Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka 020-8550, Japan.
Physiol Plant. 2013 May;148(1):25-35. doi: 10.1111/j.1399-3054.2012.01678.x. Epub 2012 Sep 13.
The supercooling capability of xylem parenchyma cells (XPCs) in boreal hardwood species differs depending not only on species, but also season. In this study, the roles of cell walls and intracellular contents in supercooling capability of XPCs were examined in three boreal hardwood species, Japanese beech, katsura tree and mulberry, whose supercooling capability differs largely depending on species and season. XPCs in these species harvested in winter and summer were treated by rapid freezing and thawing (RFT samples) or by RFT with further washing (RFTW samples) to remove intracellular contents from XPCs in order to examine the roles of cell walls in supercooling. RFT samples were also treated with glucose solution (RFTG samples) to examine roles of intracellular contents in supercooling. The supercooling capabilities of these samples were examined by differential thermal analysis after ultrastructural observation of XPCs by a cryo-scanning electron microscope to confirm effects of the above treatments. XPCs in RFTW samples showed a large reduction in supercooling capability to similar temperatures regardless of species or season. On the other hand, XPCs in RFTG samples showed a large increase in supercooling capability to similar temperatures regardless of species or season. These results indicate that although cell walls have an important role in maintenance of supercooling, change in supercooling capability of XPCs is induced by change in intracellular contents, but not by change in cell wall properties.
木质部薄壁细胞（XPCs）的过冷能力不仅取决于物种，还取决于季节。在这项研究中，我们研究了三个北方硬木物种（日本山毛榉、桂树和桑树）的细胞壁和细胞内物质在 XPCs 过冷能力中的作用，这三个物种的 XPCs 的过冷能力因物种和季节的不同而有很大的差异。我们从冬季和夏季收获的这些物种中提取 XPCs，然后通过快速冷冻和融化（RFT 样品）或 RFT 与进一步清洗（RFTW 样品）来处理 XPCs，以去除细胞内物质，从而研究细胞壁在过冷中的作用。RFT 样品也用葡萄糖溶液处理（RFTG 样品），以研究细胞内物质在过冷中的作用。通过冷冻扫描电子显微镜对 XPCs 进行超微结构观察后，用差示热分析（differential thermal analysis）来检测这些样品的过冷能力，以确认上述处理的效果。RFTW 样品中的 XPCs 的过冷能力无论物种或季节都大大降低到相似的温度。另一方面，RFTG 样品中的 XPCs 的过冷能力无论物种或季节都大大增加到相似的温度。这些结果表明，尽管细胞壁在维持过冷能力方面起着重要作用，但 XPCs 过冷能力的变化是由细胞内物质的变化引起的，而不是由细胞壁性质的变化引起的。
