Plasmodesmata: Dynamic Channels for Symplastic Transport

Plasmodesmata (PDs) are cytoplasmic structures that link adjacent cells to form the symplast of a plant. PDs are involved extensively in a plant's life by mediating symplastic transport of a wide range of ions and molecules. Major components of a plasmodesma (PD) include a plasma membrane, a desmotubule, and a cytoplasmic annulus, all of which are readily detectable by electron microscopy. Both the plasma membrane and the desmotubule contain proteinaceous particles, thought to be involved in altering the size of the cytoplasmic annulus. Cytoskeleton elements (actin and myosin) are essential for maintaining the integrity of PDs. Together with these elements, calcium_binding proteins probably play a significant role in regulating PD function. Symplastic transport occurs through the cytoplasmic annulus for the great majority of solutes, while other substances may traverse through the desmotubule internal compartment, the desmotubule shell, or the plasma membrane. The symplast is subdivided into several domains with varying molecular size exclusion limits (ranging from <1 kD to >10 kD). Plasmodesmata can be either primary or secondary; the former are developed during new wall formation and the latter are made in existing walls. The dynamic nature of plasmodesmata is also reflected by their changing frequencies, which, in turn, depend on the developmental and physiological status of the tissue or the entire plant. While diffusion is the major mechanism of symplastic transport, plasmodesmata are selective for certain ions and molecules. Upon viral infection, viral movement proteins interact with PD receptor proteins and, as a result of yet unknown mechanisms, the plasmodesmata are remarkably dilated to allow viral movement proteins and the bound viral genome to enter healthy cells. Some proteins of plant origin are also able to traverse plasmodesmata, presumably in ways similar to viral movement proteins. Some of these plant proteins are probably signal molecules contributing to cell differentiation and other activities. Other proteins move cell_to_cell in a non_specific manner.

Estimation of citrus canker lesion size using hyperspectral reflectance imaging

The Citrus industry has need for effective approaches to remove fruit with canker before they are shipped to selective international market such as the European Union.This research aims to determine the detectable size limit for cankerous lesions using hyperspectral imaging approaches.Previously developed multispectral algorithms using visible to near-infrared wavelengths,were used to segregate cankerous citrus fruits from other peel conditions(normal,greasy spot,insect damage,melanose,scab and wind scar).However,this previous work did not consider lesion size.A two-band ratio method with a simple threshold based classifier(ratio of reflectance at wavelengths 834 nm and 729 nm),which gave maximum overall classification accuracy of 95.7%,was selected for lesion size estimation in this study.The smallest size of cankerous lesion detected in terms of equivalent diameter was 1.66 mm.The effect of variation of threshold values and number of erosion cycles(applying morphological erosion multiple times to the image)on estimation of smallest detectable lesion was observed.It was found that small threshold values gave better canker classification accuracies,while exhibiting a lower overall classification accuracy.Meanwhile,higher threshold values portrayed the opposite tendency.The threshold value of 1.275 gave the optimum tradeoff between canker classification accuracy,overall classification accuracy and minimal lesion size detection.Increasing the number of erosion cycles reduced detection rates of smaller canker lesions,leading to the conclusion that a single erosion cycle gave the best size estimation results.The erosion kernel of the size 3 mm×3 mm was used during the exploration.

Strain gradient induced grain refinement far below the size limit in a low carbon hypoeutectoid steel(0.19 wt%C)via pipe inner surface grinding treatment

A low carbon hypoeutectoid steel(0.19 wt%C)with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding(PISG)at room temperature.The deformation microstructures for each component were systematically characterized along depth,and the patterns of structural evolution toward nanometer regime as well as the governing parameters were addressed.Proeutectoid ferrite grains were refined down to 17 nm,and the pattern covering a length scale of 4–5 orders of magnitude from micron-to nanometer-scale follows:formation of cellular dislocation structure(CDS),elongated dislocation structure(EDS),ultrafine lamellar structure(UFL)and finally the nanolaminated structure(NL).The pearlite experiences the deformation and refinement,and finally the transforming the ultrafine pearlite(UFP)into nanolaminated pearlite(NLP)with the ferrite lamellae as thin as 20 nm.Refinement for both UFL(UFP)and NL(NLP)can be realized via forming novel extended boundaries within ferrite lamellae.A critical lattice curvature of~2.8°is required for forming such extended boundary,corresponding to a minimum strain gradient of 0.25μm^(-1)for a 100 nm-thick lamella.Refinement below size limit(expressed by lamellar thickness d_Tin nm)is correlated with the strain gradient(χ,inμm^(-1))by:d_T=12.5/x.Refinement contributions from strain gradient caused by PISG processing and material heterogeneity were discussed.

System size dependence in backward relativistic hadron production in pA and AA collisions

Abstract： In this comprehensive study the multiplicity characteristics of the backward emitted relativistic hadron （shower particle） through hadron-nucleus and nucleus-nucleus are overviewed in three dimensions. These dimensions are the projectile size, target size, and energy. To confirm the universality in this production system, wide ranges of system size and energy （Elab～2.1 A up to 200 A GeV） are used. The multiplicity characteristics of this hadron imply a limiting behavior with respect to the projectile size and energy. The target size is the main effective parameter in this production system. The exponential decay shapes is a characteristic feature of the backward shower particle multiplicity distributions. The decay constant changes with the target size to be nearly 2.02, 1.41, and 1.12 for the interactions with CNO, Era, and AgBr nuclei, respectively, irrespective of the projectile size and energy. While the backward production probability and average multiplicity are constants at different projectile sizes and energies, they can be correlated with the target size in power law relations.