Palisade cell geometry in relation to leaf optical and photosynthetic properties in Viburnum.

The optical properties of lobed palisade mesophyll cells remain poorly understood despite their presence in diverse taxa and the critical role of the palisade layer in leaf-light interactions and carbon assimilation. Using micro-computed tomography, 3D ray tracing simulations, and physiological experiments, we tested the interactions between palisade cell geometry, chloroplast localization, light directional quality, and leaf optical and photosynthetic performance in the model taxon Viburnum. Simulations showed that lobed cells shifted between absorptance- or transmittance-dominated states depending on chloroplast localization, irrespective of light directional quality.

Tree drought physiology: critical research questions and strategies for mitigating climate change effects on forests.

Droughts of increasing severity and frequency are a primary cause of forest mortality associated with climate change. Yet, fundamental knowledge gaps regarding the complex physiology of trees limit the development of more effective management strategies to mitigate drought effects on forests. Here, we highlight some of the basic research needed to better understand tree drought physiology and how new technologies and interdisciplinary approaches can be used to address them.

Into the spongy-verse: structural differences between leaf and flower mesophyll.

As the site of almost all terrestrial carbon fixation, the mesophyll tissue is critical to leaf function. However, mesophyll tissue is not restricted only to leaves but also occurs in the laminar, heterotrophic organs of the floral perianth, providing a powerful test of how metabolic differences are linked to differences in tissue structure. Here, we compared mesophyll tissues of leaves and flower perianths of six species using high-resolution X-ray computed microtomography (microCT) imaging.

Sensitive Hydraulic and Stomatal Decline in Extreme Drought Tolerant Species of California Ceanothus.

Identifying the physiological mechanisms by which plants are adapted to drought is critical to predict species responses to climate change. We measured the responses of leaf hydraulic and stomatal conductances (K and g, respectively) to dehydration, and their association with anatomy, in seven species of California Ceanothus grown in a common garden, including some of the most drought-tolerant species in the semi-arid flora. We tested for matching of maximum hydraulic supply and demand and quantified the role of decline of K in driving stomatal closure.

Stomatal closure as a driver of minimum leaf conductance declines at high temperature and vapor pressure deficit in Quercus.

Rising global temperatures and vapor pressure deficits (VPDs) are increasing plant water demand and becoming major drivers of large-scale plant mortality. Controlling transient leaf water loss after stomatal closure (minimum stomatal conductance [gmin]) is recognized as a key trait determining how long plants survive during soil drought. Yet, substantial uncertainty remains regarding how gmin responds to elevated temperatures and VPD and the underlying mechanisms.

Wind speed affects the rate and kinetics of stomatal conductance.

Understanding the relationship between wind speed and gas exchange in plants is a longstanding challenge. Our aim was to investigate the impact of wind speed on maximum rates of gas exchange and the kinetics of stomatal responses. We conducted experiments in different angiosperm and fern species using an infrared gas analyzer equipped with a controlled leaf fan, enabling precise control of the boundary layer conductance.

Weak link or strong foundation? Vulnerability of fine root networks and stems to xylem embolism.

Resolving the position of roots in the whole-plant hierarchy of drought-induced xylem embolism resistance is fundamental for predicting when species become isolated from soil water resources. Published research generally suggests that roots are the most vulnerable organ of the plant vascular system, although estimates vary significantly. However, our knowledge of root embolism excludes the fine roots (< 2 mm diameter) that form the bulk of total absorptive surface area of the root network for water and nutrient uptake.

Stomatal behaviour and water relations in ferns and lycophytes across habits and habitats.

Stomatal anatomy and behaviour are key to managing gas exchange fluxes, which require coordination with the plant vascular system to adequately supply leaves with water. Stomatal response times and regulation of water loss are generally understudied in ferns, especially across habits (i.e.

Xylem-dwelling pathogen unaffected by local xylem vessel network properties in grapevines (Vitis spp.).

Background And Aims: Xylella fastidiosa (Xf) is the xylem-dwelling bacterium associated with Pierce's disease (PD), which causes mortality in agriculturally important species, such as grapevine (Vitis vinifera). The development of PD symptoms in grapevines depends on the ability of Xf to produce cell-wall-degrading enzymes to break up intervessel pit membranes and systematically spread through the xylem vessel network. Our objective here was to investigate whether PD resistance could be mechanistically linked to xylem vessel network local connectivity.

Starch depletion in the xylem and phloem ray parenchyma of grapevine stems under drought.

While nonstructural carbohydrate (NSC) storage can support long-lived woody plants during abiotic stress, the timing and extent of their use are less understood, as are the thresholds for cell mortality as NSCs and water supplies are consumed. Here, we combine physiological and imaging tools to study the response of to a 6-week experimental drought. We focused on the spatial and temporal dynamics of starch consumption and cell viability in the xylem and phloem of the stem.

Anatomy of an agricultural antagonist: Feeding complex structure and function of three xylem sap-feeding insects illuminated with synchrotron-based 3D imaging.

Many insects feed on xylem or phloem sap of vascular plants. Although physical damage to the plant is minimal, the process of insect feeding can transmit lethal viruses and bacterial pathogens. Disparities between insect-mediated pathogen transmission efficiency have been identified among xylem sap-feeding insects; however, the mechanistic drivers of these trends are unclear.

Back to life: Techniques for developing high-quality 3D reconstructions of plants and animals from digitized specimens.

