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BackgroundEnhancing the upward translocation of heavy metals such as Zn from root to shoot through genetic engineering has potential for biofortification and phytoremediation. This study examined the contribution of the heavy metal-transporting ATPase, AtHMA4, to the shoot ionomic profile of soil-grown plants, and investigated the importance of the C-terminal domain in the functioning of this transporter.Principal FindingsThe Arabidopsis hma2 hma4 mutant has a stunted phenotype and a distinctive ionomic profile, with low shoot levels of Zn, Cd, Co, K and Rb, and high shoot Cu. Expression of AtHMA4 (AtHMA4-FL) under the CaMV-35S promoter partially rescued the stunted phenotype of hma2 hma4; rosette diameter returned to wild-type levels in the majority of lines and bolts were also produced, although the average bolt height was not restored completely. AtHMA4-FL expression rescued Co, K, Rb and Cu to wild-type levels, and partially returned Cd and Zn levels (83% and 28% of wild type respectively). In contrast, expression of AtHMA4-trunc (without the C-terminal region) in hma2 hma4 only partially restored the rosette diameter in two of five lines and bolt production was not rescued. There was no significant effect on the shoot ionomic profile, apart from Cd, which was increased to 41% of wild-type levels. When the AtHMA4 C-terminal domain (AtHMA4-C-term) was expressed in hma2 hma4 it had no marked effect. When expressed in yeast, AtHMA4-C-term and AtHMA4-trunc conferred greater Cd and Zn tolerance than AtHMA4-FL.ConclusionThe ionome of the hma2 hma4 mutant differs markedly from wt plants. The functional relevance of domains of AtHMA4 in planta can be explored by complementing this mutant. AtHMA4-FL is more effective in restoring shoot metal accumulation in this mutant than a C-terminally truncated version of the pump, indicating that the C-terminal domain is important in the functioning of AtHMA4 in planta.

We studied the extent and degree of homogenization of chemical zoning of olivines in type 3 ordinary chondrites in order to obtain some constraints on cooling histories of chondrites. Based on Mg‐Fe and CaO zoning, olivines in type 3 chondrites are classified into four types. A single chondrule usually contains olivines with the same type of zoning. Microporphyritic olivines show all four zoning types. Barred olivines usually show almost homogenized chemical zoning. We have calculated cooling rates or burial depths needed to homogenize the chemical zoning by solving the diffusion equation, using the zoning profiles as an initial condition. Mg‐Fe zoning of olivine may be altered during initial cooling, whereas CaO zoning is hardly changed. Barred olivines may be homogenized during initial cooling because their size is relatively small. To simulated microporphyritic olivine chondrules, cooling from just below the liquidus at moderately high rates is preferable to cooling from above the liquidus at low rates. For postaccumulation metamorphism of type 3 chondrites in order to keep Mg‐Fe zoning unaltered, the maximum metamorphic temperature must be less than about 400°C if we assume cooling rates based on Fe‐Ni data. Calculated cooling rates for both Fa and CaO homogenization are consistent with those by Fe‐Ni data for type 4 chondrites. A hot ejecta blanket several tens of meters thick on the surface of a parent body is sufficient to homogenize Mg‐Fe zoning if the temperature of the blanket is 600–700°C. Burial depths for petrologic types of ordinary chondrites in a parent body heated by 26Al are broadly consistent with those previously proposed.

We studied thermal metamorphism in the surface layer of a eucrite parent body by examining pyroxene zoning. Ca‐Mg‐Fe zoning of pyroxenes in the Pasamonte eucrite can be classified into three types: type 1 with a core composition of Ca5Mg62Fe32 and rim of Ca41Mg20Fe4o; type 2 with core of Ca5Mg62Fe32 and rim of Ca25Mg34Fe41; and type 3 with core of Ca5Mg66Fe29 and rim of Ca7Mg32Fe61. Type 1 typically occurs adjacent to a mesostasis, type 2 typically occurs adjacent to a surrounding plagioclase, and type 3 is common in pyroxenes in the matrix. Pasamonte is less metamorphosed than previously believed because of the wide range of composition of zoned pyroxenes. On the basis of Ca‐Mg‐Fe variation data, we have calculated the degree of homogenization of zoned pyroxenes by numerically solving the diffusion equation. A Pasamonte‐type pyroxene may yield a Juvinas‐type pyroxene by thermal metamorphism. The homogenization of Juvinas pyroxene could not have taken place during initial cooling and may be related to reheating events, although our calculation rests upon some assumptions.