Department of Botany, University of Innsbruck, Innsbruck, Austria.
Institute of Biophysics, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria.
Physiol Plant. 2023 Jan;175(1):e13865. doi: 10.1111/ppl.13865.
Conifer (Pinaceae) needles are the most frost-hardy leaves. During needle freezing, the exceptional leaf anatomy, where an endodermis separates the mesophyll from the vascular tissue, could have consequences for ice management and photosynthesis. The eco-physiological importance of needle freezing behaviour was evaluated based on the measured natural freezing strain at the alpine treeline. Ice localisation and cellular responses to ice were investigated in mountain pine needles by cryo-microscopic techniques. Their consequences for photosynthetic activity were assessed by gas exchange measurements. The freezing response was related to the microchemistry of cell walls investigated by Raman microscopy. In frozen needles, ice was confined to the central vascular cylinder bordered by the endodermis. The endodermal cell walls were lignified. In the ice-free mesophyll, cells showed no freeze-dehydration and were found photosynthetically active. Mesophyll cells had lignified tangential cell walls, which adds rigidity. Ice barriers in mountain pine needles seem to be realised by a specific lignification patterning of cell walls. This, additionally, impedes freeze-dehydration of mesophyll cells and enables gas exchange of frozen needles. At the treeline, where freezing is a dominant environmental factor, the elaborate needle freezing pattern appears of ecological importance.
针叶是最抗冻的叶子。在针叶冻结过程中，特殊的叶片解剖结构，其中内皮层将叶肉与维管束组织隔开，可能对冰的管理和光合作用产生影响。基于高山林线的自然冻结应变测量，评估了针叶冻结行为的生态生理重要性。通过 cryo-microscopic 技术研究了高山松针叶中的冰定位和细胞对冰的反应。通过气体交换测量评估了它们对光合作用活性的影响。冻结反应与细胞壁的微化学有关，用拉曼显微镜进行了研究。在冷冻的针叶中，冰被局限在由内皮层包围的中央维管束中。内皮层细胞壁木质化。在无冰的叶肉中，细胞没有发生冻结脱水，并且被发现具有光合作用活性。叶肉细胞具有木质化的切线细胞壁，这增加了刚性。高山松针叶中的冰屏障似乎是通过细胞壁的特定木质化模式来实现的。这还可以阻止叶肉细胞的冻结脱水，并使冷冻针叶进行气体交换。在林线处，冻结是主要的环境因素，因此这种精细的针叶冻结模式具有生态重要性。
