Recently, Weizmann Institute of Science scientists discovered that under certain conditions, plants adjust their level of photosynthesis to changes in the intensity of sunlight through a sophisticated sensing system, reminiscent of the reaction of the pupils of our eyes
Plants apparently do not see, taste or smell, but their control mechanisms sometimes work similar to our senses. Recently, Weizmann Institute of Science scientists discovered that under certain conditions, plants adjust their level of photosynthesis to changes in the intensity of sunlight through a sophisticated sensing system, reminiscent of the reaction of the pupils of our eyes. As reported in the scientific journal iScience, this "sensory" control operates at relatively low light intensities, when the molecular machinery of photosynthesis is very efficient, but also particularly vulnerable in the event of a sudden increase in the level of radiation - similar to a person who has become accustomed to a dim place and is suddenly exposed to a strong beam of light.
Since plants need light energy to grow, the popular opinion was that the level of photosynthesis in a plant increases and goes in direct proportion to the intensity of sunlight, until it reaches a level that is too high, which produces stress and causes the plant to activate repair mechanisms and slow down photosynthesis. But when Prof. Avihai Danon and members of his group in the Department of Plant and Environmental Sciences at the Institute measured plant fluorescence at low light levels - radiation emitted by the plant during photosynthesis and which is an indication of the level of photosynthesis - they discovered a surprising pattern of photosynthesis that alternately increases and decreases.
Following the findings, Prof. Danon initiated a collaboration with the research group of Prof. Uri Alon from the department of molecular biology of the cell, which specializes in biological circuits and networks. Research student Avihai Tendler from Prof. Alon's lab and Dr. Bat-chen Wolff and Dr. Vyuknand Tiwari from Prof. Danon's lab revealed plants from the mustard family, called Arabidopsis thaliana, in light of the fact that its strength increases every 10 minutes, rank by rank, In a low to medium light range corresponding to the sun's radiation in the morning - that is, below the level that causes stress to plants. The experiment showed that the fluorescence level did not increase permanently with increasing light, but jumped for a short time and then returned to its previous level; At each beat, the peak was smaller than the previous rank. The scientists found that whenever the light got stronger, fewer photons than expected reached the photosynthetic reaction center in the plant, which is why the fluorescence peaks became progressively smaller. In fact, at each level the scientists had to double the light intensity in order to create the same fluorescence peak as in the previous pulse - a pattern typical of sensory mechanisms in bacteria, animals and humans.
These findings indicate that at low light intensities, the control mechanisms for photosynthesis resemble sensory systems, such as the human visual system. When our pupil adjusts itself to the light intensity, the adjustments not only protect the retina, but also ensure that we remain sensitive to the environment. In strong light, when the pupils are narrow, we distinguish only between large light contrasts, but in weak light, when the pupils dilate to let in a greater number of photons, we are able to recognize objects that differ slightly in the light reflected from them, and thus we can see what happens at dusk, at night or in cave. Similarly, it is known that the antennae of photosynthesis - light-harvesting complexes of proteins and chlorophyll molecules - shrink in strong light and expand in weak light. Like the pupils, when the antennae are spread out, they gather light more efficiently and become more sensitive to small changes in its intensity, especially sudden changes.
This is probably the reason why the control of the level of photosynthesis at low light intensities is conducted in an extremely careful manner. The research shows that the plant reacts immediately to sudden increases in the light level, including very small increases, as if it had prepared for the worst, that is, to a dangerous increase in light intensity. It then checks the actual light conditions and adjusts the level of photosynthesis accordingly. This way he reaches the right balance between security and efficiency.
"The plants manage photosynthesis in a careful way, which sacrifices efficiency in the short term for stability in the long term," says Prof. Danon. "The photosynthesis machines actually 'sense' the environment and adapt themselves quickly to the amount of light received before the situation gets out of control, instead of increasing the activity in an uncontrolled way until damage is caused."
The control mechanism discovered in the study responds quickly to changes in light intensity and "buys" the plant precious time until slower mechanisms are activated that adjust the level of photosynthesis to the developing conditions. This mechanism is one of the plant's coping strategies, which allows it to utilize sunlight optimally under changing conditions, for example, when clouds come and go or when the wind changes the angle of the leaves in relation to the sun.
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