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Background Soil salinization is a major limiting factor for crop cultivation. Switchgrass is a perennial rhizomatous bunchgrass that is considered an ideal plant for marginal lands, including sites with saline soil. Here we investigated the physiological responses and transcriptome changes in the roots of Alamo (alkaline-tolerant genotype) and AM-314/MS-155 (alkaline-sensitive genotype) under alkaline salt stress. Results Alkaline salt stress significantly affected the membrane, osmotic adjustment and antioxidant systems in switchgrass roots, and the ASTTI values between Alamo and AM-314/MS-155 were divergent at different time points. A total of 108,319 unigenes were obtained after reassembly, including 73,636 unigenes in AM-314/MS-155 and 65,492 unigenes in Alamo. A total of 10,219 DEGs were identified, and the number of upregulated genes in Alamo was much greater than that in AM-314/MS-155 in both the early and late stages of alkaline salt stress. The DEGs in AM-314/MS-155 were mainly concentrated in the early stage, while Alamo showed greater advantages in the late stage. These DEGs were mainly enriched in plant-pathogen interactions, ubiquitin-mediated proteolysis and glycolysis/gluconeogenesis pathways. We characterized 1480 TF genes into 64 TF families, and the most abundant TF family was the C2H2 family, followed by the bZIP and bHLH families. A total of 1718 PKs were predicted, including CaMK, CDPK, MAPK and RLK. WGCNA revealed that the DEGs in the blue, brown, dark magenta and light steel blue 1 modules were associated with the physiological changes in roots of switchgrass under alkaline salt stress. The consistency between the qRT-PCR and RNA-Seq results confirmed the reliability of the RNA-seq sequencing data. A molecular regulatory network of the switchgrass response to alkaline salt stress was preliminarily constructed on the basis of transcriptional regulation and functional genes. Conclusions Alkaline salt tolerance of switchgrass may be achieved by the regulation of ion homeostasis, transport proteins, detoxification, heat shock proteins, dehydration and sugar metabolism. These findings provide a comprehensive analysis of gene expression dynamic and act network induced by alkaline salt stress in two switchgrass genotypes and contribute to the understanding of the alkaline salt tolerance mechanism of switchgrass and the improvement of switchgrass germplasm.

Cynodon species can be used for multiple purposes and have high economic and ecological significance. However, the genetic basis of the favorable agronomic traits of Cynodon species is poorly understood, partially due to the limited availability of genomic resources. In this study, we report a chromosome-scale genome assembly of a diploid Cynodon species, C. transvaalensis, obtained by combining Illumina and Nanopore sequencing, BioNano, and Hi-C. The assembly contains 282 scaffolds (~423.42 Mb, N50 = 5.37 Mb), which cover ~93.2% of the estimated genome of C. transvaalensis (~454.4 Mb). Furthermore, 90.48% of the scaffolds (~383.08 Mb) were anchored to nine pseudomolecules, of which the largest was 60.78 Mb in length. Evolutionary analysis along with transcriptome comparison provided a preliminary genomic basis for the adaptation of this species to tropical and/or subtropical climates, typically with dry summers. The genomic resources generated in this study will not only facilitate evolutionary studies of the Chloridoideae subfamily, in particular, the Cynodonteae tribe, but also facilitate functional genomic research and genetic breeding in Cynodon species for new leading turfgrass cultivars in the future.

Leaf senescence is a typical symptom of heat damage in cool-season plant species. The objective of this study was to determine whether melatonin could suppress heat-induced leaf senescence in perennial ryegrass (Lolium perenne L.) and whether melatonin interacted with abscisic acid (ABA) and cytokinin (CK) to exert its biological function. Perennial ryegrass (cv. ‘Pinnacle’) plants were foliar sprayed with melatonin or water and exposed to heat stress at 38/33 °C (day/night) and non-stress condition at 22/17 °C for 28 d in growth chambers. Exogenous application of melatonin alleviated growth inhibition and leaf senescence induced by heat stress, as manifested by significant higher tiller number, above-ground dry weight, plant height, turf quality, leaf chlorophyll (Chl) content, photochemical efficiency (Fv/Fm), net photosynthesis rate, and cell membrane stability in melatonin-treated plants compared to non-melatonin treatment under heat stress. The suppression of heat-induced leaf senescence by melatonin was also reflected by the reduction of transcript levels of senescence-associated genes (LpSAG12.1 and Lph36) in plants exposed to heat stress. Melatonin treatment increased the endogenous content of melatonin and CK content, whereas it decreased ABA content under heat stress. The expression of CK biosynthesis genes and its signaling response transcription factors (type B ARRs) were up-regulated, while the biosynthesis and signaling genes involved in ABA were down-regulated by melatonin treatment under heat stress. These results indicate that the suppression of heat-induced leaf senescence by exogenous melatonin could be associated with activating CK synthesis and signaling while inhibiting ABA synthesis and signaling in perennial ryegrass.

Highlight The relationship between an adenine isopentenyltransferase transgene, reactive oxygen species (ROS) content and the ROS-scavenging system, mechanistically contributing to improved root growth under drought stress in creeping bentgrass, is discussed., Drought stress limits root growth and inhibits cytokinin (CK) production. Increases in CK production through overexpression of isopentenyltransferase (ipt) alleviate drought damages to promote root growth. The objective of this study was to investigate whether CK-regulated root growth was involved in the alteration of reactive oxygen species (ROS) production and ROS scavenging capacity under drought stress. Wild-type (WT) creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) and a transgenic line (S41) overexpressing ipt ligated to a senescence-activated promoter (SAG12) were exposed to drought stress for 21 d in growth chambers. SAG12-ipt transgenic S41 developed a more extensive root system under drought stress compared to the WT. Root physiological analysis (electrolyte leakage and lipid peroxidation) showed that S41 roots exhibited less cellular damage compared to the WT under drought stress. Roots of SAG12-ipt transgenic S41 had significantly higher endogenous CK content than the WT roots under drought stress. ROS (hydrogen peroxide and superoxide) content was significantly lower and content of total and free ascorbate was significantly higher in S41 roots compared to the WT roots under drought stress. Enzymatic assays and transcript abundance analysis showed that superoxide dismutase, catalase, peroxidase, and dehydroascorbate reductase were significantly higher in S41 roots compared to the WT roots under drought stress. S41 roots also maintained significantly higher alternative respiration rates compared to the WT under drought stress. The improved root growth of transgenic creeping bentgrass may be facilitated by CK-enhanced ROS scavenging through antioxidant accumulation and activation of antioxidant enzymes, as well as higher alternative respiration rates when soil water is limited.

