Light switch in autumn leaves

Before trees lose their leaves in the winter, they offer us a bright autumnal display of reds, oranges, and yellows. This result from the decomposition of the compound that makes leaves green: chlorophyll. Among the decomposition products are yellow phyllobilins that demonstrate unusual chemical properties, these compounds act as four-step molecular “switches” that are triggered by light in different ways depending on the environment according to Science daily.

During the summer, green leaves use their chlorophyll to convert sunlight into chemical energy. Before they lose their leaves in the cold season, trees reclaim important nutrients like nitrogen and minerals. “The chlorophyll released in this process must be broken down because it has a damaging effect on the tree when it is irradiated by light while unbound,” explains Bernhard Kräutler. “Presumably, the chlorophyll decomposition products play a physiological role as well.”

The decomposition of chlorophyll leads to the formation of phyllo bilins. Most of these are colorless, but in leaves there are also yellow ones, known as phylloxanthobilins. Researchers have now demonstrated that these compounds act as unique four-stage “switches” that react to light (photoswitches). The molecular environment determines which “switching mechanism” is used.

In polar media, such as the aqueous environment inside a cell, phylloxanthobilins are found as simple molecules. When irradiated with light, they switch reversibly between two forms that have slightly different spatial structures around one double bond (Z/E-isomerization). This is similar to important plant photos witches. In nonpolar media and presumably in cellular membrane systems, the Z-isomers pair up and are held together by hydrogen bonds. Irradiation with light leads to a chemical reaction between the two paired molecules. In this cycloaddition, the paired molecules are bound together into a dimer through a ring made of four carbon atoms. Slight heating reverses this process.

“By using X-ray crystallographic analysis, we were able to determine the precise spatial arrangement (stereo structure) of a phylloxanthobilins and the hydrogen-bonded pair structure they adopt when crystallized,” reports Kräutler. “The fascinating chemistry of these substances also suggests that phyllobilins may have important, unknown physiological roles, possibly in the photoregulation of plants. Our new insights will help to elucidate this role.”

 

N.H.Kh

 

You might also like
Latest news
Autumn exhibition 2024atBanias palace of culture Palestinian resistance confronts Zionist occupation forces in several areas The farmers of Hasakah province finished harvesting the areas planted with cotton The Lebanese resistance targets the Israeli enemy forces in Maroun al-Ras and in the “Dovif” barrack... Health Ministry: About 98,000 medical services provided to Lebanese coming to Syria 4 Palestinians martyred and others detained in the West Bank Palestinian Ministry of Education: More than 11,900 students have been martyred since the beginning ... Martyrs, wounded due to the Israeli enemy raids on a number of areas and towns in Lebanon 29 martyrs due to the zionist bombing of homes and tents of displaced people in Gaza Strip Syria participates in China International Import Expo Czech Republic provides financial aid to Lebanon worth 3.5 million Korunas The annual exhibition of new and used clothes kicks off in Aleppo Syria participates in High-Level International Conference to enhance cooperation in combating terror... Abbas: International community is required to hold the occupation accountable for its crimes Syria calls on UN member states to take firm measures and stop Israeli attacks Israeli aggression targets civilian sites south of Damascus Russian Trade Representation in Syria holds a sports marathon to celebrate National Unity Day in Rus... Settlers burn Palestinian lands and homes east of Ramallah Lebanese resistance targets Meron base, settlements and gatherings of the Israeli enemy 43,374 martyrs since the beginning of the Israeli war of extermination on the Gaza Strip