Phytohemagglutinin gene expression during seed development of the runner bean, Phaseolus coccineus

The expression of phytohemagglutinin (PHA) genes was studied in various tissues during the development of the seeds of Phaseolus coccineus cv. Hammond's Dwarf Scarlet by means of northern hybridization and reverse transcription polymerase chain reaction (RT-PCR). The expression is highly development-dependent, starting in the late stage (cotyledons begin to fill the endosperm cavity, i.e. 17 to 24 days after pollination), and tissue-specific. The highest levels of PHA-mRNA are found in the cotyledons (at a very late stage), much lower levels in the embryo axis. Very low levels could be detected in earlier stages of the endosperm, the integument, the funiculus, and probably also in the embryo suspensor. Some PHA mRNA was found in the cotyledons of dry seeds, indicating the presence of undegraded transcripts in mature seeds.