Zoysiagrass (Zoysia spp.), a warm-season turfgrass species, experiences freezing damage in many regions. The mechanisms of its cold acclimation and freezing tolerance have not been well understood. This study was designed to investigate effects of cold acclimation treatment on leaf abscisic acid (ABA), cytokinin (transzeatin riboside (t-ZR), and antioxidant metabolism associated with freezing tolerance in zoysiagrass (Zoysia japonica). ‘Chinese Common’ zoysiagrass was subjected to either cold acclimation treatment with temperature at 8/2 °C (day/night) and a photosynthetically active radiation (PAR) of 250 µmol·m−2·s−1 over a 10-hour photoperiod or normal environments (temperature at 28/24 °C (day/night), PAR at 400 µmol·m−2·s−1 and 14-hour photoperiod) for 21 days in growth chambers. Cold treatment caused cell membrane injury as indicated by increased leaf cell membrane electrolyte leakage (EL) and malondialdehyde (MDA) content after 7 days of cold treatment. Cold treatment increased leaf ABA and hydrogen peroxide content and reduced t-ZR content. Leaf superoxide dismutase (SOD), ascorbate peroxidase (APX) activity, and proline content increased, whereas catalase (CAT) and peroxidase (POD) activity declined in response to cold treatment. Cold treatment increased freezing tolerance as LT50 declined from −4.8 to −12.5 °C. The results of this study indicated that cold acclimation treatment might result in increases in ABA and H2O2, which induce antioxidant metabolism responses and improved freezing tolerance in zoysiagrass.

Tall fescue is an important cool-season grass widely used for forage and turf, and its genotypic variation for morphological traits has not been well documented. One hundred and fifteen tall fescue accessions, including 25 commercial cultivars, were divided into five groups based on their origination. The morphological traits, including plant height, spike length, pulvinus distance, spikelet count, branch count per spike, spike count per plant, and spike weight in different accessions were determined under field conditions in 2013 and 2014. There was significant genotypic variation in morphological traits among the 115 tall fescue accessions. Wild accessions exhibited a greater variation in the morphological traits than commercial cultivars. Close correlations were found among plant height, spike length, pulvinus distance, and spikelet count. The results of this suggest plant height, spike length, pulvinus distance, and spikelet count could be used as key morphological traits for evaluating all fescue germplasm effectively.

Brassinosteroids (BR) regulate plant tolerance to salt stress but the mechanisms underlying are not fully understood. This study was to investigate physiological mechanisms of 24-epibrassinolide (EBR)'s impact on salt stress tolerance in perennial ryegrass (Lolium perenne L.) The grass seedlings were treated with EBR at 0, 10, and 100 nM, and subjected to salt stress (250 mM NaCl). The grass irrigated with regular water without EBR served as the control. Salt stress increased leaf electrolyte leakage (EL), malondialdehyde (MDA), and reduced photosynthetic rate (Pn). Exogenous EBR reduced EL and MDA, increased Pn, chlorophyll content, and stomatal conductance (gs). The EBR applications also alleviated decline of superoxide dismutase (SOD) and catalase (CAT) and ascorbate peroxidase (APX) activity when compared to salt treatment alone. Salt stress increased leaf abscisic acid (ABA) and gibberellin A4 (GA4) content but reduced indole-3-acetic acid (IAA), zeatin riboside (ZR), isopentenyl adenosine (iPA), and salicylic acid (SA). Exogenous EBR at 10 nm and 100 nM increased ABA, and iPA content under salt stress. The EBR treatment at 100 nM also increased leaf IAA, ZR, JA, and SA. In addition, EBR treatments increased leaf proline and ions (K+, Mg2+, and Ca2+) content, and reduced Na+/K+ in leaf tissues. The results of this study suggest that EBR treatment may improve salt stress tolerance by increasing the level of selected hormones and antioxidant enzyme (SOD and CAT) activity, promoting accumulation of proline and ions (K+, Ca2+, and Mg2+) in perennial ryegrass.

Proline is an important osmoprotectant in plant in response to osmotic stresses. Delta 1-pyrroline-5-carboxylate synthetase (P5CS) is a key enzyme in proline biosynthesis. In this study, two P5CS genes (PrP5CS1 and PrP5CS2) were isolated for the first time from perennial ryegrass. Expression analysis revealed that the transcript of PrP5CS1 in leaves was significantly up-regulated in two ryegrass cultivars exposed to 255 mm NaCl. The up-regulated level of PrP5CS1 was higher in salt-tolerant ‘Overdrive’ than in sensitive ‘Pizzazz’. PrP5CS2 was significantly induced in ‘Overdrive’ but suppressed in ‘Pizzazz’ by NaCl treatment. In stems, however, there was no significant transcript change for both genes under salt treatment. The proline accumulation was significantly induced in both cultivars after salt treatment, and it was higher in ‘Overdrive’ than in ‘Pizzazz’ after 2 days of salt treatment. The results suggested that both genes are salt inducible and may be associated with salt-stress tolerance in perennial ryegrass.

Small heat shock proteins (sHSPs) are by far the most complex group of HSPs that function to protect practically all cellular compartments in plants under stress due to their unusual abundance and diversity. Recent advances in proteomics, genomics, and other cellular and molecular techniques have facilitated the identification and characterization of sHSPs in higher plants, especially grass plants from the family of Poaceae that are economically important as crops and grasslands. Here we introduce the structure and function of plant sHSPs, and then summarize recent research progress on the role of sHSPs in grass tolerance to heat stress.

