Effect of heat stress during seed development and maturation on wheat (Triticum durum) seed quality

Abstract

<p>The influence of temperature on yield and yield components has been extensively studied, but seed quality was often ignored in most of these studies. The present study investigates the influence of temperature during seed development and maturation on resultant seed quality as assessed by physical, physiological and biochemical traits. Two durum wheat cultivars, "Marzak" and "Oum-rabia", were grown in growth chambers under three temperature conditions (20/15, 28/21, 36/29°C) beginning 10 days after anthesis through maturity. At maturity seeds were harvested and stored in a cold room (10°C, 45% RH) for subsequent laboratory analyses. Tests performed on either seed or excised embryo included: physical seed characteristics, germination, seedling vigor tests, embryo oxygen uptake, embryo growth potential, nucleotide levels, isolated mitochondria respiration and electron microscopy. As expected high temperature resulted in low seed number per ear, seed mass and seed dimensions. Heat stress during seed development and maturation had no consistent influence on seed germination per se among cultivars. However, seed vigor was reduced as indicated by reduced shoot and root dry weight, root number and root length per seedling, embryo respiration and a delay in isolated embryo germination. Also, exposing seeds during their development to high temperatures resulted in some metabolic changes as indicated by lowered mitochondrial activities, energy (ATP) and adenylate energy charge during early stages of seed germination. Results from electron microscopy provided additional information for these changes in seed metabolism during early germination. Mitochondria from low temperature embryos were well developed with visible membranes and cristae whereas those from high temperature embryos were degenerating. This provides clear evidence for damaged mitochondria as the probable main target of high temperatures during seed growth. Through the measurement of these different parameters, the current study may be the first one to demonstrate that wheat seed quality is strongly influenced by the parent growing temperature at least under controlled conditions. In addition to its effect on seed mass, heat stress resulted in mitochondrial damage that leads to low vigor seed.</p>