植物組織の氷核活性の検索

抄録

Ice nucleation is the primary event that a plant undergoes at subfreezing temperatures. How plants controls the freezing of their tissues is an important mechanism in cold hardiness. Ice nucleation activity (INA), the ability to cause heterogeneous ice nucleation of water, in plant tissues seems to be a key element contributing to this mechanism. Here I summarize the results of surveying INA in various tissues from more than 600 plant species using a newly revised test tube INA assay. Cold tender plants (tropical and subtropical) had low levels of INA whilst cold hardy plants had high levels of INA in specific tissues. The localization of INA in cold hardy plants corresponded closely to the intrinsic freezing behaviors of the tissues: bark tissues which undergo extracellular freezing and bud scales which act as an ice sink in extraorgan freezing had high levels of INA whilst florets which remain deeply supercooled had low levels of INA. INA was classified into heat-stable and -labile types with regard to the resistance to autoclaving (121℃, 15 min), which were specific to tissues and species. This allowed us to determine the distributions of these types of INA within a plant family and the inheritance of this trait using interspecific hybrids. The supernatant of autoclaved plant tissues tended to show anti-nucleation activity (the ability to suppress INA) at low osmolality (< 5 mOsm) irrespective of plant origins (cold hardy or sensitive). The high INA may act as a subfreezing temperature sensor to avoid excess supercooling of the tissues and to readily initiate freezing in the specific portion of the tissues, which likely allows the tissues to properly undergo the intrinsic freezing behaviors (e.g., extracellular freezing, extraorgan freezing). The applicability and precautions required in utilizing the revised test tube INA assay are discussed.