diversity in lodging tendencies and major phenotypic traits, were tested under two field environments to investigate tef lodging and related traits. Four selected lines were subjected to more intense sampling as well as anatomical analysis of crown roots. In both field studies, taller lines were associated with greater lodging shortly before flowering, but not at plant maturity, whereas crown root diameter exhibited an association with reduced lodging, which became highly significant at maturity. Moreover, a greater proportion of root cortical aerenchyma developed in lodging‐susceptible genotypes, possibly reducing plant anchorage. A positive association between grain yield and lodging presents a major challenge for tef breeding. Our results suggest that root traits play a central role in tef lodging responses. We propose that semi‐dwarfism should be complemented by targeting root traits, to promote lodging resistance in tef. Crop diversification is considered key to ensuring agricultural sustainability and food security. Tef (Eragrostis tef (Zucc.) Trotter) is a cereal crop grown mainly in Ethiopia, where it thrives in a wide range of environments, including stress‐prone habitats. It is considered a promising new crop and is gaining popularity in cultivation and in research worldwide. Lodging, the greatest factor limiting tef productivity and its wide adoption was targeted in this study. The results highlight the central role of root traits in tef lodging, thus paving the way to reducing lodging and improving tef productivity, crop diversification, and food security.

The wild grapevine, Vitis vinifera subsp. sylvestris, grows naturally throughout the northern hemisphere, including the Mediterranean region. Wild grapevines have also been observed sporadically across the southern Levant and are considered a non-native feral plant. Nevertheless, no formal characterization has been conducted for wild grapevines in this region; thus, its taxonomical assignment remains elusive. Previously, we have shown that the wild grapevine populations growing in northern Israel are genetically separated from the feral domesticated forms. This work aimed to comprehensively describe the morphological, anatomical, and ecological traits of wild grapevines naturally thriving in two distinct habitats in Israel. The dioicous nature of the wild grapevine, the flower and pollen morphology, and the characteristic Sylvestris fruit and seed morphology, in addition to the occurrence of the natural germination of seeds in close vicinity of the mother plant, have all led to the conclusion that these plants belong to Vitis vinifera subsp. sylvestris and should be included in the Flora Palaestina. These findings, combined with the recently published genetic evidence for these populations, significantly advance our understanding of the species’ ecology and the importance of its preservation.

A special feature found in Amaryllidaceae is that some guard cells of the neighboring stomata form a “connection strand” between their dorsal cell walls. In the present work, this strand was studied in terms of both its composition and its effect on the morphology and function of the stomata in Pancratium maritimum L. leaves. The structure of stomata and their connection strand were studied by light and transmission electron microscopy. FM 4–64 and aniline blue staining and application of tannic acid were performed to detect cell membranes, callose, and pectins, respectively. A plasmolysis experiment was also performed. The composition of the connection strand was analyzed by fluorescence microscopy after immunostaining with several cell-wall-related antibodies, while pectinase treatment was applied to confirm the presence of pectins in the connection strand. To examine the effect of this connection on stomatal function, several morphological characteristics (width, length, size, pore aperture, stomatal distance, and cell size of the intermediate pavement cell) were studied. It is suggested that the connecting strand consists of cell wall material laid through the middle of the intermediate pavement cell adjoining the two stomata. These cell wall strands are mainly comprised of pectins, and crystalline cellulose and extensins were also present. Connected stomata do not open like the single stomata do, indicating that the connection strand could also affect stomatal function. This trait is common to other Amaryllidaceae representatives.

Ancient burial caves represent some of the most important sources of information on human history. In a world heritage site in Israel, such caves are under threat due to tree root growth penetrating from the ceilings and causing a risk of cave collapse. To facilitate historical conservation, while avoiding cutting of the mixed forest above the caves, we identified the tree species responsible for the damage, facilitating their specific cutting. Accurate identification of tree roots balances the needs to protect human structures on one side, while conserving the majority of vegetation on the other. Our approach is applicable to the management of ancient sites, as well as to urban management more broadly. Societal Impact Statement Ancient burial caves represent some of the most important sources of information on human history. In a world heritage site in Israel, such caves are under threat due to tree root growth penetrating from the ceilings and causing a risk of cave collapse. To facilitate historical conservation, while avoiding cutting of the mixed forest above the caves, we identified the tree species responsible for the damage, facilitating their specific cutting. Accurate identification of tree roots balances the needs to protect human structures on one side, while conserving the majority of vegetation on the other. Our approach is applicable to the management of ancient sites, as well as to urban management more broadly. Summary Tree roots have penetrated the ceiling of burial caves in a ~1,800‐years‐old necropolis in the Galilee, Israel, damaging the antiquities and risking the catacombs with collapse. Root identification was needed to enable selective cutting (at the species level), facilitating the conservation of the world heritage site, while maintaining the majority of trees growing on top of the burial caves. Samples of roots penetrating the cave ceilings were collected and identified both by using DNA barcoding, which has become a standard method for the reliable identification of organisms in their natural environment, and also by traditional morpho‐anatomical methods. However, woody plant species of the Mediterranean region are under‐represented in DNA databases. Therefore, we added relevant species to the ITS2 database by sequencing the internal transcribed spacer (ITS)2 of the 18S‐26S rDNA from sampled leaves of 19 woody species of the Mediterranean maquis. The identification of these tree species facilitated their selective removal, balancing antiquities, and nature conservation needs.

Fruits are the dominant sinks for assimilates. At optimal conditions, assimilates supply can meet the demand of fruits and those of the vegetative organs; however, extreme circumstances such as strong sink strength or an environmental stress may disturb this fine balance. While most studies focus on aboveground parameters, information regarding root growth dynamics under variable sink strength are scarce. The objective of this study was to evaluate the effect of sink strength (represented by fruit load) and salinity on bell-pepper root development. Three levels of fruit load were combined with two salinity levels in plants grown in an aeroponic system. Root growth was determined both by root capacitance and destructive measurements. Salinity and sink strength significantly affected root, shoot and fruit growth dynamics. Root growth was less affected by fruit load. Salinity stress was negatively associated with shoot growth, but after an acclimation period, salinity enhanced root development. Additionally, this study shows for the first time that root capacitance is a valid approach for non-destructive measurement of root development in aeroponic systems. The good correlation measured by us (r2 0.86) opens new opportunities for continuous root growth monitoring in aeroponic systems in the future.

Plants rely on innate immunity to perceive and ward off microbes and pests, and are able to overcome the majority of invading microorganisms. Even so, specialized pathogens overcome plant defenses, posing a persistent threat to crop and food security worldwide, raising the need for agricultural products with broad, efficient resistance. Here we report a specific mutation in a tomato ( S. lycopersicum ) helper nucleotide-binding domain leucine-rich repeat H-NLR, SlNRC4a , which results in gain of function constitutive basal defense activation, in absence of PRR activation. Knockout of the entire NRC4 clade in tomato was reported to compromise Rpi-blb2 mediated immunity. The SlNRC4a mutant reported here possesses enhanced immunity and disease resistance to a broad-spectrum of pathogenic fungi, bacteria and pests, while lacking auto-activated HR or negative effects on plant growth and crop yield, providing promising prospects for agricultural adaptation in the war against plant pathogens that decrease productivity. Lorena Pizarro, Meirav Leibman-Markus et al. explore the genetic mechanisms for plant innate immunity. They functionally characterize a gain of function mutation in SlNRC4a in tomato. They characterize the structure of the mutant protein and functionally demonstrate that it confers broad-spectrum resistance without triggering a hypersensitive response or negatively impacting plant growth and crop yield.