Sporophytic and gametophytic heat shock protein synthesis in Sorghum bicolor

Abstract

The general characteristics of the heat-shock response in the sporophytic and gametophytic phases of Sorghum bicolor, a species well adapted to tropical environments, are examined. At the sporophytic level, heat shock protein (HSP) synthesis in sorghum is still induced after an extreme (well over 50°C) or prolonged heat stress: the so-called late HSPs are first induced after 14 h continuous exposure at 45°C, and persist up to at least 28 h shock. A normal protein pattern is not resumed, as is the case in most organisms. In contrast to plant species typical of temperate climates, sorghum pollen also retains the capability to synthesize HSPs in post-germinative stages. In addition to several classic HSPs, those synthesized in all sporophytic tissues, some gametophyte specific heat inducible polypeptides are expressed in both immature and germinating pollen. Taking into account the likely role of HSPs in cellular thermo-protection, these data support the hypothesis that acquisition of themotolerance shows between species variability, in relation to climatic adaptation. In addition, the results concerning HSP synthesis in the male gametophyte suggest the possible use of gametophytic selection in crop improvement for thermotolerance.