PERSISTENT SUPERCOOLING AND SILICA DEPOSITION IN CELL-WALLS OF PALM LEAVES
PERSISTENT SUPERCOOLING AND SILICA DEPOSITION IN CELL-WALLS OF PALM LEAVES
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DOI：
10.1016/s0176-1617(11)80599-7
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发表时间：
1991-12-01
影响因子：
4.3
通讯作者：
ISHIKAWA, M
中科院分区：
文献类型：
--
作者：
LARCHER, W;MEINDL, U;ISHIKAWA, M
将生长在欧洲和日本暖温带地区的棕榈科植物Trachycarpus fortunei的叶片冷却至低温，并使用差热分析（DTA）跟踪冰的形成过程。通过体内叶绿素荧光测定光合功能的失活，并通过解冻后的活力试验测定冷冻过程中的损伤进展。用透射电镜观察了叶肉细胞的超微结构。用能量色散X射线分析（EDAX）方法对棕榈（Trachycarpus fortunei）、华竹（Washingtonia filifera）和日本竹（Pseudosasa japonica）的细胞壁进行了定性分析，发现了硅质结壳的存在。DTA显示了典型的冻结模式，在-6 ~-8 ℃之间有一个高温带，在-13 ~-14 ℃之间有一个宽的低温带。一旦组织冻结，特征性变化出现在体内荧光的动力学。没有不可逆的光合作用失活或损害是检测到的温度以上的外观的低CO2。在达到峰值后的短时间内，发现叶段受到致命损害。根据Rajashekar和Burke（1982）的公式计算了棕榈属植物叶片在过冷阈值温度下的水张力状态，结果表明棕榈属植物叶片在过冷阈值温度下的水张力状态约为-14MPa。对于从热力学平衡永久维持如此大的位移的解释可能是，如EDXA所揭示的，二氧化硅结壳通过增加细胞壁的刚性和/或对冰晶生长的阻力而有利于过冷。
Leaves of Trachycarpus fortunei from palms growing in warm temperate regions of Europe and Japan as outdoor ornamentals were cooled down to low subfreezing temperatures, and the process of ice formation was followed using differential thermal analysis (DTA). Inactivation of photosynthetic function was determined by in vivo chlorophyll fluorescence, and the progress of injuries during freezing was assayed by viability tests after thawing. Ultrastructure of mesophyll cells was investigated by transmission electron microscopy. Silica incrustation of cell walls was documented by means of qualitative energy dispersive X-ray analysis (EDAX) on samples of Trachycarpus fortunei, Washingtonia filifera, and of the bamboo Pseudosasa japonica.DTA revealed typical freezing patterns, with a high temperature exotherm at about -6 to -8-degrees-C and a broad low temperature exotherm rising from about -13 to -14-degrees-C. As soon as the tissues froze, characteristic changes appeared in the kinetics of in vivo fluorescence. No irreversible inactivation of photosynthesis or damage was detectable at temperatures above appearance of the low exotherm. Within a short time after attainment of the exotherm peak, the leaf segments were found to be lethally damaged. Both of in vivo fluorescence and viability tests clearly indicated that Trachycarpus leaves remain in the persistent supercooled state down to quite low temperatures.The tensile state of water at threshold supercooling temperatures of Trachycarpus leaves was calculated according to the equation of Rajashekar and Burke (1982) and found to be about - 14 MPa. An explanation for the permanent maintenance of such a large displacement from thermodynamic equilibrium could be that silica incrustation, as revealed by EDXA, favours supercooling by increasing the rigidity of the cell walls and/or resistance to the growth of ice crystals.