Heat-shock effects on photosynthesis and sink!!source dynamics in wheat (Triticum aestivum L.)

Abstract

To assess the mechanisms causing genotypic differences in heat tolerance of wheat (Triticum aestivum L.), physiological responses to a heat shock in a vegetative (‘end of tillering’) or a reproductive (‘early grain filling’) stage were studied. Three cultivars  Lavett, Ciano-79 and Attila  differing in adaptation to heat were grown in a glasshouse at a day/night temperature regime of 15/10 C and a 12-h daylength from sowing to ‘end of tillering’ and next at two day/night regimes of 25/20 and 18/13 ºC under natural daylength. The heat-shock treatment consisted of an exposure of plants to temperatures raised gradually over a time-span of 12 hours to above 30 °C with a maximum of 38 °C during three hours at midday for three days either at the ‘end of tillering’ or at ‘grain filling’. A heat shock at the ‘end of tillering’ strongly reduced the rate of leaf photosynthesis. A similar heat shock during ‘grain filling’ decreased both rate of photosynthesis (source) and grain growth (sink). The rate of leaf photosynthesis was decreased by 40 to 70%, depending on cultivar and developmental stage. Photosynthesis fully recovered within 4 days after the heat-shock treatment was ended. The effects of the heat shock on biomass yield were more pronounced for treatments at ‘early grain filling’ than at ‘end of tillering’. However, the impact of a 3-day heat shock on biomass yield was less than the effects of the pre- and post-treatment growing temperature.