TITLE:
Qualitative Assessment of Postharvest Stomata and Chloroplast Degradation in Contrasting Abscission Resistant Balsam Fir (Abies balsamea (L.) Mill.)
AUTHORS:
Gaye MacDonald, Rajasekaran R. Lada, C. D. Caldwell, Chibuike C. Udenigwe, Mason T. Maconald
KEYWORDS:
Abies balsamea, Balsam Fir, Christmas Tree, Fluorescence, Needle Abscission Resistance, Scanning Electron, Transmission Electron
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.14 No.9,
September
26,
2023
ABSTRACT: Balsam fir is an important Christmas tree species, especially in eastern
Canada. The natural Christmas tree industry faces a challenge in postharvest
needle abscission. Though there have been many studies describing the physiological
triggers and consequences in postharvest balsam fir, there have been no studies
describing morphological or ultrastructural changes. Therefore, the objective
of this study was to examine changes in stomata and chloroplast of postharvest
needles. Branches were collected from low and high needle abscission resistance
balsam fir genotypes, placed in water, and displayed in typical household
conditions for 11 weeks. Needle abscission, chlorophyll fluorescence, and water
uptake were monitored throughout. Needles stomata and chloroplasts were
examined under a scanning and transmission electron microscope, respectively,
each week. All branches had increased abscission, decreased chlorophyll
fluorescence, and decreased water uptake over time. Needle surfaces accumulated
fungal hyphae, especially in stomata. Chloroplasts demonstrated some
dysfunction within two weeks, with notable decreases in chloroplast starch and
increases in plastoglobulins. Within several weeks thylakoid membranes had been
dismantled as chloroplasts transformed into gerontoplasts. All biophysical and
structural changes were more pronounced in low needle abscission resistant
genotypes. This research identifies a potential role for needle fungi in
postharvest needle abscission and confirms the postharvest senescence of
chloroplasts. Though it was previously speculated that chloroplasts must
senesce postharvest, this study identifies how quickly this process occurs and
that it occurs at different rates in contrasting genotypes.