Heterosis in the freezing tolerance, and sugar and flavonoid contents of crosses between Arabidopsis thaliana accessions of widely varying freezing tolerance

Heterosis is defined as the increased vigour of hybrids in comparison to their parents. We investigated 24 F1 hybrid lines of Arabidopsis thaliana generated by reciprocally crossing either C24 or Col with six other parental accessions (Can, Co, Cvi, Ler, Rsch, Te) that differ widely in their freezing tolerance. The crosses differed in the degree of heterosis for freezing tolerance, both in the non-acclimated state and after a 14 d cold acclimation period. Crosses with C24 showed more heterosis than crosses with Col, and heterosis was stronger in acclimated than in non-acclimated plants. Leaf content of soluble sugars and proline showed more deviation from mid-parent values in crosses involving C24 than in those involving Col, and deviations were larger in acclimated than in non-acclimated plants. There were significant correlations between the content of different sugars and leaf freezing tolerance, as well as between heterosis effects in freezing tolerance and sugar content. Flavonoid content and composition varied between accessions, and between non-acclimated and acclimated plants. In the crosses, large deviations from the mid-parent values in the contents of different flavonols occurred, and there were strikingly strong correlations between both flavonol content and freezing tolerance, and between heterosis effects in freezing tolerance and flavonol content

Extreme sensitivity of biological function to temperature in Antarctic marine species

1. Biological capacities to respond to changing environments dictate success or failure of populations and species over time. The major environmental feature in this context is often temperature, and organisms across the planet vary widely in their capacity to cope with temperature variation. With very few exceptions, Antarctic marine species are more sensitive to temperature variation than marine groups elsewhere, having survivable temperature envelopes between 5degreesC and 12degreesC above the minimum sea temperature of -2degreesC. 2. Our findings show that in biological functions important to long-term survival these animals are even more tightly constrained. The Antarctic bivalve mollusc Laternula elliptica and limpet Nacella concinna both survive a few days in experiments at 9-10degreesC, but suffer 50% failure in essential biological activities at 2-3degreesC and complete loss at 5degreesC. The Antarctic scallop Adamussium colbecki is even more sensitive, and loses the ability to swim as temperature approaches 2degreesC. 3. These failures of activity are caused by a loss of aerobic capacity, and the animals investigated are so sensitive that a 2degreesC rise in sea temperature could cause population or species removal from the Southern Ocean