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Observations contradict the textbooks
The researchers examined thale cress plants (Arabidopsis thaliana) which were transformed with the newly developed potassium reporter protein GEPII. This reporter protein enables the microscopic detection of the concentration and distribution of potassium ions in cells and tissues. Even when there was no potassium deficiency, the research team made a very surprising discovery: the concentration of this nutrient in the cytoplasm of the cells increased with each cell layer within the root, from the outside to the inside.
“These observations were really surprising,” says Prof. Jörg Kudla from the Institute of Plant Biology and Biotechnology at the University of Münster (Germany). “They contradict the textbooks, which say that the nutrients are passed on evenly, from the outside to the inside, towards the root’s vascular tissue—not only from cell to cell but also through the intercellular spaces.”
“Potassium-sensitive niche” reacts to potassium deficiency
The team of researchers subsequently examined how roots react to potassium deficiency. In doing so, they demonstrated for the first time that if plants are subjected to potassium deficiency, the concentration of potassium is reduced only within certain cells in the root tip. These “postmeristematic cells” directly above the viable stem cells in the root tip react extremely rapidly to potassium deficiency; the concentration of potassium inside the cell (in the cytoplasm) decreases within seconds. It had not previously been known that a certain group of cells located centrally inside the root tip reacts to a potassium deficiency in its surroundings. The researchers named this group of cells “potassium-sensitive niche”.
“These observations, too, were very surprising,” says Kudla. “If plants are deprived of potassium, only the cells in the potassium-sensitive niche show a reaction; the concentration of potassium in the other root cells remains unchanged. Previously it was assumed that naturally the cells in the outermost cell layer, the epidermis, would react first to a reduction in the concentration of potassium in the soil.”
Visualizing the path of potassium
Simultaneously with the decrease in the potassium concentration in the potassium-sensitive niche, calcium signals occur in these cells and spread out in the root. As a messenger substance, calcium controls many processes in living organisms—just as it does here: the calcium signals start off a complex molecular signaling cascade. This chain of signals, which the researchers were the first to define in detail, ultimately causes not only an increased formation of potassium transport proteins, but also brings about changes in tissue differentiation in the root. This facilitates a more efficient absorption of potassium ions and maintains its distribution in the plant. “For the first time,” says Kudla, “using imaging methods, we have visualized the path of potassium in a living organism.”
The results provide fundamental insights into where plants detect the availability of the essential nutrient potassium and how they adapt to it. Understanding these processes could in future help to breed better plants for agricultural purposes and deploy fertilizers in a more tailor-made way.
To visualize the distribution of potassium in the plant’s roots, the researchers used special microscopic methods (for example, Förster resonance energy transfer, FRET), in combination with sensor proteins for potassium, calcium and hydrogen peroxide. In order to examine the molecular mechanisms, the researchers produced and compared transgenic Arabidopsis plants which, due to different genetic mutations, showed symptoms of potassium deficiency. They used a variety of genetic, molecular-biological and biochemical methods to identify and characterize the proteins and mechanisms involved in the transmission of the potassium and calcium signals.
Feng-Liu Wang et al, A potassium-sensing niche in Arabidopsis roots orchestrates signaling and adaptation responses to maintain nutrient homeostasis, Developmental Cell (2021). DOI: 10.1016/j.devcel.2021.02.027
Researchers show where and how plants detect the nutrient potassium (2021, March 23)
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Hexbyte Glen Cove
Plants have the same variation in body clocks as that found in humans, according to new research that explores the genes governing circadian rhythms in plants.
The research shows a single letter change in their DNA code can potentially decide whether a plant is a lark or a night owl. The findings may help farmers and crop breeders to select plants with clocks that are best suited to their location, helping to boost yield and even the ability to withstand climate change.
The circadian clock is the molecular metronome which guides organisms through day and night—cockadoodledooing the arrival of morning and drawing the curtains closed at night. In plants, it regulates a wide range of processes, from priming photosynthesis at dawn through to regulating flowering time.
These rhythmic patterns can vary depending on geography, latitude, climate and seasons—with plant clocks having to adapt to cope best with the local conditions.
Researchers at the Earlham Institute and John Innes Centre in Norwich wanted to better understand how much circadian variation exists naturally, with the ultimate goal of breeding crops that are more resilient to local changes in the environment—a pressing threat with climate change.
To investigate the genetic basis of these local differences, the team examined varying circadian rhythms in Swedish Arabidopsis plants to identify and validate genes linked to the changing tick of the clock.
Dr. Hannah Rees, a postdoctoral researcher at the Earlham Institute and author of the paper, said: “A plant’s overall health is heavily influenced by how closely its circadian clock is synchronised to the length of each day and the passing of seasons. An accurate body clock can give it an edge over competitors, predators and pathogens.
“We were interested to see how plant circadian clocks would be affected in Sweden; a country that experiences extreme variations in daylight hours and climate. Understanding the genetics behind body clock variation and adaptation could help us breed more climate-resilient crops in other regions.”
The team studied the genes in 191 different varieties of Arabidopsis obtained from across the whole of Sweden. They were looking for tiny differences in genes between these plants which might explain the differences in circadian function.
Their analysis revealed that a single DNA base-pair change in a specific gene—COR28—was more likely to be found in plants that flowered late and had a longer period length. COR28 is a known coordinator of flowering time, freezing tolerance and the circadian clock; all of which may influence local adaptation in Sweden.
“It’s amazing that just one base-pair change within the sequence of a single gene can influence how quickly the clock ticks,” explained Dr. Rees.
The scientists also used a pioneering delayed fluorescence imaging method to screen plants with differently-tuned circadian clocks. They showed there was over 10 hours difference between the clocks of the earliest risers and latest phased plants—akin to the plants working opposite shift patterns. Both geography and the genetic ancestry of the plant appeared to have an influence.
“Arabidopsis thaliana is a model plant system,” said Dr. Rees. “It was the first plant to have its genome sequenced and it’s been extensively studied in circadian biology, but this is the first time anyone has performed this type of association study to find the genes responsible for different clock types.
“Our findings highlight some interesting genes that might present targets for crop breeders, and provide a platform for future research. Our delayed fluorescence imaging system can be used on any green photosynthetic material, making it applicable to a wide range of plants. The next step will be to apply these findings to key agricultural crops, including brassicas and wheat.”
The results of the study have been published in the journal Plant, Cell and Environment.
Hannah Rees et al, Naturally occurring circadian rhythm variation associated with clock gene loci in Swedish Arabidopsis accessions, Plant, Cell & Environment (2020). DOI: 10.1111/pce.13941
Plants can be larks or night owls just like us (2020, December 19)
retrieved 19 December 2020
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