Irrigation and Seed Quality Development in Rapid-cycling Brassica: Accumulation of Stress Proteins

Abstract

The accumulation of representatives from three classes of stress proteins [a class 1 low molecular weight heat-shock protein (HSP); a dehydrin (group 2 LEA); and a group 3 LEA protein] were studied during seed development in rapid-cycling brassica [ Brassica campestris (rapa) L.] under different irrigation regimes. Withholding irrigation to plants altered the timing of events during seed development. All three proteins studied accumulated in seeds towards the end of seed development on well-irrigated plants, as seed moisture content declined. As irrigation was withheld from plants progressively earlier, these proteins appeared earlier both in time and in relation to physiological developmental markers, consistent with a protective role. However, seeds became desiccation tolerant during development before they had accumulated appreciable amounts of the two LEA proteins and the timing of accumulation was unaffected by post-harvest seed drying. This suggests that these particular LEA proteins are not absolutely required for desiccation tolerance. Although the HSP studied was also not present in seeds from well-irrigated plants as desiccation tolerance increased, its synthesis was induced by post-harvest drying at this stage of development. However, the amounts of HSP produced during drying subsequently declined later in development, but seeds remained desiccation tolerant. During the period when seeds were desiccation tolerant at least one of the three proteins was present either before drying, or produced in significant quantities upon drying. In general, the proteins studied continued to accumulate in seeds after mass maturity at the same time that potential longevity was increasing. Copyright 1998 Annals of Botany Company