<p>Lettuce (<em>Lactuca sativa</em> L.) is one of the most popular vegetables worldwide, but is often viewed as low in nutritional value. However, lettuce contains health-promoting nutrients and biosynthesis of such phytochemicals varies depending on cultivar, leaf color and growing conditions. Studies of such parameters on the nutritional value have not been conclusive because the lettuce samples were collected from heterogeneous growing conditions and/or various developmental stages. In our study nutritional composition was evaluated in the two most popular lettuce types in Western diets, romaine and crisphead ‘Iceberg’, with red or green leaves grown under uniform cultivating conditions and harvested at the same developmental stage. In the investigated lettuce cultivars, insoluble fiber content was higher (<em>P </em>≤ 0.05) in romaine than crisphead lettuces. Alpha-linolenic acid (omega-3 polyunsaturated fatty acid) was the predominant fatty acid and was higher in romaine than crisphead. Iron and bone health-promoting minerals (Ca, Mg and Mn) were significantly higher (<em>P</em> ≤ 0.001) in romaine. The content of Beta-carotene and lutein in romaine (668.3 ug g<sup>-1</sup> dry weight) was ~45% higher than in crisphead (457.3 ug g<sup>-1</sup>dry weight). For leaf color comparison, red cultivars provided higher amount of minerals (Ca, P, Mn and K), total carotenoids, total anthocyanins and phenolics than green cultivars. Based on our study results, romaine was generally higher in nutrients analyzed, especially red romaine contained significantly higher amount of total carotenoids, total anthocyanins and phenolics. Therefore, romaine type lettuces with red rather than green leaves may offer a better nutritional choice.</p>
Microgreens and red colored plants have been suggested to contain higher level of health promoting phytochemicals. Kale (Brassica oleracea L. and other species) is regarded as a ‘superfood’ due to its antioxidant properties. In our study, three kale cultivars (B. oleracea L. ‘Dwarf Blue Curled’ and ‘Scarlet’, and B. napus ‘Red Russian’) differing in leaf pigmentation were harvested at five different leaf developmental stages and the concentrations of bioactive antioxidants compounds were evaluated. Carotenoids were measured by high performance liquid chromatography, and spectrometry analyses were used for total phenolics and anthocyanin measurements. Red leaf kale (‘Scarlet’) was generally higher in total carotenoids, phenolics, and anthocyanins than green leaf kales (‘Dwarf Blue Curled’ and ‘Red Russian’). As kale matured, water content decreased and dry mass increased. On a dry weight basis, total carotenoids were more abundant in microgreens and young seedlings with 4 to 6 true leaves (baby greens) than adult stage. In contrast, on a fresh weight basis, baby greens or adult kales generally contained more carotenoids and total phenolic compounds than microgreens, more likely due to the lower dry mass and phytochemical accumulation at microgreen stages. Although some microgreens vegetables may contain more health promoting phytochemicals, based on our study, higher phytochemicals were detected in young seedlings or mature leaves of kale.
Floriculture crops can lose their aesthetic quality due to water deficit during postproduction. Calcium is a secondary messenger in plant stress signaling, and the treatment of calcium has been proposed to alleviate damage by various abiotic stresses. The objective of this research was to evaluate application methods of calcium to delay plant wilting under water deficiency in three species of bedding plants: viola (Viola cornuta), impatiens (Impatiens walleriana), and petunia (Petunia grandiflora). Three application methods were compared including spray, drench, and pre-drench. Calcium was applied as CaCl2 and Ca(NO3)2 at three concentrations ranging from 50 to 300 mM. The effect of calcium on shelf life was species-dependent, increasing shelf life in viola and impatiens, but not in petunia. Viola showed increased shelf life up to 154% and 400% in drench and pre-drench applications, respectively, compared to the control. In impatiens, spray and pre-drench applications delayed wilting symptoms by 53% and 200%, respectively. Comparing calcium sources, CaCl2 was the most effective as a drench, while Ca(NO3)2 pre-drench application effectively delayed wilting. There was no difference between CaCl2 and Ca(NO3)2 in spray application. These results provided the optimum application methods to delay plant witling and the potential of calcium application on enhancing water deficit tolerance in floriculture crops.
Water deficit limits plant growth and development, resulting in quality loss of horticultural crops. However, there is limited information on gene regulation and signaling pathways related to water deficit stress response at multiple time points. The objective of this research was to investigate global gene expression patterns under water deficit stress to provide an insight into how petunia (Petunia ×hybrida ‘Mitchell Diploid’) responded in the process of stress. Nine-week-old petunias were irrigated daily or placed under water stress by withholding water. Stressed plants reduced stomatal conductance after five days of water deficit, indicating they perceived stress and initiated stress response mechanisms. To analyze transcriptomic changes at the early stage of water deficit, leaf tissue samples were collected 1, 3, and 5 days after water was withheld for RNA sequencing. Under water deficit stress, 154, 3611, and 980 genes were upregulated and 41, 2806, and 253 genes were downregulated on day 1, 3, and 5, respectively. Gene Ontology analysis revealed that redox homeostasis processes through sulfur and glutathione metabolism pathways, and hormone signal transduction, especially abscisic acid and ethylene, were enriched under water deficit stress. Thirty-four transcription factor families were identified, including members of AP2/ERF, NAC, MYB-related, C2H2, and bZIP families, and TFs in AP2/ERF family was the most abundant in petunia. Interestingly, only one member of GRFs was upregulated on day 1, while most of TFs were differentially expressed on day 3 and/or 5. The transcriptome data from this research will provide valuable molecular resources for understanding the early stages of water stress-responsive networks as well as engineering petunia with enhanced water stress tolerance.
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