what is phenomenon of losing plastids in absence of sunlight called?
Answers
Answer:
Plastid is another important energy transducing cell organelle found only in plants. Shimper coined the name Plastids for those structures responsible for photosynthesis. In actuality, photosynthesis provides chemical energy directly or indirectly, for all other living organism, Chloroplasts are unique organells for they are capable of capturing, converting and conserving solar energy in the form of chemical energy. Plastids are found in almost all cells of the plant body either in the form of colorless plastids or colored plastids or proplastids.
Classification:
On the basis of presence or absence of pigments, and the stage of development, plastids have been classified into proplastids, leucoplasts and chromoplasts.
Proplastids:
Small vesicular structures present in meristematic cells are called proplastids. They are colorless and undeveloped. As cells mature into different cell types, depending upon the organs and presence or absence of light, proplastids undergo transformation and develop into either colorless leucoplasts or colored chromoplasts including green chloroplasts. Proplastids continuously divide and redivide and provide them for cells undergoing differentiation into various types.
Leucoplasts:
Colorless plastids that are found in storage parenchyma and other colorless tissues are refereed to as leucoplasts. Most of them act as storage organelles. Based on the kind of substance they store they are further classified into amyloplasts. If such leucoplasts are exposed to sunlight they will be transformed into colored plastids, which suggest that these plastids have retained all the genetic potentiality to develop and perform photosynthesis.
Chromoplasts:
All plastids containing different colored pigments are grouped under chromoplasts, of which green colored ones are called chloroplasts. Depending upon the dominant pigments present in plastids, they are further classified into Rhodoplasts rich in red pigment i.e. phycoerythrin. Phaeoplasts and Xanthoplasts contain yellow pigments i.e. xanthophylls, carotinoids. Along with the above pigments phycocyanin and other pigments are also present in other colored plastids.
Other plastids: Such colored plastids, other than chloroplasts are predominantly found in certain class of plants and plant organs including floral parts. Though floral parts are derived from the same set of proplastids, produce different pigments in petals. The exact process differentiation is not known for different plants do produce different colored petals and it is genetically programmed.
Interconversion:
Proplastids divide and redivide in meristematic cells, and then they are distributed to cell derivatives on exposure to light, depending upon the structures in which they found and also depending upon the intra cellular factors they develop into colorless plastids or colored plastids. Leucoplasts on exposure to light develop into green plastids. Similarly chloroplasts may become leucoplasts; but colored plastids as in petals are mostly terminally differentiated.