Photosynthesis, chilling acclimation and the response of antioxidant enzymes to chilling stress in mulberry seedlings

This study investigates the effects of cold-acclimation in conferring chilling tolerance in seedlings of the mulberry (Morus alba) variety ‘Qiuyu’. Changes in photosynthesis and antioxidant enzymes in chilling acclimatized (CA), and non-acclimatized (NA) seedlings were recorded during chilling stress (3 °C) and a recovery period (25 °C) each for 3 days. The results showed that CA plants had higher net photosynthetic rates (Pn), stomatal conductance (Gs), and maximum photochemical efficiency of photosystem II (Fv/Fm) in response to chilling stress compared to NA. The seedlings maintained the same trends during the recovery stage. The responses of QA reduction degree \((1 - {\text{q}}_{\text{P}} )\) and prime electronic transfer rates (Fo) were lower in acclimatized than in non-acclimatized seedlings. Low-temperature acclimation and chilling stress also caused an increase in leaf proline and soluble sugar contents. Leaf malondialdehyde levels were significantly lower while ascorbate peroxidase (APX) activity was significantly higher in acclimatized seedlings, suggesting that elevated osmolytes and APX confer resistance to chilling temperatures. In this study on the response of mulberry seedlings to chilling stress, we also looked at the recovery process. The response to chilling determines whether mulberry leaves can survive under cold temperatures, while the recovery process determines whether photosynthesis can recover as soon as possible to avoid any secondary damage.