Operators should take a closer look at likely survivability given current field experience from other similar arrays. For low sloped roof and ground array types, operators can utilize guidance produced by the Structural Engineers Society of California to examine the integrity of existing structures. Though intended to be used for new systems, operators can use the guidance to identify weaknesses and then engineer a retrofit. System operators have been confronted with solar arrays vulnerable to even minor and routine wind forces, indicating a design or installation flaw more than a severe weather vulnerability. Post-storm inspections of solar arrays have found significant damage from routine thunderstorms that had wind speeds of 70 mph or less. In one example, lab inspectors found a ground array in Prescott, Arizona completely destroyed due to fastener and racking weaknesses. A weather station located within feet of the array recorded 70 mph winds from a summer monsoon storm that caused the damage. Cannabis sativa L. belongs to the Cannabaceae family that contains the genera Cannabis and Humulus , as well as eight genera that were previously classified as Celtidaceae. 1 In the formal botanical nomenclature of C. sativa, this single species of the Cannabis genus contains two subspecies, each with two varieties. These include C. sativa subsp. sativa var. sativa, C. sativa subsp. sativa var. spontanea, C. sativa subsp. indica var. indica, and C. sativa subsp. indica var. kafiristanica. Aside from the botanical classification, drying room it has been proposed that, instead of the commonly used designations of “cultivars” and “strains”, C. sativa should be categorized as chemovars according to the chemical profiles of phytocannabinoids and terpenes in flowers. 

Among the chemicals produced in C. sativa, two phytocannabinoids, the psychoactive compound Δ9 -tetrahydocannabinol and the medicinally important, but nonpsychoactive, compound cannabidiol , have been intensively studied for their structures, biosynthesis, and biological activities. Additional phytocannabinoids, and other classes of plant chemicals, such as terpenes, flavonoids, and alkaloids, have also been identified in C. sativa. These other plant chemicals exert synergistic effects to enhance the bio-activities of phytocannabinoids, known as “the entourage effect”. However, the underlying mechanisms of the entourage effect are not well understood. As such, studies on non-phytocannabinoid compounds, such as terpenes and flavonoids, are valuable for developing therapeutics in C. sativa. More than 20 flavonoids have been identified in C. sativa, most of which are flavone and flavonol aglycones and glycosides. Interestingly, three prenylated/geranylated flavones, cannflavin A, B, and C, were isolated in C. sativa . It is worth noting that, although cannflavins are often referred to as flavonoids unique to C. sativa, cannflavin A has also been identified in Mimulus bigelovii, a plant in the Phrymaceae family. Since biosynthesis of the core flavonoid skeleton in plants and bio-activities of the common flavones and flavonols have been widely studied and reported, this mini-review will focus on the biosynthesis and bio-activities of the relatively unique cannflavins as well as the applications of C. sativa flavonoids.The phenylpropanoid and flavonoid biosynthetic pathways build the core skeletons of flavonoids in C. sativa . Genes encoding two enzymes in the phenylpropanoid biosynthetic pathway, phenylalanine ammonia-lyase and p-coumaroyl: CoA ligase , were isolated in C. sativa var. Futura by searching expressed sequence tags using homologous PAL and 4CL sequences from other plants. 

Conversion of p-coumaroyl CoA to luteolin encompasses condensation with three molecules of malonyl CoA to form naringenin chalcone by chalcone synthase ,ring closure of naringenin chalcone to generate naringenin by chalcone isomerase , formation of apigenin from naringenin by flavone synthase , and 3-hydroxylation of apigenin to derive luteolin by flavonoid 3′-hydroxylase . Based on their chemical structures, cannflavin A and B could be derived from luteolin through transferring a methyl group to the 3′-O position by a methyltransferase activity as well as a geranyl group or a prenyl/ dimethylallyl group to the C6-position by a prenyltransferase activity . Candidate methyltransferases and prenyltransferases responsible for these reactions were identified from a draft C. sativa genome assembly based on sequence homology to previously characterized enzymes and phylogenetic analysis. Upon functional characterization using purified recombinant proteins, it was shown that a regiospecific O-methyltransferase methylates the 3′-O position of luteolin and forms chrysoeriol, and a prenyltransferase adds a geranyl or a prenyl group to chrysoeriol and produces cannflavin A and B. However, the function of CsOMT21 and CsPT3 in cannflavin biosynthesis has not been demonstrated in a plant system. To date, flavonoid identification in C. sativa has focused on plants that are grown under non-stressed conditions. While flavonoids are present in most tissues studied in C. sativa, including seedlings, leaves, flowers, and fruits, they are undetectable in roots and seeds. In addition to the tissue specific distribution, flavonoid profiles were also shown to vary in bracts during plant development. As many flavonoids possess protective functions for plants, their production is responsive to environmental factors, which is also observed in C. sativa. For example, cannflavin A accumulation is determined not only by the genetic background, but as a response to temperature, solar radiation, rainfall, and humidity in the environment. 

