Limits...
Ice nucleation activity in various tissues of Rhododendron flower buds: their relevance to extraorgan freezing.

Ishikawa M, Ishikawa M, Toyomasu T, Aoki T, Price WS - Front Plant Sci (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences Tsukuba, Japan.

ABSTRACT
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.

No MeSH data available.


Seasonal changes in the INA of intact flower bud parts of R. japonicum(A) and INA after autoclaving and replacement of water (B) showing the stability of INA at 121°C for 15 min. INA was determined as the 50% ice nucleation temperature (median INT) using the test tube INA assay as shown in Figure 4. OS, outer scale; IS, inner scale; FL, floret. The data are mean ± SE (n = 3).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4373250&req=5

Figure 5: Seasonal changes in the INA of intact flower bud parts of R. japonicum(A) and INA after autoclaving and replacement of water (B) showing the stability of INA at 121°C for 15 min. INA was determined as the 50% ice nucleation temperature (median INT) using the test tube INA assay as shown in Figure 4. OS, outer scale; IS, inner scale; FL, floret. The data are mean ± SE (n = 3).

Mentions: To know how the INA in flower bud scales develops and seasonally changes, the INA in flower bud tissues were followed from August until May except for mid-winter (the plants were covered with snow from January until early April) using the natural populations in Tochigi Prefecture (Figure 5). Flower bud morphogenesis starts from late June or early July and comes to an end in late August or early September. The INA level of the outer bud scales in late August was about -7°C and increased to the highest level (-5.2°C) in late October when they experience the first autumnal frost or freeze. In contrast, the INA level of the inner bud scales was low (> -14°C) in late August, but rapidly increased to -6.7°C in late October and to -6.4°C in early December (Table 1; Figure 5), just in time for their frequent exposure to subfreezing temperatures when a freezing sensor function is required. The INA in the outer and inner bud scales remained at high levels during the winter but it gradually declined in the spring (May 4 ∼ May 27) when flower buds resumed growth (the bud scales still attached). The INA in the floret stayed at low levels from August until the end of winter but it went up in the spring as the floret dry weight rapidly increased by 1.5- (May 4), 3- (May 18), and 6-fold (May 27).


Ice nucleation activity in various tissues of Rhododendron flower buds: their relevance to extraorgan freezing.

Ishikawa M, Ishikawa M, Toyomasu T, Aoki T, Price WS - Front Plant Sci (2015)

Seasonal changes in the INA of intact flower bud parts of R. japonicum(A) and INA after autoclaving and replacement of water (B) showing the stability of INA at 121°C for 15 min. INA was determined as the 50% ice nucleation temperature (median INT) using the test tube INA assay as shown in Figure 4. OS, outer scale; IS, inner scale; FL, floret. The data are mean ± SE (n = 3).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4373250&req=5

Figure 5: Seasonal changes in the INA of intact flower bud parts of R. japonicum(A) and INA after autoclaving and replacement of water (B) showing the stability of INA at 121°C for 15 min. INA was determined as the 50% ice nucleation temperature (median INT) using the test tube INA assay as shown in Figure 4. OS, outer scale; IS, inner scale; FL, floret. The data are mean ± SE (n = 3).
Mentions: To know how the INA in flower bud scales develops and seasonally changes, the INA in flower bud tissues were followed from August until May except for mid-winter (the plants were covered with snow from January until early April) using the natural populations in Tochigi Prefecture (Figure 5). Flower bud morphogenesis starts from late June or early July and comes to an end in late August or early September. The INA level of the outer bud scales in late August was about -7°C and increased to the highest level (-5.2°C) in late October when they experience the first autumnal frost or freeze. In contrast, the INA level of the inner bud scales was low (> -14°C) in late August, but rapidly increased to -6.7°C in late October and to -6.4°C in early December (Table 1; Figure 5), just in time for their frequent exposure to subfreezing temperatures when a freezing sensor function is required. The INA in the outer and inner bud scales remained at high levels during the winter but it gradually declined in the spring (May 4 ∼ May 27) when flower buds resumed growth (the bud scales still attached). The INA in the floret stayed at low levels from August until the end of winter but it went up in the spring as the floret dry weight rapidly increased by 1.5- (May 4), 3- (May 18), and 6-fold (May 27).

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences Tsukuba, Japan.

ABSTRACT
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.

No MeSH data available.