Drought stress is one of the major limiting factors for plant growth and development. The mechanism of drought tolerance has not been well understood. This study was designed to investigate proline and antioxidant metabolism associated with drought tolerance in transgenic tobacco (Nicotiana tabacum) plants overexpressing the OjERF gene relative to wild-type (WT) plants. The OjERF gene was isolated from mondo grass (Ophiopogon japonicus). The OjERF gene, driven by the CaMV35S promoter, was introduced into tobacco through agrobacterium (Agrobacterium tumefaciens)-mediated transformation. Five transgenic lines were regenerated, of which transgenic Line 5 (GT5) and Line 6 (GT6) were used to examine drought tolerance in comparison with WT plants in a growth chamber. Drought stress caused an increase in leaf malondialdehyde (MDA) and electrolyte leakage (EL), proline content, superoxide dismutase (SOD), and catalase (CAT) activity in both transgenic lines and WT plants. However, the transgenic lines had lower MDA content and EL and higher proline content, SOD and CAT activity relative to WT under drought stress. The activities of SOD and CAT were also greater in the transgenic lines relative to WT plants under well-watered conditions (Day 0). The OjERF activated the expression of stress-relative genes, including NtERD10B, NtERD10C, NtERF5, NtSOD, and NtCAT1 in tobacco plants. The results of this study suggest that the OjERF gene may confer drought stress tolerance through upregulating proline and antioxidant metabolism.

Salinity stress may involve the accumulation of glycine betaine (GB). The objective of this study was to examine whether exogenous GB would ameliorate the detrimental effect of salinity stress on perennial ryegrass (Lolium perenne). The grass was subjected to two salinity levels (0 and 250 mm NaCl) and three GB levels (0, 20, and 50 mm). Salinity resulted in a remarkable decrease in vertical shoot growth rate (VSGR), shoot and root fresh weight, relative water content (RWC), relative transpiration rate (Tr), and chlorophyll (Chl) content, superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities. Plants subjected to salt exhibited an increase in leaf electrolyte leakage (EL), lipid peroxidation (MDA), and proline content. Application of GB reduced EL, MDA, and proline content in salt-stressed plants. Perennial ryegrass subjected to salt stress plus GB had a greater level of VSGR, RWC, relative Tr, Chl content, and activities of SOD, CAT, and APX when compared with salt-stressed without GB. Salt stress increased Na+ and decreased K+ content, which resulted in a higher Na+/K+ ratio in perennial ryegrass. Application of 20 mm GB suppressed Na+ accumulation, whereas the K+ content was significantly increased in shoot, which led to a higher K+/Na+ ratio under saline conditions. These results suggested that GB-enhanced salt tolerance in perennial ryegrass was mainly related to the elevated SOD, CAT, and APX activity and alleviation of cell membrane damage by reducing oxidation of membrane lipid and improving the ion homeostasis under salt stress.

Switchgrass (Panicum virgatum L.) is used horticulturally as an ornamental and agronomically as an animal feedstock and a putative bio-energy crop. Genetic transformation, using somatic embryogenic (SE) callus derived from mature seeds, is one strategy for improving switchgrass traits. A superior switchgrass line, HR8, was developed in this study using recurrent tissue culture selection from cv. Alamo. Eighty two percent of HR8 seeds germinated after harvest comparing to 26.8% for unselected ‘Alamo’. HR8 seeds that germinated produced 84.9% SE callus. HR8 seeds had higher endogenous abscisic acid (ABA) contents and responded differently to exogenous additions of ABA in culture. Endophytes were isolated from switchgrass seeds and callus. HR8 callus had less endophytic contamination than that of ‘Alamo’ callus. HR8 SE calli were genetically transformable using Agrobacterium. Therefore, HR8 is a superior line for generating SE callus and Agrobacterium-mediated transformation.

Perennial ryegrass (Lolium perenne L.), widely used in temperate climates, is one of turf grasses that enrich cadmium (Cd). The objective of this study was to explore the physiological responses and candidate gene expression in perennial ryegrass to Cd stress. Grasses were subjected to three levels of 0, 0.2, and 0.5 mM Cd for 7 days in the greenhouse. The results indicated that soluble protein content was lower in the Cd-treated perennial ryegrass compared to untreated plants. The Cd-treated perennial ryegrass exhibited a greater level of malondialdehyde and activity of the peroxidase (POD), catalase, and superoxide dismutase (SOD) relative to the control. The Cd stress induced up-regulated expression of FeSOD, MnSOD, Chl Cu/ZnSOD, Cyt Cu/ZnSOD, APX, GPX, GR and POD at 4-24 h after treatment began for perennial ryegrass. Results suggested that the gene transcript profile was related to the enzyme activity under Cd stress.

Bermudagrasses (Cynodon spp.) grown in the U.S. transition zone and other regions with a similar climate undergo cold acclimation in fall and deacclimation in spring. Physiological mechanisms of cold acclimation and deacclimation associated with freezing tolerance and spring green-up are not well documented. This study investigated changes in cytokinin (t-zeatin riboside [t-ZR]) and abscisic acid (ABA) during cold acclimation and deacclimation in five bermudagrass entries in growth chambers. One ecotype (GA-851) and four cultivars (Patriot, Riviera, Tifway, and Princess-77) were subjected to cold acclimation at 8/4°C (day/night) for 28 d and then deacclimation at 10/5, 21/7, 23/8, and 26/14°C for either 3 wk (standard deacclimation) or 1 wk (fast deacclimation treatment). Stolon t-ZR content declined while ABA content increased during cold acclimation. Patriot and Riviera had higher levels of stolon ABA relative to Princess-77 at the end of cold acclimation. During deacclimation, t-ZR increased as the temperature increased to 26/14°C, while ABA declined as the temperature increased from 10/5 to 21/7°C. Patriot, GA-851, and Tifway had higher levels of t-ZR relative to Riviera and Princess-77. Abscisic acid level during cold acclimation may be associated with freezing tolerance, while cytokinin level during deacclimation may be associated with rate of spring green-up of bermudagrass. The results suggest that selection and use of entries with higher levels of ABA during cold acclimation and cytokinin during deacclimation could improve bermudagrass winter survival and spring green-up in transition zone climates.

