Heat shock response of germinating embryos of wheat : effects of imbibition time and seed vigor

Seeds frequently face a hostile environment during early germination. In order to determine whether seeds have evolved unique mechanisms to deal with such environments, a survey of the heat shock response in isolated embryos of wheat (Triticum aestivum L.) was undertaken. Embryos simultaneously heat shocked and labeled following several different periods of prior imbibition up to 12 hours synthesized many groups of heat shock proteins (hsps) typical of other plant and animal systems. Also, five developmentally dependent hsps, present only in treatments imbibed less than 6 hours prior to heat shock, were detected. These proteins have relative molecular masses of 14, 40, 46, 58, and 60 kilodaltons. One of the developmentally dependent hsps is among the most highly labeled hsps found in early imbibed embryos. The possibility that this protein is the E_m protein is discussed. The hypothesis that the capacity for hsp synthesis is affected by seed vigor was also tested. The heat shock responses of embryos from two high and two low vigor seed lots were compared using one- and two-dimensional electrophoresis of labelled protein extracts. The results indicate that both of the low vigor lots tested had weaker heat shock responses than their high vigor counterparts overall. Not all hsps were relatively less abundant in low vigor embryos. The developmentally dependent hsps showed little relationship to vigor. Some of the developmentally dependent hsps were actually made in greater amounts, relative to other proteins, in the low vigor seed lots. The results presented here demonstrate that imbibing embryos are capable of expressing an enhanced heat shock response, and that this response is related to seed vigor.