Question

How are ethylene levels regulated and perceived?

What is the triple response?

What is controlled by ethylene levels and signaling?

Answer 1

a) Ethylene levels are regulated as their rate of production depends on type of tissue undergoing senescence or ripening . It's biosynthesis is increased with stress conditions such as drought, flood, chills etc.
Auxin also regulates it's synthesis by promoting it
Componenets of primary signal transduction pathway that includes ethylene receptors,pathway intermediates and familiess of transcription factor regulates ethylene levels. The EIN3 (ethylene insensitive gene 3) is an important transcription factor regulating plant response. This gene regulates the  expression by different DNA-binding sequences in the gene promoters.Researches shows that chromatin state 4 is mainly responsible for regulation of ethylene levels in plants.
Ethylene perception occurs at the membrane of Endoplasmic reticulum inside the cell ,and transcriptional cascade processes are intiated by signal transduction method that give rise to diverse responses, often in conjunction or simultaneously with other signals.
b) Triple response - Ethylene is produced in all higer plants and is assoiated with fruit ripening and triple response , The triple response as seen in dark grwon seedlings mainly includes i.) Reduced stem elongation ii) Increased stem thickening iii) horizontal growth habit .
c) Ethylene levels and signalling controls :
i) Abscission: Shedding of leaves ,fruits, flowers.
ii) Epinasty - The downward curvature of leaves occuring when upper side grows faster than the lower side and this epinasty is induced by ethylene.
iii)Fruit ripening: Ripening includes color development, softening, starch hydrolysis , sugar accumulation and aroma production and these are all induced by increase in ethylene levels. Fruits that ripen in response to ethylene exhibit respiratory rise before ripening phase called a climacteric. eg- Apple, banana.