Identification of symplasmic domains in the embryo and seed of Sedum acre L. (Crassulaceae).

MAIN CONCLUSION: Our study demonstrated that symplasmic communication between Sedum acre seed compartments and the embryo proper is not uniform. The presence of plasmodesmata (PD) constitutes the structural basis for information exchange between cells, and symplasmic communication is involved in the regulation of cell differentiation and plant development. Most recent studies concerning an analysis of symplasmic communication between seed compartments and the embryo have been predominantly performed on Arabidopsis thaliana. The results presented in this paper describe the analysis of symplasmic communication on the example of Sedum acre seeds, because the ultrastructure of the seed compartments and the embryo proper, including the PD, have already been described, and this species represents an embryonic type of development different to Arabidopsis. Moreover, in this species, an unusual electron-dense dome associated with plasmodesmata on the border between the basal cell/chalazal suspensor cells and the basal cell/the endosperm has been described. This prompted the question as to whether these plasmodesmata are functional. Thus, the aim of this study was to describe the movement of symplasmic transport fluorochromes between different Sedum seed compartments, with particular emphasis on the movement between the basal cell and the embryo proper and endosperm, to answer the following questions: (1) are seeds divided into symplasmic domains; (2) if so, are they stable or do they change with the development? The results have shown that symplasmic tracers movement: (a) from the external integument to internal integument is restricted; (b) from the basal cell to the other part of the embryo proper and from the basal cell to the endosperm is also restricted;

Colonization and modulation of host growth and metal uptake by endophytic bacteria of Sedum alfredii.

Sedum alfredii Hance is a Zn and Cd co-hyperaccumulating plant species found in an old mining area in China. Four bacterial strains, Burkholderia sp. SaZR4, Burkholderia sp. SaMR10, Sphingomonas sp. SaMR12 and Variovorax sp. SaNR1, isolated from surface-sterilized S. alfredii plants were used to investigate their endophytic nature and root colonization patterns and effects on phytoextraction of Zn and Cd. Laser scanning confocal microscopy revealed that gfp-tagged SaZR4, SaMR12, and SaNR1 cells formed biofilms on roots and that SaZR4 and SaMR12 cells could invade root tissues. SaMR10 showed the lowest total population associated with S. alfredii and little effect on plant growth and phytoextraction. SaZR4 significantly promoted Zn-extraction but not Cd-extraction. SaMR12 and SaNR1 significantly promoted plant growth in substrates supplemented with Zn or Cd and phytoextraction of Zn and Cd. Together, this study have shown that the four native endophytic bacteria differently colonize the host plants and modulate metal uptake and growth of host plant, and that SaMR12 and SaNR1 strains are promising assistants of S. alfredii plants for phytoremediation of Zn/Cd-contaminated soil.

Cellular sequestration of cadmium in the hyperaccumulator plant species Sedum alfredii.

Spatial imaging of cadmium (Cd) in the hyperaccumulator Sedum alfredii was investigated in vivo by laser ablation inductively coupled plasma mass spectrometry and x-ray microfluorescence imaging. Preferential Cd accumulation in the pith and cortex was observed in stems of the Cd hyperaccumulating ecotype (HE), whereas Cd was restricted to the vascular bundles in its contrasting nonhyperaccumulating ecotype. Cd concentrations of up to 15,000 µg g(-1) were measured in the pith cells, which was many fold higher than the concentrations in the stem epidermis and vascular bundles in the HE plants. In the leaves of the HE, Cd was mainly localized to the mesophyll and vascular cells rather than the epidermis. The distribution pattern of Cd in both stems and leaves of the HE was very similar to calcium but not zinc, irrespective of Cd exposure levels. Extended x-ray absorption fine structure spectroscopy analysis showed that Cd in the stems and leaves of the HE was mainly associated with oxygen ligands, and a larger proportion (about 70% in leaves and 47% in stems) of Cd was bound with malic acid, which was the major organic acid in the shoots of the plants. These results indicate that a majority of Cd in HE accumulates in the parenchyma cells, especially in stems, and is likely associated with calcium pathways and bound with organic acid (malate), which is indicative of a critical role of vacuolar sequestration of Cd in the HE S. alfredii.

Functional analysis of metal tolerance proteins isolated from Zn/Cd hyperaccumulating ecotype and non-hyperaccumulating ecotype of Sedum alfredii Hance.

