Locally optimal geometry for surface-enhanced diffusion.

Molecular diffusion in bulk liquids proceeds according to Fick's law, which stipulates that the particle current is proportional to the conductive area. This constrains the efficiency of filtration systems in which both selectivity and permeability are valued. Previous studies have demonstrated that interactions between the diffusing species and solid boundaries can enhance or reduce particle transport relative to bulk conditions.

Cell wall is a dead metaphor.

It was recently suggested to end the usage of the term cell wall in microbiology (including prokaryotes and fungi) because it represented an inappropriate and potentially misleading metaphor (Casadevall and Gow, 2022). The analysis of the arguments for such a move from the viewpoint of the plant physiologist indicates that the suggestion is based on misunderstandings, first, of the early history of cell biology and its terminology; second, of the development of modern concepts of cell wall function since the late 19th century; and third, of the nature of metaphors and their role in scientific communication. We conclude that misconceptions concerning cell walls may arise due to pedagogical shortcomings in introducing students to our technical terminology rather than from the fact that part of this terminology originated from metaphors.

Pavement cells distinguish touch from letting go.

A micro-cantilever technique applied to individual leaf epidermis cells of intact Arabidopsis thaliana and Nicotiana tabacum synthesizing genetically encoded calcium indicators (R-GECO1 and GCaMP3) revealed that compressive forces induced local calcium peaks that preceded delayed, slowly moving calcium waves. Releasing the force evoked significantly faster calcium waves. Slow waves were also triggered by increased turgor and fast waves by turgor drops in pressure probe tests.

How Münch's adaptation of Pfeffer's circulating water flow became the pressure-flow theory, and the resulting problems - A historical perspective.

Long-distance transport of photoassimilates in the phloem of vascular plants occurs as bulk flow in sieve tubes. These tubes are arrays of cells that lose nuclei, cytoskeleton, and some organelles when they differentiate into mature sieve elements. Symplasmic continuity is achieved by perforations that turn the cell walls between adjoining sieve elements into sieve plates.

Diversity of funnel plasmodesmata in angiosperms: the impact of geometry on plasmodesmal resistance.

In most plant tissues, threads of cytoplasm, or plasmodesmata, connect the protoplasts via pores in the cell walls. This enables symplasmic transport, for instance in phloem loading, transport and unloading. Importantly, the geometry of the wall pore limits the size of the particles that may be transported, and also (co-)defines plasmodesmal resistance to diffusion and convective flow.

Proteomics of isolated sieve tubes from : sieve element-specific proteins reveal differentiation of the endomembrane system.

Symplasmicly connected cells called sieve elements form a network of tubes in the phloem of vascular plants. Sieve elements have essential functions as they provide routes for photoassimilate distribution, the exchange of developmental signals, and the coordination of defense responses. Nonetheless, they are the least understood main type of plant cells.

Plasmodesmata and the problems with size: Interpreting the confusion.

Plant tissues exhibit a symplasmic organization; the individual protoplasts are connected to their neighbors via cytoplasmic bridges that extend through pores in the cell walls. These bridges may have diameters of a micrometer or more, as in the sieve pores of the phloem, but in most cell types they are smaller. Historically, botanists referred to cytoplasmic bridges of all sizes as plasmodesmata.

Aspartate Residues in a Forisome-Forming SEO Protein Are Critical for Protein Body Assembly and Ca2+ Responsiveness.

Forisomes are protein bodies known exclusively from sieve elements of legumes. Forisomes contribute to the regulation of phloem transport due to their unique Ca2+-controlled, reversible swelling. The assembly of forisomes from sieve element occlusion (SEO) protein monomers in developing sieve elements and the mechanism(s) of Ca2+-dependent forisome contractility are poorly understood because the amino acid sequences of SEO proteins lack conventional protein-protein interaction and Ca2+-binding motifs.

Size-dependent locomotory performance creates a behaviorally mediated prey size refuge in the marine snail : a study in the natural habitat.

The effects of the variability of individual prey locomotory performance on the vulnerability to predation are poorly understood, partly because individual performance is difficult to determine in natural habitats. To gain insights into the role(s) of individual variation in predatory relationships, we study a convenient model system, the neotropical sandy beach gastropod and its main predator, the carnivorous snail . The largest size class of is known to be missing from 's spectrum of subdued prey, although the predator regularly captures much larger individuals of other taxa.

Sieve elements rapidly develop 'nacreous walls' following injury - a common wounding response?

Thick glistening cell walls occur in sieve tubes of all major land plant taxa. Historically, these 'nacreous walls' have been considered a diagnostic feature of sieve elements; they represent a conundrum, though, in the context of the widely accepted pressure-flow theory as they severely constrict sieve tubes. We employed the cucurbit Gerrardanthus macrorhizus as a model to study nacreous walls in sieve elements by standard and in situ confocal microscopy and electron microscopy, focusing on changes in functional sieve tubes that occur when prepared for microscopic observation.

The diffusive injection micropipette (DIMP).

The microinjection of fluorescent probes into live cells is an essential component in the toolbox of modern cell biology. Microinjection techniques include the penetration of the plasma membrane and, if present, the cell wall with micropipettes, and the application of pressure or electrical currents to drive the micropipette contents into the cell. These procedures interfere with cellular functions and therefore may induce artifacts.

Complexity of the prey spectrum of (Caenogastropoda: Olividae), a dominant predator in sandy beach ecosystems of Pacific Central America.

