क्लोरोप्लास्ट

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क्लोरोप्लास्टया दुनेया भाग

क्लोरोप्लास्ट धाःगु वनस्पति सेल व मेमेगु युकेरियोटिक सेलय् दैगु छगू अर्‍ग्यानेल ख। थ्व अर्‍ग्यानेलया ज्या फोटोसिन्थेसिस याकिगु ख। क्लोरोप्लास्टं जः उर्जायात छ्येला वःगु फ्रि उर्जायात एडिनोसिन ट्राइफस्फेटय् स्वथनिगु व एनएडिपियात एनएडिपिएचय् हिलिगु जटिल प्रक्रिया फोटोसिन्थेसिस याइ।[१]

नां[सम्पादन]

क्लोरोप्लास्ट धाःगु खंग्वः युनानी खँग्वः क्लोरोस अर्थात वांगु व प्लास्ट अर्थात एन्टिटि स्वाना वःगु खंग्वः ख। क्लोरोप्लास्ट प्लास्टिड नां दूगु अर्‍ग्यानेल क्लासया छगू सदस्य ख।

वैकाशिक उत्त्पत्ति[सम्पादन]

वनस्पति सेलय् खने दूगु क्लोरोप्लास्ट।

क्लोरोप्लास्ट विभिन्न सेल अर्‍ग्यानेलय् छगू ख। साधारण कथं थ्व अर्‍ग्यानेलया पलिस्था इन्डोसिम्बायोटिक सायनोब्याक्टेरिया (वा ब्लु-ग्रीन अल्गेइ)या कथं जूगु धैगु विश्वास दु। This was first suggested by Mereschkowsky in 1905 [२] after an observation by Schimper in 1883 that chloroplasts closely resemble cyanobacteria. [३] All chloroplasts are thought to derive directly or indirectly from a single endosymbiotic event (in the Archaeplastida), except for Paulinella chromatophora, which has recently acquired a photosynthetic cyanobacterial endosymbiont which is not closely related to chloroplasts of other eukaryotes.[४] In that they derive from an endosymbiotic event, chloroplasts are similar to mitochondria but chloroplasts are found only in plants and protista. The chloroplast is surrounded by a double-layered composite membrane with an intermembrane space; further, it has reticulations, or many infoldings, filling the inner spaces. The chloroplast has its own DNA which codes for redox proteins involved in electron transport in photosynthesis.

In green plants, chloroplasts are surrounded by two lipid-bilayer membranes. The inner membrane is now believed to correspond to the outer membrane of the ancestral cyanobacterium. Chloroplasts have their own genome, which is considerably reduced compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities with the cyanobacterial genome. Plastids may contain 60-100 genes whereas cyanobacteria often contain more than 1500 genes.[५] Many of the missing genes are encoded in the nuclear genome of the host. The transfer of nuclear information has been estimated in tobacco plants at one gene for every 16000 pollen grains.[६]

In some algae (such as the heterokonts and other protists such as Euglenozoa and Cercozoa), chloroplasts seem to have evolved through a secondary event of endosymbiosis, in which a eukaryotic cell engulfed a second eukaryotic cell containing chloroplasts, forming chloroplasts with three or four membrane layers. In some cases, such secondary endosymbionts may have themselves been engulfed by still other eukaryotes, thus forming tertiary endosymbionts. In the alga Chlorella, there is only one chloroplast, which is bell shaped.

In some groups of mixotrophic protists such as the dinoflagellates, chloroplasts are separated from a captured alga or diatom and used temporarily. These klepto chloroplasts may only have a lifetime of a few days and are then replaced.[७]

संरचना[सम्पादन]

Chloroplasts are observable morphologically as flat discs usually 2 to 10 micrometer in diameter and 1 micrometer thick. In land plants they are generally 5 μm in diameter and 2.3 μm thick. The chloroplast is contained by an envelope that consists of an inner and an outer phospholipid membrane. Between these two layers is the intermembrane space. A typical parenchyma cell contains about 10 to 100 chloroplasts.

The material within the chloroplast is called the stroma, corresponding to the cytosol of the original bacterium, and contains one or more molecules of small circular DNA. It also contains ribosomes, although most of its proteins are encoded by genes contained in the host cell nucleus, with the protein products transported to the chloroplast.

Chloroplast ultrastructure:
१. आउटर मेम्ब्रेन
२. इन्टरमेम्ब्रेन स्पेस
३. इनर मेम्ब्रेन (१+२+३: इन्भेलोप)
४. स्ट्रोमा(एक्वश फ्लुड)
५. थाइलाकोइड ल्युमेन (थाइलाकोइड दुने)
६. थाइलाकोइड मेम्ब्रेन
७. ग्र्यानम (थाइलाकोइडतेगु पं)
८. थाइलाकोइड (ल्यामेल्ला)
९. स्टार्च
१०. राइबोसोम
११. प्लास्टिडल DNA
१२. प्लास्टोग्लोब्युल (लिपिडया फुति)

Within the stroma are stacks of thylakoids, the sub-organelles which are the site of photosynthesis. The thylakoids are arranged in stacks called grana (singular: granum).[८] A thylakoid has a flattened disk shape. Inside it is an empty area called the thylakoid space or lumen. Photosynthesis takes place on the thylakoid membrane; as in mitochondrial oxidative phosphorylation, it involves the coupling of cross-membrane fluxes with biosynthesis via the dissipation of a proton electrochemical gradient.

