Qualitative Assessment of Postharvest Stomata and Chloroplast Degradation in Contrasting Abscission Resistant Balsam Fir (Abies balsamea (L.) Mill.)

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.

Advancement in Indoor Vertical Farming for Microgreen Production

With the growing global urban population and the emergence of megacities, there is a huge demand for arable land to meet the food demand and reduce malnutrition. Conventional agricultural practices lead to deforestation of the land for crop production and agricultural intensification to produce higher yield per unit area. These activities have been established to have negative impact on the environment thereby causing soil and water pollution. It is important to consider the use of vertical farming technology, which utilizes both horizontal and vertical space, and efficiently uses nutrients, water, and time (off season production with artificial lighting) more effectively to produce higher yield per unit volume of space than the conventional outdoor farming. Microgreens are taken into consideration to be grown under innovative vertical farming technology since they are rich in phytonutrients and they can be harvested in a short period of time. This paper reviews the current growing conditions of microgreens in vertical farming such as crop selection, media, light, nutrient solution, and containers while identifying knowledge gaps. Further, study in this area may lead to improved growing conditions to help solve the global issues and challenges surrounding food security, safety, and resource optimization.

Mechanical Shaking and Baling of Balsam Fir Trees Influence Postharvest Needle Senescence and Abscission

This study investigated the influence of both shaking duration and number of trees per bale on postharvest needle characteristics such as percentage needle loss, needle retention duration and explored the physiological roles of endogenous ethylene and volatile terpene compounds (VTCs). To accomplish these objectives, 25 six-year-old trees were detached and exposed to a range of shaking durations (0 to 60 sec.), and 30 six-year-old detached trees were exposed to baling treatments from 0 to 5 trees. Response variables measured were percent needle loss, needle retention duration, average water use, ethylene and volatile terpene compound evolution. Trees shaken for 60 seconds lost 16% less needle compared to control, which was consistent with the decrease in percent needle loss with increasing shaking duration. Baled trees lost 13% more needles compared to control, but percent needle loss was observed to decrease with increasing number of trees in a bale. These trends corresponded with increasing ethylene and VTC evolutions, where the longer the shaking duration or larger number of trees in a bale, the higher the ethylene and VTC evolutions. One can therefore draw inference that mechanical perturbation as a result of shaking and baling induce biosynthesis and regulation of ethylene and VTC in balsam fir trees in an effort to regulate postharvest needle abscission.

Potential Roles of Fatty Acids and Lipids in Postharvest Needle Abscission Physiology

Our understanding of postharvest needle abscission physiology in conifers has greatly improved in the last decade. Abscission is initially triggered by root detachment, which begins a cascade of changes such as decreased water uptake, water potential, and auxins and increased membrane injury, ethylene, abscisic acid, volatile terpenes, and catalytic enzymes. Needle abscission is also affected by environmental factors. For example, a period of cold acclimation generally delays postharvest abscission. The aforementioned pieces of evidence, along with previous studies, strongly points to a role for plant lipids and fatty acids. Studies from other species have pointed out key roles in abscission and stress responses for a variety of phospholipids and galactolipids, which has not been studied in balsam fir. It is imperative to have an understanding of the role of plant lipids and fatty acids to further our overall understanding of the physiological mechanisms of postharvest abscission and needle abscission resistance. This review is an overview of membrane lipids and fatty acids, changes that occur postharvest and the interaction that lipids may have in the phenomenon of postharvest abscission.