Difference in the distribution and speciation of cellular nickel between nickel-tolerant and non-tolerant Nicotiana tabacum L. cv. BY-2 cells.

To evaluate Ni dynamics at the subcellular level, the distribution and speciation of Ni were determined in wild-type (WT) and Ni-tolerant (NIT) tobacco BY-2 cell lines. When exposed to low but toxic levels of Ni, NIT cells were found to contain 2.5-fold more Ni (14% of whole-cell Ni values) in their cell walls than WT cells (6% of whole-cell Ni values). In addition to higher levels of Ni in the apoplast, a higher proportion (94%) of symplastic Ni was localized in the vacuoles of NIT cells than in the vacuoles of WT cells (81%). The concentration of cytosolic Ni in the NIT cells was significantly lower (18 nmol g(-1) FW) than that in the WT cells (85 nmol g(-1) FW). In silico simulation showed that 95% of vacuolar Ni was in the form of Ni-citrate complexes, and that free Ni(2+) was virtually absent in the NIT cells. On the other hand, the amount of free metal ions was markedly increased in WT cells because free citrate was depleted by chelation of Ni. A protoplast viability assay using BCECF-AM further demonstrated that the main mechanism that confers strong Ni tolerance was present in the symplast as opposed to the cell wall.

Common reed produces starch granules at the shoot base in response to salt stress.

Common reed (Phragmites australis) is a well known salt-tolerant plant and it is suggested that reeds recover Na(+) in the xylem sap of the shoot base (basal part of the shoot), store it temporarily in the shoot base, release it into the phloem sap, and then retranslocate it to the roots. To investigate whether Na(+) is retained in the shoot base of reeds, confocal laser scanning microscope (CLSM) observations were conducted using an intracellular Na(+)-specific fluorescent probe. The CLSM observations revealed that reeds produced a large number of the starch granules at the shoot base when salt-stressed, and that the fluorescence indicating the location of intracellular free Na(+) was observed in the same position as the starch granules. The Na content of starch granules was considerably greater than that of the shoot base, whereas the potassium (K) contents of the granules was only slightly greater than that of the shoot base. Reeds produced Na(+)-binding starch granules in the parenchyma cells of the shoot base when salt-stressed; these starch granules may decrease intracellular free Na(+). It is proposed that the site-specific production of Na(+)-binding starch granules constitutes a novel salt tolerance mechanism.