| Phloem transport is a fundamental and complex process in higher plants. Recent studies by others have identified genes encoding proteins hypothesized to play crucial roles in this process. In this dissertation, two classes of these proteins, sucrose transporters and phloem proteins (P-proteins), were studied in the model plant Arabidopsis thaliana. Through a reverse genetic screen, T-DNA insertions were identified in the sucrose transporter genes SUC1 and SUC2 and in the P-protein gene PP21. The altered phenotypes caused by these knockout disruptions were then characterized.; The insertion in PP21 appeared to be lethal as the mutant allele was never found in the homozygous state. Among the offspring of a selfed PP21 heterozygote, there were fewer wild type plants than expected and more heterozygotes than expected. Reciprocal crosses between PP21 heterozygotes and wild type plants failed to identify a specific gametophytic defect caused by the mutant allele. PP21 appears to have a role in reproduction and/or embryogenesis.; suc1 homozygous mutant plants showed no obvious growth phenotypes. suc2 homozygous mutant plants, however, had a clear growth defect. They were unable to grow beyond seedling stage without exogenously supplied sucrose. Their leaves appeared packed with starch, and labeled sucrose was not exported efficiently out of these leaves. These results indicate that SUC2 plays a vital role in efficient phloem loading and transport. |
