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Hello everyone, SCIEN-SPOT is a podcast that shines a spotlight on the latest scientific technology from Japan.
Your host is REN from SCIEN-TALK.
花の生存戦略
In this episode, I want to talk about the flower bloomings.
Have you ever taken a moment to truly observe the flowers blooming by the roadside?
You might have noticed that on a sunny day, they seem to happily face upward towards the sun,
but when it rains, they gently bow their heads downward.
This isn't just a coincidence or a sign of weakness.
In fact, just like how we humans use umbrellas or seek shelters from the rain,
plants are intelligently changing their posture in response to the weather.
For plants, having their pollen transported by insects is incredibly vital for producing offsprings,
so they need to make their flowers stand out and appeal to insects.
However, flowers are also very delicate and vulnerable to rain and wind,
especially rain which can wash away or damage crucial pollen.
During bad weather, when insects aren't very active, plants also need to protect their valuable pollen.
How do plants manage to balance these contradictory needs?
The desire to attract and the need to protect.
ハクサンハタザオの生存戦略
Until now, the significance and the mechanism behind how plants change their flowers' direction
according to the weather were not fully understood.
But recently, a research group led by Professor Yo Kudo from Kyoto University,
they focused on a plant called Haksan Hatasawo,
from the Brassica family and revealed the secrets of its amazing survival strategy.
The plant they studied is a native Japanese plant that produces many small white flowers.
Through meticulous observation in the wild, they clearly confirmed the phenomenon.
On sunny days, the flowers uniformly face the sun's direction, while on rainy days, they face downwards.
To unravel the mystery of this phenomenon,
their research employed various scientific methods, including field surveys,
manipulation experiments, and gene expression analysis.
First, they conducted field surveys in the natural population in Takacho, Hyogo Prefecture,
to investigate which environmental factors influence the direction of the flowers.
Then, using a special experimental device called the Glow Chamber,
which can precisely control environmental factors like light, temperature, and humidity,
they narrowed down the environmental factors affecting flower's direction.
花の光への適応
The results showed that during daytime hours, when the temperature is relatively high,
the flowers turn toward blue lights.
This condition perfectly coincides with the environment where pollinating insects are actively moving.
It's as if the flower itself is moving to the best possible meeting spot.
So what exactly is happening inside the flowers?
On sunny days, flowers face upward because the stem just below the flower,
known as a flower stalk or a pedicel, elongates toward the blue light.
This phenomenon is called phototropism, where a plant bends toward the direction of light,
imagining the flower saying cheese and showing its best smile to the sun and insects maximizing its pollen appeal.
The study confirmed that this upward posture promotes pollen carry-out by pollinators,
leading to an improved fruit set, meaning more seeds are produced.
On the other hand, on rainy days, flowers face downwards because,
under low temperature and weak blue light conditions, the flower stalk elongates towards gravity.
This is related to a phenomenon called gravitotropism,
where a plant responds and bends in the direction of gravity.
It's like quickly closing an umbrella to protect something precious from the rain.
植物の花の方向制御
The research also found that when raindrops hit pollen, the pollen rapidly dies.
By facing downwards, the plant reduces damage to pollen from raindrops and increases pollen survival rates.
Furthermore, the cellular mechanism behind the change in flower direction was also elucidated.
The study compared gene expression levels in the upper and lower halves of the flower stalk
and found that a plant hormone called auxin plays a crucial role.
Auxin is a hormone that controls cell elongation in plants.
When flowers faced upwards, auxin-related gene expression was higher on the flower side of the flower stalk.
When they faced downwards, auxin-related gene expression was higher on the upper side of the flower stalk.
This suggests that by unevenly elongating a cell only on one part of the flower stalk,
much like bending a horse by applying more water pressure to one side,
the entire flower changes its direction.
With this mechanism clarified,
the research group conducted manipulation experiments where they artificially changed the direction of the flowers by exposing them to blue light.
The results were remarkable.
Under rain, downward-facing flowers had less pollen loss and higher survival rates than upward-facing ones.
植物の花の向きの変化
And in sunny weather, upward-facing flowers showed increased pollen carried out under more seas than downward-facing ones.
These experimental results strongly support that the movement of this plant changing its flower direction according to the weather
is not accidental but an active response of the plant and a clever trait for adapting to its environment.
From this research, it has become clear that the weather-dependent flower movement of this plant is not simply the flower following the sun or avoiding rain.
Instead, it is a highly sophisticated active tropic response that cleverly achieves the dual purpose of attracting insects and protecting pollen simultaneously.
This shows us that even within the small, often overlooked activities of wild plants,
there are surprisingly ingenious strategies hidden for organisms to adapt to their environment and ensure their offspring survive.
