Abstract
Drought strongly influences root activities in crop plants and weeds. This paper is focused on the performance of the heavy metal accumulator Solanum nigrum, a plant which might be helpful for phytoremediation. The water potential in a split root system was decreased by the addition of polyethylene glycol (PEG 6000). Rubidium, strontium and radionuclides of heavy metals were used as markers to investigate the uptake into roots, the release to the shoot via the xylem, and finally the basipetal transport via the phloem to unlabeled roots. The uptake into the roots (total contents in the plant) was for most makers more severely decreased than the transport to the shoot or the export from the shoot to the unlabeled roots via the phloem. Regardless of the water potential in the labeling solution, 63Ni and 65Zn were selectively redistributed within the plant. From autoradiographs, it became evident that 65Zn accumulated in root tips, in the apical shoot meristem and in axillary buds, while 63Ni accumulated in young expanded leaves and roots but not in the meristems. Since both radionuclides are mobile in the phloem and are, therefore, well redistributed within the plant, the unequal transfer to shoot and root apical meristems is most likely caused by differences in the cell-to-cell transport in differentiation zones without functional phloem (immature sieve tubes).
Highlights
During extended drought periods, species composition and productivity of grasslands are affected [1,2,3,4,5,6].Plants are often exposed to strong soil water potential gradients [7,8]
Since the two parts of the root system can be subjected to different water potentials, such experiments may allow a deeper insight into the uptake into the roots, the transfer of the labels in the transpiration stream via the xylem to the shoot and the symplastic transport from the shoot to the other part of the root system via the phloem
The shoot biomass at the end of the experiment was significantly higher in unstressed plants than in plants with one or both parts of the root system exposed to a lowered water potential
Summary
Plants are often exposed to strong soil water potential gradients [7,8]. Roots from the same plant may be in soil regions differing in their water availability. Experiments with split root systems might be helpful to elucidate interactions between differently stressed roots and the shoot. Markers applied to a part of the root system can be used to elucidate the uptake into the roots, the root-to-shoot transfer, and the basipetal transport via the phloem. Since the two parts of the root system can be subjected to different water potentials, such experiments may allow a deeper insight into the uptake into the roots, the transfer of the labels in the transpiration stream via the xylem to the shoot and the symplastic transport from the shoot to the other part of the root system via the phloem
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