Freezing Tolerance Of Spinach Research Articles

Pre-stress salicylic-acid treatment as an intervention strategy for freeze-protection in spinach: Foliar versus sub-irrigation application and duration of efficacy

Exogenous application of salicylic acid (SA) to plant tissues has been shown to confer tolerance against various abiotic stresses. Recently, SA application through sub-irrigation was shown to improve plant freezing tolerance (FT). For SA treatment to be employable as an effective intervention strategy for frost protection under field conditions, it is important to study its effect on FT when applied as a foliar spray to whole plants. It is also important to determine for how long the FT-improvement by SA lasts. Present study was conducted to compare SA-induced FT of spinach (Spinacia oleracea L. ‘Reflect’) seedlings following SA-application by foliar spray vs. sub-irrigation. Durability of FT-promotive effect of SA was evaluated using three freeze-tests over a 4-d period, i.e., at 10-d, 12-d, and 14-d after the SA application. Freezing stress was applied using a temperature-controlled freeze-thaw protocol, and FT was assessed by visual observations (leaf flaccidness vs. turgidity) as well as ion-leakage assay. Data indicated that both foliar spray and sub-irrigation methods improved FT of the seedlings against a relatively moderate (−5.5 °C) as well as severe stress (−6.5 °C). Moreover, improved FT against moderate stress was sustained over a 4-d period, whereas such benefit waned somewhat against the severe stress. SA-treated leaves' growth performance was similar to the non-treated control based on dry weight, fresh weight, leaf area, and dry weight/leaf area parameters. Our results suggest that SA application as a foliar spray can potentially be used to protect field-grown transplants against episodic frosts.

A metabolomics study of ascorbic acid-induced in situ freezing tolerance in spinach (Spinacia oleracea L.).

Freeze–thaw stress is one of the major environmental constraints that limit plant growth and reduce productivity and quality. Plants exhibit a variety of cellular dysfunctions following freeze–thaw stress, including accumulation of reactive oxygen species (ROS). This means that enhancement of antioxidant capacity by exogenous application of antioxidants could potentially be one of the strategies for improving freezing tolerance (FT) of plants. Exogenous application of ascorbic acid (AsA), as an antioxidant, has been shown to improve plant tolerance against abiotic stresses but its effect on FT has not been investigated. We evaluated the effect of AsA‐feeding on FT of spinach (Spinacia oleracea L.) at whole plant and excised‐leaf level, and conducted metabolite profiling of leaves before and after AsA treatment to explore metabolic explanation for change in FT. AsA application did not impede leaf growth, instead slightly promoted it. Temperature‐controlled freeze–thaw tests revealed AsA‐fed plants were more freezing tolerant as indicated by: (a) less visual damage/mortality; (b) lower ion leakage; and (c) less oxidative injury, lower abundance of free radicals (O2·- and H2O2). Comparative leaf metabolite profiling revealed clear separation of metabolic phenotypes for control versus AsA‐fed leaves. Specifically, AsA‐fed leaves had greater abundance of antioxidants (AsA, glutathione, alpha‐ & gamma‐tocopherol) and compatible solutes (proline, galactinol, and myo‐inositol). AsA‐fed leaves also had higher activity of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, and catalase). These changes, together, may improve FT via alleviating freeze‐induced oxidative stress as well as protecting membranes from freeze desiccation. Additionally, improved FT by AsA‐feeding may potentially include enhanced cell wall/lignin augmentation and bolstered secondary metabolism as indicated by diminished level of phenylalanine and increased abundance of branched amino acids, respectively.

Salicylic acid-induced freezing tolerance in spinach (Spinacia oleracea L.) leaves explored through metabolite profiling

