Desiccation and minimal drying treatments of seeds of castor bean and Phaseolus vulgaris which terminate development and promote germination cause changes in protein and messenger RNA synthesis

Premature desiccation imposed during seed development results in the onset of germination upon subsequent imbibition. The synthesis of developmental proteins is more or less permanently suppressed as a consequence of drying, and the types of proteins synthesized in the rehydrated seed arc those normally associated with germination/growth of the mature dry seed. The switch in protein synthesis from a developmental to a germinative mode is due to changes in transcriptional activity. The mRNAs for developmental proteins (e.g. storage proteins) are no longer produced after drying, and during germination most residual messages are degraded; new mRNAs associated with both germination and growth are transcribed following imbibition of the prematurely desiccated seed. Immature developing seeds removed from the capsule, and placed in liquid water do not germinate and maintain a developmental pattern of protein synthesis. When such seeds are removed and placed in an atmosphere of high relative humidity for a few days (equivalent to the time required to achieve premature desiccation) their water content declines only slightly, but upon placing in liquid water they will germinate. Moreover, developmental protein synthesis ceases, and that associated with germination and growth commences. As with premature drying, this switch is effected largly due to transcriptional changes, accompanied by some post-transcriptional degradation of residual developmental mRNAs. Hence conditions can be imposed on developing seeds where they do not have to experience extensive (whole seed) water loss in order to acquire germinability. Rather, a combination of time of detachment (i.e. separation from the influence of the maternal environment), with some water loss, may be sufficient to elicit the switch from development to germination.