The properties of (1,3)-β-glucans (i.e., callose) remain largely unknown despite their importance in plant development and defence. Here we use mixtures of (1,3)-β-glucan and cellulose, in ionic ...liquid solution and hydrogels, as proxies to understand the physico-mechanical properties of callose. We show that after callose addition the stiffness of cellulose hydrogels is reduced at a greater extent than predicted from the ideal mixing rule (i.e., the weighted average of the individual components' properties). In contrast, yield behaviour after the elastic limit is more ductile in cellulose-callose hydrogels compared with sudden failure in 100% cellulose hydrogels. The viscoelastic behaviour and the diffusion of the ions in mixed ionic liquid solutions strongly indicate interactions between the polymers. Fourier-transform infrared analysis suggests that these interactions impact cellulose organisation in hydrogels and cell walls. We conclude that polymer interactions alter the properties of callose-cellulose mixtures beyond what it is expected by ideal mixing.
The woody secondary cell walls of plants are the largest repository of renewable carbon biopolymers on the planet. These walls are made principally from cellulose and hemicelluloses and are ...impregnated with lignin. Despite their importance as the main load bearing structure for plant growth, as well as their industrial importance as both a material and energy source, the precise arrangement of these constituents within the cell wall is not yet fully understood. We have adapted low temperature scanning electron microscopy (cryo-SEM) for imaging the nanoscale architecture of angiosperm and gymnosperm cell walls in their native hydrated state. Our work confirms that cell wall macrofibrils, cylindrical structures with a diameter exceeding 10 nm, are a common feature of the native hardwood and softwood samples. We have observed these same structures in Arabidopsis thaliana secondary cell walls, enabling macrofibrils to be compared between mutant lines that are perturbed in cellulose, hemicellulose, and lignin formation. Our analysis indicates that the macrofibrils in Arabidopsis cell walls are dependent upon the proper biosynthesis, or composed, of cellulose, xylan, and lignin. This study establishes that cryo-SEM is a useful additional approach for investigating the native nanoscale architecture and composition of hardwood and softwood secondary cell walls and demonstrates the applicability of Arabidopsis genetic resources to relate fibril structure with wall composition and biosynthesis.
As sessile organisms, terrestrial plants have evolved sophisticated mechanisms to coordinate the growth and development of two distinct systems, the shoot and the root, in response to environmental ...fluctuations. Adaptive systemic responses are accomplished by shoot–root communication, which involves diverse long-distance signalling molecules. During the last few decades, various genetic, biochemical, molecular, and grafting studies have identified multiple long-distance signalling molecules which are crucial for plants to adapt to external changes. In this minireview, the long-distance signals implicated in systemic responses to various environmental cues are discussed.
Ko and Helariutta survey the mechanisms in plants mediating long distance communication between the shoot and root that help coordinate nutrient acquisition, growth, and stress responses across the plant body.
Understanding the development of vascular tissues in plants is crucial because the evolution of vasculature enabled plants to thrive on land. Various systems and approaches have been used to advance ...our knowledge about the genetic regulation of vasculature development, from the scale of single genes to networks. In this review, we provide a perspective on the major approaches used in studying plant vascular development, and we cover the mechanisms and genetic networks underlying vascular tissue specification, patterning, and differentiation.
Vascular tissue in plants is unique due to its diverse and dynamic cellular patterns. Signals controlling vascular development have only recently started to emerge through biochemical, genetic, and ...genomic approaches in several organisms, such as Arabidopsis, Populus, and Zinnia. These signals include hormones (auxin, brassinosteroids, and cytokinins, in particular), other small regulatory molecules, their transporters, receptors, and various transcriptional regulators. In recent years it has become apparent that plant growth regulators rarely act alone, but rather their signaling pathways are interlocked in complex networks; for example, polar auxin transport (PAT) regulates vascular development during various stages and an emerging theme is its modulation by other growth regulators, depending on the developmental context. Also, several synergistic or antagonistic interactions between various growth regulators have been described. Furthermore, shoot-root interactions appear to be important for this signal integration.
Stem cell populations in meristematic tissues at distinct locations in the plant body provide the potency of continuous plant growth. Primary meristems, at the apices of the plant body, contribute ...mainly to the elongation of the main plant axes, whereas secondary meristems in lateral positions are responsible for the thickening of these axes. The stem cells of the vascular cambium-a secondary lateral meristem-produce the secondary phloem (bast) and secondary xylem (wood). The sites of primary and secondary growth are spatially separated, and mobile signals are expected to coordinate growth rates between apical and lateral stem cell populations. Although the underlying mechanisms have not yet been uncovered, it seems likely that hormones, peptides, and mechanical cues orchestrate primary and secondary growth. In this review, we highlight the current knowledge and recent discoveries of how cambial stem cell activity is regulated, with a focus on mobile signals and the response of cambial activity to environmental and stress factors.
Through the diversity of cytokinin regulated processes, this phytohormone has a profound impact on plant growth and development. Cytokinin signaling is involved in the control of apical and lateral ...meristem activity, branching pattern of the shoot, and leaf senescence. These processes influence several traits, including the stem diameter, shoot architecture, and perennial life cycle, which define the development of woody plants. To facilitate research about the role of cytokinin in regulation of woody plant development, we have identified genes associated with cytokinin signaling and homeostasis pathways from two hardwood tree species.
Taking advantage of the sequenced black cottonwood (Populus trichocarpa) and peach (Prunus persica) genomes, we have compiled a comprehensive list of genes involved in these pathways. We identified genes belonging to the six families of cytokinin oxidases (CKXs), isopentenyl transferases (IPTs), LONELY GUY genes (LOGs), two-component receptors, histidine containing phosphotransmitters (HPts), and response regulators (RRs). All together 85 Populus and 45 Prunus genes were identified, and compared to their Arabidopsis orthologs through phylogenetic analyses.
In general, when compared to Arabidopsis, differences in gene family structure were often seen in only one of the two tree species. However, one class of genes associated with cytokinin signal transduction, the CKI1-like family of two-component histidine kinases, was larger in both Populus and Prunus than in Arabidopsis.
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