Photosynthesis. Energy storage. Photobreath

you are: Photosynthesis. Energy storage

The Plants using only a way of Calvin - Bensona. It is accepted to name Sz-plants as the first stable product of photosynthesis is presented at them by three-carbon connection - FGK. At Sz-plants the considerable part of the carbon fixed at photosynthesis there and then is lost owing to disintegration of products of fixing and allocation СО2 in the reactions going with consumption of oxygen. This process occurs only on light and consequently it has been named by photobreath. Photobreath is opened rather recently. It speaks after its opening by that allocation СО2 at breath on light masks absorption СО2 in the course of photosynthesis. It was originally supposed, as in a quantitative sense, and in sense of a used way light breath is identical to breath in the dark, however then was found out that on light is allocated more - than

СО2. It managed to be established as a result of careful measurements of gas exchange directly after inclusion or light deenergizing. Additional allocation СО2 observed on light speaks, how was found out, not strengthening of normal process of breath, and addition in these conditions of absolutely other way - photobreath.

Photobreath is caused by that in the presence of oxygen operating in Calvin's cycle enzyme RuBp-karboksilaza can attach to RuBP not only СО2, but also СО2, carrying out thus role RuBp-oksigenazy. Joining of oxygen to molecule RuBP leads to its such splitting at which instead of two molecules FGK containing on three atoms of carbon, one molecule fosfoglikolevoj acids (containing two atoms of carbon) and one molecule FGK is formed. Thus, in oksigenaznoj reactions do not occur any fixing СО2. Fosfoglikolat later defosforiliruetsja also turns in glikolat which arrives from hloroplasta in another organellu, also surrounded with a membrane, - in peroksisomu. In peroksisome glikolat enters reaction

With oxygen therefore are formed glioksilat and hydrogen peroxide. Peroxide there and then breaks up to water and oxygen, and glioksilat turns to amino acid glitsin. Then out of peroksisomy, namely in mitohondrijah, from glitsina series amino acid is formed (which it can be used directly in albuminous synthesis or to undergo the further transformations conducting to formation of glucose). At this reaction one molecule is formed of two molecules glitsina serila and simultaneously allocated СО2. Thus, any part of the carbon fixed in a cycle of Calvin - Bensona, is lost without that the plant could though somehow this carbon to use. The sense of photobreath is not clear to us yet, but, maybe, its useful function (if that exists) is connected by that it plays a necessary role in a metabolism of nitrogenous connections or in their carrying over from one organelly in another, providing transformation glikolata in glitsin. Probably also that photobreath has arisen at early stages of existence of the Earth with photosynthesis development. At that time in terrestrial atmosphere, obviously, there was no oxygen, therefore fosfoglikolat could not be formed under the influence of RuBp-karboksilazy. However, when the oxygen allocated in the course of photosynthesis, has started to collect in atmosphere, in plants, probably, accumulation fosfoglnkolata has begun, and, maybe, photobreath has arisen in the course of evolution as the means, allowing to limit this accumulation.

Not at all plants photobreath equally intensively. Considerably fluctuates as well efficiency from which different kinds of plants in the course of photosynthesis fix СО2. Intensity of photosynthesis at subtropical cereals, for example at corn, a sugar cane and sorgo (tab. 4.1), twice with superfluous above, than at spinach, wheat, rice and beans. The plants which more effectively are carrying out this process (them name С4-растениями; we still will speak about them more low), use other way of mastering СО2 to facings of vascular bunches of sheet (a so-called d-metabolism), and we here in brief will discuss this way. To less effective group all Sz-plants belong; they can lose at light breath to half of all carbon assimilated in the course of photosynthesis.

Possibility to regulate photobreath represents a great interest for physiologists of plants as crops of some cultures it would be possible, obviously to double if only it was possible to reduce somehow these losses of potential reserves of a plant. Attempts such are conducted divergently. Dependence of photobreath on experimental conditions is investigated, for example, so that, changing these conditions there where it is possible, to reduce such way of a photo -

Breath to a minimum. High concentration СО2, low concentration of oxygen and low intensity of light limit photobreath, than, by the way, partly and that fact speaks that ' fertilizer carbonic acid ' raises growth rate at many plants. Are tested also chemical ingibitory photobreath which should not be toxic neither for plants, nor for animals eating them. Selectors search for variants or mutants of plants with low intensity of photobreath and try to include this sign in a genotype of created grades. It is necessary to remember, however, that photobreath suppression can have harmful consequences at some plants. Recently, for example, in experiences on studying of growth of plants of the soya, different high level of photobreath, it was found out that though at low concentration of oxygen photobreath decreases also plants vegetativno develop better, than in usual atmosphere, they do not form mature seeds if concentration О2 appears below 5%. From here it is possible to conclude that at some plants photobreath or any reactions accompanying it are necessary that life cycle proceeded normally. It is valid, difficult to imagine, as photobreath could arise in the course of evolution and remain on all its extent if it has been deprived any adaptive value.