Bermudagrasses (Cynodon spp.) grown in the U.S. transition zone and other regions with a similar climate undergo cold acclimation in fall and deacclimation in spring. Physiological mechanisms of cold acclimation and deacclimation are not well documented or understood. This study investigated changes in quality, photochemical efficiency, N metabolite (proline, total amino acid [AA], and protein) content, and dehydrin expression during cold acclimation and deacclimation in five bermudagrass entries. One ecotype (GA-851) and four cultivars (Patriot, Riviera, Tifway, and Princess-77) were subjected to cold acclimation at 8/4°C (day/night; 10-h photoperiod) for 28 d and then deacclimation at 10/5, 21/7, 23/8, and 26/14°C sequentially (11-h photoperiod) for either 3 wk (standard deacclimation) or 1 wk (fast deacclimation treatment) at each temperature. In response to cold acclimation, turfgrass quality and photochemical efficiency declined, while proline, AA, protein, and abundance of 25 kDa dehydrin increased. Patriot and Riviera had higher levels of stolon proline, AA, protein, and abundance of 25 kDa dehydrin relative to Princess-77 at the end of cold acclimation. Significant deacclimation occurred as temperature changed from 21/7 to 23/8°C. Patriot, GA-851, and Tifway had greater turfgrass quality ratings and photochemical efficiency and also higher levels of N metabolites relative to Princess-77 and Riviera during deacclimation. A similar response was observed with fast deacclimation treatment. The results suggest that selection and use of entries with higher levels of N metabolites during cold acclimation and deacclimation could improve bermudagrass persistence and spring green-up in transition zone climates.

Ultraviolet-B (280–320 nm) radiation is one of the major factors causing quality decline of transplanted turfgrass sod. Information on physiological parameters for assessing turfgrass tolerance to ultraviolet-B stress is lacking. The objective of this study was to evaluate ultraviolet-B tolerance of four cool-season turfgrass species and varieties using selected physiological parameters under artificial ultraviolet-B radiation stress. The physiological performance of 18 varieties of tall fescue (TF; Festuca arundinacea Schreb.), chewings fescue (CF; Festuca rubra L. ssp. commutata Gaud.), perennial ryegrass (PRG; Lolium perenne L.), and kentucky bluegrass (KBG; Poa pratensis L.) were subjected to continuous, artificial ultraviolet-B radiation (70 μmol·m−2·s−1) for 10 days. Visual quality ratings of TF, CF, PRG, and KBG measured at Day 10 were reduced by 49%, 18%, 51%, and 74%, respectively, relative to that at trial initiation. Ultraviolet-B tolerance in CF was the greatest, KBG was the least, and TF and PRG were intermediate. ‘Ebony’ was the most ultraviolet-B-tolerant TF variety, whereas ‘BlueTastic’, ‘BlueRiffic’, and ‘747’ had greater ultraviolet-B tolerance than the other four KBG varieties. No differences were observed in ultraviolet-B tolerance between varieties in either CF or PRG. The ultraviolet-B-tolerant species had less electrolyte leakage (EL), greater canopy photochemical efficiency (PEc), and relatively smaller and slower upregulation in antioxidant superoxide dismutase (SOD) activity relative to ultraviolet-B-sensitive ones. The results suggest that EL, PEc, and SOD may be used as physiological parameters in selecting ultraviolet-B-tolerant species and varieties for sod production and lawn establishment.

Recent advances in bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon] breeding and cultural management practices have enabled its use as a sports surface in U.S. Department of Agriculture cold hardiness zones 5 and 6. Use of these more cold-hardy bermudagrass cultivars further into transition- and cool-season zones increases the probability of freezing injury and increases the need for an improved understanding of physiological responses to chilling and freezing temperatures. Abscisic acid (ABA) has been shown to increase during cold acclimation (CA) and play a role in dehydration tolerance. This study investigated changes in ABA metabolism and dehydrin expression during CA and their association with freezing tolerance in four bermudagrass cultivars. Two cold-tolerant (‘Patriot’ and ‘Riviera’) and two relatively cold-sensitive (‘Tifway’ and ‘Princess’) cultivars were either subjected to CA at 8 °C day/4 °C night with a light intensity of 250 μmol·m−2·s−1 over a 10-h photoperiod for 21 days or maintained at 28 °C day/24 °C night over a 12-h photoperiod. In a separate study, exogenous ABA at 0, 50, 100, and 150 μm was applied to ‘Patriot’ bermudagrass without CA. ABA content in leaf and stolon tissues increased substantially during the first week of CA and remained relatively stable thereafter. ‘Patriot’ and ‘Riviera’ had greater ABA content and less stolon electrolyte leakage (EL) relative to ‘Tifway’ and ‘Princess’. Expression of a 25 kDa dehydrin protein increased during CA in all four cultivars. A significant correlation was found between ABA content and freezing tolerance. Exogenously applying ABA to ‘Patriot’ at 50, 100, and 150 μm significantly increased endogenous ABA content and the 25 kDa dehydrin expression and reduced stolon EL. The results suggest that alteration of ABA metabolism during CA is closely associated with freezing tolerance. Selection and use of cultivars with substantial accumulation of ABA and certain dehydrins during CA or in response to exogenous ABA could improve bermudagrass persistence in transition zone climates.

Heat stress is the primary factor limiting summer performance of creeping bentgrass (Agrostis stolonifera L.) in many temperate to subtropical regions. Seaweed extract (SWE)-based cytokinins have been used to improve stress tolerance, but their specific effects on creeping bentgrass under supraoptimal temperatures are lacking. This study was designed to determine whether SWE-based cytokinins affect creep-ing bentgrass heat tolerance, and to compare effects of SWE-based cytokinins to those of a trans-zeatin riboside (t-ZR)-standard. Concentrations of t-ZR in two SWE sources (referred to as Oce and Aca) were determined. Treatments were applied twice to creeping bentgrass at an equivalent t-ZR concentration of 10 μM. One week after the initial treatment, heat stress was imposed (35/25°C [day/night]) for 42 d. The Oce SWE, Aca SWE, and t-ZR treatments resulted in leaf t-ZR concentrations that were 39, 32, and 28% higher, respectively, relative to the control at 14 d of heat stress. The Oce SWE, Aca SWE, and t-ZR treatments also increased superoxide dismutase activity and alleviated the decline of turfgrass quality, photochemical efficiency, and root viability. Ashed SWE provided results similar to the water control. Beneficial effects of SWE on heat tolerance appear to be associated with their organic, especially cytokinin, components and not the mineral (ashed) fraction. Proper application of SWE-based cytokinins may be an effective approach to improve summer performance of creeping bentgrass.

