Is leaf age a predictor for cold tolerance in winter oilseed rape plants?

Area of Science:

• Plant Physiology
• Crop Science
• Biochemistry

Background:

• Low temperatures significantly impact crop physiology, affecting photosynthetic efficiency and leading to oxidative stress.
• Winter oilseed rape (Brassica napus L.) cultivars exhibit varying tolerance levels to cold, influenced by leaf age and endogenous defense mechanisms.

Purpose of the Study:

• To investigate the physiological and biochemical responses of two winter oilseed rape cultivars (Eurol and Hansen) to low temperatures, focusing on leaf age-dependent differences.
• To compare the cold tolerance mechanisms, including photosynthetic activity and antioxidant enzyme function, between young and mature leaves of different cultivars.

Main Methods:

• Measurements of chlorophyll fluorescence parameters (F0, Fm, Fv/Fm, 1-qp, NPQ) to assess photosynthetic activity under cold stress.
• Assays for antioxidant enzyme activities including superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR).
• Quantification of oxidative damage markers such as malondialdehyde (MDA), hydrogen peroxide (H2O2), and chlorophyll content.

Main Results:

• Low temperature decreased photosynthetic activity in both cultivars, but young Hansen leaves showed higher tolerance with better chlorophyll fluorescence parameters and increased antioxidant enzyme activities (SOD, APX, GR).
• Young Eurol leaves exhibited decreased APX and GR activity, leading to increased oxidative damage (MDA, H2O2), membrane damage, and reduced chlorophyll content.
• Mature leaves of both cultivars displayed similar antioxidant capacities and photosynthetic efficiency under cold stress, with Hansen showing higher tolerance attributed to increased SOD, APX, GR activities, and soluble sugar/proline accumulation.

Conclusions:

• Young leaves of the Hansen cultivar possess superior tolerance to low temperatures compared to Eurol, mediated by enhanced photosynthetic apparatus stability and a robust antioxidant defense system.
• The ascorbate-glutathione cycle plays a critical role in mitigating cold-induced oxidative stress, with its efficiency varying between cultivars and leaf ages.
• Understanding cultivar-specific and leaf age-dependent responses to cold stress is vital for developing more cold-hardy winter oilseed rape varieties.