Ice nucleation activity in various tissues of Rhododendron flower buds: their relevance to extraorgan freezing.
Ice nucleation activity in various tissues of Rhododendron flower buds: their relevance to extraorgan freezing.
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DOI：
10.3389/fpls.2015.00149
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发表时间：
2015
影响因子：
5.6
通讯作者：
Price WS
中科院分区：
文献类型：
--
作者：
Ishikawa M;Ishikawa M;Toyomasu T;Aoki T;Price WS
耐寒杜鹃越冬的花芽缓慢冷却到零度以下，已知会经历器官外冷冻，其机制尚不清楚。我们重新审视了这一材料，以证明为什么芽鳞在水分较低的情况下首先冻结，为什么小花保持深度过冷，以及如何在花蕾中发生器官外冻结的季节性适应反应。我们用试管法测定了不同花蕾组织的冰核活性(INA)。无论采集地点如何，在器官外冷冻中充当冰槽的外部和内部芽鳞具有较高的INA水平，而保持过冷并作为水源的小花则缺乏INA。在花芽形成结束的8月下旬，芽鳞中的INA水平并不高，但在第一次秋冻前的10月下旬，INA水平上升到最高水平。结果支持以下假设：芽鳞中较高的INA是冰冻的感受器，在较温暖的零下温度下保证了芽鳞中的初冻，这可能允许小花水分向芽鳞迁移并在芽鳞内积累冰柱。小花中较低的INA有助于它们在深度过冷的情况下保持解冻。花蕾鳞片中的INA耐磨和在121∘C高压灭菌15min，暗示INA的内在性质而不是微生物来源，而茎皮中的INA是高压灭菌不稳定的。高压灭菌芽鳞的渗滤液中含有抗核活性(ANA)，它在毫摩尔浓度水平上抑制INA，可能与溶质的综合作用不同。组织INA水平可能通过确保组织中冻结的顺序来促进冻结行为的建立：从第一次冻结到最后一次未冻结的组织。
Wintering flower buds of cold hardy Rhododendron japonicum cooled slowly to subfreezing temperatures are known to undergo extraorgan freezing, whose mechanisms remain obscure. We revisited this material to demonstrate why bud scales freeze first in spite of their lower water content, why florets remain deeply supercooled and how seasonal adaptive responses occur in regard to extraorgan freezing in flower buds. We determined ice nucleation activity (INA) of various flower bud tissues using a test tube-based assay. Irrespective of collection sites, outer and inner bud scales that function as ice sinks in extraorgan freezing had high INA levels whilst florets that remain supercooled and act as a water source lacked INA. The INA level of bud scales was not high in late August when flower bud formation was ending, but increased to reach the highest level in late October just before the first autumnal freeze. The results support the following hypothesis: the high INA in bud scales functions as the subfreezing sensor, ensuring the primary freezing in bud scales at warmer subzero temperatures, which likely allows the migration of floret water to the bud scales and accumulation of icicles within the bud scales. The low INA in the florets helps them remain unfrozen by deep supercooling. The INA in the bud scales was resistant to grinding and autoclaving at 121∘C for 15 min, implying the intrinsic nature of the INA rather than of microbial origin, whilst the INA in stem bark was autoclaving-labile. Anti-nucleation activity (ANA) was implicated in the leachate of autoclaved bud scales, which suppresses the INA at millimolar levels of concentration and likely differs from the colligative effects of the solutes. The tissue INA levels likely contribute to the establishment of freezing behaviors by ensuring the order of freezing in the tissues: from the primary freeze to the last tissue remaining unfrozen.
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影响因子：
4.2
作者：
CHALKERSCOTT, L
通讯作者：
CHALKERSCOTT, L
影响因子：
--
作者：
Wiegand, KM
通讯作者：
Wiegand, KM
影响因子：
7.4
作者：
Ishikawa, M;Price, WS;Arata, Y
通讯作者：
Arata, Y
影响因子：
7.3
作者：
ISHIKAWA, M;SAKAI, A
通讯作者：
SAKAI, A
影响因子：
7.4
作者：
GEORGE, MF;BURKE, MJ
通讯作者：
BURKE, MJ