The antioxidant enzyme activities and gene expressions in leaves of Kentucky bluegrass (Poa pratensis L.) were investigated in response to waterlogging stress and subsequent drainage. Two cultivars contrasting in waterlogging tolerance, ‘Moonlight’ (waterlogging-tolerant) and ‘Kenblue’ (waterlogging-sensitive), were subjected to waterlogging for 28 days (d) followed by 7 d of drainage recovery. Waterlogging stress increased malondialdehyde (MDA), superoxide anion (O 2 ·− ) and hydrogen peroxide (H2O2) in both cultivars. Moonlight exhibited greater turfgrass quality (TQ) rating and chlorophyll (Chl) content than Kenblue during the waterlogging and drainage period. After 7 d of drainage, all physiological parameters returned to the control level for Moonlight, but not for Kenblue. Higher activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) as well as more abundance of isozymes were found in Moonlight relative to Kenblue under waterlogging stress. Moonlight showed higher SOD and APX activity and isozymes intensity when compared with Kenblue during the drainage period. The transcript levels of chloroplastic Cu/ZnSOD (Chl Cu/ZnSOD), MnSOD, FeSOD, POD and cytosolic APX (Cyt APX) were higher in Moonlight relative to Kenblue under waterlogging conditions, and higher transcript activities of Chl Cu/ZnSOD, FeSOD and Cyt APX were observed in Moonlight than in Kenblue at 7 d of drainage. The results of this study indicate that higher SOD and APX activity, isozymes intensity and gene expression level in Moonlight relative to Kenblue may play crucial roles in Kentucky bluegrass tolerance to waterlogging stress.

This study was conducted to examine the changes in the levels of carbohydrates and N-rich defense compounds during cold acclimation associated with freezing tolerance. Two bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon] cultivars, Riviera (cold tolerant) and Princess-77 (cold sensitive), were selected and either subjected to cold acclimation at 8/4°C (day/night) with a light intensity of 200 μmol m -2 s -1 over a 10-h photoperiod for 21 d or maintained at 25/23°C (day/ night) with natural sunlight in a glasshouse. Cold acclimation induced accumulation of sugars and proline in both cultivars and also an increase in total nonstructural carbohydrates (TNC) and protein in Riviera, but not in Princess-77. Superoxide dismutase (SOD) increased during the first 7 d and then declined, while catalase (CAT) and ascorbate peroxidase (APX) activity decreased in response to cold acclimation in both cultivars. Electrolyte leakage (EL) was reduced in both cultivars following cold acclimation. The LT50 was reduced by 2.2°C (from -6.1°C to -8.3°C) in Riviera and 1.7°C (from -4.6°C to -6.3°C) for Princess-77 following cold acclimation. Riviera had more carbohydrates and N-rich compounds and less EL than Princess-77 at the end of cold acclimation. Significant correlations of LT50 with sugars, proline, protein, CAT, and APX were obtained in Riviera, but only with proline and the antioxidant enzymes in Princess-77. The results suggest selection and use of cultivars with rapid accumulation of C- and N-rich compounds during cold acclimation could improve bermudagrass persistence in transition zone climates.

Late-season fertilization of bermudagrasses (Cynodon spp. L.C. Rich.) in the transition zone of the United States has traditionally been not recommended. This study was conducted to determine whether late-season fertilization could extend the duration of turfgrass color retention and visual quality without negatively impacting cold tolerance. Field plots of 'Midiron' and 'Tifway' bermudagrasses (C. dactylon x C. transvaalensis Burtt Davy), as well as 'Princess-77' and 'Riviera' bermudagrasses [C. dactylon (L.) Pers. var. dactylon] received applications of seaweed extract (SWE) (0.54 kg ha -1 ), N (49 kg ha -1 ), and Fe (1 kg ha -1 ) every 3 wk during the fall of 2001 and 2002. Visual turfgrass assessment showed that cultivar color ratings decreased as the fall progressed, with Princess-77 having greatest color retention in November of both years. Nitrogen was the only treatment to increase turfgrass color ratings relative to the control at the end of each growing season. Stolon samples removed from acclimated plants were artificially frozen to determine freezing tolerance. Midiron displayed the best freezing tolerance followed by Riviera, Tifway, and Princess-77. Chemical treatments did not have a significant effect on shoot regrowth from stolon nodes after freezing. In both years Midiron and Riviera displayed the quickest and greatest amount of spring greenup followed by Tifway and then Princess-77. Cold tolerance indicators proline and linolenic acid were highest in Midiron, followed by Riviera, Tifway, and Princess-77. Nitrogen, SWE, and Fe did not generally have an effect on linolenic acid and no consistent effects of these chemical treatments were noted on proline concentration. The results of this study indicate that judicious N applications during the fall can promote color retention and do not have a negative effect on bermudagrass cold tolerance.

Background Tall fescue (Festuca arundinacea Schreb.) is major cool-season forage and turf grass species worldwide, but high-temperature is a major environmental stress that dramatically threaten forage production and turf management of tall fescue. However, very little is known about the whole-genome molecular mechanisms contributing to thermotolerance. The objectives of this study were to analyzed genome-wide gene expression profiles in the leaves of two tall fescue genotypes, heat tolerant ‘PI578718’ and heat sensitive ‘PI234881’ using high-throughput RNA sequencing. Results A total of 262 million high-quality paired-end reads were generated and assembled into 31,803 unigenes with an average length of 1,840 bp. Of these, 12,974 unigenes showed different expression patterns in response to heat stress and were categorized into 49 Gene Ontology functional subcategories. In addition, the variance of enrichment degree in each functional subcategory between PI578718 and PI234881 increased with increasing treatment time. Cell division and cell cycle genes showed a massive increase in transcript abundance in heat-stressed plants and more activated genes were detected in PI 578718 by Kyoto Encyclopedia of Genes and Genomes pathways analysis. Low molecular weight heat shock protein (LMW-HSP, HSP20) showed activated in two stressed genotypes and high molecular weight HSP (HMW-HSP, HSP90) just in PI578718. Assimilation such as photosynthesis, carbon fixation, CH4, N, S metabolism decreased along with increased dissimilation such as oxidative phosphorylation. Conclusions The assembled transcriptome of tall fescue could serve as a global description of expressed genes and provide more molecular resources for future functional characterization analysis of genomics in cool-season turfgrass in response to high-temperature. Increased cell division, LMW/HMW-HSP, dissimilation and antioxidant transcript amounts in tall fescue were correlated with successful resistance to high temperature stress. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-1147) contains supplementary material, which is available to authorized users.

