Regulation of NO-Generating System Activity in Cucumber Root Response to Cold.

Area of Science:

• Plant Physiology
• Environmental Stress Response
• Biochemistry

Background:

• Nitric oxide (NO) is a crucial signaling molecule in plant adaptation to environmental changes.
• Low temperatures (LTs) trigger increased NO levels in plants, but the underlying production pathways remain unclear.
• Understanding NO generation mechanisms under cold stress is vital for plant resilience.

Purpose of the Study:

• To investigate the specific roles of different nitric oxide (NO) sources in cucumber roots under short-term (1 day) and long-term (6 days) cold stress (10 °C).
• To elucidate the contribution of nitrate reductase (NR) and nitric oxide synthase (NOS)-like activities to NO production during cold acclimation.

Main Methods:

• Cucumber seedlings were exposed to 10 °C for 1 and 6 days.
• Assessed plasma membrane-bound NR (PM-NR) and cytoplasmic NR (cNR) activities.
• Measured nitrite reductase (NiR) activity and NO2-/NO3- ratio.
• Quantified nitric oxide synthase (NOS)-like activity.
• Analyzed the expression of NR (CsNR1-3) and ARC (CsARC) genes.

Main Results:

• Short-term LT (1 day) increased PM-NR activity and CsNR1-3 gene expression.
• Long-term LT (6 days) elevated cNR activity and induced CsARC gene expression.
• A decreased NiR activity and higher NO2-/NO3- ratio under short-term LT suggested NR-dependent NO production.
• NOS-like activity significantly increased, particularly under long-term LT.

Conclusions:

• Cucumber roots activate diverse NO-producing pathways, including NR-dependent and NOS-like routes, in response to cold stress.
• The contribution of different NO sources varies with the duration of cold exposure.
• These findings highlight the complex role of NO in plant cold acclimation.