A gerontoplast is a
plastid
The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosy ...
that develops from a chloroplast during the
senescing of plant
foliage
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
.
Gerontoplast development is generally seen to be the process of
grana being unstacked, loss of
thylakoid membranes
Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thyl ...
, and large accumulation of
plastoglobuli.
Transformation of chloroplasts to gerontoplasts
The term ''gerontoplast'' was first introduced in 1977 to define the unique features of the plastid formed during leaf senescence.
The process of senescence brings about regulated dismantling of
cellular organelles
In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...
involved in
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. Chloroplasts responsible for
gas exchange
Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...
in
stomata
In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
are the last organelles to degrade during senescence, and give plants the green color.
The formation of gerontoplasts from chloroplasts during senescence involves extensive structural modifications of the thylakoid membrane with the concomitant formation of a large number of plastoglobuli with lipophilic materials. The envelope of the plastid, however, remains intact.
References
External links
*
Organelles
Photosynthesis
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