Ultraviolet-B [UV-B (280-320 nm)] radiation is one of the major factors causing quality decline of transplanted sod. Pigments and antioxidants are associated with plant stress resistance, but their roles in turfgrass tolerance to UV-B damage are not well understood. The objectives of this study were to determine if kentucky bluegrass (Poa pratensis L.) cultivars with darker green genetic leaf color possessed greater pigment and antioxidant defense capacities and if such characteristics were associated with greater resistance to UV-B. Two cultivars, `Moonlight' (dark green) and `Limerick' (light green), were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m-2·s-1). UV-B irradiation reduced turf quality by 58% (`Moonlight') and 77% (`Limerick') relative to day 1 when measured 10 days after initiation of UV-B exposure. Higher canopy photochemical efficiency (PEc) was found in `Moonlight' relative to `Limerick' under UV-B stress and during recovery. `Moonlight' contained greater levels of chlorophyll (1.5 to1.6-fold), carotenoids (1.3-fold), superoxide dismutase [SOD (1.0-fold)] and catalase [CAT (1.5-fold)] than `Limerick' when measured at 10 days after UV-B initiation. Turfgrass quality and PEc were positively correlated with pigments (chlorophyll and carotenoids) and antioxidant enzymes (SOD and CAT), and negatively correlated with lipid peroxidation. The results suggest that selecting dark-green cultivars with greater pigment content and antioxidant activity may be an effective approach for turfgrass breeders and sod producers to improve tolerance of newly transplanted sod to environments with higher UV-B radiation.

High ultraviolet-B (UV-B; 290-320 nm wavelength) radiation may significantly contribute to the quality decline and death of kentucky bluegrass (Poa pratensis L.) sod during summer transplanting. Antioxidants and protective pigments may be involved in plant defense against oxidative stress caused by UV-B. Selected exogenous hormones may alleviate UV-B damage by upregulating plant defense systems. The objectives of this study were to determine if exogenous hormone or hormone-like substances could alleviate UV-B damage to `Georgetown' kentucky bluegrass (Poa pratensis L.) under greenhouse conditions. The hormone salicylic acid at 150 mg·m-2 and the hormone-containing substances, humic acid (HA) at 150 mg·m-2 and seaweed extract (SWE) at 50 mg·m-2, were applied to plugs of kentucky bluegrass and then subjected to UV-B radiation (70 μmol·m-2·s-1). The UV-B irradiation stress reduced turf quality by 51% to 66% and photochemical efficiency by 63% to 68% when measured 10 or 12 days after initiation of UV-B. Endogenous alpha-tocopherol (AT) and antioxidant enzymes (superoxide dismutase (SOD) and catalase) were reduced by UV-B stress. Anthocyanin content was increased from day 1 to 5 and then decreased from day 5 to 10 of continuous UV-B irradiation. Application of SA and HA + SWE enhanced photochemical efficiency by 86% and 82%, respectively, when measured 10 or 12 days after UV-B initiation. In addition, application of the hormonal supplements increased AT concentration, SOD, catalase activity, and anthocyanin content when compared to the control at 10 days after UV-B initiation. Bluegrass with greater AT concentration and SOD and catalase activity exhibited better visual quality under UV-B stress. The results of this study suggest that foliar application of SA and HA + SWE may alleviate decline of photochemical efficiency and turf quality associated with increased UV-B light levels during summer.

Additional index words. alpha-tocopherol, antioxidant enzyme activity, ascorbic acid, ascorbate peroxidase, catalase, chlorophyll fl uorescence, photochemical effi ciency, superoxide dismutase, turf injury Abstract. High ultraviolet-B (UV-B; 290-320nm wavelength) may signifi cantly contribute to kentucky bluegrass (Poa pratensis L.) sod death at harvest and transplanting. As terrestrial UV-B levels continue to increase due to a depletion of the stratospheric ozone layer this problem may worsen. Epidermal attenuation from pigments and detoxifi cation of reactive oxygen species by antioxidant metabolites and enzymes are involved in plant defense against oxidative stress caused by UV-B. Our objective was to determine whether the attenuation and detoxifi cation systems of kentucky bluegrass could be artifi cially boosted by exogenous applications of ascorbic acid (AA), alpha-tocopherol (AT), or a colorant before exposure to high levels of UV-B. Ascorbic acid, AT, and the colorant Green Lawnger (GL), were ap- plied to plugs of mature kentucky bluegrass alone or in combination, and then subjected to artifi cial, continuous UV-B exposure (70 µmol·m -2 ·s -1 ); three greenhouse experiments were conducted. By 3 to 5 days after UV-B initiation, visual quality and photochemical effi ciency, as measured by chlorophyll fl uorescence were signifi cantly reduced. However, in Expt. 1, AA alleviated decline of visual quality, delayed loss of photochemical effi ciency, and increased recovery relative to the control. In Expt. 3, decreased endogenous AT and antioxidant enzyme activities were measured due to UV-B stress. Application of AA, AA + AT, or GL partially alleviated photochemical effi ciency decline from 4 to 12 days after initiation of UV-B. In addition, application of the chemical treatments increased leaf tissue AT concentrations by 32% to 42%, increased SOD activity by 30% to 33% and increased catalase activity by 37% to 59%, relative to the control as measured 10 days after UV-B initiation. Greater AT concentration and SOD and catalase activities were associated with greater visual quality under UV-B stress. The results of these studies indicate that kentucky bluegrass UV-B toler- ance may be increased by supplementing its pigment and antioxidant defense systems with foliar applications of AA, AT or GL.

