Plant Love in Action

In plants, food for the developing embryo is stored in a part of the seed called the "endosperm." In flowering plants, there is a complicated double-fertilization mechanism that goes on between embryo and endosperm so that the two develop together into mature seeds: after pollen first lands on a flower's stigma, it forms a pollen tube and sends out two sperm—one to fertilize the egg cell, from which the embryo hatches, and another to fertilize the central cell, where the endosperm grows.

To better understand how this process unfolds and how the two parts of the seeds communicate with each other, German researchers at the Max Planck Institute for Plant Breeding Research and the University of Cologne have isolated a mutant plant whose pollen sends out only a single sperm instead of the usual two.

The above image shows a pollination tube generated by a normal and mutant version of Arabidopsis thaliana. In the normal case, two sperm cells are transferred to the female for fertilization. In the mutant, only one sperm cell was transferred and only the egg cell was fertilized.

But here, the scientists made a surprising discovery: although the central cell was unfertilized in the mutant, it still developed endosperm. The researchers deduced that shortly after the egg cell was fertilized, a positive signal was sent out to its environment, which appears to be necessary for normal growth of an endosperm. In the next few months, the researchers to find out how exactly the signal functions and what chemical reactions are behind it.

--Ker Than

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Credit: : Art Schnittger/Max Planck Institute for Plant Breeding Research