the Cage of a green plant. Hloroplasty and others plastidy

you are: the Cage of a green plant

Unique feature of vegetative cages is presence at them of some various cytoplasms of ethical little bodies, so-called plastid. Among these plastid the major role in a green vegetative cage play hloroplast (fig. 2.19 and 2.20) - the centres of photosynthetic activity in which the auxiliary pigments connected with photosynthesis are concentrated all chlorophyll and a dog.

At the higher plants hloroplasta under the form remind a lens. Their diameter is equal 5-8 microns, and a thickness - approximately 1 microns. Everyone hloroplast is surrounded by a double membrane (possessing selective permeability) and contains also difficult internal system of membranes. The basic structural unit hloroplastov - tilakoid - represents the thin, flat sack limited to a single-layered membrane. In it there is a chlorophyll, auxiliary pigments and the enzymes which are taking part in photochemical reactions of photosynthesis. Tilakoidy are collected in groups like a rouleau. Uti piles are called granami. All space between granami is filled colourless stromoj in which many enzymes participating in fixing С02 contain. In a cage is available on the average nearby 50 hloroplastov, and everyone hloroplast develops, as believe, from proplastidy. Apparently, proplastidy are capable replitsirovatsja by any division (and their number in a cage increases); Mature hloroplasta also sometimes show ability to replikatsii, however it is observed less often. At etiolirovannyh (grown in the dark) plants proplastidy are called etioplastami.

Being more small hloroplastov, proplastidy do not possess also peculiar hloroplastam lamelljarnoj (layered) structure. Instead they contain prolamelljarnoe a body - ordered, ' paracrystal ' the centre of channels which after appropriate stimulation by light change the orientation and turn to parallel layers.

At floral, or pokrytosemennyh, plants mature hloroplasty can develop from proplastid only at illumination whereas at some golosemennyh this transformation comes to the end and in full darkness. Other distinction between the majority golosemennyh I pokrytosemennyh is connected with their relative ability to transform a pigment a protochlorophyll in a chlorophyll, i.e. To carry out reaction in which two atoms of hydrogen and the rest join a protochlorophyll molecule fitola (' fitolnyj a tail ').

At all pokrytosemennyh light is necessary for this transformation, and at some golosemennyh it can occur and in the dark. In root fabrics hloroplasty usually do not develop even on light, however at some plants, in particular at carrots and at ipomei, root cages can turn green on light. The question on why plastidy in cytoplasm of some cages do not reach a maturity, remains while opened.

Hloroplasty contain, specific, DNA which differs from nuclear DNA and is descended through proplastidy, being in cytoplasm of a parent cage (jajtsekletki); from a fatherly plant (through a pollen cage) hloroplastnaja DNA is not inherited. Containing in hloroplaste enzymes are coded or nuclear, or hloroplastnoj DNA some of them, for example ribulozobisfos-fatkarboksilaza, consist of two albuminous subedinits from which one is coded by nuclear DNA, and another - DNA plastidy. In hloroplastah ribosomes, RNK, amino acids and the enzymes necessary for synthesis of fiber contain also. all it gives hloroplastam known autonomy, i.e. Does them in some measure independent of other cellular structures. Therefore some biologists believe that hloroplasta - it is descendants of any extraneous organisms who once have casually taken root into not green cages and by that have made them avtotrofnymi (capable independently to create nutrients necessary for them by photosynthesis). According to this hypothesis, the photosynthesizing unicells deprived surrounded membrane organell (prokarioty), there is no time casually have united with geterotrofnymi organisms (incapable of photosynthesis and, hence, depending in the food from the preformed nutrients). In evolutionary sense it has appeared favourable and consequently such symbiotic (mutually advantageous) union has remained in the form of modern eukarioticheskoj the vegetative cage having a kernel surrounded with a membrane and others organelly. In favour of such point of view results of researches of ultrastructure of cages testify. In these researches striking similarity between hloroplastami the higher plants and blue-green seaweed at which is not present either kernels, or surrounded with a membrane hloroplastov has come to light, and are available only penetrating cytoplasm lamelly. Mitohondrii also contain specific DNA and the device of albuminous synthesis and consequently, and they, probably, are descendants any svobodnozhivushchih organisms. It is noticed that mitohondrii find out known structural similarity to some primitive bacteria, and their DNA in the chemical relation is related DNA prokarioticheskih organisms.

Supporters of a hypothesis about which there is a speech, specify that if, for example, monocelled zhgutikovoe Eugtena to grow up throughout several generations at enough heats reproduction of cages will advance their reproduction hloroplastov so cages gradually will turn pale more and more. Eventually as a result of such ' razbavlenija ' absolutely colourless cages in which there will be already no hloroplasta and any proplastidy are formed. These cages and remain not green, for ever lost ability to avtotrofii. It is possible to cause also disappearance hloroplastov, influencing cages streptomycin and some other substances. Differently, cages can ' be cured ' from ' occupied ' them hloroplastov with the help either thermal therapy, or chemotherapy.

Biologists have learnt to allocate from cages intaktnye hloroplasty with a method differential tsentrifugirovanija. It is possible to show that these hloroplasty during some time keep all properties inherent in the photosynthetic device of a cage. Isolated intaktnye hloroplasty on light fix СО2, liberate О2 and generate high-energy phosphatic communications. However out of a cage hloroplasty not in a condition neither to support own existence, nor to breed. If they really are present at a cage as ' aggressors ', there is no time pronikshie in it from the outside it is necessary to recognise that their existence to a great extent depends now on other cellular structures.

In hloroplastah various pigments are localised. Most important of them, a chlorophyll, - the unique pigment directly participating in photosynthesis, - meets in the several forms, slightly different one from another on absorption spectra. At some seaweed hloroplasty are especially rich fikobilinami - dark blue or red, and in hloroplastah the majority of the higher plants are present the painted in yellow, orange or red colour karotinoidy. Apparently, karotinoidy on light protect a chlorophyll from destroying action of molecular oxygen. Besides, they raise efficiency of photosynthesis, absorbing and transferring to a chlorophyll energy of those lengths of will which are not absorbed by a chlorophyll thanks to what this energy can be used nevertheless for photosynthesis. Throughout almost all vegetative period karotinoidy in leaves are imperceptible, as their colouring masks high concentration of a chlorophyll; In the autumn when concentration of a chlorophyll in growing old leaves decreases, brightly painted karotinoidy act on the foreground so autumn colouring of foliage depends basically on them. In some measure, the truth, it is influenced also by some other pigments which are out of hloroplastov, for example bright red antotsiany, present in cellular vakuoljah.

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