BromeOli

30/11/2021

Study: Tree Leaves Have Built-In Thermostat
Whether in Canada or the Caribbean, tree leaves don't have to worry about the temperature outside — they have their own built-in climate control that always aims to keep them comfortable, a new study finds. The long-standing view of plant biologists was that the temperature of a photosynthesizing leaf would be the same as that of the surrounding air. But in a survey of 39 tree species ranging over 50 degrees of latitude across North America (between Puerto Rico and Canada), biologists at the University of Pennsylvania found that tree leaves stay at a nearly constant temperature while they're converting sunlight and carbon dioxide into food. The study, detailed in the June 12 issue of the journal Nature, finds that tree photosynthesis most likely occurs when a leaf's temperature is about 69.8 degrees Fahrenheit (21.4 degrees Celsius), with the latitude and average growing-season of the plant's environment playing little, if any, role in its temperature. Instead, the leaves likely have physiological and structural adaptations that help them stabilize their internal systems (we humans do this when we sweat or shiver in response to hot and cold temperatures to maintain our body temperature). This discovery comes as something of a surprise to biologists. "It is not surprising to think that a polar bear in northern Canada and a black bear in Florida have the same internal body temperature. They are endothermic [warm-blooded] mammals like us and they generate their own heat," said study team member Brent Helliker of Penn. "However, to think that a black spruce in Canada and a Caribbean Pine in Puerto Rico have the same average leaf temperature is quite astonishing, particularly since trees are most definitely not endothermic." Helliker and his colleagues think that increasing evaporation and leaf angle (which affects how much sunlight it reflects) help cool leaves in warm climes, while decreasing evaporation and the clustering of many leaves on each branch help keep leaves warm in colder places. The results of the study, funded by the Department of Biology at the University of Pennsylvania and the Andrew W. Mellon Foundation, have implications for how trees in northern climates will react to global warming: They might overheat due to mechanisms they have evolved to "keep warm." The results also have implications for scientists studying past climate change by measuring the ratios of different isotopes of oxygen (which have different numbers of neutrons) in tree-ring cellulose. The amount of a particular isotope present in the cellulose is influenced by the temperature of the leaves, and scientists had assumed that leaf temperature was the same as the ambient temperature. The new study has shown this isn't the case.

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30/11/2021

Plants Cry For Help
When injured, plants can cry for help via a chemical phone call to the roots.

If under attack by a pathogen, such as disease-causing bacteria, a plant's leaf can send out an S.O.S. to the roots for help, and the roots will then secrete an acid that brings beneficial bacteria to the rescue, scientists announced today. The finding builds on research earlier this year showing that parasitic plants can tap into a host plant's communication system.

"Plants are a lot smarter than we give them credit for," said Harsh Bais, assistant professor of plant and soil sciences at the University of Delaware. "People think that plants, rooted in the ground, are just sitting ducks when it comes to attack by harmful fungi or bacteria, but we've found that plants have ways of seeking external help," he notes.
To figure this out, Bais and colleagues infected the leaves of the small flowering plant Arabidopsis thaliana with a pathogenic bacterium, Pseudomonas syringae. The plants started to look sickly.
However, the infected plants whose roots had been inoculated with the beneficial microbe Bacillus subtilis were perfectly healthy.

Farmers often add B. subtilis to the soil to boost plant immunity. It forms a protective biofilm around plant roots and also has antimicrobial properties, Bais said.

Using molecular biological tools, the scientists detected the transmission of a long-distance signal, a “call for help,” from the leaves to the roots in the plants that had Bacillus in the soil. The roots responded by secreting a carbon-rich chemical — malic acid.

All plants biosynthesize malic acid, Bais explains, but only under specific conditions and for a specific purpose. In the lab tests, the chemical was actively secreted to attract Bacillus. Magnified images of the roots and leaves showed the ratcheted-up defense response provided by the beneficial microorganisms.

The scientists are now trying to figure out exactly what the signal is that's sent down to the roots.

The research, funded by the National Science Foundation and the university, will be detailed in the November issue of the journal Plant Physiology.

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30/11/2021

How Plants Become Annuals vs. Perennials
Scientists with the Flanders Institute for Biotechnology in Gent, Belgium, have determined what makes plants either "annual," meaning they live one growing season and die, or "perennial," meaning they regrow every spring.

The difference, according to work done by scientist Siegbert Melzer, comes down to two critical flower-inducing genes that, when turned off, can turn an annual into a perennial.

The rapid growth of flowers, and then seeds, is the strategy most annuals use to propagate from one generation to the next and one growing season to the next. Annuals experience "rapid growth following germination and rapid transition to flower and seed formation, thus preventing the loss of energy needed to create permanent structures," said a statement about the research from the institute. "They germinate quickly after the winter so that they come out before other plants, thus eliminating the need to compete for food and light. The trick is basically to make as many seeds as possible in as short a time as possible."
Perennials instead build "structures" such as overwintering buds, bulbs or tubers, that contain cells that are not yet specialized and, when the next growing season begins, can be converted into stalks and leaves.
An annual uses up all of its non-specialized cells making flowers, and thus, after dropping seeds, it dies. The growth of the flowers is triggered by the plant sensing the length of day and amount of sunlight. When the light is just right, "blooming-induction genes" are triggered.

By deactivating two of the genes that induce flower growth in the thale cress, a flowering plant whose genome has been entirely sequenced, the researchers created mutant plants that "can no longer induce flowering, but . . . can continue to grow vegetatively or come into flower much later." Because the plants don't use up the store of non-specialized cells making flowers, they become perennials, able to continue to grow for a long time.

And, like true perennials, the altered annuals show secondary growth with wood formation.

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30/11/2021

30/11/2021