A Plant Sexual Thermostat? – New Information About Temperature Controlled Flowering

5435347642_1ec64f6696_nHothouse Flowers

Unlike animals, plants are not born with their “naughty bits”.

That is, the sexual organs of plants, a.k.a., flowers, are typically formed after a period of so-called vegetative growth. In other words, plants first go through a vegetative stage of development (think shoots and leaves, over and over again) and then make a transition into their flowering stage of life.

What actually controls this vegetative-to-floral transition and how it works at the cellular and genetic levels have been some of the most important and highly-investigated subjects in plant physiology. (You can read about it in my e-book “How Plants Make Flowers”.)

The two most important environmental factors that can trigger floral initiation in most angiosperms are the photoperiod (relative length of the night) and the temperature.

I don’t want to get into complex subject of photoperiod and flowering now. (You can read about it elsewhere, such as here and here.) Let’s stick to temperature.

Generally speaking, low temperatures tend to suppress flowering and warm temperatures tend to promote flowering. In a previous post, we’ve seen how warmer temperatures (due to global warming, for instance) may promote premature flowering by the early production of the plant flower-promoting substance called florigen.

Timing Is Everything

The precise timing of flowering in many plant species is a critical event because too early or too late flowering may seriously jeopardize the reproductive success of the plant. For example, if insect pollinated flowers appear before the pollinators do or if a plant flowers too late in the season, both of these events may significantly reduce the seed production.

So, in addition to using the relative length of the night, plants also use the relative temperature as a clue for floral timing.

We’ve seen previously that warm temperatures tend to promote flowering through the production of the flower-inducing substance florigen.

A report published by a team of researchers from Germany and the Netherlands in the November 21 2013 issue of Nature magazine has shown that the flowering thermostat is perhaps more complicated than this.

Briefly, what they have shown is that warm temperatures may also “take the foot off the brakes” for flowering.

Lurching Toward Flowering

What makes flowering mechanisms so complicated in plants is that the floral transition is controlled not only by flower-promoting substances such as florigen but also by substances that actually inhibit or block the expression of flowering genes.

Most of these blocking substances are DNA-binding proteins called transcription factors (TFs), which may specifically attach to flower-promoting genes and prevent their expression.

Think of it this way: If flowering is like driving a car, then the flower-promoting substances are the gas, and the flower inhibiting substances are the brakes. So, even if you give the car a little gas, if you stomp on the brakes, the car won’t go.

This new report has shown us at least two things. First, at lower temperatures, strong flower-repressing TFs are produced, which may effectively block the floral transition. (That is, the brakes on flowering may be strongly applied under cool temperatures.) Secondly, at warmer temperatures, much “weaker” flower-repressing TFs are produced, which may then allow the floral transition. (That is, when it’s warmer, the plant takes the foot off the flowering “brakes”.)

Bottom line: Warm temperatures may promote flowering in a plant by not only “giving it the gas” but also by “releasing the brakes”.

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