Some Plants Use an Internal Thermometer to Trigger Growing Season by Dr. Mercola
Some Plants Use an Internal Thermometer to Trigger Growing Season
November 12, 2016|3,824views
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By Dr. Mercola
Although they may look like bystanders in your garden, plants are
actually active communicators and engage in a complex relationship with
their environment. They don't just soak up the sun each day.
More than just providing food, plants have played an important part
in human history. Before modern-day medicine, there were plants that
provided for medicinal needs. Ancient Egyptian scrolls detail 700 herbs and how they were used to treat patients.1
The World Health Organization (WHO) estimates that 80 percent of the world's population primarily uses traditional remedies, a major part of which is derived from plants.2
They also play a significant role in the development of the majority
of new medications, as manufacturers are using plants to model their
synthetic drugs.3
Plants have a unique interconnectedness between each other, soil,
microbes, pests and human health. Some of the newest research has now
detected how plants know exactly when to increase their growth patterns
in preparation for spring and summer.
Phytochromes Have Dual Function
This short 1.5-minute video explains the process researchers from the
University of Cambridge have discovered and how they anticipate it may
be used in the future. An international team of scientists has found
previously discovered plant molecules, phytochromes, serve two
functions.4
Initially, scientists believed that plants only used phytochromes to
detect light during the daylight hours. Phytochromes are a photoreceptor
pigment used mainly to detect the red and far-red visible light
spectrum.5 In the plant, it was mainly believed to be responsible for germination, shade avoidance and light detection.
Exposure to red light produces a chemical reaction that moves
chromprotein to a functional active form, while darkness makes it
inactive.6 The plant will grow toward the sun as the red light converts the chromprotein to an active form that triggers an increased growth in the plant cells.
Although farmers and gardeners have known for centuries that as the
weather warms, plants begin to grow faster and flower, researchers are
now discovering the mechanism behind this phenomenon.
As the sun goes down, phytochromes found in every plant cell take on
another role in the health of some plants and gauge the temperature of
the night air.7
The scientists found that the pace at which they change function is
directly proportional to the temperature of their surroundings.
In colder temperatures this switch from active to inactive is slower,
and so is the growth of the plant. In warmer weather the phytochromes
inactivate faster, triggering a growth spurt in the plant. This is the
function that is responsible for earlier flowering of spring plants
during a warmer winter.
Active Phytochromes Mean Slower Growth
Phytochromes are activated during the sunlight hours. In this state
they are bound to the plant DNA, purposefully slowing growth. At night
the phytochromes gradually become inactivated, separating from the DNA
and allowing the plant to resume growth.
The deactivation of phytochromes in the plant is called "dark
reversion." Lead research author, Philip Wigge, Ph.D., from Cambridge's
Sainsbury Laboratory at the University of Cambridge, explains their
discovery:8
"Just as mercury rises in a thermometer, the rate at which
phytochromes revert to their inactive state during the night is a direct
measure of temperature. The lower the temperature, the slower
phytochromes revert to inactivity, so the molecules spend more time in
their active, growth-suppressing state.
This is why plants are slower to grow in winter. Warm
temperatures accelerate dark reversion, so that phytochromes rapidly
reach an inactive state and detach themselves from DNA — allowing genes
to be expressed and plant growth to resume."
This same process helps plants to avoid the shade of other plants and
get more sun. Once in the shade, phytochromes are quickly inactivated,
which increases the rate of growth. This growth helps the plant to find sunlight.9 Interestingly, these light-driven changes to phytochromic activity can occur in less than a second.10
Plants Use Either Day Length or Temperature to Gauge Growth
Not all plants use this method of determining when to increase
growth. Some plants use the length of the day instead. During a warm
winter you may see daffodils flowering much earlier than expected, as
they are temperature sensitive.
A well-known garden rhyme inadvertently relies on the science
recently discovered. This rhyme was used to predict rainfall in the
coming season: "Ash before oak, we're in for a soak; oak before ash,
we're in for a splash."
The oak tree relies on temperature to determine the start of growing
season, where the ash relies on day length. Between 1751 and 1788,
Robert Marsham recorded plant activity during spring on his estate in
the U.K.11 He noted it was more common for ash trees to leaf out before oak trees.12
However, over the past years, this has not been the case. Only two
years in the recent past have ash trees come into leaf earlier than oak,
in 2010 and 2013.13 Wigge explains it this way:
"Oak trees rely much more on temperature, likely using
phytochromes as thermometers to dictate development, whereas ash trees
rely on measuring day length to determine their seasonal timing.
A warmer spring, and consequently a higher likelihood of a hot
summer, will result in oak leafing before ash. A cold spring will see
the opposite. As the British know only too well, a colder summer is
likely to be a rain-soaked one."
Farmers and Gardeners Use Plant Behavior to Predict Weather and Harvest
The impact of warming temperatures is being felt around the globe.
While this research was performed in the U.K., other researchers are
documenting similar changes in budding and leafing patterns in the U.S.
A pilot project begun in 2007 called Project Budburst allows people
living anywhere in the U.S. to make a contribution to the data being
collected.14
Measurements are made of tree buds as they emerge and are then
uploaded into a national database. Scientists around the world are
studying these records to determine how a changing climate may affect the timing of spring plant growth.
Scientists have noted that some plants are extending their growing season in response to climate change.
However, while the plants have methods to accommodate some of the
changes, insects often breed and disperse based on sunlight rather than
temperature. This may result in a mismatch between plant growth and the
activities of pollinating insects.15
Researchers have also looked at the relationship between heat and how long it takes to achieve harvest.
In one study using cucumbers,
researchers found plants cultivated earlier in the season required more
days to flower and produce fruit than those planted later.16
It appears the plants exposed to warmer temperatures grew faster and
produced fruit sooner, despite not having been planted earlier.
Montana State University Extension developed a plan of Growing Degree
Days, or those days when the average temperature was ideal for plant
growth, to help famers and gardeners better predict the best time to
harvest.17
As the number of warmer days begins to grow throughout the world,
scientists at Cambridge University hope to use their research to breed
wheat and rice plants more resistant to warmer temperatures.
Plants Talk to Each Other and Protect Themselves From Predators
Plants do more than grow. They also communicate with each other and
with predators. For instance, when an insect begins munching on a leaf,
the plant "hears" or senses the vibrations from the insect and immediately begins to mount a defense.18
Researchers have found the plant then produces a phytochemical the
insect finds inedible, which deters the bug. In this experiment the
researchers recorded the plants' responses to the vibrational sounds of a
caterpillar chewing. They found when plants were exposed to these
feeding sounds later, they released higher amounts of the phytochemicals
to repel the insect.
This research suggests that minor pest attacks on plants
may play an important role in promoting plant growth that have higher
levels of important nutrients to humans. One of the researchers remarked
on the curious ability of the plant to distinguish between vibrations
made by a gentle wind and those of a chewing insect.19
Another application to this finding is to help boost the natural
chemical defense of the plants by using vibrations to increase chemical
production. One of the researchers commented:20
"This research also opens the window of plant behavior a little
wider, showing that plants have many of the same responses to outside
influences that animals do, even though the responses look different."
Scientists have also found plants use an underground connection of mycorrhizal fungi, which form a symbiotic relationship with plants.
The fungi colonize the roots and send many extremely fine filaments out
into the soil, acting as root extensions. Researchers discovered these
filaments conducted signals between plants, acting as an early warning
system.21 This is part of the reason why tilling the soil is so harmful, as it disrupts and destroys these important filaments.
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