Chlorophyll the last step, the conversion of protochlorophyllide to chlorophyll, is light-dependent and such plants are pale (etiolated) if grown in darkness. Non-vascular plants and green algae have an additional light-independent enzyme and grow green even in darkness. Chlorophyll itself is bound to proteins and can transfer the absorbed energy in the required direction. Protochlorophyllide occurs mostly in the free form and, under light conditions, acts as a photosensitizer, forming highly toxic free radicals. Hence, plants need an efficient mechanism of regulating the amount of chlorophyll precursor. In angiosperms, this is done at the step of aminolevulinic acid (ALA), one of
Deep chlorophyll maximum of phytoplankton that have adapted to functioning in low light conditions. To adapt to low light conditions, some phytoplankton populations have been found to have increased amounts of chlorophyll counts per cell, which contributes to the formation of the DCM. Rather than an increase of overall cell numbers, seasonal light limitation or low irradiance levels can raise the individual cellular chlorophyll content. As depth increases within the mixing zone, phytoplankton must rely on having higher pigment counts (chlorophyll) to capture photic energy. Due to the higher concentration of chlorophyll in the phtoplankton present, the DCM does not predict the depth