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Root elongation, hematoxylin staining, and changes in the ultrastructure of root-tip cells of an Al-tolerant maize variety (Zea mays L. C 525 M) exposed to nutrient solutions with 20 M Al (2.1 M Al 3؉ activity) for 0, 4, and 24 h were investigated in relation to the subcellular distribution of Al using scanning transmission electron microscopy and energy-dispersive x-ray microanalysis on samples fixed by different methods. Inhibition of root-elongation rates, hematoxylin staining, cell wall thickening, and disturbance of the distribution of pyroantimoniate-stainable cations, mainly Ca, was observed only after 4 and not after 24 h of exposure to Al. The occurrence of these transient, toxic Al effects on root elongation and in cell walls was accompanied by the presence of solid Al-P deposits in the walls. Whereas no Al was detectable in cell walls after 24 h, an increase of vacuolar Al was observed after 4 h of exposure. After 24 h, a higher amount of electron-dense deposits containing Al and P or Si was observed in the vacuoles. These results indicate that in this tropical maize variety, tolerance mechanisms that cause a change in apoplastic Al must be active. Our data support the hypothesis that in Al-tolerant plants, Al can rapidly cross the plasma membrane; these data clearly contradict the former conclusions that Al mainly accumulates in the apoplast and enters the symplast only after severe cell damage has occurred.It is largely recognized that root tips are the primary site of Al-induced injury in plants (Ryan et al., 1993). The accumulation of Al in root tips has been found to be significantly correlated with root-growth inhibition in maize (Zea mays L.) varieties differing in Al tolerance (Llugany, 1994; Llugany et al., 1994). In Al-sensitive maize plants an inhibition of root elongation has been observed after only 30 min of exposure to Al (Llugany et al., 1995). Such a short response time, in addition to the common belief (Kochian, 1995) that Al accumulates mainly in the apoplast and crosses the plasma membrane slowly, has led to the hypothesis that Al-induced inhibition of root elongation may be caused by toxicity mechanisms that occur in the apoplast (Rengel, 1990(Rengel, , 1996 Horst, 1995) and that there is no need for Al to enter the symplast to cause primary toxicity effects (Rengel, 1992). However, investigations using the highly Al-sensitive technique of secondary ion MS have shown that significant Al concentrations accumulate in the symplast of root-tip cells of soybean plants after only 30 min of exposure to Al (Lazof et al., 1994(Lazof et al., , 1996. Recent experiments on giant algae (Chara corallina) cells, where cell walls were separated from the cells by microsurgery, have also shown that Al uptake across the plasmalemma may be linear and occurs without delay (Rengel and Reid, 1997). These investigations support the view that symplastic phytotoxicity mechanisms may also be responsible for Alinduced inhibition of root elongation after short exposure times (Kochian, 1995).More information...

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The current study was aimed at investigating whether the single nucleotide polymorphism (SNP) (rs12979860), upstream of the IL28B gene, had any effect on the incidence rate and the features of active CMV infection in the Allogeneic stem cell transplantation setting. This was a retrospective observational study including 151 patients undergoing T cell-replete Allo-SCT. Donor and recipient IL28 SNP genotype was determined by allele-specific real-time PCR. The incidence rate of active CMV infection was not significantly associated with either the donor or the recipient IL28B SNP genotype. Nevertheless, a trend towards a lower incidence of active CMV infection was noted in the donor T/T population with respect to the donor C/T and C/C population. The duration of first episodes of CMV DNAemia was significantly shorter in patients carrying the donor T/T genotype with respect to their C/C or C/T counterparts (P = 0.038). Peak CMV DNAmeia levels tended to be lower in patients carrying the T/T genotype (donor or recipient) than in C/C or C/T patients, although statistical significance was not reached. In conclusion the data presented pointed to a protective effect of the T allele (recessive genetic model) against CMV infection in the Allo-SCT setting.

A relationship between aluminum (Al) toxicity, endocytosis, endosomes and vesicle recycling in the root transition zone has recently been demonstrated. Here the importance of filamentous actin (F-actin)-based vesicle trafficking for Al tolerance has been investigating in maize varieties differing in their Al sensitivities. More Al was internalized into root tip cells of the Al-sensitive variety 16x36 than in the Al-tolerant variety Cateto. The actin cytoskeleton and vesicle trafficking were primary targets for Al toxicity in the root tips of the sensitive variety. Visualization of boron-cross-linked rhamnogalacturonan II (RGII)-containing brefeldin A (BFA) compartments revealed that Al inhibited the formation of these compartments, especially in variety 16x36. The time sequence of Al effects on pectin recycling matches the growth effects of Al in this sensitive variety. These results support the hypothesis that Al binding to pectin-rich cell walls can contribute to reversible inhibition of root elongation. Al-induced alterations on F-actin were most evident in the central part of the transition zone of Al-sensitive 16x36, where Al was localized inside the nucleoli. In relation to this observation, a role for symplastic Al in both irreversible growth inhibition and amelioration of BFA-induced inhibition of root elongation is discussed.