Ask A Scientist© Biology Archive

Question:
 What causes a Morning Glory flower to open in the AM ?  Also, what makes 
the Morning Glory flower turn purple only on cool days? On hot and bright 
days mine stay a bright blue.
 My name is Ginnie Gale. I'm in 6th grade at Glen Crest Middle
School. Thanks for your help.

Answer:
Robert,
Thanks for your questions.  As far as the Morning Glory flower goes,
its 'purpose' in life is plant reproduction.  With that 'goal', you can
see how the flower would need to be open in the daytime when most of
the likely insect pollinators would be visiting the flowers.  You can
see how the plant has evolved with this feature being important.
Another way to look at it is in view of natural selection, where those
plants whose flowers happen to be open in the daytime get pollinated
and are therefore 'successful' in survival.  Those plants whose genes
perhaps directed 'late-night' flower opening were rarely if at all
pollinated and did not therefore survive to the present day.
As far as the actual opening process, it is most likely directed by
sunlight and rising temperature directing an increase of water supply
to the flower...causing it to unfurl.  At nighttime the reverse happens
and the flower closes. Some species remain open all night...these might
actually attract night pollinators or perhaps have not yet evolved
specialized mechanisms to open/close in day/night.  As far as the color
change goes, again, I suspect there is some 'motive' to the plant's
coloration. Perhaps the insects early in the day are attracted to a
particular hue, and the plant has evolved to make this color pre-
dominate in the morning. Later afternoon insects might notice a differ-
ant hue and the plant has also 'learned' this by natural selection. The
mechanism again would be chemical in nature.  Frequently chemicals of
coloration are faded or altered by exposure to sunlight as they break
down. You can see this yourself in old color photographs.
Therefore I suspect that the chemicals produced by the plant in the
morning for coloration age along with the flower and by nighttime,
assuming the job of pollination is done, those components of the
flower which can be reabsorbed by the plant are taken back by the
plant and the extraneous part of the flower is shed.  Naturally the
plant will continue to hold the fertilized (pollinated) ovary to
produce seeds.
One final interesting note....some of the plants produced by man in
laboratories for special characteristics are sterile, that is, they
go through the whole pollination process but they are not fertile
and pollination will not produce viable seeds.
I hope this information answers your questions. Thanks for using
NEWTON.
 
Ric  (rickru)