Why are tender leaves of certain plants brownish in color

"Brownish color in tender leaves are due to the presence of  the pigment anthocyacin. The presence of anthocyacin in tender leaves serves the function of protecting the young leaf from the damaging effects of intense sunlight."

 

       Anthocyanins, a group of pigments are responsible for the brownish color of tender new leaves. Such a pigmentation is common in most plant species of the family Myrtaceae, which are commonly found in tropical regions.

       The presence of the pigment anthocyanin helps protect the developing photosynthesis mechanism in tender leaves from the ultraviolet radiations of sunlight.

       Leaves when exposed to intense sunlight can lead to over loading of chlorophyll pigment, which in turn results in low efficiency termed as photo-inhibition. Anthocyanins helps guard the chlorophyll the pigment that helps in photosynthesis from photo-inhibition. In this manner anthocyanins can help perform more efficient photosynthesis. 

       Anthocyanins are also known to act as 'anti-oxidants'. Cellular componets of the plants such as membranes, protein etc are protected against highly reactive oxygen species by anthocyacins. Damage from oxidizing species are observed at sites subjected to insect damage. However in plants and leaves containing antocyanins, the damage susstained is found to be minimal. Therefore anthocyacins could be used to minimise damage to the tender-young leaves.

       It is also found that most herbivores do not prefer the odd-colored leaves, thereby providing additional protection. 

References


[1] http://www.hindu.com/seta/2006/02/23/stories/2006022300191600.htm
[2] http://en.wikipedia.org/wiki/Anthocyanin