探索用差热分析技术测定麻栎叶片的自由水含量

An approach to quantify the free water content in leaves of Quercus acutissima Carruth.with differential thermal analysis

探索了用差热扫描曲线分析麻栎(Quercus acutissima Carruth.)在不同状态下的自由水含量的方法。结果显示,在降温过程中以时间为主轴的时域差热扫描曲线能够清楚地显示叶片降温过程中样品的结冰温度、放热峰高度和峰下积分面积与组织含水量的关系,而以温度为主轴的温域差热扫描曲线具有更大的峰下积分面积,在测定样品中的自由水含量时有更高的灵敏度。结冰麻栎叶片在升温过程中的温域差热分析曲线显示,组织内自由水与束缚水的分界点为(-8.23±0.21)MPa,接近2 mol/kg NaCl溶液的渗透势(-8.71 MPa)。死亡麻栎叶片的结冰放热峰显示出均一溶液的结冰特征,即快速结冰升温和快速降温形成尖锐的峰形和高峰值(活叶片峰高的1.91倍),而活叶片的的结冰放热过程则有明显的受细胞膜系统阻碍和迟滞的特征,出现较低的峰值和缓慢的散热峰。研究结果表明,差热分析不仅能够获得植物组织的结冰-融冰过程的自由水相变参数,也能够定量分析植物组织的自由水含量。

An approach was devised to quantify free water content in the leaves of sawtooth oak(Quercus acutissima Carruth.)under different states using differential thermal analysis.The freezing temperatures,peak heights of the exotherms and the areas under the exotherms were clearly observed in the time-domain scanning curve of the differential thermal analysis during cooling,while the larger areas under the exotherms were seen in the temperature-domain scanning curve of the differential thermal analysis,providing a higher sensitivity in quantifying the free water content in the samples.The boundary between free and bound water in the tissues was(−8.23±0.21)MPa,close to the osmotic potential of a 2 mol/kg NaCl solution(−8.71 MPa).Freeze-killed leaves demonstrated uniform solution freezing features with sharp,narrow peaks and higher peak values(1.91 times that of living leaves)attributed to rapid temperature changes.In living leaves,the peaks were broader,and values were lower,suggesting notable delays in water phase change within cellular membranes.Thus,differential thermal analysis could effectively determine the phase change parameters of free water in plant tissues during freeze-thaw cycles and quantify the free water content in plant tissues.