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I find it intriguing that it’s hard to define the principal ecological function of such a highly evolved protein. Could it actually have multiple functions or do we lack insight?
Hirano and Upper (2000) wrote “there is no clear selection for destroying the leaf habitat. For most organisms, habitat destruction is regarded as highly unfavorable…..the bacteria reward themselves for success [as colonists] by destroying their habitat! Is this not paradoxical?” But could IN bacteria be protecting their property by triggering high temp freezing? Once nucleation occurs freezing travels extensively throughout the xylem. The ice demands water and sucks it out of cell’s protoplasts, protecting them. If this happens slowly the cells survive. I notice that on grapevines tissue near the nucleation point and adjacent to the xylem freezes but leaves and mesophyll further away does not, and then the plant re-shoots vigorously, investing in more leaves and not fruit.
The diversity of IN alleles suggests they have been evolving for hundreds of millions of years. So what did they do in the former – the real – world? Before our patchwork quilt world. Pangaea is perhaps where the IN gene evolved. Pangaea had dinosaurs, vast ecosystems and deserts (with OM-enriched dust floating over them). How important were bioaerosols in that world? Was it the same repertoire of forces that operate in a vineyard or a field of beans?
Where do the INA bugs call home now? If the 10^9 nuclei (active at -10 C) per gram of leaf litter in Canada and Russia, found by Russ Schnell and Gabor Vali, are INA bacteria then isn’t this their real home, and the IN protein is for water gathering or for freezing leaf litter and its decomposer community (freeze/thaw cycles stimulate decomposition in soil).
Tom Hill
tchill@unimelb.edu.au
Hirano and Upper (2000) wrote “there is no clear selection for destroying the leaf habitat. For most organisms, habitat destruction is regarded as highly unfavorable…..the bacteria reward themselves for success [as colonists] by destroying their habitat! Is this not paradoxical?” But could IN bacteria be protecting their property by triggering high temp freezing? Once nucleation occurs freezing travels extensively throughout the xylem. The ice demands water and sucks it out of cell’s protoplasts, protecting them. If this happens slowly the cells survive. I notice that on grapevines tissue near the nucleation point and adjacent to the xylem freezes but leaves and mesophyll further away does not, and then the plant re-shoots vigorously, investing in more leaves and not fruit.
The diversity of IN alleles suggests they have been evolving for hundreds of millions of years. So what did they do in the former – the real – world? Before our patchwork quilt world. Pangaea is perhaps where the IN gene evolved. Pangaea had dinosaurs, vast ecosystems and deserts (with OM-enriched dust floating over them). How important were bioaerosols in that world? Was it the same repertoire of forces that operate in a vineyard or a field of beans?
Where do the INA bugs call home now? If the 10^9 nuclei (active at -10 C) per gram of leaf litter in Canada and Russia, found by Russ Schnell and Gabor Vali, are INA bacteria then isn’t this their real home, and the IN protein is for water gathering or for freezing leaf litter and its decomposer community (freeze/thaw cycles stimulate decomposition in soil).
Tom Hill
tchill@unimelb.edu.au