Moreover, higher elevation positively impacts the content of cannflavin A, B, and C in cloned C. sativa plants grown at different altitudes. With these observations taken into consideration, it is tempting to postulate that, aside from the flavonoids that have already been isolated in C. sativa tissues, some yet unidentified flavonoids may only be produced under specific environmental conditions, such as biotic and abiotic stresses. It is also possible that certain flavonoids only accumulate in significant quantities in specific C. sativa chemovars, such as cannflavin C that was isolated and identified from a high THC chemovar. As such, unraveling the identity of additional flavonoids, particularly those unique to C. sativa, will facilitate a comprehensive understanding of the biosynthesis and functions of flavonoids in this important plant.Besides the antioxidative effects that cannflavins share with many other flavonoids, a relatively well-studied bio-activity for cannflavins is their anti-inflammatory properties. An intriguing observation was first reported in 1981, showing that compounds present in a phytocannabinoid-free extract of C. sativa leaves could be involved in the production or release of prostaglandin E2 in mice. Further work showed that cannflavins in ethanolic extracts of C. sativa leaves inhibited 12-O-tetradecanoylphorbol-13-acetate – induced PGE2 production in cultured human rheumatoid synovial cells. Chemical structures of cannflavin A and B were subsequently solved using nuclear magnetic resonance and demonstrated to be prenylated/geranylated flavones. More recently, it was shown in in vitro enzyme assays that cannflavin A and B exert anti-inflammatory activities by inhibiting the microsomal PGE2 synthase-1 and the 5- lipoxygenase activities, leading to reduced PGE2 and leukotriene production, respectively. Cannflavin A and B show promise as an anti-inflammatory therapeutic agent because they were about 30 times more effective than aspirin in inhibiting PGE2 release when assayed in human rheumatoid cells. An additional advantage is that cannflavin A only weakly inhibits cyclooxygenases COX-1 and COX-2, and therefore can circumvent the adverse side effects exhibited by COX inhibitors , such as gastrointestinal erosion. The neuroprotective role of cannflavin A was explored in neuronal PC12 cells. At 10 μM or lower concentrations, cannflavin A enhanced the viability of neuronal PC12 cells against amyloid β -induced cytotoxicity by reducing Aβ1−42 aggregation and fibril formation. Anticancer activities were reported for a synthetic 8-prenylated isomer of cannflavin B, isocannflavin B . Isocann- flavin B suppressed the proliferation of estrogen-dependent T47-D human breast cancer cells through a G0/G1 cell cycle arrest. It also increased apoptosis in two pancreatic cancer cell lines Panc-02 and Ptf1/p48-Cre . Treatment with isocannflavin B caused a delay in both local and metastatic tumor progression and increased survival in mice with pancreatic cancer . These reports suggest the potential of isocannflavin B as an anticancer drug, though translational studies should be undertaken to determine its activities in humans. A combination of in vitro bioassays and in silico molecular docking analysis established antiparasitic activities of cannflavins. Cannflavin A and cannflavin B exhibited moderate anti-leishmanial activities against a culture of Leishmania donovani promastigotes. The bio-assay results were corroborated by strong docking energy of cannflavin A to one of the protein targets in L. donovani, Leishmania pteridine reductase 1. Besides L. donovani, cannflavin A also showed moderate inhibitory activity against the parasite Trypanosoma brucei brucei with an IC50 value of 1.9 μg/mL. The mechanistic basis for the antiparasitic effects of cannflavins remains to be elucidated. To date, vertical farming units only molecular docking/computational analysis has been employed to evaluate the antiviral activities of cannflavins. Cannflavin A showed a relatively high binding affinity and high reactivity against HIV-1 protease, an enzyme that renders human immunodeficiency viruses infectious, as determined by the density functional theory analysis. A molecular docking study of multiple protein targets of Dengue virus revealed cannflavin A as a strong docking ligand for the Dengue virus envelope protein. Cannflavin A is also among the phytochemicals that are predicted to show efficient docking to the helicase , helicase , methyltransferase , and RNA-dependent RNA polymerase of Zika virus. Although the computational analysis suggests cannflavins as potential antiviral drug leads, further empirical evidence is still needed to precisely determine their bio-activities.

