BIP, HSP70, NDK AND PDI IN WHEAT ENDOSPERM - II - EFFECTS OF HIGH-TEMPERATURE ON PROTEIN AND MESSENGER-RNA ACCUMULATION

The effects of high temperature on accumulation of the 70-kDa heat sho ck protein (HSP70) and nucleoside diphosphate kinase (NDK) as well as two other proteins that have roles in the biosynthesis of storage prot eins were examined during grain development. An HSP70 homolog and a 17 -kDa NDK were co-purified from wheat endosperm, their identity verifie d, and a cDNA for an HSP70 expressed in endosperm was isolated. Wheat plants (Triticum aestivum, cvs Butte and Vulcan) were heat shocked at 40 degrees C or exposed to maximum daily temperatures of 37 or 40 degr ees C during early or mid-grain fill. Antibodies and cDNA probes for B iP, HSP70, NDK and PDI were used to examine the effect of high tempera tures on the accumulation of protein and mRNA in the endosperm. HSP70 mRNA levels increased substantially when plants were exposed to heat s hock or to a 1-day gradual increase to 40 degrees C. The effects of a 5-day heat treatment on mRNA levels were more complicated and depended on the developmental stage of the grain. A treatment that began at 7 days post-anthesis (DPA) decreased the level of mRNA for HSP70, BiP, P DI and NDK, whereas a treatment that began at 14 DPA slightly increase d mRNA levels. The same treatments increased the accumulation of HSP70 but did not affect BiP, PDI, or NDK protein levels. This is the first detailed report on the effects of heat on mRNA and protein levels for HSP70 in a developing seed storage tissue.