Freezing tolerance and metabolome changes were investigated for spinach (Spinacia oleracea L. ‘Reflect’) seedlings treated with 0.5 mM salicylic acid by sub-fertigation. Experiments included seedlings treated with salicylic acid at both the ambient (non-acclimation; NA) and cold acclimation (CA) temperatures, i.e. NASA and CASA. Except for slight reduction in the leaf size, salicylic acid-fed plants exhibited, in general, similar growth performance as non-treated controls based on the dry weight/fresh weight ratio, percent water content, and dry weight/leaf area. Temperature-controlled in situ freeze-thaw of seedlings revealed NASA plants were more freeze-tolerant (visual estimates and ion-leakage test) and had higher salicylic acid content than NA control. Metabolite profiling revealed NASA had higher trehalose, ascorbic acid, γ-tocopherol, proline, and leucine, whereas lower mannose and aconitic acid than NA tissues. Excised leaf freeze-thaw tests revealed CASA leaves to be the most freeze-tolerant of the four conditions followed, respectively, by CA, NASA, and NA. Principal component analysis distinctly separated metabolic phenotypes for NA, NASA, CA, and CASA, indicating salicylic acid differentially affected metabolism at warm vs. cold. CASA leaves had higher compatible solutes (osmolytes), antioxidants, and salicylic acid than CA control. Our data suggests that altered accumulation of trehalose, ascorbic acid, and aconitic acid was a salicylic acid-specific response. Additionally, 7 metabolites (5-oxoproline, fructose, glucose, maltose, proline, sucrose, and tartaric acid) were quantitatively associated with the freezing tolerance levels across four conditions.

Exogenous salicylic acid improves freezing tolerance of spinach (Spinacia oleracea L.) leaves

Salicylic acid (SA)-treatment has been reported to improve plant tolerance to various abiotic stresses. However, its effect on freezing tolerance has not been well investigated. We investigated the effect of exogenous SA on freezing tolerance of spinach (Spinacia oleracea L.) leaves. We also explored if nitric oxide (NO) and/or hydrogen peroxide (H2O2)-mediation was involved in this response, since these are known as primary signaling molecules involved in many physiological processes. A micro-centrifuge tube-based system used to apply SA to petiolate spinach leaves (0.5 mM over 4-d) was effective, as evident by SA content of leaf tissues. SA-treatment did not hamper leaf growth (fresh and dry weight; equatorial and longitudinal length) and was also not significantly different from 25% Hoagland controls vis-à-vis growth. SA application significantly improved freezing tolerance as evidenced by reduced ion-leakage and alleviated oxidative stress (lower accumulation of O2·- and H2O2) following freeze-thaw stress treatments (−6.5, −7.5, and −8.5 °C). Improved freezing tolerance of SA-treated leaves was paralleled by increased proline and ascorbic acid (AsA) accumulation. A 9-d cold acclimation (CA) treatment also improved leaf freezing tolerance (compared to non-acclimated control) and was accompanied by accumulation of SA and proline. Our results indicate that increased freezing tolerance may be associated with accumulation of compatible solutes (proline) and antioxidants (AsA). Notably, the beneficial effect of SA on freezing tolerance was abolished when either H2O2- or NO-scavenger (1 μM N-acetylneuraminic acid, NANA or 100 μM hemoglobin, HB, respectively) was added to SA as pretreatment. Our data suggest that SA-induced freezing tolerance in spinach may be mediated by NO and H2O2 signaling.

無加温パイプハウス栽培におけるホウレンソウとコマツナの秋から早春にかけての耐凍性の変化

The relationships between freezing tolerance of spinach (Spinacia oleracea L.) and komatsuna (Brassica campestris L.) plants and air temperature, water content, and sugar concentration were investigated in an unheated greenhouses from autumn to early spring in 1996-99. Freezing tolerance was expressed as the temperature at which 15% (TEL15) or 50% (TEL50) of electrolyte leakage from leaf blade tissues occurred. The TEL15 and TEL50 of spinach and komatsuna decreased gradually from October to January. In the coldest season, the TEL15 and TEL50 were decreased to -12--16°C and -13--18°C in spinach, and -12--14°C and -13--17°C in komatsuna, respectively. From mid-February, the TEL15 and TEL50 of spinach and komatsuna increased with a rise of air temperature. There was a high correlation between the freezing tolerance and the mean minimum air temperatures for 7 days before the measurement were made. The freezing tolerance of spinach and komatsuna increased only slightly when the mean minimum air temperature was between 8 and 2°C, but increased considerably when the temperature decreased below 2°C. The changes in the freezing tolerance of spinach and komatsuna also correlated with leaf water content. The freezing tolerance increased as the leaf sugar content increased from 10 to 20 mg·g-1 FW in spinach and from 10 to 35 mg·g-1 FW in komatsuna. Further increases in sugar content had no effect on freezing tolerance in both species.

Heat-Stable COR (<underline>Co</underline>ld-<underline>R</underline>egulated) Proteins Associated with Freezing Tolerance in Spinach

Heat-Stable COR (<underline>Co</underline>ld-<underline>R</underline>egulated) Proteins Associated with Freezing Tolerance in Spinach