THE NATURE AND DYNAMICS OF CHANGES IN LIPIDS AND FATTY ACIDS DURING POSTHARVEST NEEDLE ABSCISSION, THEIR ROLE IN COLD ACCLIMATION, ULTRA-STRUCTURAL CHANGES, AND NEEDLE ABSCISSION RESISTANCE IN BALSAM FIR, ABIES BALSAMEA, L.
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Balsam fir is an important species of Atlantic Canada’s Christmas tree and greenery industries that is suffering due to excessive needle loss postharvest. A series of investigations were carried out to: (i) characterize and establish links between polar lipid and fatty acids (FA) and postharvest needle loss; (ii) uncover the differences in the nature and quantity of polar lipid and fatty acids in contrasting genotypes with high and low needle retention duration (NRD); (iii) explore temporal changes in polar lipids and fatty acids; (iv) establish the genotypic differences in polar lipids and FA during temporal changes, and (v) confirm the ultrastructural changes of cells of balsam fir postharvest using scanning and transmission electron microscopy. Polar lipids decreased significantly postharvest in all studies (p < 0.001). The mean percentage of monogalactosyldiacylglycerol (MGDG) decreased significantly postharvest (p < 0.0001), caused mostly by a decrease in MGDG 36:6 and 36:7. There was also a significant decrease in the MGDG: DGDG (digalactosyldiacylglycerol) ratio in all studies (p < 0.05), earlier in the poorer needle retaining clone. During cold acclimation, Clone 506 was identified as a high needle abscission resistant (NAR) clone, while Clones 9, 37, and 566 all proved to be lower. MGDG decreased during the fall and early winter in all clones, with a subsequent increase in DGDG and a significant decrease in the MGDG: DGDG ratio in all clones tested (p < 0.001). There was a significant decrease also in the GL: PL ratio (p < 0.001). There was significantly less DGDG in Clone 506 than in Clone 9 (p < 0.05). LPG 16:1 was eight times higher in Clone 506. In balsam fir, there was a significant reduction (p < 0.001) in α – linolenic acid in all clones postharvest. During cold acclimation, there was an increase in α – linolenic acid in one of the lower clones, Clone 566, but an increase in Δ5-UPIFA, 18:3 (pinolenic acid) in the other clones, suggesting different metabolism (p < 0.001). Chloroplast disorganization was confirmed. In addition, most of all stoma were closed in both clones, however, there was more fungal hyphae associated with the poorer NRD clone.