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内容記述 |
As an effect of global warming, it is a great concern that many crops are facing a change in progress in their suitable locations for growth. In recent years, Japan has experienced high temperatures in the fall (i.e. hot fall), with many regions recording record highs in 2024. A report showed that an extended fruit growth period due to the hot fall changes the acid content and sugar concentration of apple fruits, leading to poor coloration and a decline in overall quality. Then, this matter force farmers to improve their cultivation management. To understand how hot fall affects carbon dynamics in apple trees could be an important clue to solving this matter. Using positron-emitting tracer imaging system (PETIS) to visualize translocation under environmental changes, we examined temperature-responsive carbon dynamics in apple tree.We used 80 cm tall, two-year-old apple plantlets (Malus pumila), pollinated in May and grown in a greenhouse at 28-30°C until October. Under these cultivation conditions, the apple trees not only bear fruit but also continue to develop new leaves. The plantlets were transferred to a chamber with PETIS, and temporarily exposed to 20°C for 2, 6, or 10 days before returning to 30°C, simulating short-term cooling in hot fall. After completing exposure at 20°C for a period of time and just after the shifted back to 30°C, Carbon-11 (¹¹C) gas was applied to newly developed leaves and the ¹¹C transports to branch and fruits were monitored for approximately 3 hours in each.As a result, 11C translocation from leaves to branches was observed after 2 days of 20°C-exposure, and it decreased after 6 days and further declined after 10 days. This suggests that the 6 to 10 days 20°C-exposure may have been gradually perceived as low-temperature stress, or prioritized carbon allocation to newly developed leaves, which 11C was applied. Next, we confirmed that ¹¹C translocation was reactivated under all exposure terms when the plantlets were shifted from each 20°C-exposure period back to 30°C. However, longer 20°C exposure required more time for translocation activity to resume. A similar trend was observed in fruits. Although an unknown mechanism induced by low-temperature stress would be inactivated upon shifting back to 30°C, the time required for inactivation may depend on the intensity of the induction. Additionally, some fruits did not show an obvious signal. This was thought to be due to unidentified selectivity in translocation to individual fruits, which may not have been detected during the PETIS imaging. Finally, we analyzed the changes in transport velocity when the temperature shifted from 20°C to 30°C. In the 2 days 20°C-exposure, transport velocity slightly increased, whereas after 6 days, a stronger increase was observed. However, transport velocity did not change within 3 hours of the experimental time after 10 days exposure to 20°C. All these results showed that carbon translocation was not only reactivated but also enhanced transport activity when shifted to 30°C. These results conclude that prolonged high-temperature exposure acclimatizes apples to warm environment and returning them to the 20°C in which they were once grown in Japan unexpectedly reduces transport activity. Although strict observations are required, these findings might contribute to optimizing the temperature control strategies against global warming. |
