Effects Of Toxin Produced By Potato Rhizoctonia Solani On Cell Structures And Resistant Physiology Of Potato Seedlings

Black scurf disease caused by Rhizoctonia solani(R.solani)has become one of the main soil-born diseases which limits the healthy development of potato industry.And it severely affects the yield and quality of potato tubers.The toxin produced by R.solani is probably one of the main reasons of the disease.It has a great significance for the prevention and control of potato stem canker,to proven the role of the toxin in the course of the plant.In this study,the experiment was carried out by means of hydroponics experiment,using transmission electron microscopy techniques,to study the effect of the toxin on the structure and resistance of potato seedling cells.The main results are as follows:1.The site of the toxin prodecud by Rhizoctonia solani is not only in the membrane,but in the entire membrane system.It can cause damage to the structure of organelles such as mitochondria,chloroplast,nucleus and endoplasmic reticulum.Different organs have different sensitivity to the treatment of toxins,the damage occurs first in the cell walls and membranes of the root cells,followed by stem and leaf cell ultrastructure damage.Compared with the control,the root cells were separated in 48 h after the toxin treatment,and the cell walls are deformed and broken,the membrane is partially broken,the nucleoli disappear,the mitochondrial crest is missing finally.The nucleus dissolved with the treatment time extended.With the delivery to the ground organs of toxin,the microstructure of the stem cells also showed partial defects in the cell wall,the endoplasmic reticulum is swollen,deformed,and the structure of the chloroplasts disappears.After processing 96 h,the fracture of the cell wall can be observed,the cell membrane is broken,the mitochondrial crest disappears,and the number of starch grains decreases.The leaf cells are characterized by the chlorophyll is irregular in structure and membrane partial meltdowns,mitochondrial structure deformations andthe loss of the crest.2.The toxin can cause severe damage to the cell membrane,increase the membrane permeability,and infiltrate the inner electrolyte,resulting in an increase in the electrical conductivity of the external fluids.In a certain time period,the toxin can also activate the cell membrane H~+-ATPase activity,but with the duration of the experiment,toxin inhibits the activity of H~+-ATPase.The sensitive degree of different organs in the processing of the toxin had significant difference,root system is most sensitive,followed by the stem and leaves at base.3.The toxin of Rhizoctonia solani can significantly reduce the content of chlorophyll in the leaf of potato seedlings,and chlorophyll b was more sensitive to Rhizoctonia solani toxin,which was more likely to degrade.4.Rhizoctonia solani toxin can make the storage of potato seedlings in the hydrolysis of starch into sugar,resulting in increased soluble sugar content,starch content and change trend of the changes of the soluble sugar is verified;with the extension of the test time,the soluble sugar content reached the peak after the decline is due to the soluble sugar into the sugar plant glycolytic pathway involved in the synthesis of some resistant substances,harmful toxin resistance.5.The toxin of Rhizoctonia solani can induce the host to produce some resistance functional proteins,It helps increasing the resistance of plants.With the duration of the experiment,the toxin destroys the balance of protein metabolism,and a large amount of soluble protein is broken down.The soluble protein content was highest in the leaves,followed by the base of the stalk and lowest in the root system.6.Free proline content were greatly increased after treating with toxin in the roots,basal and leaf of potato seedlings,but free proline content were different in different organs,and the increase was varied.It is shown that the toxin can cause the increase of the content of free proline in potato,and protect the plant.7.The toxin can cause the changes of the enzyme PAL activity in the roots,the base of the stem and the leaf of potato seedlings.The PAL activity in the seedling can be activated after treating with the toxin,and start a series of defensive reactions to reduce the toxic effect of the toxin to potato seedlings.But the change of PAL activity in different organ varied in the potato seedlings,and the timing of the enzyme peak is also inconsistent.