The Influence of Light on Chloroplast Development and Movement

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The Influence of Light on Chloroplast Development and Movement

Light is an important regulator of both chloroplast development and

chloroplast movement in plants. In terms of chloroplast development,

light regulates the biogenesis of the photosynthetic apparatus in

chloroplasts and the adaptation of that apparatus to the environment

so as to maximise photosynthesis. In terms of chloroplast movement,

weak light induces chloroplasts to undergo accumulation movement,

while strong light induces avoidance movement. In this way,

chloroplasts are able to move within cells to positions where they can

obtain higher efficiency of photosynthesis while avoiding

photo-damage. In this essay, I will review the role that light plays

in the regulation of both chloroplast development and chloroplast

movement.

(1) Chloroplast development

(a) The development of chloroplasts from proplastids is regulated by

light

Meristematic cells in the shoot and root apices and leaf primordia

contain low numbers of small, undifferentiated proplastids. The

ultrastructure of these non-green proplastids is simple and consists

of the envelope, often with some invaginations from the inner

membrane, and a stroma with some ribosomes, nucleoids, plastoglobuli,

sometimes some inner membranes, and a limited amount of prokaryotic

type DNA [1].

In those tissues and organs destined to become green and

photosynthesising in light, the proplastids develop into etioplasts in

darkness. Etioplasts are the end product of a differential route in

dark-grown angiosperm seedlings that begins with the proplastid stage.

A characteristic feature of the etioplast is the ...

... middle of paper ...

...ight) by modulating the

composition of their photosynthetic membranes to enhance

photosynthesis.

Chloroplast movement is also regulated by (mainly blue) light. Under

weak light conditions, chloroplasts undergo accumulation movement

whereby they move into the illuminated area in order to obtain higher

efficiency of photosynthesis. In contrast, under strong light

conditions, chloroplasts undergo avoidance movement whereby they move

away from the illuminated area, therefore avoiding photo-damage.

Response to the light environment is mediated through photoreceptors

(protochlorophyllide, phytochrome, and UV blue light receptors) that

are already present at the earliest stages of development. Activation

of these photoreceptors initiates and continuously regulates the

structure, function, and movement of chloroplasts.

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