To investigate the microbial metabolism of cannflavins, cannflavin A and B were fermented with Mucor ramannianus and Beauveria bassiana , which resulted in 6″S,7″-dihydroxycannflavin A, 6″S,7″-dihydroxycannflavin A 7-sulfate, and 6″S,7″-dihydroxycannflavin A 4′-O- α-L-rhamnopyranoside from cannflavin A, and cannflavin B 7-O- β-D-4′″-O-methylglucopyranoside and cannflavin B 7-sulfate from cannflavin B. However, these microbial transformed metabolites do not possess the antimicrobial and antiparasitic activities reported for cannflavin A and B. Whether and how the geranylation and prenylation at C6 of cannflavin A and B and at C8 of cannflavin C and isocannflavin B contribute to their anti-inflammatory, neuroprotective, anticancer, antiparasitic, and antiviral activities should be further investigated. Insights into the structure− function relationship of these prenylated/geranylated flavones will inform the effective development of therapeutics. Furthermore, microbial degradation products of cannflavins in humans need to be elucidated to better understand drug metabolism and biological functions of cannflavins in humans.Molecular and genetic studies in C. sativa have lagged behind many other plant species due to its historically prohibited status. However, the advancements in omics methods and the availability of genome and transcriptome sequences in the public domain have largely facilitated molecular studies in C. sativa. A draft genome of cultivated C. sativa was released in 2011, although it was not assembled to the chromosomal level. Recently, a high-quality reference genome of a wild C. sativa variety was obtained using PacBio, a single-molecule real-time sequencing technology, and Hi-C, a next-generation sequencing technology for chromosome conformation capture. With the assistance of transcriptome sequencing, 38,828 protein-coding genes were delineated, over 98% of which were functionally annotated. In the past few years, there have also been increasing efforts in sequencing the transcriptomes of multiple chemovars and wild C. sativa. As of January 2021, 59 C. sativa-related bioprojects have been registered in the National Center for Biotechnology Information Sequence Read Archive database, a repository of high-throughput sequencing data. Of these bio-projects, 37 contain genome or transcriptome sequences of plant materials. These bio-projects aim to discover genes responsible for the biosynthesis of C. sativa phytochemicals, to elucidate the evolution and genetic diversity of C. sativa accessions, or to examine changes in transcriptomes when C. sativa plants are exposed to abiotic stresses. These sequencing data collectively are invaluable for gene discovery, biological application, and genetic improvement of C. sativa. Indeed, the utility of C. sativa genome sequences has already been demonstrated in cloning genes encoding the prenyltransferase and methyltransferase enzymes for cannflavin biosynthesis. On the other hand, transcriptome data that are publicly available or generated in individual research groups will be useful for elucidating the flavonoid biosynthetic and regulatory genes using gene coexpression analysis. In addition to transcriptomic analysis, integrated analysis of transcriptome, metabolome, and proteome data can be utilized to reveal genes responsible for the spatial and temporal distribution of flavonoids in C. sativa regulated by plant development and/or the environment. Because it is an integral part of the complex metabolic network, understanding the control of flavonoid production will have implications in the accumulation of phytocannabinoids and other non-phytocannabinoid chemicals in C. sativa. Moreover, understanding the control of stressinduced flavonoids will facilitate the development of environmentally resilient C. sativa plants. The bio-activities of cannflavins and other flavonoids make them a desirable bioproduct that will require the biosynthesis of a large amount of flavonoids for downstream applications. However, flavonoids are present at low levels in C. sativa tissues grown under normal conditions.