Expanded use of 3D imaging in organismal biology and paleontology has substantially enhanced the ability to visualize and analyze specimens. These techniques have improved our understanding of the anatomy of many taxa, and the integration of downstream computational tools applied to 3D datasets have broadened the range of analyses that can be performed (e.g.

Localized growth and remodelling drives spongy mesophyll morphogenesis.

The spongy mesophyll is a complex, porous tissue found in plant leaves that enables carbon capture and provides mechanical stability. Unlike many other biological tissues, which remain confluent throughout development, the spongy mesophyll must develop from an initially confluent tissue into a tortuous network of cells with a large proportion of intercellular airspace. How the airspace in the spongy mesophyll develops while the tissue remains mechanically stable is unknown.

Hydraulic failure as a primary driver of xylem network evolution in early vascular plants.

The earliest vascular plants had stems with a central cylindrical strand of water-conducting xylem, which rapidly diversified into more complex shapes. This diversification is understood to coincide with increases in plant body size and branching; however, no selection pressure favoring xylem strand-shape complexity is known. We show that incremental changes in xylem network organization that diverge from the cylindrical ancestral form lead to progressively greater drought resistance by reducing the risk of hydraulic failure.

Functional xylem characteristics associated with drought-induced embolism in angiosperms.

Hydraulic failure resulting from drought-induced embolism in the xylem of plants is a key determinant of reduced productivity and mortality. Methods to assess this vulnerability are difficult to achieve at scale, leading to alternative metrics and correlations with more easily measured traits. These efforts have led to the longstanding and pervasive assumed mechanistic link between vessel diameter and vulnerability in angiosperms.

Burning questions for a warming and changing world: 15 unknowns in plant abiotic stress.

We present unresolved questions in plant abiotic stress biology as posed by 15 research groups with expertise spanning eco-physiology to cell and molecular biology. Common themes of these questions include the need to better understand how plants detect water availability, temperature, salinity, and rising carbon dioxide (CO2) levels; how environmental signals interface with endogenous signaling and development (e.g.

Leaf cell-specific and single-cell transcriptional profiling reveals a role for the palisade layer in UV light protection.

Like other complex multicellular organisms, plants are composed of different cell types with specialized shapes and functions. For example, most laminar leaves consist of multiple photosynthetic cell types. These cell types include the palisade mesophyll, which typically forms one or more cell layers on the adaxial side of the leaf.

Conduit position and connectivity affect the likelihood of xylem embolism during natural drought in evergreen woodland species.

Background And Aims: Hydraulic failure is considered a main cause of drought-induced forest mortality. Yet, we have a limited understanding of how the varying intensities and long time scales of natural droughts induce and propagate embolism within the xylem.

Methods: X-ray computed tomography (microCT) images were obtained from different aged branch xylem to study the number, size and spatial distribution of in situ embolized conduits among three dominant tree species growing in a woodland community.

Pathogen-induced hydraulic decline limits photosynthesis and starch storage in grapevines (Vitis sp.).

Xylella fastidiosa (Xf) is the bacterial pathogen responsible for Pierce's Disease (PD) in grapevine (Vitis vinifera L.) and numerous diseases in agriculturally and ecologically important species. Current theory suggests that localized inoculations via insect feeding lead to bacterial spread through the xylem, reducing water transport capacity, leading to declines in productivity, and ultimately death.

Desiccation of the leaf mesophyll and its implications for CO diffusion and light processing.

Leaves balance CO and radiative absorption while maintaining water transport to maximise photosynthesis. Related species with contrasting leaf anatomy can provide insights into inherent and stress-induced links between structure and function for commonly measured leaf traits for important crops. We used two walnut species with contrasting mesophyll anatomy to evaluate these integrated exchange processes under non-stressed and drought conditions using a combination of light microscopy, X-ray microCT, gas exchange, hydraulic conductance, and chlorophyll distribution profiles through leaves.

Foliar water uptake does not contribute to embolism repair in beech (Fagus sylvatica L.).

Background And Aims: Foliar water uptake has recently been suggested as a possible mechanism for the restoration of hydraulically dysfunctional xylem vessels. In this paper we used a combination of ecophysiological measurements, X-ray microcomputed tomography and cryo-scanning electron microscopy during a drought treatment to fully evaluate this hypothesis.

Key Results: Based on an assessment of these methods in beech (Fagus sylvatica L.

Structural organization of the spongy mesophyll.

Many plant leaves have two layers of photosynthetic tissue: the palisade and spongy mesophyll. Whereas palisade mesophyll consists of tightly packed columnar cells, the structure of spongy mesophyll is not well characterized and often treated as a random assemblage of irregularly shaped cells. Using micro-computed tomography imaging, topological analysis, and a comparative physiological framework, we examined the structure of the spongy mesophyll in 40 species from 30 genera with laminar leaves and reticulate venation.

Desiccation and rehydration dynamics in the epiphytic resurrection fern Pleopeltis polypodioides.

The epiphytic resurrection-or desiccation-tolerant (DT)-fern Pleopeltis polypodioides can survive extreme desiccation and recover physiological activity within hours of rehydration. Yet, how epiphytic DT ferns coordinate between deterioration and recovery of their hydraulic and photosynthetic systems remains poorly understood. We examined the functional status of the leaf vascular system, chlorophyll fluorescence, and photosynthetic rate during desiccation and rehydration of P.