Olivid gastropods of the genus are dominant predators within invertebrate communities on sandy beaches throughout Pacific Central America. At Playa Grande, on the Pacific Coast of Costa Rica, we observed 327 natural predation events by . For each predation event, we documented prey taxa and body size of both predator and prey.

Non-dispersive phloem-protein bodies (NPBs) of consist of a SEOR protein and do not respond to cell wounding and Ca.

Differentiating sieve elements in the phloem of angiosperms produce abundant phloem-specific proteins before their protein synthesis machinery is degraded. These P-proteins initially form dense bodies, which disperse into individual filaments when the sieve element matures. In some cases, however, the dense protein agglomerations remain intact and are visible in functional sieve tubes as non-dispersive P-protein bodies, or NPBs.

Sieve-element differentiation and phloem sap contamination.

Sieve elements (SEs) degrade selected organelles and cytoplasmic structures when they differentiate. According to classical investigations, only smooth ER, mitochondria, sieve element plastids, and, in most cases, P-proteins remain in mature SEs. More recent proteomics and immuno-histochemical studies, however, suggested that additional components including a protein-synthesizing machinery and a fully developed actin cytoskeleton operate in mature SEs.

What actually is the Münch hypothesis? A short history of assimilate transport by mass flow.

In the 1920s, the German forestry scientist Ernst Münch postulated that photo-assimilate transport is a mass flow driven by osmotically induced pressure gradients between source organs (high turgor) and sink organs (lower turgor). Two crucial components of Münch's hypothesis, the translocation by mass flow from sources to sinks and the osmotic mechanism of pressure flow, were established notions at the time, but had been developed by two institutionally separated groups of scholars. A conceptual separation of whole-plant biology from cellular physiology had followed the institutional separation of forestry science from botany in German-speaking central Europe during the so-called Humboldtian reforms, and was reinforced by the delayed institutionalization of plant physiology as an academic discipline.

In situ microscopy reveals reversible cell wall swelling in kelp sieve tubes: one mechanism for turgor generation and flow control?

Kelps, brown algae (Phaeophyceae) of the order Laminariales, possess sieve tubes for the symplasmic long-distance transport of photoassimilates that are evolutionarily unrelated but structurally similar to the tubes in the phloem of vascular plants. We visualized sieve tube structure and wound responses in fully functional, intact Bull Kelp (Nereocystis luetkeana [K. Mertens] Postels & Ruprecht 1840).

The gelatinous extracellular matrix facilitates transport studies in kelp: visualization of pressure-induced flow reversal across sieve plates.

Background And Aims: In vascular plants, important questions regarding phloem function remain unanswered due to problems with invasive experimental procedures in this highly sensitive tissue. Certain brown algae (kelps; Laminariales) also possess sieve tubes for photoassimilate transport, but these are embedded in large volumes of a gelatinous extracellular matrix which isolates them from neighbouring cells. Therefore, we hypothesized that kelp sieve tubes might tolerate invasive experimentation better than their analogues in higher plants, and sought to establish Nereocystis luetkeana as an experimental system.

SEORious business: structural proteins in sieve tubes and their involvement in sieve element occlusion.

The phloem provides a network of sieve tubes for long-distance translocation of photosynthates. For over a century, structural proteins in sieve tubes have presented a conundrum since they presumably increase the hydraulic resistance of the tubes while no potential function other than sieve tube or wound sealing in the case of injury has been suggested. Here we summarize and critically evaluate current speculations regarding the roles of these proteins.

Long-distance translocation of photosynthates: a primer.

The storage of light energy in chemical form through photosynthesis is the key process underlying life as we know it. To utilize photosynthates efficiently as structural materials or as fuel to drive endergonic processes, they have to be transported from where they are produced to where they are needed. In this primer, we provide an overview of basic biophysical concepts underlying our current understanding of the mechanisms of photosynthate long-distance transport, and briefly discuss current developments in the field.

Forisome performance in artificial sieve tubes.

In the legume phloem, sieve element occlusion (SEO) proteins assemble into Ca(2+)-dependent contractile bodies. These forisomes presumably control phloem transport by forming reversible sieve tube plugs. This function, however, has never been directly demonstrated, and appears questionable as forisomes were reported to be too small to plug sieve tubes, and failed to block flow efficiently in artificial microchannels.

Legume phylogeny and the evolution of a unique contractile apparatus that regulates phloem transport.

Protein bodies called forisomes undergo Ca(2+)-dependent deformations to occlude sieve tubes reversibly, providing a unique regulatory mechanism of phloem transport. Because forisomes are known exclusively from the Papilionoideae (Leguminosae), the evolution of forisome function may have played a role in the rapid radiation of this huge taxon. The unexpected discovery of a papilionoid species lacking forisomes led us to evaluate a representative set of species covering 33 of the 36 legume tribes traditionally recognized.

Geometric constraints and the anatomical interpretation of twisted plant organ phenotypes.

The study of plant mutants with twisting growth in axial organs, which normally grow straight in the wild-type, is expected to improve our understanding of the interplay among microtubules, cellulose biosynthesis, cell wall structure, and organ biomechanics that control organ growth and morphogenesis. However, geometric constraints based on symplastic growth and the consequences of these geometric constraints concerning interpretations of twisted-organ phenotypes are currently underestimated. Symplastic growth, a fundamental concept in plant developmental biology, is characterized by coordinated growth of adjacent cells based on their connectivity through cell walls.