CHANGES IN LATE-EMBRYOGENESIS-ABUNDANT (LEA) MESSENGER-RNAS AND DEHYDRINS DURING MATURATION AND PREMATURE DRYING OF RICINUS-COMMUNIS L SEEDS

In Ricinus communis L. (castor bean) endosperms, two classes of Late E mbryogenesis Abundant (Lea) transcripts were first detected during mid -development (at 30-35 days after pollination, DAP) and peaked at 50 D AP,just prior to the onset of desiccation. Most of the Class I mRNAs d eclined substantially during desiccation itself; Class II mRNAs remain ed abundant in the mature dry (60 DAP) seed. Following imbibition, all Lea mRNAs abundant in the mature dry seed declined rapidly (within 5- 24 h). Premature drying of developing 35-DAP seeds resulted in the los s of storage-protein mRNAs (Leg B Mat I); following rehydration, mRNAs encoding postgerminative proteins (Germ D91, D30 and D38) increased i n the endosperm. The Lea mRNAs present in the developing fresh seed at 35 DAP were preserved, but did not increase in response to premature desiccation; upon rehydration these Lea mRNAs declined within 5 h. Dur ing seed development, substantial changes occurred in the synthesis of a subset of LEA proteins referred to as 'dehydrins'; in particular, n ew dehydrin polypeptides were induced between 40 and 60 DAP. Such prot eins were not as evident in prematurely dried endosperms. In contrast to the rapid loss of Lea mRNAs during germination, many of the dehydri n proteins abundant in the dried seed persisted following imbibition o r rehydration.