Foliar calcium application alleviates cold stress-induced photosynthetic inhibition in peanut

  Objectives  Chilling damage in early spring is one of the main environmental limiting factors in peanut production in northern China. Calcium has been proven to enhance chilling tolerance and photosynthetic carbon fixation in peanut, hence, we investigated the regulatory mechanisms underlying the alleviation effect of exogenous Ca to low temperature stress in peanut.

  Methods  Peanut cultivar ‘Xiaobaisha’ was used as the experimental material in the study conducted in an artificial climate chamber. The control room temperature was 20°C/28°C (night/day) with foliar spraying of ultrapure water. The low temperature stress was set as 9°C/15°C, with foliar spraying of ultrapure water (+H₂O), 15 mmol/L CaCl₂ (+Ca), or 5 mmol/L ethylene glycol tetraacetic acid (+EGTA). At one week of true leaf expansion, the peanut seedlings were grown in the vessels and foliar spray was treated for two consecutive days, then treated under low temperature stress for 7 days, followed by normal temperature for 7 days. The plant growth, photochemical activity, non-structural carbohydrates and reactive oxygen species accumulation were measured.

  Results  Low temperature stress inhibited peanut growth, leading to excessive accumulation of non-structural carbohydrates and reactive oxygen species (ROS) in peanut leaves. The low temperature stress also caused severe photo-damage such as significant increments of regulated-energy dissipation Y(NPQ) and unregulated energy dissipation Y(NO), and decrements of the unregulated energy dissipation of PSI Y(I) and PSII Y(II). Exogenous Ca²⁺ enhanced plant height, leaf area and relative chlorophyll concentration of peanut seedlings, and also significantly alleviated low temperature-induced photodamage, reduced excessive accumulation of non-structural carbohydrates in leaves, and enhanced photosynthesis in peanut. Further, exogenous Ca²⁺ reduced the excessive accumulation of ROS and protected photosynthetic apparatus effectively.

  Conclusions  During low temperature stress and normal temperature recovery, exogenous Ca²⁺ can alleviate chilling-induced photo-inhibition by effectively stimulating peanut growth and photochemical activities, maintaining non-structural carbohydrates efflux, and reducing excessive accumulation of non-structural carbohydrates and ROS.