Mechanisms Of Membrane Injury Caused By Toxin Produced By Potato Rhizoctonia Solani

Gansu province is one of the main potato producing areas in C hina, also is China’s major commercial potato production base and starch processing base. However, inrecent years, the potato Rhizoctonia disease(potato black scurf) caused by Rhizoctonia solani has become one of the main soil borne diseases which limited the healthy development of the potato industry in Gansu Province. The pathogenic mechanism of the Rhizoctonia solani is very complicated, and the toxin produced by it is probably one of the main reasons of the disease.So we studied through culture experiment to of potato toxin of Rhizoctonia solani on potato seedlings, to reveal the process of membrane injury of stem and leave tissues, including the effect of permeability of cell membrane, active oxygen metabolism, anti enzyme activity and membrane peroxidation; at the same time, the toxin of Rhizoctonia solani was separated into six fractions by column chromatography, and the effects of different components on the degree of the cell membrane injury were studied on the potato seedlings. In order to provide a basis for revealling the mechanism of the membrane injury of potato seedlings. The main results were as follows:1. The cell membrane permeability of potato seedlings’ stem and lea vewere increased by the toxin of Rhizoctonia solani, and the relative electrical conductivity of the cel s was increased.Red ink absorption tests show, Rhizoctonia solani toxin treatment will lead to membrane permeability loss, and control compared to toxin treatment of potato seedling root absorbed a large number of red ink and transport to leaves; red ink absorption test results showed, toxin treatment of potato seedling stems and leaves accumulated in red ink, significantly more than the control;After disposing of the toxins, potato seedling stem and leaf cell leaching extract relative electrical conductivity(REC) is significantly higher than that of the control, it had significant difference in 96 h after the toxin treatment, in the treatment of T3(High concentration), the stem ell leaching provided liquid REC increased compared with control 75.5% and leaves increased 137.0%.The sensitive degree of leaf and stem in the processing of the toxin had significant difference, the damage effects of toxin is first expressed in the leaves and in high level continued for a long time, the performance for leaf tissue membrane damage is far greater than the rate of stem tissue, were 41.7% and 23.5%, the difference of 18 percentage points; effect of membrane injury are aggravate with toxin treatment time prolonged, and increases with the increase of the concentration of the toxin.2.The active oxygen content of potato seedlings was increased by the toxin of Rhizoctonia solaniThe production rate of superoxide anion(O2-) increased in the stem and leaf tissue of potato seedlings, and increased with the increase of toxin concentration.The changes of O2- production rate in potato seedlings’ stem and leaf tissue had different response to the toxin treatment, the O2- production rate in stem tissue is faster than it in the leaf tissue, and had 24 hours in advance to achieve maximum production rate than that in leaf, when the O2- generation rate reaches a maximum when, stem and leaf tissue compared with the control(CK) were increased 6 times and 1 times respectivelyRhizoctonia solani toxin causedthe hydrogen peroxide(H2O2) content of potato seedlings increased, and with the increase of concentration of toxin, H2O2 content of potato seedling stem and leaf tissue increased gradually. After 96 h with toxin treatment, H2O2 Content in the stem and leaf tissue reached maximum, compared with CK, H2O2 Content in stem and leaf tissue increased 156.1% and 256.2% respectively in the treatment of T3(High concentration).The result showed that the toxin could cause the rate of O2- production and H2O2 content increased, which resulted in the accumulation of the stem and leaf tissue of a large number of reactive oxygen species, which caused damage to the cell membrane.3.The activity of the anti – enzyme andthe plasma membrane peroxidationof potato seedlings was increased by the toxin of Rhizoctonia solaniToxin treatment for 144 h, compared to CK the activity of SOD in leaf and stem tissues respectively increased 31.0% and 50.6%, and the activity of CATin the stems and leaves of the plants respectively increases the 2 times and 2.6 times. That toxin caused potato seedling stem and leaf tissue cell membrane injury, and stress increased the activity of the enzyme.After treated with Rhizoctonia solani toxin, malondialdehyde(MDA) content of potato seedlings’ leave and stem tissues were significantly increased,compared with CK treatment, the content of MDA, in stem and leaf tissue respectively compared increased 92.6% and 96.7%. It proved that toxin increased the MDA content of seedling stems and leaves, the p lant plasma membrane peroxidation, causing the potato seedlings cell membrane injury. The plasma membrane over the degree of oxidation intensified with the increase of the concentration of toxin.The different organs of potato seedlings had difference affecte by toxin, and their sensitivity to toxin was higher in leave than that of the stem, and the plasma membrane had a greater degree of oxidation.4.The damage degree of the cell membrane of potato seedlings was different in different fractions of the Rhizoctonia solani toxinThe test results show that different fractions caused different degrees of cell membrane injury on potato seedlings. To stem tissue, divided into six groups, except fraction 3(TF3), the other groups branch leads to potato seedlings ce ll REC increased, but no significant difference among the treatments, and to leaf tissue which were more sensitive to the toxin, TF1 and TF5 processing potato seedling stem and leaf tissue REC higher.Preliminary proven, after separation and purification in the six groups of potato Rhizoctonia solani toxin, TF1 and TF5 may is caused by a toxin is the main component of the membrane injury of potato seedlings, and the leaves of injury was greater in the leaves than that in the stem. stems.