Bermudagrass [Cynodon dactylon (L.) Pers.] is widely used along its northern limit of adaptation. However, cold hardiness and winter survival are common concerns facing turfgrass managers in these areas. The objective of this study was to determine the effects of moderate salinity applications on bermudagrass cold hardiness. Two trials were conducted in Summer 2002. The cultivar Princess was seeded into pots in a glasshouse at a rate of 24 kg·ha-1. Pots received a weekly solution of 20-20-20 at a rate of 4.9 kg·ha-1 N. Bi-weekly salinity treatments began ≈2 months after germination and consisted of 0, 5, 20, and 40 dS·m-1 in the form of NaCl. These treatments continued for ≈8 weeks. Weekly quality ratings and chlorophyll fluorescence measurements showed similar results, with the high salinity treatments having the poorest quality. Soil electrical conductivity measurements showed a significant increase for the high salinity rates over the lower rates at the end of the trials. Proline concentrations increased with increasing salinity treatments in Trial 1 and were highest with the 20 dS·m-1 rate in Trial 2. Plants were acclimated in a growth chamber, and artificial freezing tests revealed that the 5 and 20 dS·m-1 treatments had the highest percentage of regrowth after freezing. These results indicate that moderate applications of salt or the use of effluent water prior to hardening may be an important way to increase bermudagrass cold hardiness.

A variety of organic materials such as humic substances, seaweed extracts (SWE), organic matter, and amino acids are being used as fertilizer supplements in commercial turfgrass management. Among them, SWE and humic acid (HA) are widely used in various biostimulant product formulations. These compounds have been reported to contain phytohormones and osmoprotectants such as cytokinins, auxins, polyamines, and betaines. Manufacturer claims are that these products may supplement standard fertility programs by reducing mineral nutrient requirements while improving stress tolerance. There is a lack of season-long, fi eld-based evidence to support these claims. This study was conducted to investigate the infl uence of monthly fi eld applications of SWE, HA, and high and low seasonal fertilization regimes on the physiological health of fairway-height creeping bentgrass (Agrostis stolonifera L.). Plots were treated monthly with SWE at 16 mg·m -2 and HA (70% a.i.) at 38 mg·m -2 alone, or in combination, and were grown under low (20 kg·ha -1 /month) or high nitrogen (50 kg·ha -1 /month) fertilization regimes during 1996 and 1997. Endogenous anti- oxidant superoxide dismutase (SOD) activity, photochemical activity (PA), and turf quality were measured in July of each year. Superoxide dismutase activity was increased by 46% to 181%, accompanied by a PA increase of 9% to 18%, and improved visual quality of bentgrass in both years. There was no signifi cant fertilization × supplement interaction. Although not part of our original objectives, it was noted that signifi cantly less dollar spot (Sclerotinia homoeocarpa F.T. Bennett) disease incidence occurred in supplement-treated bentgrass. Our results indicate that increased SOD activity in July due to SWE and/or HA applications improved overall physiological health, irrespective of fertiliza- tion regime. This suggests that these compounds may be benefi cial supplements for reducing standard fertilizer and fungicide inputs, while maintaining adequate creeping bentgrass health. mic acid (HA) are two novel materials that have shown promise for protecting turfgrasses against oxidative stress. Much early work by Schmidt and collaborators focused on refi ning appropri- ate dilution rates of seaweed extracts and HA based on turfgrass responses such as leaf growth rate and senescence (Goatley and Schmidt, 1990), nutrient uptake (Yan, 1993), root mass (Nabati et al., 1994), and photochemical activity (Zhang, 1997). These studies have shown that certain rates of generic and commercial formulations of SWE and/or HA can improve turfgrass quality and resistance to environmental stresses such as drought (Zhang, 1997) and salinity (Nabati, et al., 1994). Further research indicated that improved stress resistance was associated with increases in anti- oxidant contents and activities (Zhang and Schmidt, 1997; Zhang and Schmidt, 1999, 2000b). All of these studies were conducted under uniform fertilization. Because the chemical components of SWE and HA have yet to be completely characterized and tested for specifi c activity, we do not currently understand the physiological or biochemical bases of SWE and/or HAʼs effects on antioxidants and other stress responses. However, information from other researchers has provided some clues as to constituents and possible modes of action. Fike et al. (2001) reported that SWE derived from A. no- dosum contains various compounds including amino acids and micronutrients; they also reported hormonal activity equivalent to 50 mg·L-1 kinetin. Additionally, auxin and cytokinins have been identifi ed and quantifi ed in SWE using GC-MS techniques (Crouch and Van Staden, 1993; Sanderson and Jameson, 1986; Sanderson et al., 1987; Senn, 1987). Lastly, three betaine forms have been quantifi ed in A. nodosum extracts (Blunden et al., 1986). Quarternary ammonium compounds such as the betaines are thought to play a pivotal role in plant cytoplasmic adjustment

Decline of sod quality during the transportation, storage, and transplant stages of sale is a primary economic concern of sod producers. However, the mechanisms of extending sod quality during storage, transportation, and transplantation remain unclear. This study was conducted to investigate the influences of selected plant metabolic enhancers (PMEs) seaweed (Ascophyllum nodosum Jol.) extract (SWE), humic acid [93% a.i. (HA)], and propiconazole (PPC), on sod tolerance to stress during storage and posttransplant root growth of tall fescue (Festuca arundinacea Schreb.) sod. The SWE + HA, and PPC were applied alone, or in a combination, to tall fescue 2 weeks before harvest. Photochemical efficiency (PE) of photosystem II was measured immediately before harvest. The harvested sod was subjected to high temperature stress (40 °C) for 72 or 96 hours. The heated sod was replanted in the field and posttransplant injury and root strength were determined. On average over 1999 and 2000, application of SWE (50 mg·m-2) + HA (150 mg·m-2), PPC (0.30 mL·m-2), and a combination of SWE + HA with PPC (0.15 mL·m-2), enhanced PE of preharvest sod by 8.5%, 9.1%, and 11.2%, respectively, and increased posttransplant rooting by 20.6%, 34.6%, and 20.2%, respectively. All PME treatments reduced visual injury except SWE + HA and SWE + HA + PPC in 1999. Extension of heat duration from 72 to 96 hours caused significantly more injury to the sod and reduced posttransplant rooting by 22.9% averaged over 2 years. The data suggest that foliar application of SWE + HA, PPC alone, or in a combination with SWE + HA, may reduce shipment heat injury and improve posttransplant rooting and quality of tall fescue sod. Chemical name used: 1-(2-(2,4-dichloropheny)-4-propyl-1,3-dioxolan-2yl)methyl-1-H-1,2,4-triazole [propiconazole (PPC)].

