A research was carried out to evaluate the influence of temperature on seed respiration response of maize, cotton, grain sorghum and sunflower during imbibition, and to define reliable indices for a fast evaluation of cold-sensitivity at germination level in plants. The seed respiration activity was measured during seed imbibition at 25 ºC (optimal) and 15 ºC (suboptimal) constant temperatures, using a homemade respiration chamber adapted to an infrared gas analyzer. At 15 ºC, sunflower and sorghum maintained high levels of seed germination (C90 %), whilst this last dropped in cotton (36.7 %) and maize (27.8 %). With respect to this, cotton and maize seem to be cold sensitive during germination. Instantaneous seed respiration during imbibition versus temperature or thermal time could not be used as a good indicator for cold tolerance, since the levels of CO2 recorded at 15 ºC in cotton (higher than the other species) and maize (similar to that of sorghum and sunflower) did not correspond to adequate seed germination. Differently, the rates (b coefficient of linear regressions) of accumulation of CO2 respired at optimal and suboptimal temperatures during the first hours of imbibition (up to approximately 24 h from the start of experiment), were significantly different in maize and cotton, whilst they did not differ in sorghum and sunflower. Therefore, the shift between slopes may represent a reliable index for seed cold-sensitivity assessment during early germination.
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