Flowers, Jorge, Plants

Why do Plants Flower in Winter?

cherry-tree-flower-in-winter

Plants are intelligent inasmuch as they only flower when the light, age and energy conditions are appropriate to allow the plant to reproduce successfully. To do this, they have developed at least 20 different senses to monitor the complex conditions in their environment and are able to take into account factors like humidity, gravity and even electromagnetic fields. Plants differ greatly in their evolutionary strategy, and possess a diffused brain of sorts as to process information. This is why unlike, say mammals, plants are able to survive a significant loss of body mass.

Most plants flower in the spring or summer when the heat-sensitive bees are ready to facilitate conjugation with trees nearby. Spring is usually preferred because it gives the resultant fruit more months to soak in the heat and sunlight to produce fructose, which feed the sugar-crazed mammals and birds that the plant needs to spread its off-spring far from the mothership. Winter doesn’t work so well as the worker bees are otherwise occupied maintaining the temperature of the queen bee.

bluebells-flower-in-winter

Some, however, such as snowdrops and bluebells, have carved out a niche that allows them to gain a step up over their competitors. By flowering in winter, they are able to survive quite happily in real-estate that most plants can’t – that is, under the heavy bows of large deciduous trees, deep inside the ancient woods. In places where even grass can’t grow, these plants thrive as they utilise their bulbs as an energy storage device that they fill up in the early spring when the sun is weak and the trees leafless. By the time the big trees are fully-leaved, the plants have done their work for the year and their dark leaves are already dying off by the end of spring. The sugars produced by photosynthesis are converted to starch and withdrawn deep into the earth-bound bulb for protection. And by choosing this tactic – the protection of the mighty deciduous trees – they’ve avoided competing with the most ruthless of summer plants like grass.

But what of the winter-flowering trees like the Mahonia and Cherry tree? Most likely, the winter-flowering trees found just a few insects to spread the pollen. And because there were no other flowers around at the time, the winter-flowering trees had hit on a limited but good-enough niche.

mahonia-flower-in-winter

And what are the winter-pollinating insects and why do they seek out flowering-plants in winter? Recent research has shown that one of the UK’s most common bumblebees (Bombus terrestris) is achieving comparable foraging success in winter on plants such as Mahonia to that achieved in summer months. There are also a few moths that, just like many plants, have evolved antifreeze in their blood to prevent the formation of ice-crystals when the temperature falls below zero.

So, therefore just like the winter-flowering plants, insects have crafted themselves their own niches to ensure the survival of their species.

bombus-terrestris

The Science

Many plants flower in time for a particular season by responding to the length of day, a process known as photoperiodism. While scientists do not fully understand how plants do this, it is accepted that when a plant flowers is related to its genes and external environment.

In plants, scientists have identified the CONSTANS and DNF (DAY NEUTRAL FLOWERING) genes as the key mechanisms that regulate a plant’s flowering time in response to day length. In the Arabidopsis plant, scientists recently identified a faulty DNF gene that led to abnormal flowering times in mutant plants. The DNF acted to repress the activation of the CONSTANS gene until light levels rise above a certain threshold in daytime. Hence, once a functional DNF was introduced into the plant, the abnormal flowering was corrected.

In a separate study, scientists identified the sugar molecule trehalose-6-phosphate (T6P) in the Arabidopsis thaliana as playing an essential role in controlling flowering time in relation to energy reserves. As such, once a certain day length was perceived by the plant’s leaves, a mix of photoreceptors and other proteins would lead to the expression of the FLOWERING LOCUS T (FT) gene that would migrate proteins to the tip of the shoot, triggering the expression of flowers. However, as a failsafe, once the plant reaches a certain age, it would begin to flower anyway regardless of day length. As flowering is an extremely intensive process for the plant, energy too must also be available in the form of sugar. Here, the T6P sugar molecule would act as a signal for energy levels, regulating the production of FT protein. Thus, the T6P acts to influence both of the two most important pathways to flowering – the expression of the flowering gene and the production of the flowering protein.

Ultimately, greater understanding of the complex pathways that control flowering times will allow farmers to reduce uncertainty and thus boost their agricultural output.

Jorge at PrimroseJorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!

His ideal afternoon would involve a long walk, before settling down for scones.

Jorge is a journeyman gardener with experience in growing crops.

See all of Jorge’s posts.

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