monocot seedlings without chlorophyll

monocot seedlings without chlorophyll
Steve Marak via pbs (Tue, 16 Feb 2021 11:40:34 PST)

I've seen very few achlorophyllous seedlings except in a batch of
Hemerocallis seeds sent me by a friend, of which at least 20% of the
seedlings had no or almost no chlorophyll. I say it that way because
some died very quickly, presumably as soon as the energy from the
endosperm was exhausted, while others continued to grow, weakly, for as
much as a month. I assume that even though they all looked the same to
me those longer lasting ones did have some small amount of functional
chlorophyll and chloroplasts.

In theory one could grow on achlorophyllous seedlings indefinitely by
supplying energy via sugars, but the only paper I could find (my
Google-fu seems weak this morning) was from Knudson in 1919 on corn, and
he found that even in vitro with sucrose those seedlings didn't thrive.

Our experience with orchids matches yours (my wife does all our
flasking). Hybrid Cattleyas germinate like grass seed, even after years
of storage, I presume as a result of selection pressure for that. The
tuberous terrestrial species I like are more difficult, but even there,
when we do get germination I don't recall ever seeing an achlorophyllous
seedling. That seems odd to me now.

Steve

On 2/16/2021 1:04 PM, Robert Lauf via pbs wrote:

Back when I was flasking my orchid seeds, as I recall, as soon as they germinated, they turned green and you would see all these tiny green flyspecks. At the protocorm stage, they were several mm in diameter (these were mainly cattleyas). Any that didn't have chloroplasts would have been white but should continue to grow in the medium, relying on the sugar in the mix. I don't recall seeing much if any of that behavior, and certainly in the replate medium, where they would develop into plantlets, I didn't see white plants, and that medium also contained sugar. At the same time, there were plenty of seeds that never developed at all. But with a hundred thousand seeds or so, there was no shortage, unless the entire pod was a dud.

It is interesting that orchids chose to make tiny seeds with no endosperm so they could be wind-dispersed, whereas the bromeliads that they share the trees with chose to make normal seeds and rely on parachutes to keep them airborne. Reminds me of two student teams independently engineering their solutions to the same problem.

Bob

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