Why do some plants bloom in summer (off topic)

It has been known for many years that some plants respond to day length to
control certain activities such as flowering, dormancy, and general growth, etc.
The ability is called photoperiodism, and it is not limited to plants. Many
organisms take cues from the number of hours of daylight (or number of hours
of darkness).

In more recent years a number of proteins have been identified called
photoreceptors; these molecules respond to different wavelengths of light and have
been shown to effect some of the plant responses to light (e.g., shade avoidance
and choloroplast movement within cells).

One of the more obvious photoperiodic responses of plants is flowering. How
do plants know when to flower? Many plants can grow in cool temperatures and
even flower, but it would be folly to flower too early in the season—a late
frost could destroy all of the flowers, which tend to be tender. Thus, many
plants have evolved a mechanism to delay flowering till days are longer, hence
the season is more advanced and chances of a frost are reduced. Of course,
there are many other reasons plants bloom at a certain time, one major factor is
the presence of a pollinator. There are many plants that bloom only at the
precise time their pollinating insect can be expected to be present. In fact
some insect-plant pollinator relationships are very fine tuned, and the flowers
and insects are only active for a few weeks each year. If they miss each other
it might spell doom for both species; no seeds set for the plant and no
pollen or nectar for the insects.

Anyway, a molecular mechanism that controls flowering in Arabidopsis has been
worked out in the past few years. The mechanism turns out to be fairly
simple. Photoreceptors are activated by light, and when they are active they can
prevent the degradation of a protein called CONSTANS. In turn, CONSTANS can
activate certain genes that promote flowering. As with any fine tuned system
there are opposing controls. Other photoreceptors cause the degradation of
CONSTANS.

So there is a balance between the gain of CONSTANS and the loss of CONSTANS.
Finally, it turns out that the two opposing mechanisms occur late in the day
(stabilizing CONSTANS) or early in the day (degrading CONSTANS). The effect
is that levels of CONSTANS rise and fall each day. However, the stabilizing
effect is enhanced as days become longer and more CONSTANS is able to survive.
Finally, when the hours of light reach a critical value, enough CONSTANS
accumulates to activate flowering genes.

Plants are clever indeed. From what we know about them it seems likely that
CONSTANS is only one way plants regulate flowering by day length. Probably we’
ll know more in the next few years.

LINK 1: Photoreceptor Regulation of CONSTANS (Abstract)
http://ncbi.nlm.nih.gov/entrez/query.fcgi/…
list_uids=14963328&dopt=Abstract

LINK 2: Science Update Article
http://www.nature.com/nsu/020916/020916-12.html

LINK 3: Photoreceptors in Arabidopsis
http://www.pnas.org/cgi/reprint/100/4/2140.pdf

Cordially,

Joe , zone 9, Snowdrops emerged this week (Galanthus hybrid)