Studies On The Changes Of Tonoplast Proteins In The Roots And Soluble Proteins Of Tomato Seedlings Under Phosphate Starvation

The possible changes of protein components of vacuole membranes from the roots of tomato seedlings during their adaptation to phosphate starvation were studied and the specific phosphate-starvation-inducible polypeptides responsible for phosphate transport were identified. The changes of soluble protein components and contents from tomato seedlings under phosphate starvation were also analyzed to find possible changes of protein expression in response to phosphate starvation. In addition, the changes of phosphate starvation on growth state were studied. The results are as follows:1. Under phosphate starvation, the average height of the seedlings decreased to a certain degree, while the main roots of the seedlings were obviously longer than those of the controls. Therefore the root/shoot ratios of the seedlings under phosphate starvation were also obviously higher than those of the controls. The results suggested that, under phosphate starvation, tomato seedlings increased their phosphate uptake rates by increasing the length of the main roots of the seedlings.2. Phosphate starvation caused apparent changes of soluble protein contents from tomato seedlings. With the extension of phosphate starvation time, soluble protein contents from the roots of tomato seedlings were increased, while soluble protein contents were decreased in the stems and leaves of tomato seedlings. But the changes of soluble protein contents in the stems and leaves were later than that in the roots of tomato seedlings. It indicated that, the changes of soluble protein contents in the roots were more sensitive to phosphate starvation than that in the stems and leaves. Phosphate starvation also caused apparent changes of soluble protein components from tomato seedlings. SDS-PAGE pattern showed that a polypeptides of about 38.9kD was enhanced and a 51.3kD polypeptide was induced in the roots of tomato seedlings under phosphate starvation for 5 days. Two polypeptides of about 38.9kD and 45.1kD were enhanced and a 51.3kD polypeptide was induced for 9 days. The 51.3kD polypeptide had appeared indistinctly in 5 days of phosphate starvation. It was suggesting that this polypeptide wasprobably related to the development of resistance to phosphate starvation in tomato seedlings. The polypeptides of about 38.9kD and 45.1kD were probably related to the changes of soluble protein contents from tomato seedlings. However, there was no novel polypeptide induced except that two polypeptides of about 69.4kD and 61.8kD were enhanced in the stems and leaves of tomato seedlings under phosphate starvation.3. The tonoplast vesicle preparation was improved. After centrifugation of discontinuous sucrose density gradient, the tonoplast H+-ATPase activity was mainly distributed in 22% sucrose; the lowest activity was in 25%. So tonoplast-enriched vesicles were mainly on the interface 22 %.4. The changes of protein components and contents of tonoplast in the roots of tomato seedlings under phosphate starvation had also been studied. The results showed that, under phosphate starvation, the content of proteins of tonoplast from the roots of tomato seedlings almost identical to those of their controls respectively. The experimentation SDS-PAGE showed that, In 5 days of phosphate starvation, the polypeptide of 67.3kD from tonoplast in the roots of tomato seedlings showed stronger expression trend. There appeared to have a novel polypeptide of 77.4kD appeared for 7 days but not in the control. A new polypeptide of 73.2kD appeared in 9 days. It was supposed that the new polypeptides of 77.4kD and 73.2kD might be specifically induced by phosphate starvation and as the components of phosphate starvation rescue system. The polypeptide of 67.3kD may not be the novel specific polypeptide induced by phosphate starvation but reflect the changes in steady-state levels of proteins.5. Future prospect of phosphate starvation induced proteins was also discussed. The differences of protein types and contents in phosphate starvation tolerance of plants were probably associated with the plant species. Plant phosphate transporters may play important roles in increasing the capacity of phosphate transport. However, it was necessary to study on the function of plant membrane proteins. SDS-PAGE patternshowed that two tonoplast polypeptides of 77.4kD, 73.2kD were induced in the roots of tomato seedlings under phosphate starvation. Now, more experiments should be done with the clear function of these new polypeptides.