Progressive loss of desiccation tolerance in germinating pea (Pisum sativum) seeds

Loss of desiccation tolerance during germination has been described in gene ral terms for many orthodox seeds and has been used as a framework to eluci date the mechanisms that confer tolerance to quiescent embryos. A more deta iled description of the time course during which desiccation tolerance is l ost Kill allow us to build a more comprehensive picture of the events that contribute to the toss of tolerance, To more thoroughly characterize the lo ss of desiccation tolerance, we monitored the viability of germinating pea (Pisum sativum L, cv,Alaska) seeds after drying them to a range of moisture contents, Desiccation tolerance is lost in different embryonic tissues at different times during germination, Thus, Hr looked separately at the effec ts of drying on radicle and epicotyl survival and on electrolyte leakage fr om the whole embryonic asis, Using statistical and graphical analysis. ne c alculated the moisture content at which the population of germinating seeds began to be damaged by dehydration (threshold moisture content, TMC) and a t which dehydration damaged the majority of the population (critical moistu re content, CMC). CMCs and TMCs differed for each tissue and increased as g ermination progressed, TMCs appeared at 18 h of imbibition for radicle surv ival and electrolyte leakage and at 24 h for epicotyl survival. CMCs appear ed at 21 h for radicle survival and electrolyte leakage., Among the asis ti ssues, epicotyls were the least sensitive to dehydration during germination , CMCs for epicotyl survival did not appear until 30 h of imbibition and di d not increase to the extent that they did for either radicle survival or e lectrolyte leakage, Results from these experiments can be used as a framewo rk to correlate the progression of biochemical and anatomical changes to th e progressive loss of desiccation tolerance in germinating pea embryos.