Role of relative humidity, temperature and water status in dormancy alleviation of sunflower seeds during dry after-ripening

JEREMY BAZIN ; DIEGO BATLLA; STEPHANE DUSSERT; HARAT EL-MARROUF-BOUTEAU; CHRISTOPHE BAILLY

JOURNAL OF EXPERIMENTAL BOTANY

OXFORD UNIV PRESS

Año: 2011 vol. 62 p. 627 - 640

0022-0957

The effect of various combinations of temperature and relative humidities on dormancy alleviation of sunflower seeds during dry after- ripening was investigated. Rate of dormancy alleviation depended on both temperature and embryo moisture content (MC). Below embryo MC of 0.1 g H2O g dw-1, dormancy release was faster at low temperature (15°C), but it was the opposite when embryo MC was higher than this threshold value. This suggests that dormancy release at low MC was associated with negative activation energy, as revealed by Arrhenius plots, and low Q10 values. At higher MC, rate of dormancy alleviation increased with temperature thus fitting well with the temperature dependence of biochemical processes. This behaviour suggests the involvement of 2 distinct cellular mechanisms in dormancy release; non-enzymatic below 0.1 g H2O g dw-1 and associated with active metabolism above this value. Effect of temperature on seed dormancy release above the threshold MC value was analyzed using a population-based thermal time approach and we provide a model predicting rate of dormancy alleviation. Sunflower embryo dormancy release was effective at temperatures above 8 ºC (TbAR = 8.17 ºC), and the higher the after-ripening temperature above this threshold value, the higher the dormancy loss rate. Thermodynamic analyses of water sorption isotherms revealed that release of dormancy was associated with less bound water and increased molecular mobility within the embryonic axes but not the cotyledons. It is proposed that the changes in water binding properties result from oxidative processes and can in turn allow metabolic activities.