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Suejin Park, Youyoun Moon and Nicole L. Waterland

Water deficit stress can reduce the postproduction shelf life and marketability of floriculture crops. To alleviate the damage by water deficiency, plants need to limit transpirational water loss by inducing stomatal closure. Osmotic stress induces stomatal closure like the response to water deficit stress. It could be used as a convenient tool to enhance water deficit stress tolerance by reducing water loss. The objective of this research was to investigate whether osmotic treatment with a high concentration of chemical solutions could trigger a response to osmotic stress so that stomatal closure can be induced, resulting in enhanced water deficit stress tolerance in viola (Viola cornuta ‘Sorbet XP Yellow’). Osmotic treatments with CaCl2, Ca(NO3)2, NaCl, NaNO3, BaCl2, Ba(NO3)2, and mannitol were applied at the osmotic potentials (ψS) of −1.3 and −2.0 MPa. Chemical treatments [except Ca(NO3)2, NaCl, and mannitol] helped to delay wilting and gave a longer shelf life, up to 5.2 days over that of the control, 2.5 days. However, leaf necrosis was observed on the violas treated with NaCl, NaNO3, BaCl2, Ba(NO3)2, and mannitol. CaCl2 was the most effective agent in delaying wilting under water deficit stress in viola without leaf necrosis. Compared with the control, violas treated with CaCl2 at 200 and 300 mm showed an increase in shelf life by 2.6 and 1.2 days, respectively. Stomatal conductance (g S) was reduced within 4 hours after treatment with CaCl2 compared with that of control violas. Leaf relative water content (RWC) of control violas was dramatically reduced 3 days after treatment and fell below 50% on day 4, while CaCl2-treated violas maintained higher leaf RWC (70% to 81%) during the water deficit period. These results indicated that osmotic treatment with the high concentration of CaCl2 caused stomatal closure, resulting in a reduction of water loss and an extension of shelf life under water deficit stress in viola.

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Laura J. Chapin, Youyoun Moon and Michelle L. Jones

Metacaspases are cysteine proteases from plants, fungi, and protozoans that have structural similarity to metazoan caspases. They play a critical role in programmed cell death (PCD) induced by developmental cues and environmental signals. In this study, a type I metacaspase (PhMC1) was identified and characterized from Petunia ×hybrida ‘Mitchell Diploid’ (MD) (petunia). The recombinant PhMC1 had activity against the metacaspase substrate Boc-GRR-AMC (GRR). Activity was highest at pH 7–9 and was dependent on the active site C237. Quantitative polymerase chain reaction (qPCR) showed that PhMC1 transcripts increased at a later stage of petal development, when corollas were visibly senescent in both pollinated and unpollinated flowers. Gene expression patterns were similar to that of the senescence-related gene PhCP10, a homolog of Arabidopsis thaliana (arabidopsis) AtSAG12. PhMC1 transcripts were upregulated in the petals by ethylene treatment. This ethylene regulation did not require protein synthesis, indicating that PhMC1 is a primary ethylene response gene. Metacaspase-like activity against Boc-GRR-AMC increased in protein extracts from senescing petals. RNAi was used to knock down the expression of PhMC1. Transgenic PhMC1 petunias had no abnormal, vegetative growth phenotypes under normal greenhouse conditions, but flower senescence was accelerated by an average of 2 days.

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Suejin Park, Sarah A. Mills, Youyoun Moon and Nicole L. Waterland

Water stress during shipping and retailing reduces the postproduction quality and marketability of bedding plants. Antitranspirants can temporarily prevent plants from wilting by either physically blocking stomata or physiologically inducing stomatal closure, limiting transpirational water loss from leaves. The goal of this research was to evaluate the efficacy of commercially available antitranspirants on enhancing temporary water stress tolerance in bedding plants. Two physical antitranspirants [β-pinene polymer (βP) and vinyl-acrylic polymer (VP)], and three physiological antitranspirants [two sugar alcohol-based compounds (SACs) and a biologically active form of abscisic acid (s-ABA)] were applied to begonia (Begonia semperflorens-cultorum), new guinea impatiens (Impatiens hawkeri), impatiens (Impatiens walleriana), petunia (Petunia ×hybrida), african marigold (Tagetes erecta), and french marigold (Tagetes patula). Physical antitranspirants were sprayed on foliage and physiological antitranspirants were drenched to the media. All antitranspirants were applied at half (0.5×), equal to (1×), or twice (2×) the manufacturer’s recommended rate. Extended shelf life was observed when βP or s-ABA was applied. Treatment with βP increased the shelf life of impatiens and african marigold by 1 and 1.3 days compared with control plants, respectively. The application of βP at 2× was more effective at delaying visual wilting than at lower rates (0.5× and 1×) in african marigold. Applications of s-ABA delayed wilting by 1.3 to 3.7 days in all tested cultivars. The shelf lives of impatiens and petunia treated with s-ABA at 2× were extended the most by 3.7 and 3.0 days compared with control plants, respectively. A rapid reduction of stomatal conductance (g S) was observed within 4 hours of βP or s-ABA application in plants showing delayed wilting symptoms. s-ABA treatment appeared to cause marginal leaf chlorosis in impatiens, whereas application of βP damaged the opened flowers in all tested cultivars. The application of VP or SACs did not extend shelf life in any treated plants. These results suggest that foliar application of βP on selected species and treatment with s-ABA on most of species would allow bedding plants to withstand water deficit during shipping and/or retailing.

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Nicole L. Waterland, Youyoun Moon, Janet C. Tou, Moo Jung Kim, Eugenia M. Pena-Yewtukhiw and Suejin Park

Kale (Brassica oleracea L. and other species) is considered a rich source of important minerals. Kale at the early stage of leaf development is assumed to contain higher levels of minerals than at maturity. However, literature supporting this assumption is scarce. In this study, the concentrations of macronutrients [potassium (K), calcium (Ca), magnesium (Mg), and phosphorus (P)] and micronutrients [sodium (Na), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu)] either essential to plant growth and development, or important to human health, were determined. Three kale cultivars (green leaf ‘Dwarf Blue Curled’ and red leaf ‘Scarlet’ in B. oleracea, and green leaf with purple midvein ‘Red Russian’ in Brassica napus) were evaluated at five different leaf developmental stages; cotyledon [microgreen 1 (MG1)], two true leaf [microgreen 2 (MG2)], four true leaf [baby leaf 1 (BL1)], six true leaf [baby leaf 2 (BL2)], and adult. As kale matured, total mineral (ash) decreased from 14.6–19.1% at the microgreen stages to 3.9–6.4% at the adult stage, on a dry weight (DW) basis. Microgreen kale contained higher concentrations of most minerals than adult kale, on a DW basis, in all cultivars. On a fresh weight (FW) (as consumed) basis, the highest level of total mineral concentration was detected at baby leaf stage 1 (1.3–1.7%) and there was no difference between microgreen and adult stages. Fresh microgreens generally contained lower K, Ca, Mg, Fe, and Zn than fresh baby leaves, and lower concentrations of Ca and Mg and higher Na compared with fresh adult kale. Overall, water content deceased from 95.1% at MG1 stage to 80.0% at adult stage. The variation in water content and mineral accumulation during leaf development might contribute to the discrepancy. In addition, fresh leaves of ‘Scarlet’ contained higher concentration of total minerals than that of ‘Dwarf Blue Curled’ or ‘Red Russian’. Although ‘Dwarf Blue Curled’ and ‘Red Russian’ are different species, their mineral content profile during leaf development was similar. Together, cultivar and leaf developmental stage influenced mineral content in kale.