Heat Shock Proteins and Their mRNAs in Dry and Early Imbibing Embryos of Wheat

Abstract

Two-dimensional gels of in vitro translation products of mRNAs isolated from quiescent wheat (Triticum aestivum) embryos demonstrate the presence of mRNAs encoding heat shock proteins (hsps). There were no detectable differences in the mRNAs found in mature embryos from field grown, from 250C growth chamber cultivated, or from plants given 38°C heat stresses at different stages of seed development. The mRNAs encoding several developmentally dependent (dd) hsps were among those found in the dry embryos. Stained two-dimensional gels of proteins extracted from 250C growth chamber cultivated wheat embryos demonstrated the presence of hsps, including dd hsps. A study of the relationship of preexisting hsp mRNAs and the heat shock response during early imbibition was undertaken. Heat shocks (420C, 90 minutes) were administered following 1.5, 16, and 24 hours of 250C imbibition. While the mRNAs encoding the low molecular weight hsps decayed rapidly upon imbibition, the mRNAs for dd hsps persisted longer and were still detectable following 16 hours of imbibition. After 1.5 hours of imbibition, the mRNAs for the dd hsps did not accumulate in response to heat shock, even though the synthesis of the proteins was enhanced. Thus, an applied heat shock appeared to lead to the preferential translation of preexisting dd hsp mRNAs. The mRNAs for the other hsps, except hsp 70, were newly transcribed at all of the imbibition times examined. The behavior of the hsp 70 group of proteins during early imbibition was examined by RNA gel blot analysis. The mRNAs for the hsp 70 group were detectable at moderate levels in the quiescent embryo. The relative level of hsp 70 mRNA increased after the onset of imbibition at 250C and remained high through 25.5 hours of prior imbibition. The maximal levels of these mRNAs at 250C was reached at 17. stresses are endured without leaves and a root system, which help moderate extremes of temperature and water status, respectively, in postemergent plants. The study of heat stress responses during early germination has proven interesting in regard to both of these problems. We found that wheat (Triticum aestivum L.) embryos are able to synthesize a full set of hsps3 from the earliest times of imbibition. Early imbibing embryos also synthesize several hsps which cannot be produced after 12 h of imbibition (1 1). Further, embryos imbibed less than 8 h are resistant to heat stresses that are lethal to embryos imbibed 12 or more h (1). These findings suggest that stress proteins and/or their mRNAs may be present in dry embryos. If present, these proteins or mRNAs might contribute both to the strong hs response and the high thermal tolerance found during early imbibition.In order to learn more about the developmental nature of several wheat hsps, as well as the high thermal tolerance of early imbibed wheat, we studied the protein and mRNA composition of quiescent and early imbibed embryos, as well as the way in which the embryos responded to heat stress during early imbibition. Further, we examined...

Expression of sunflower low-molecular-weight heat-shock proteins during embryogenesis and persistence after germination: localization and possible functional implications

“…Use of antibodies against cytoplasmic class I LMW HSPs [ 14] has confirmed in vivo accumulation of these proteins in mature seeds from field-grown plants [ 15]. The latter observation is strongly indicative of developmental expression of these proteins during plant zygotic embryogenesis, which had been suggested by earlier studies [ 10,[16][17][18].…”

“…Preliminary observations in our laboratory (10) and other groups [15][16][17][18][19][20][21][22][23][24][25][26][27][28]29] indicated expression of LMW HSPs during zygotic embryogenesis and seed germination. The results presented in this paper demonstrate differential developmental expression of two distinct families of cytoplasmic proteins.…”

Stress hydrique: étude des mécanismes moléculaires et des modifications de l'expression du génome

“…Puis, entre 12 et 24 heures d'imbibition, les embryons présentent un grand nombre de cellules méristéma-tiques qui effectuent la réplication de leur ADN et leur mitose de manière synchrone (Helm et Abernethy, 1990).…”

“…Celui-ci apparaît dans des embryons immatures lorsqu'ils sont séparés des structures du fruit et il est sous la dépendance de facteurs génétiques (existence de mutants vivipares) ainsi que de l'ABA qui empêche une germination précoce lorsqu'il est présent au cours des derniers stades de l'embryogénèse des graines (Dure III, 1977). Abernethy, 1990). Les ARNm de la plupart des hsp fabriquées par le blé pendant la phase précoce de l'imbibition sont présents dans l'embryon sec et pour certains, dans l'embryon quiescent.…”

Molecular and Physiological Analysis of a Heat-Shock Response in Wheat

“…These been documented (1,2,6,8,12,30), and the number of low mol wt heat-shock proteins induced in several monocot species has been determined (12). These studies reveal that in wheat, 11 low mol wt proteins are induced and 1 enhanced by heat shock.…”