Growth & Development

Tea buds are prepared for the cold by remembering past weather

Cold hardiness, acclimating and de-acclimating from cold temperatures can help plants prevent or reduce frost damage to their tissues. Through complex molecular networks, plants can improve their responses to repeated stresses (“remember”) and increase their cold hardiness. 

Drs Kensuke Kimura, Masaharu Kitano and colleagues from National Agriculture and Food Research Organization (NARO), Kyushu University and Kochi University, collected the buds of two tea cultivars for a decade and compared frost damage on them. The researchers created a mathematical model to compare cold stress memory of the two cultivars and suggest that the later sprouting cultivar is relatively more sensitive to recent cold stress. Drs Kensuke Kimura and Masaharu Kitano recently revealed that the air temperature and leaf photosynthetic rate of strawberries greatly vary within a large greenhouse. 

For a decade, researchers collected 15 tea buds from two tea cultivars that sprout at different times of the year. The buds of the early sprouting cultivar (Yutakamidori) were frozen from 0°C to -1, -2 and -3°C by decreasing the temperature 1°C per hour. The buds of the later sprouting cultivar (Yabukita) were frozen at the same rate down to -14, -15 and -16°C. After three hours at the target temperature, the buds were warmed up and the scientists evaluated how much tissue was damaged (e.g. discoloured).

Flower of the tea plant, Camellia sinensis. Source: Canva

Based on the percentage of dead tissues, lethal temperatures of 10% of the samples, the researchers estimated cold hardiness, cold stress memory and the deacclimation rate in response to warm temperatures for the two cultivars. The scientists modelled the cold hardiness based on daily temperatures of the experimental tea fields.

Modelling cold stress memory in tea buds. After the buds experience the first cold stress (t=1) that is below a threshold temperature, the memory depends on the length and severity of cold stress as represented by the forgetting curves. Source: Kimura et al. 2020

Modelling showed that Yabukita, the later sprouting cultivar, is relatively more sensitive to recent cold stress and deacclimate slower than Yutakamidori. The model was overall highly accurate for both cultivars but it is relatively less accurate after the acclimation period (winter to spring) as the daily temperatures varied greatly. 

“[W]e believe that this first attempt to develop a cold hardiness model, using the concept of plant stress memory, will contribute to more accurate predictions of cold acclimation and deacclimation in future warming climates,” Kimura, Kitano and colleagues wrote. 

“To develop a more reliable process based model that considers the stress memories, we must experimentally understand how plants memorize long temperature exposures and at what point in the memory it is more effective for cold acclimation and deacclimation.”

Frost damage to tea plants resulted in losses of over $300 million for Chinese and Japanese producers in 2010 alone. This model based on controlled freezing tests enabled scientists to compare the cold hardiness of two tea plants and could inform tea growers which cultivar to grow at different locations.

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