The expression of adenine phosphoribosyltransferase during pollen development.

摘要

The involvement of adenine phosphoribosyltransferase (APRT) in pollen development has been analyzed as part of a larger objective to understand the functional significance of the adenine sarvage pathway in plants. APRT is responsible for the conversion of adenine to AMP and may also be involved in the conversion of cytokinin bases to their nucleotide forms. A mutant of Arabidopsis thaliana deficient in APRT activity was previously found to be male-sterile due to aborted pollen development. Three approaches have been used to investigate when, and in what tissues, APRT is required during pollen development. In the first approach, the development of wild-type and APRT-deficient pollen was studied in detail by cytochemical techniques to determine the timing of pollen abortion in the mutant. Several abnormalities were observed in the pollen including irregular wall formation, failure to undergo mitotic divisions, loss of enzyme activities, and a decrease in mitochondrial activity. The tapetum also appeared to degenerate prematurely in the mutant. Because these defects were observed throughout many stages of pollen development, the specific tissue(s) or developmental stage(s) affected by the lack of APRT could not be identified. However, these tests did identify a developmental 'window', from soon after meiosis until the first mitotic division, in which morphological differences occurred.;The second approach was designed to determine whether the expression of the apt gene was induced at any time during wild-type flower development. The level of apt expression was found to be equal in all tissues of the flower and increased only in mature pollen. This increase in apt expression coincided with an overall increase in gene expression in the pollen, and therefore apt expression did not appear ta be specifically induced.;The third approach used antisense expression of the apt gene to specifically down regulate apt expression in the flower. Under the control of constitutive and anther-specific promoters, antisense apt expression appeared to reduce the levels of APRT activity in some tissues. In addition, preliminary results suggest that antisense expression of apt in the microspore soon after meiosis results in aborted pollen development. This suggests that the post-meiotic microspore is one of the tissues directly affected by the lack of APRT.