Why do plants lack sodium pumps - and would they benefit from having one?

A major difference between plants and animals is that most plants do not tolerate salt whereas animals like salt. This difference has profound negative consequences for agriculture. In arid climates where farming depends on irrigation, salt accumulates with time in the soil and the soil ends up becoming infertile. Plants and animals are capable of actively pumping out H⁺ and Na⁺, respectively, in order to create the driving force for uptake of nutrients and excretion of wastes by secondary active transport. Thus, cell membrane H⁺- and Na⁺-pumps, respectively, play a central role in plant and animal cells. However, since Na⁺-pumps are lacking in plants, and cell membrane H⁺-pumps in animals, a major evolutionary question is whether they are mutually exclusive. We will evaluate whether a H⁺-pump and a Na⁺-pump can co-exist and co-function in the same cell; attempt to introduce a Na⁺-pump into a vascular plant; and estimate the effect on the salt tolerance upon successful expression.