02174naa a2200277 a 450000100080000000500110000800800410001902200140006002400390007410000260011324500890013926000090022852013660023765000160160365000260161965000220164565000150166765000170168265000130169965000120171265300230172470000220174770000230176970000180179277300860181020909002018-05-02       2018    bl uuuu     u00u1 u    #d  a1983-40637 a10.1590/1983-40632018v48504042DOI1 aSILVA, R. de C. B. da  aThermal stress and physiological changes in watermelon seeds.h[electronic resource]  c2018  aGiven that watermelon is a crop widespread around the world, there is considerable interest in verifying how its seeds physiologically behave under unfavorable temperature conditions. This study aimed to evaluate the biochemical changes mobilization and reserves degradation, as well as the enzyme activity, during seed germination and initial growth of watermelon seedlings subjected to thermal stress, using temperature, germination percentage, germination rate and relative germination frequency over the incubation time as evaluation parameters. The experimental design was completely randomized, in a 5 x 3 factorial scheme, with five temperatures (17 ºC, 20 ºC, 25 ºC, 30 ºC and 35 ºC) and three cultivars (Charleston Gray, Fairfax and Crimson Sweet), with 4 replicates of 50 seeds. Germination, seedling growth, reserve degradation and stress protection system were evaluated. Thermal stress caused deleterious effects on watermelon seeds with germination capacity at well defined temperature limits, being 25 ºC the ideal temperature, with the highest percentage of normal seedlings. Sub- (17 ºC) and supra-optimal (30 ºC) temperatures presented more than 80 % of abnormal seedlings. The α-amylase enzyme activity is intense only at the beginning of germination. Under thermal stress, the proline contents increase mainly in the cotyledons.  aGermination  aAtividade Enzimática  aCitrullus Lanatus  aFisiologia  aGerminação  aMelancia  aSemente  aEnzymatic activity1 aARAÚJO, M. do N.1 aORNELLAS, F. L. S.1 aDANTAS, B. F.  tPesquisa Agropecuária Tropical, Goiâniagv. 48, n. 1, p. 66-74, jan./mar. 2018.