In the electron microscope, thylakoid membranes appear as alternating light-and-dark bands, each 0.01 μm thick. Embedded in the thylakoid membrane is the antenna complex, which consists of the light-absorbing pigments, including chlorophyll and carotenoids, and proteins (which bind the chlorophyll). This complex both increases the surface area for light capture, and allows capture of photons with a wider range of wavelengths. The energy of the incident photons is absorbed by the pigments and funneled to the reaction centre of this complex through resonance energy transfer. Two chlorophyll molecules are then ionised, producing an excited electron which then passes onto the photochemical reaction centre.

Recent studies have shown that chloroplasts can be interconnected by tubular bridges called stromules, formed as extensions of their outer membranes.[९][१०] Chloroplasts appear to be able to exchange proteins via stromules,[११] and thus function as a network.

Transplastomic plants[सम्पादन]

Recently, chloroplasts have caught attention by developers of genetically modified plants. In most flowering plants, chloroplasts are not inherited from the male parent,[१२][१३] although in plants such as pines, chloroplasts are inherited from males.[१४] Where chloroplasts are inherited only from the female, transgenes in these plastids cannot be disseminated by pollen. This makes plastid transformation a valuable tool for the creation and cultivation of genetically modified plants that are biologically contained, thus posing significantly lower environmental risks. This biological containment strategy is therefore suitable for establishing the coexistence of conventional and organic agriculture. The reliability of this mechanism has not yet been studied for all relevant crop species. However, the research programme Co-Extra recently published results for tobacco plants, demonstrating that the containment of transplastomic plants is highly reliable with a tiny failure rate of 3 in 1,000,000.[१३]

स्वयादिसँ[सम्पादन]

नोट[सम्पादन]

  1. Campbell, Neil A., Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall.
  2. Mereschkowsky C (1905). "Über Natur und Ursprung der Chromatophoren im Pflanzenreiche". Biol Centralbl 25: 593–604. 
  3. Schimper AFW (1883). "Über die Entwicklung der Chlorophyllkörner und Farbkörper". Bot. Zeitung 41: 105–14, 121–31, 137–46, 153–62. 
  4. Patrick J. Keeling (2004). "Diversity and evolutionary history of plastids and their hosts". American Journal of Botany 91: 1481–1493. DOI:10.3732/ajb.91.10.1481. 
  5. Martin W, Rujan T, Richly E, Hansen A, Cornelson S, Lins T, Leister D, Stoebe B, Hasegawa M, Penny D (2002). "Evolutionary analysis of Arabidopsis, cyanobacterial, and chloroplast genomes reveals plastid phylogeny and thousands of cyanobacterial genes in the nucleus". Proc Natl Acad Sci 99: 12246–12251. DOI:10.1073/pnas.182432999. PMID 12218172. 
  6. Huang CY, Ayliffe MA, Timmis JN (2003-03-06). "Direct measurement of the transfer rate of chloroplast DNA into the nucleus". Nature 422 (6927): 72–6. DOI:10.1038/nature01435. 
  7. Skovgaard, A (1998) Role of chloroplast retention in a marine dinoflagellate. Aquatic Microbial Ecology 15, 293-301
  8. Campbell, Neil A., Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall.
  9. Köhler RH & Hanson MR (2000) Plastid tubules of higher plants are tissue-specific and developmentally regulated. Journal of Cell Science 113, 81–89
  10. Gray JC, Sullivan JA, Hibberd JM & Hansen MR (2001) Stromules: mobile protrusions and interconnections between plastids. Plant Biology 3, 223–233
  11. Köhler RH, Cao J, Zipfel WR, Webb WW & Hanson MR (1997) Exchange of protein molecules through connections between higher plant plastids. Science 276, 1039–1042
  12. Stegemann, S; Hartmann, S; Ruf, S; Bock, R (July 2003). "High-frequency gene transfer from the chloroplast genome to the nucleus" (Free full text). Proceedings of the National Academy of Sciences of the United States of America 100 (15): 8828–33. DOI:10.1073/pnas.1430924100. PMID 12817081. 
  13. १३.० १३.१ Ruf S, Karcher D, Bock R (2007-04-24). "Determining the transgene containment level provided by chloroplast transformation". PNAS 104 (17): 6998–7002. DOI:10.1073/pnas.0700008104. PMID 17420459. 
  14. Powell, W. (1995-08-15). "Polymorphic Simple Sequence Repeat Regions in Chloroplast Genomes: Applications to the Population Genetics of Pines". Proc Natl Acad Sci U S A. 92 (17): 7759–7763. DOI:10.1073/pnas.92.17.7759. PMID 7644491. 

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