Physiological quality and expression of genes in seeds of Handroanthus serratifolius subjected to drying

Handroanthus serratifolius seeds are considered orthodox and have some mechanisms that assist in desiccation tolerance, like heat-resistant proteins and the presence of protective systems against free radical production. In order to investigate the drying effect on the quality of Handroanthus serratifolius seeds collected with 28% water content two methods were used: slow drying (30 °C) and fast drying (45 °C) until water contents equaled 20%, 15%, 10% and 5%. Seed quality was assessed by germination test, first count of germination, speed germination, emergence and speed emergence. The expression of heat-resistant proteins and enzymes catalase, esterase and isocitrate lyase was assessed by electrophoresis. The gene expression of sHSP17.5, CAT3 and ICL6 was quantified by real time PCR. Higher values of germination and vigor were obtained in seeds with 20% water content, subjected to fast drying. There was induction of heat-resistant proteins expression for both drying methods. There was variation in the electrophoretic pattern of catalase, esterase and isocitrate lyase in seeds subjected to different treatments. The gene expression in Handroanthus serratifolius seeds varies depending on methods of drying and water content of seeds. The drying of Handroanthus serratifolius seeds until the water content between 15 and 10% compromises their physiological quality.

黄钟木（Handroanthus serratifolius）种子属于正常型种子（orthodox seed），具备多种辅助其获得脱水耐性的机制，例如耐热蛋白的存在以及对抗自由基生成的保护系统。为探究干燥处理对初始含水量为28%的黄钟木种子品质的影响，本研究采用两种干燥方式：慢速干燥（30℃）与快速干燥（45℃），将种子含水量分别降至20%、15%、10%与5%。通过发芽试验、发芽势、发芽速率、出苗率及出苗速率对种子品质进行评价。采用电泳技术分析耐热蛋白以及过氧化氢酶（catalase）、酯酶（esterase）、异柠檬酸裂解酶（isocitrate lyase）的表达情况。通过实时定量PCR（real time PCR）对小热激蛋白17.5（sHSP17.5）、CAT3及ICL6的基因表达量进行定量检测。经快速干燥处理且含水量为20%的种子，其发芽率与活力指标均表现最优。两种干燥方式均可诱导耐热蛋白的表达。经不同处理的种子，其过氧化氢酶、酯酶与异柠檬酸裂解酶的电泳图谱存在差异。黄钟木种子的基因表达水平随干燥方式与种子含水量的不同而发生变化。将黄钟木种子干燥至含水量介于10%~15%之间时，会损害其生理品质。