2.2. Effect of1cadmium on chloroplast ultrastructure
The toxic symptoms of plants under cadmium stress are caused by chlorophyll degradation and chloroplast dysfunction, and photosynthesis cannot be carried out. Chloroplast is the main organelle of photosynthesis in plants, and cadmium will damage its ultrastructure. The toxicity of cadmium to chloroplasts varies with plant development stages. It was found that cadmium treatment in soil had no visible effect on the ultrastructure of chloroplasts in young leaves, but the chloroplast membrane system in mature leaves was greatly destroyed. Under the condition of high cadmium, chloroplasts are mostly spherical, and the membrane system is seriously damaged, which leads to the separation and necrosis of plasma wall. Studies have shown that the integrity and order of thylakoid structure are very necessary for chloroplasts to carry out normal and effective light energy conversion in photosynthesis. It can be seen that the destruction of chloroplast structure is one of the mechanisms of cadmium ion poisoning plants.
2.2.2 Effects of cadmium on photosynthetic pigments
Chlorophyll content is the material basis that affects photosynthesis. In a certain range, chlorophyll content is positively correlated with photosynthesis, and the higher chlorophyll content, the stronger photosynthesis; But when the chlorophyll content exceeds a certain limit, it has no effect on photosynthesis. Cadmium can replace magnesium ions in chlorophyll molecules, interfere with the activity of chlorophyll synthase, hinder the synthesis of chlorophyll, and increase the activity of chlorophyll decomposing enzyme to decompose chlorophyll. Cadmium salt was found in maize (ze. Mays) can reduce chlorophyll biosynthesis, and similar results have been found in spring wheat and oats. In addition, cadmium salt will also hinder the synthesis of chlorophyll. Song Dongjie and others studied the medicinal materials treated with cadmium ion solutions with different concentrations, and found that the leaves in winter buds turned yellow and green, and the chlorophyll content gradually decreased with the increase of cadmium ion concentration.
2.3 Effect of cadmium on photosynthetic rate (intensity)
A large number of studies have shown that the destruction of chloroplast ultrastructure and the decrease of photosynthetic pigments (especially chlorophyll) are one of the main factors that cause the decline of plant photosynthetic intensity. Because chlorophyll has the function of receiving and transforming energy, photosynthesis is carried out in all green parts of plants with chlorophyll. In a certain range, the more chlorophyll content, the stronger photosynthesis. With the senescence of leaves, chlorophyll content decreased, chloroplast internal structure disintegrated and photosynthetic rate decreased. As mentioned above, cadmium destroys the ultrastructure of chloroplasts and reduces the content of photosynthetic pigments, thus reducing the photosynthetic rate of plants. At different growth stages of the same plant, the effects of cadmium on photosynthesis are different. Cadmium is absorbed by plant roots and enters the body, causing imbalance of nutrients in plants, causing imbalance of metabolism and inhibiting plant growth, thus reducing the assimilation area of leaves, shortening the life span of leaves and reducing the photosynthetic rate; Cadmium can reduce or even close stomatal opening, CO2 can enter leaves, starch hydrolysis in leaves is enhanced, and the transportation of photosynthetic products is slow, which leads to sugar accumulation and increased respiratory consumption. , leading to the decrease of photosynthetic rate.
2.4 Effects of cadmium on photosynthesis
To study the process of photosynthesis is mainly to study light reaction and dark reaction, that is, to study the photosystem H(PSH) in light reaction.
And the activity of carbon assimilator (PSIg) enzyme in dark reaction. one
On the one hand, cadmium hinders the activity of PSH and photophosphorylation and affects the formation of ATP; On the other hand, cadmium inhibits ribulose-1, 5-
RuBP activity, which is used to fix carbon in the photosynthetic carbon cycle of plants.
Key enzyme, the activity change of this enzyme directly affects carbon fixation, and then affects the metabolic process in the body.
2.4. Effect of1cadmium on photoreaction process
Cadmium compounds are widely used as herbicides in agriculture, which can inhibit the electron transfer of PSll in photosynthesis.
! '""'02]。 Because photophosphorylation is coupled with electron transfer, some cadmium-containing herbicides introduce I from P through inhibition.
Electrons transfer from the wake (Q) to the plastid wake (PQ), or occupy the position of QB competitively (D! On the skin
The binding site of plastid awakening is used to block the electron transfer from Q 8 (D: plastid awakening on multiple skin) to q.83]. Except for ...
The principle of herbicides to kill weeds is complicated and not completely clear at present. But generally speaking, herbicides are mainly through interference and
Destroy the physiological and biochemical process of weeds and make them out of balance, thus inhibiting the growth and development of weeds and leading to their death. because
Weeds and crops are different in morphology, structure, physiology and growth time, so herbicides are enough.
Using these differences, through morphological selection, root distribution selection, germination time selection and physiological and biochemical selection.
