Thermal stress and physiological changes in watermelon seeds

ABSTRACT Given 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.

摘要 西瓜是全球广泛种植的作物，探明其种子在非适宜温度条件下的生理表现具有重要学术价值。本研究旨在评估热胁迫下西瓜种子萌发及幼苗初期生长过程中的生化物质动员、储备降解及酶活性变化，选取萌发温度、发芽率、发芽速率以及萌发周期内的相对发芽频率作为评价参数。实验采用完全随机设计，设置5×3因子试验方案，包含5个温度梯度（17℃、20℃、25℃、30℃及35℃）与3个西瓜品种（Charleston Gray、Fairfax及Crimson Sweet），每组设置4次重复，每次重复含50粒种子。本研究对种子萌发、幼苗生长、储备降解及逆境防护系统进行了测定。热胁迫对具备萌发能力的西瓜种子产生了不利影响，且该影响存在明确的温度阈值，其中25℃为最适温度，正常幼苗占比最高。亚适宜温度（17℃）与超适宜温度（30℃）条件下，异常幼苗占比均超过80%。α-淀粉酶（α-amylase）仅在萌发初期活性较强。在热胁迫环境中，脯氨酸（proline）含量主要在子叶中升高。