RE: HYB - Embryo Rescue
Walter is right in that attention to detail and technique is critical.
The most significant difference between plant tissue culture and embryo
culture is the use of hormones. Generally, you do not need them with embryo
culture, as the embryo is programmed to grow without them. I didn't really want to
get into the details here, but a little clarification is in order. In tissue
culture, the concentration and proportion of hormones is critical for the
stages of development. It is usually species specific. There are many
references on this subject.
As for which media to use, it is not nearly so important as controlling
contamination. There are many different formulas for the media. By far, the most
common is Murashige and Skoog, commonly referred to as MS. There are
variations in this formula also. I have found that 1/2 strength MS media without
micronutrients works quite well for embryo culture. By the way, MS media (which
was first reported in the literature in 1962) differs significantly from the
formula that Randolph used in his early work (reported in 1945) with embryo
It is important to make a distinction between embryo culture and embryo
rescue. It is based on where the embryo comes from. Embryo CULTURE is the growth
of the embryo from the complete healthy seed. This is what Randolph did. The
reasons he cited were avoiding stratification and reliable germination.
Embryo RESCUE is the growth of the embryo from a seed lacking endosperm. Embryo
culture is much easier than embryo rescue.
Technically, the most difficult part of embryo culture is excising the
embryo. With embryo rescue, it may be finding a healthy embryo. However, my
experience is that few embryo rescue attempts are successful. Remember that embryo
rescue is fighting against nature. By failure of the endosperm to develop
correctly, it has already been determined that this embryo should not be allowed
to live. The results that you get might be spectacular, the it is more
likely that the embryo will not develop properly or that the resultant plant will
have some terrible flaw. I have a few plants in my garden and many more that
died in the test tube to back up this statement. Perhaps, judicious use of
plant hormones could help produce a viable plant from some of these ill-fated
embryos, but that's an endeavor that will require much time and effort.
If anyone is interested, I published an anecdotal report of one of the
failures in the Review of the Society for Japanese Irises a few years ago.
Cedar Hill, MO
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