I can attest to one of its properties. It replicates every 24 hours doubling in amount. So could it become a food source for humans? I know my turtles loved it but could we acquire a taste for this plant?
Duckweed, which goes by two different Latin names, Wolffia, and Lemna minor. It apparently tastes like spinach and can be found in Southeast Asian cuisine where it is called Khai-nam, translating into English as water eggs.
The plant which appears as a flat oval leaf, no more than 0.6 centimetres (0.25 inches) in size, floats on water surfaces. It largely reproduces asexually, although I remember seeing it flower upon occasion in my tanks. When it flowers outdoors small insects or water movement creates pollination opportunities. But the vast majority of new duckweed comes about asexually. How fast? I used to turn my tank lights off at night only to find in the morning an entirely new crop of tiny plants floating on the surface. A 75-litre (20-gallon) tank could see the water surface covered in a week. The amount that grew was often thick enough to support the weight of my resident salamanders. frogs, and turtles.
It is its reproductive capacity that has attracted interest from scientists at the Salk Institute for Biological Studies in La Jolla, California, who have been studying the plant’s genome to determine what makes that aspect of it tick. Scientists have isolated the genes responsible for the plant’s reaction to day/night cycles a key stimulus for most plant growth. Surprisingly the plant has only half the number of regulatory light and darkness cycle genes found in most plants. The La Jolla researchers speculate that the absence of genes may be the reason the plant replicates so rapidly in an almost uncontrolled fashion.
This rapid growth in the wild has often been seen as a nuisance because duckweed can physically cover a small water surface in record time. But that fast growth has many uses for an increasingly challenged world dealing with climate change and food insecurity.
Today, other than Khai-nam on Southeast Asian plates, duckweed, where harvested, is used as a livestock feed supplement. It also is proving to be good at remediating contaminated water sources where nitrogen and phosphorous runoff from farms is polluting rivers, ponds, and lakes. Tinkering with the genome is giving biomedical companies the opportunity to use new versions of the plant to produce medicines including insulin.
Back in my youth when I was scooping up these tiny plants from my many aquariums regularly, who knew of their enormous potential.
]]>What is a chimera?
In ancient Greek mythology a chimera was a monster combining a lion’s head, goat’s body and serpent’s tail. In human genetics a chimera is an individual containing two distinctive DNAs. What the scientists at the Salk Institute believe is they have discovered in rsPSCs a mechanism by which they can create artificial chimeras by introducing human cells into another species to grow human organs.
They currently are cultivating rsPSCs which they inject into 7.5-day-old mice embryos where they integrate to form chimeric embryos. This doesn’t happen generally throughout the mouse embryo but displays a region selectivity. Hence the name.
The potential benefit of being able to grow a human organ in an animal host and then harvest it for transplant is enormous. The organ built from an individual’s own rsPSCs would when integrated into his or her body never experience rejection.
But creating chimeras will raise ethical issues which may end this line of research.
What other approach can this type of research take?
Isolating rsPSCs for implantation within a human donor host to regrow a damaged organ would be a highly desirable line of enquiry. Back in 2006 a doctor at Wake Forest School of Medicine published a study describing the successful transplant of bladders grown from host cells cultivated in the laboratory and then implanted back into the donor. Six surgical implants were performed using a biodegradable scaffold upon which the bladder cells grew. Since that study a larger clinical trial was conducted. But note that to date the work at Wake Forest has not become a commonly used protocol for dealing with diseased bladders. So I can imagine if we were to move from animal studies to human hosts using rsPSCs we are talking about decades before we would see medical research progress.
We may, however, see chimeras in the next few years with pig embryonic stem cells transplanted into human hosts to grow replacement organs. According to an article that appeared in National Geographic News back in February of this year, a recent study indicates embryonic pig tissue could become a source for organ transplants. The researchers have been putting pig stem cells into immune-deficient mice to grow liver, pancreas and lung tissue. The work is being done at the Weizmann Institute of Science, Rehovot, Israel.
The impetus behind all of this research comes from two sources. One is the high demand for human organ transplants with insufficient supply from donors. Two, is a way of overcoming rejection, the greatest challenge for current transplant protocols.
So xenotransplantation, taking tissue from one species and putting into another is no longer over the horizon but almost at our doorstep.
