Emerging and Established Model Systems for Endosperm Weakening

摘要

Endosperm rupture is the main germination-limiting process in members of the Asteraceae (e.g. lettuce (Lactuca sativa L.)) and Solanaceae (e.g. tomato (Lycopersicon esculentum Mill.) and tobacco (Mcotiana tabacum L.)). About four decades ago a 'hatching enzyme' was proposed to cause endosperm weakening (i.e. a decline in the mechanical resistance of the micropylar endosperm), which is likely to be essential for seeds to complete germination. Although, there are established model systems among Asteraceae and Solanaceae for endosperm weakening, its molecular mechanism(s) still remain(s) a mystery. No single 'hatching enzyme' or universal molecular mechanism has been demonstrated explicitly. For the time being, the provisional conclusion is that endosperm weakening is likely to be achieved by the collaborative or successive action of several distinct molecular mechanisms. The knowledge gained from these established model systems will be compared and discussed. However, consideration of their severe experimental limitations shows that there is an urgent need for novel model systems. Such an optimal system has been recently found within the Brassicaceae. In this emerging model system for endosperm weakening, a complete study of the process is possibleon each experimental level, from the direct measurement of the weakening by 'puncture force' to molecular investigations (e.g. proteome and transcriptome analyses).