The Zn/Cd hyperaccumulating ecotype (HE) of Sedum alfredii Hance can accumulate 24- and 28-fold higher leaf and stem Zn concentrations when compared with the non-hyperaccumulating ecotype (NHE) of Sedum. Heterologous expression of a metal tolerance protein (MTP1) encoding gene from HE plants (SaMTP1) or the homologous gene from NHE plants (SnMTP1) suppressed Zn(2+) hypersensitivity in the Δzrc1 yeast mutant. In plants, SaMTP1 localized to the tonoplast. Furthermore, MTP1 transcript level in the shoot of HE plants was more than 80-fold higher than that of NHE plants. The transcript level of SaMTP1 in shoot was up-regulated 1-fold by Zn(2+) while the expression of SnMTP1 was slightly inhibited. These data suggest that SaMTP1 can play an important role in Zn accumulation in HE plants.

Stem and leaf sequestration of zinc at the cellular level in the hyperaccumulator Sedum alfredii.

* Sedum alfredii is a fast-growing, high-biomass zinc (Zn) hyperaccumulator native to China. Here, the characteristics of in vivo Zn distribution in stems and leaves of the hyperaccumulating (HE) and nonhyperaccumulating ecotypes (NHE) of S. alfredii were investigated by synchrotron radiation X-ray fluorescence (SRXRF) analysis, together with a Zn probe. * Preferential Zn accumulation in leaf and stem epidermis was observed in both ecotypes, but to a much greater extent for HE. Epidermal Zn increased largely in leaves and stems of HE as exposure time was prolonged, while Zn saturation occurred relatively early in HE leaf mesophyll cells and stem vascular bundles. A second peak of Zn enrichment in stem and leaf vascular systems was shown in both ecotypes. However, the proportion of Zn accumulated in stem vascular bundles relative to other tissues was much greater for HE than for NHE. * Leaf and stem distribution patterns of phosphorus (P) and sulphur (S) in the HE were very like that for Zn, while the calcium (Ca) distribution pattern was the reverse of that for Zn. No such relationship was observed in NHE. * Our study mainly suggested that epidermal layers serve as important storage sites for accumulated Zn in the S. alfredii HE.

[Studies on identification of Sedum emarginatum].

OBJECTIVE: To establish methods for identification of the whole plant of Sedum emarginatum Migo. METHODS: Macroscopic and microscopic observation and FTIR technique were used to authenticate this crude drug, and the identification characteristics were studied. RESULTS: The stem cross section and the whole plant powder had some notable micro-characters. The infrared spectras of the samples collected in the different habitats and seasons were very consistent with each other. CONCLUSION: The results can be used as the evidence for identification of this ethnomedicine.

[Subcellular distribution and chemical forms of Cd and Zn in Sedum jinianum].

With water culture and by using differential centrifugation technique and sequential extraction, the subcellular distribution and chemical forms of Cd and Zn in the root, stem and leaf of Sedum jinianum were studied. In treatment 10 micromol Cd x L(-1), most of Cd in S. jinianum was in the soluble fraction of cell; while in treatment 100 miromol Cd x L(-1), the Cd in root was mainly deposited on cell wall, the Cd in stem was mainly on cell wall and in soluble fraction, and over 90% of Cd in leaf were in soluble fraction. In treatment 100 micromol Cd x L(-1), the proportion of Cd on the cell walls of root, stem and leaf increased, while that in soluble fraction decreased. In treatments 1 and 800 micromol Zn x L(-1), the Zn in root, stem and leaf mainly presented in soluble fraction; while in treatments with the Zn level between 1.0 and 800 micromol x L(-1), there were no differences in the proportions of Zn in the soluble fraction and on the cell walls of root, stem and leaf. Very low proportions of Cd and Zn were found in cell organelle. The Cd in the root, stem and leaf was predominated with NaCl- and water-extractable forms, while Zn in the plants were existed in numerous chemical forms.

Zinc adsorption and desorption characteristics in root cell wall involving zinc hyperaccumulation in Sedum alfredii Hance.

Radiotracer techniques were employed to characterize (65)Zn adsorption and desorption in root-cell-wall of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) species of Sedum alfredii Hance. The results indicated that at the end of a 30 min short time radioisotope loading period, comparable amounts of (65)Zn were accumulated in the roots of the two ecotypes Sedum alfredii, whereas 2.1-fold more (65)Zn remains in NHE root after 45-min desorption. At the end of 60 min uptake period, no difference of (65)Zn accumulation was observed in undesorbed root-cell-wall of Sedum alfredii. However, 3.0-fold more (65)Zn accumulated in desorbed root-cell-wall of NHE. Zn(2+) binding in root-cell-wall preparations of NHE was greater than that in HE under high Zn(2+) concentration. All these results suggested that root-cell-wall of the two ecotypes Sedum alfredii had the same ability to adsorb Zn(2+), whereas the desorption characteristics were different, and with most of (65)Zn binding on root of HE being available for loading into the xylem, as a result, more (65)Zn was translocated to the shoot.