Melatonin is secreted by the ________.

                          COLUMN I

                              COLUMN II

A) Physical sensing

i) usually results from the detection of by-products that accumulate in cells due to the uncoupling of enzymatic or electron transfer reactions, such as the accumulation of ROS during stress caused by too much light.

B) Biophysical sensing

ii) often involves the presence of specialized proteins that have evolved to sense a particular stress; for example, calcium channels that can sense changes in temperature and alter Ca2+ homeostasis.

C) Metabolic sensing

iii) refers to modifications of DNA or RNA structure that do not alter genetic sequences, such as the changes in chromatin that occur during temperature stress.

D) Biochemical sensing

iv) refers to the mechanical effects of stress on the plant or cell structure, for example, the contraction of the plasma membrane from the cell wall during drought stress.

E) Epigenetic sensing

v) might involve changes in protein structure or enzymatic activity, such as the inhibition of different enzymes during heat stress.