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  • Author or Editor: Bo Yuan x
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Amino acid and protein metabolism are interrelated and both play important roles in plant adaptation to heat stress. The objective of this study was to identify amino acids and soluble proteins associated with genetic variation in heat tolerance of hard fescue (Festuca trachyphylla). According to a previous screening experiment, the hard fescue cultivars Reliant IV and Predator were selected as heat-tolerant and heat-sensitive cultivars, respectively. Plants of these two hard fescue cultivars were exposed to heat stress at 38/33 °C (day/night) or optimal temperature at 21/18 °C in growth chambers. Each cultivar had four replications under each temperature, and the experimental design was a split-plot design, temperature as the main plots and cultivars as the subplots. Under heat stress, ‘Reliant IV’ exhibited higher turf quality (TQ) and greater membrane stability than ‘Predator’. In response to heat stress, total amino acid content increased, whereas total soluble protein content decreased in both cultivars. The greater accumulation of amino acids in ‘Reliant IV’ was contributed by the greater increase of proteins involved in the glycolysis and the tricarboxylic acid (TCA) cycle that provided carbon skeleton for amino acid synthesis. ‘Reliant IV’ leaves exhibited greater extent of increases in the content of six individual amino acids (histidine, glutamine, proline, threonine, aspartate, and tryptophan) than ‘Predator’ under heat stress. Several soluble proteins were upregulated in response to heat stress, to a greater extent in ‘Reliant IV’ than ‘Predator’, including the proteins involved in photosynthesis, protein folding, redox hemostasis, stress signaling, stress defense, cell organization, and metabolism. These differentially accumulated free amino acids and soluble proteins could be associated with the genetic variation in heat tolerance of hard fescue.

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Effects of amino acids and nitrogen on plant regrowth or recovery from drought stress remain largely unknown. The objectives of this study were to examine how gamma-aminobutyric acid (GABA) or proline, alone and in combination, or inorganic nitrogen [ammonium nitrate (NN)] may differentially affect turf performance during drought stress and rewatering, and to determine which specific endogenous amino acids regulated by GABA, proline, or NN priming were associated with plant tolerance to drought stress and postdrought recuperation in cool-season grass species. Creeping bentgrass (Agrostis stolonifera cv. Penncross) planted in porous ceramic fritted clay medium were exposed to well-watered conditions or drought stress by withholding irrigation for 21 days in growth chambers. Plants were treated with water (untreated control), GABA, or proline alone and in combination, or NN through foliar spray before drought stress and every 7 days during the 21-day stress period. For postdrought recovery, at 21 days of drought treatment, plants were rewatered for 14 days to return soil water content to prestress levels. Plants treated with GABA or proline alone or in combination maintained higher turf quality (TQ), dark green color index (DGCI), and stolon length by 21 days of drought stress, whereas proline-treated plants also maintained higher leaf relative water content (RWC) during drought as well as longer stolon length during rewatering. Plants treated with NN maintained higher TQ and leaf RWC during drought and had improved percent canopy cover, DGCI, and stolon length during postdrought rewatering. Accumulation of endogenous amino acids under drought stress, including proline and alanine, for proline-treated creeping bentgrass may have contributed to the enhancement of drought tolerance and postdrought regrowth. Nitrogen-enhanced accumulation of GABA, proline, and glutamic acid may have played a role in active amino acid assimilation and subsequent postdrought regrowth. Results from this study indicate that GABA or proline were mainly effective in promoting the tolerance of creeping bentgrass to drought stress while inorganic NN was effective in promoting rapid postdrought recovery and regrowth potential through the activation of amino acid metabolism. Endogenous amino acids, including GABA, proline, alanine, and glutamic acid, may be used as biomarkers to select for drought-tolerant plants and biostimulant components for improvement of drought stress tolerance and poststress recovery in cool-season turfgrass species.

Open Access

The relationship between lipoxygenase (LOX) pathway-derived volatiles and LOX gene expression was evaluated in kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa cv. Bruno] during postharvest ripening at 20 °C. The C6 aldehydes n-hexanal and (E)-2-hexenal were abundant in peel compared with flesh tissue and declined as kiwifruit ripened. Esters such as ethyl butanoate and methyl butanoate were lower in the peel than flesh and accumulated when the fruit underwent a climacteric rise in ethylene production. Total LOX activity was higher in the peel than in the flesh and increased as kiwifruit ripened. Expression of AdLox2, AdLox3, AdLox4 and AdLox6 was high in the peel, whereas AdLox1 and AdLox5 showed similar levels in the peel and flesh at the ethylene climacteric. AdLox1 and AdLox5 transcript levels increased and AdLox2, AdLox3, AdLox4 and AdLox6 levels decreased during postharvest fruit ripening. Principal component analysis showed that n-hexanal and (E)-2-hexenal were grouped with LOX genes that were downregulated as kiwifruit ripened. The possible roles of LOX genes in relation to kiwifruit volatile formation during fruit ripening are discussed.

Free access