Short versus prolonged freezing differentially impacts freeze – thaw injury in spinach leaves: mechanistic insights through metabolite profiling

Abstract

Plant tissues subjected to short or prolonged freezing to a fixed sub-freezing temperature are expected to undergo similar freeze-desiccation but the former causes substantially less injury than the latter. To gain metabolic insight into this differential response, metabolome changes in spinach (Spinacia oleracea L.) leaves were determined following short-term (0.5 and 3.0 h) vs. prolonged freezing (5.5 and 10.5 h) at −4.5 ∘ C resulting in reversible or irreversible injury, respectively. LD 50 , the freezing duration causing 50% injury, was estimated to be ∼3.1 h and defined as the threshold beyond which tissues were irreversibly injured. From 39 identified metabolites, 19 were selected and clustered into 3 groups: (1) signaling-related (salicylic acid, aliphatic and aromatic amino acids), (2) injury-related (GABA, lactic acid, maltose, fatty acids, policosanols, TCA intermediates) and (3) recovery-related (ascorbic acid, -tocopherol). Initial accumulation of salicylic acid during short-term freezing followed by a decline may be involved in triggering tolerance mechanisms in moderately injured tissues, while its resurgence during prolonged freezing may signal programmed cell death. GABA accumulated with increasing freezing duration, possibly to serve as a 'pH-stat' against cytoplasmic acidification resulting from lactic acid accumulation. Mitochondria seem to be more sensitive to prolonged freezing than chloroplasts since TCA intermediates decreased after LD 50 while salicylic acid and maltose, produced in chloroplasts, accumulate even at 10.5-h freezing. Fatty acids and policosanols accumulation with increasing freezing duration indicates greater injury to membrane lipids and epicuticular waxes. Ascorbic acid and -tocopherol accumulated after short-term freezing, supposedly facilitating recovery while their levels decreased in irreversibly injured tissues.

Impact of Plasma-Activated Water Treatment on Quality and Shelf-Life of Fresh Spinach Leaves Evaluated by Comprehensive Metabolomic Analysis

“…Metabolites identified in all treatment groups with changing intensities from D1 to D8 included amino acids, carboxylic and sugar acids and nucleosides. These changes corresponded to some previously reported differences in metabolite occurrences that were associated with storage conditions and leaf senescence [ 32 , 33 ]. Senescence in plants is a transformational phase, where plant cells undergo complex changes in gene expression, metabolism and structure [ 11 ].…”

“…The latter functions are of special relevance for cell maintenance in the early phase of senescence and could contribute to the upregulation of other mechanisms of cell protection. It was shown, e.g., that polyphenolic derivatives of aromatic amino acids help to preserve the nutritional quality of stored fruits by increasing injury-related organic acids, including malate and succinate, and antioxidants such as ascorbate [ 32 , 39 , 40 , 41 ]. Interestingly, we observed the prevalence of the same metabolites in the spinach leaves at D8.…”

The Effects of Biostimulants, Biofertilizers and Water-Stress on Nutritional Value and Chemical Composition of Two Spinach Genotypes (Spinacia oleracea L.)

“…Although α-tocopherol has been already reported in spinach leaves [51,52], to the best of our knowledge, the effect of biostimulants application on tocopherols content in spinach plants and leafy vegetables in general has not been previously assessed. Moreover, the overall increase of αand total tocopherols under water-holding conditions is associated with the plant defense mechanisms against abiotic stressors [53,54] and stress recovery processes [55]. On the other hand, Ca supplementation may also up-regulate the content of non-enzymatic antioxidants such as tocopherols [56,57], while nitrogen containing-compounds such as amino acids and tocopherols were associated with the increased efficiency of sunflowers against drought stress [58].…”

Dendrobium Multi-Omics Reveal Lipid Remodeling in Response to Freezing

“…Freezing stress can lead to serious reductions in agricultural yields. Some economic crops are naturally adapted to low temperatures but not sub-zero temperatures, including apples, tea, pepper, spinach, and cucumber [1][2][3][4][5]. Membranes are major injury sites in plants during periods of freezing because low temperature decreases their fluidity [6].…”