Transcript levels of AtMRPs after cadmium treatment: induction of AtMRP3

In yeasts, the ABC-type transporters are involved in vacuolar sequestration of cadmium. In plants, transport experiments with isolated vacuoles indicate that this is also true. In order to know more about the response of AtMRPs, a subclass of Arabidopsis ABC transporters, to cadmium, their expression pattern was analysed using the microchip technology and semi-quantitative reverse transcriptase-polymerase chain reaction. From 15 putative sequences coding for AtMRPs, transcript levels were detected for 14. All were expressed in the roots as well as in the shoots, although at a different level. In 4-week-old Arabidopsis, transcript levels of four AtMRPs were up-regulated after cadmium treatment. In all cases up-regulation was exclusively observed in the roots. The increase of transcript levels was most pronounced for AtMRP3. A more detailed analysis revealed that induction of AtMRP3 could also be observed in the shoot when leaves were cut and cadmium allowed to be taken up in the shoot. In young plantlets, a far higher portion of Cd2+ was translocated in the aerial part compared with adult plants. Consequently, AtMRP3 transcript levels increased in both root and shoot of young plants. This suggests that 7-day-old seedlings do not exhibit such a strict root–shoot barrier as 4-week-old plants. Expression analysis with mutant plants for glutathione and phytochelatin synthesis as well as with compounds producing oxidative stress indicate that induction of AtMRP3 is likely due to the heavy metal itself.

3D-modeling of Mercury's solar wind sputtered surface-exosphere environment

The efficiency of sputtered refractory elements by H+ and He++ solar wind ions from Mercury's surface and their contribution to the exosphere are studied for various solar wind conditions. A 3D solar wind-planetary interaction hybrid model is used for the evaluation of precipitation maps of the sputter agents on Mercury's surface. By assuming a global mineralogical surface composition, the related sputter yields are calculated by means of the 2013 SRIM code and are coupled with a 3D exosphere model. Because of Mercury's magnetic field, for quiet and nominal solar wind conditions the plasma can only precipitate around the polar areas, while for extreme solar events (fast solar wind, coronal mass ejections, interplanetary magnetic clouds) the solar wind plasma has access to the entire dayside. In that case the release of particles form the planet's surface can result in an exosphere density increase of more than one order of magnitude. The corresponding escape rates are also about an order of magnitude higher. Moreover, the amount of He++ ions in the precipitating solar plasma flow enhances also the release of sputtered elements from the surface in the exosphere. A comparison of our model results with MESSENGER observations of sputtered Mg and Ca elements in the exosphere shows a reasonable quantitative agreement. (C) 2015 Elsevier Ltd. All rights reserved.