CHANGES IN PHOSPHOLIPASE-D EXPRESSION IN SOYBEANS DURING SEED DEVELOPMENT AND GERMINATION

Activation of phospholipase D (PLD) has been linked to accumulation of nonhydratable phosphatides and lipid degradation leading to soybean s eed deterioration during preharvest and postharvest events. This study examined the changes in PLD activity, protein, and mRNA in soybeans d uring seed development and germination. RNA blotting analysis indicate d that expression of the gene that encodes PLD was highest during the early and middle stages of seed development. However, the amount of PL D activity accumulated per cotyledon reached the highest level in matu re seeds. During germination and early seedling growth, PLD mRNA was n ot detected one day after imbibition, while a significant increase in PLD expression occurred in the cotyledons of three- and seven-day seed lings, Similarly, PLD activity and protein concentration showed little change during the first day of imbibition and increased afterward in three- and seven-day seedlings. These results suggested that expressio n of PLD is developmentally regulated and that the changes in its amou nt of activity and protein are controlled primarily at the mRNA level, Immunoblotting analysis further revealed the presence of PLD variants that were associated with specific stages of seed development and see dling growth. The PID variants present in the cotyledons of mature see ds appeared to be distinct from those observed in the early stage of s eed development and in young seedlings.