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shedding their leaves – or , as they call it , abscission – was abscisic acid . Despite its name , it turns out this substance is not that chief in abscission . Two different plant hormones , ethylene and auxins , play a much more significant role .
Auxins- a group of plant hormones that play a big part in trees ’ autumnal extravaganza
Abscisic acid – despite its name – plays only a small role in abscission or the loss of leaves
Ethylene , the simplest alkene , is a gas that quickens fruit ripening , but reduces leaf growth and encourages abscission . Ethylene is produced from the amino acid methionine via a long chain of biochemical reactions . As darkness excites the biosynthesis of this gas , plants increase their ethylene production in autumn and winter , initiating their leaves to shred . Auxins are a family of indole derivatives that control cell growth . A healthy , green leaf harvests ample number of auxins and so keeps growing . It also carries auxins to the rest of the plant through its petiole – the stalk that links the leaf to the tree . However , when autumn comes and chlorophyll levels decrease , so do auxins . The tree no longer gets chemical signals from the leaves that they are green and healthy , and so the abscission commences .