Get the ideal weeding effect! '",]。 As far as herbicides affecting photosynthesis are concerned, they are mainly selective inhibition.
The photosynthetic electron transport chain of weeds shunts electrons in the photosynthetic electron transport chain, which inhibits photosynthetic phosphorylation and pigment synthesis.
Process and inhibit the photolysis of water, thus inhibiting photosynthesis. "}。
Hill: Reaction is the most unique and important part of photosynthesis, and chloroplasts participate in photosynthesis.
Decompose in water and release oxygen! 0, L Hill reactivity is an important index reflecting the photosynthetic intensity of 20 leaves.
Mark. When the concentration of cadmium is 1omolL ",it can promote the photosynthetic oxygen release rate of cyanobacteria cells, and then with the concentration of cadmium,
It decreases with the increase of photosynthetic oxygen evolution rate ['06 1]. The results of spinach research show that mercury and arsenic affect the activity of Hill reaction.
To restraint. H3Aso made the photochemical efficiency of Ps 1 1 of oat leaves the highest (FvzF. ) Reduce [9,]. Stoje Eva and others I "] to jade.
Master of Science in Kunming, T:, Dissertation
Rice's research also got similar results. In addition, the inhibitory effect of most heavy metal ions on photosynthetic bacteria is far greater than that on Psl.
It is worth noting that PSll is the most sensitive site to heavy metal ions. 7 a 08 1. At present, many studies show that the key points are
Some changes in the optical system (especially PSH) under metal pollution precede other visible damage symptoms.
Chemistry (such as quantum yield, etc. ) will happen sensitively and quickly! . 9 Yichuan}.
As homologous elements of phosphorus, their chemical properties are similar. Cadmium can pass through the plasma membrane through the phosphorus transport system, once it enters the cell.
Quality, it can compete with phosphorus, for example, it can replace ATP (one of the earliest relatively stable photoreactions)
Products) and form unstable ADP-As, interfering with the energy flow of cells! Therefore, cadmium
Toxicity mainly comes from interference with phosphorus metabolism I "" 1. Studies show that increasing the content of cadmium in soil can reduce Canolla.
Phosphorus uptake by (rape) seedlings. Cadmium interferes with the metabolic pathway of phosphorus in crops, and cadmium toxicity can make crops absorb phosphorus.
Close the channel [63]. However, phosphorus, potassium and other elements participate in carbohydrate metabolism, which will affect the transformation and transportation of carbohydrates when lacking.
Lose indirectly inhibits photosynthesis; At the same time, phosphorus also participates in the transformation and energy supply of photosynthetic intermediates.
Transmission, so it has a great influence on photosynthesis! 00]。 Plants lack the energy necessary for growth and development and are seriously poisoned.
Will lead to cell death! "6}。 Cadmium can enter plants through phosphorus channels, so plants grow in cadmium-polluted soil.
Will absorb a lot of cadmium into the body NL6,8226; ，，6-l！ 7]。
4.2 Effect of Cadmium on Dark Reaction Process
The whole process of dark reaction is divided into three stages: shuttle, reduction and regeneration. In the shuttle stage of carbon assimilation, ribulose-1,
5- diphosphate (RuBP) is combined with CO2 under the catalysis of ribulose-1, 5- diphosphate shuttle enzyme/oxygenase (Rubisco).
Close. Rubisco is the key enzyme of photosynthetic carbon assimilation, also known as rate-limiting enzyme. According to the current literature, about
The effect of cadmium on enzyme activity in dark reaction is less studied. Compared with other heavy metals (such as cadmium, lead and copper),
People have not fully studied the physiological response of plants under cadmium pollution ["8! . However, studies have shown that cadmium can interfere with some
Metabolism of some essential elements (such as nitrogen and phosphorus). ), which are directly related to light reaction or dark reaction,
Therefore, cadmium indirectly interferes with the photosynthesis process. For example, nitrogen has the most significant effect on photosynthesis, and within a certain range,
Nitrogen content, chlorophyll content and Rubisco content in leaves were positively correlated with photosynthetic rate, respectively. Nitrogen content in leaves
80% in chloroplast, nitrogen application can not only increase chlorophyll content, accelerate photoreaction, but also increase photosynthetic enzyme content and
Activity, accelerate the dark reaction. Rubisco extracted from leaves with good nitrogen nutrition is not only rich, but also active.
High Igvl. However, the toxicity of cadmium changed flue-cured tobacco. Tabacum) nitrogen metabolism, resulting in the same nitrogen in the early growth stage.
With the decrease of chemical capacity, nitrate reductase activity decreased, and the contents of total nitrogen and protein were lower than the control! ""。
In addition, crops often have symptoms of nitrogen deficiency in soil polluted by cadmium [9' I]. Therefore, it can be inferred that cadmium affects plant nitrogen metabolism.
Noise may affect the content of Rubisco, and then interfere with the dark reaction process.