Subject: Re: Black plants

From: [email-masked] (Peter Jordan)
Date: 30 Apr 1995 17:47:58 GMT

[email-masked] (Tony Travis) writes:

>I agree, Marco, and that was my point:  black leaves would absorb all
>the incident light - evolution has produced photosystem I/II and
>auxilliary pigments to utilise more of the available wavelengths.  The
>ultimate effect of utilising _all_ the incident light would be that the
>leaves would then appear to be black.  Just an interesting thought ...

>One last thought - black leaves would compromise the plant's
>phototropic and photoperiodic responses, so perhaps they're not such a
>good idea after all!!

>Maybe an ideal plant should be black with white stripes:  drat! that
>opens the door to a 'zebra' plant thread >:-)

I don't know about zebra plants (4 oclocks ?)
	but ..
	wouldn't black leaves make for a very high rate of transpiration.

If water is a limiting factor, maybe having only the most efficient pigments
(reds and blues) helps avoid needing too much water ?

Peter Jordan

---

From: [email-masked] (Tony Travis)
Date: 30 Apr 1995 10:15:05 +0100

Marco_Bleeker ([email-masked]) wrote:
: >An interesting thought occured to me about black plants:

: >Objects appear black when all the light incident upon them is absorbed
: >so an entirely black plant should, in principle, be the most efficient
: >for photosynthesis and would _prevent_ light reaching plants in lower
: >strata of a canopy that are competing with it!!

:   First: we were talking about flowers here, not about leaves and 
: photosynthesis.

Well, the issue of black flowers made me think about black leaves
because I wondered what would make a flower appear black (petals are
modified leaves, but I agree they are not the photosynthetic organs).

:   Second: a leaf looks green, because the chlorophyl filtered out a lot 
: of the red.  Red is the most active wave-length for photosynthesis (to a 
: lesser extent also blue).  So, an efficient leaf, that filters out all the 
: light it could use, might still look green: deflecting the wavelenghts it does 
: not need.

I didn't say a black leaf would be the most efficient PAR filter!

:   On the other hand, there are pigments that are able to 'activate' 
: wavelenghts of light for photosynthesis. Without these pigments, certain 
: wavelenghts would not be used. We find these pigments mostly in seaweeds 
: (brown and red algae), perhaps an adaptation to a changed light spectrum at 
: greater depths.  So in this sence you have a point: a very efficient leaf 
: should be black...  (You stated the opposit - a black leaf is not necessarily 
: very efficient).

	Tony.
--
Dr. A.J.Travis,                       |  JANET: <[email-masked]>
Rowett Research Institute,            |  other: <[email-masked]>
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