Why plants stop producing amylase after 6-7 days when grown in the dark?

Question

Why plants stop producing amylase after 6-7 days when grown in the dark?

Answer 1

Plants need to stop actively using their starch and actively store food in the final stages of preparing for cold hardiness and freezing tolerance for winter dormancy. So light is a key abiotic modulator especially when paired with a drop in temperature. Starch synthesis responds to light while starch degradation responds to both dark and cold/dark. Alpha amylase and starch phosphorylase both respond strongly to cold/dark and down regulate more than beta amylase.

http://www.pubmedcentral.nih.gov/article...

Alpha amylase is also controlled by both hormones and a feed-back sugar repression in the promoter to the gene. If sugar is present it will bind and block transcription preventing alpha amylase protein production. Going in to dormancy the sugar is not being used as growth and repair is limited so less amylase will be needed. In general sugars up-regulate genes for synthesis and and reserves storage for dormancy. Then they down-regulate photosynthesis and reserve mobilization. Hormones then enhance the plant's tissues responses to sugar and abiotic regulation.

http://linkinghub.elsevier.com/retrieve/...

http://jxb.oxfordjournals.org/cgi/reprin...

Beta amylase is found in photosynthetic & storage sites but may not be required to degrade starch granules as some plants lack it.  

http://www.blackwell-synergy.com/doi/pdf...

Answer 2

Amylase is an enzyme that breaks starch to maltose. It is produced in the presence of starch. However, if the plant is kept in the dark, it does not photosynthesise and consequently it does not produce starch. Chloroplasts need light to activtes mechenisms that produce starch. Therefore, when a plant is kept in the dark, it does not produce any starch and therefore, no aylase is produced either becuase it has no substrate to act on.