A primary economic concern of sod producers is loss of sod quality during the transportation, storage, and transplant stages of sale. Although a number of cultural methods have been documented for potentially reducing sod heating, many of the biological mechanisms are yet to be investigated. This study investigated the influences of selected plant growth regulators (PGRs) on sod tolerance to stress during storage by examining the relationship between preharvest photochemical efficiency (PE) and transplant rooting of Kentucky bluegrass (Poa pratensis L., KBG) sod. The PGRs, including propiconazole (propiconazole [1-(2-(2,4-dichloropheny)-4-propyl-1,3-dioxolan-2yl) methyl-1-H-1,2,4-triazole]; PPC), and seaweed (Ascophyllum nodosum Jol.) extract (SWE) plus humic acid (93% a.i.; HA), were applied alone, or in combination, to the KBG 2 wk before harvest in 1999 and 2000. Photochemical efficiency was measured immediately before harvest. The harvested sod was subjected to high temperature stress (37 degrees C) for 72 or 96 h. The heated sod was replanted in the field and transplant visual turf injury and rooting were determined. Foliar application of SWE at 0.5 kg ha(-1) plus HA at 1.50 kg ha(-1), PPC at 0.44 kg ha(-1) alone, or a combination of SWE + HA with 0.22 kg ha(-1) PPC, enhanced PE of preharvest sod in both years. Extension of heat duration from 72 to 96 h caused significantly more injury to the sod in 1999. All PGR treatment combinations reduced visual turf injury. On average in 1999 and 2000, SWE + HA, PPC, and SWE + HA + PPC enhanced transplant rooting by 21.8, 34.7, and 44.2%, respectively. Regression analysis indicated that KBG with higher preharvest PE suffered less turf injury and produced greater rooting after transplantation. The data suggest that foliar application of SWE + HA, PPC alone, or in a combination, may improve shelf life and transplant rooting of KBG sod.

Creeping bentgrass (Agrostis palustris Huds.) is an extensively used cool-season grass for fine turf areas such as golf course putting greens, but suffers from poor summer stress tolerance. These studies were conducted to investigate the influences of natural plant growth regulators (NPGR) and Fe on creeping bentgrass photochemical activity (PA), antioxidant superoxide dismutase (SOD) activity, root growth and leaf color under two fertilization regimes. The bentgrass was maintained in well-watered field conditions or water-stressed glasshouse conditions. A mature bentgrass was treated monthly during the field season with seaweed (Ascophyllum nodosum Jol.) extract (SWE) at 50 mg·m-2 or humic acid (HA) at 150 mg·m-2 or in combination with or without FeSO4 at 520 mg·m-2 and grown under a low or a high fertilization regime. Foliar application of SWE + Fe increased PA (14% to 15%), while applications of SWE + HA or SWE + HA + Fe increased SOD activity (49% to 114%) of creeping bentgrass in Summer 1997 and Summer 1998. There was no significant fertilization × NPGR interaction for PA and SOD activity. Bentgrass PA was increased by 13% to 46% when treated with NPGR with or without Fe compared to the control measured in May. The addition of Fe with each NPGR application improved fall and winter leaf color. All NPGR and Fe treatments increased root mass (17% to 29%) in Aug. 1997 and 1998, except HA alone in 1998. Under sustained low soil moisture (-0.5 MPa) conditions, application of NPGR with or without Fe increased PA and SOD activity. The data indicate that SWE and HA enhance the physiological function of `Southshore' creeping bentgrass, resulting in improved root growth regardless of low or high fertilization regime. However, addition of Fe to these NPGR served primarily to improve late season leaf color. The results suggest that, in addition to maintaining adequate plant-available nutrients, applications of natural PGRs, such as SWE and HA, prior to and during summer abiotic stresses would be beneficial.

To improve the salinity tolerance of turfgrass and investigate the effect of spermidine (Spd) on antioxidant metabolism and gene expression under salinity stress condition, exogenous Spd was applied before two kentucky bluegrass (Poa pratensis L.) cultivars (‘Kenblue’ and ‘Midnight’) were exposed to 200 mM sodium chloride (NaCl) stress for 28 d. Salinity stress decreased the turfgrass quality, increased the content of malonyldialdehyde (MDA), superoxide anion (O2·−) and hydrogen peroxide (H2O2), and enhanced activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) and isozymes intensity in both cultivars. In addition, the expression level of Cu/ZnSOD was down-regulated in ‘Kenblue’ but up-regulated in ‘Midnight’ after salt treatment. Salinity stress also enhanced the expression of APX but inhibited the expression of CAT and POD in both cultivars. Exogenous Spd treatment alleviated the salinity-induced oxidative stress through decreasing MDA, H2O2 and O2·− contents in both cultivars. Besides, exogenous Spd further enhanced the activities of SOD, CAT, POD and APX accompanied with the increased intensity of specific isozymes of SOD, CAT and APX in both cultivars and POD in ‘Kenblue’. Moreover, Spd further up-regulated expression levels of Cu/ZnSOD and APX, but down-regulated those of CAT and POD in both cultivars. These results indicated that exogenous Spd might improve turfgrass quality and promote the salinity tolerance in the two cultivars of kentucky bluegrass through reducing oxidative damages and increasing enzyme activity both at protein and transcriptional levels.

Heat stress is a primary factor causing summer bentgrass decline. Changes in gene expression at the transcriptional and/or translational level are thought to be a fundamental mechanism in plant response to environmental stresses. Heat stress redirects protein synthesis in higher plants and results in stress protein synthesis, particularly heat shock proteins (HSPs). The goal of this work was to analyze the expression pattern of major HSPs in creeping bentgrass (Agrostis stolonifera L.) during different heat stress periods and to study the influence of nitrogen (N) on the HSP expression patterns. A growth chamber study on ‘Penn-A4’ creeping bentgrass subjected to 38/28°C day/night for 50 days, was conducted with four nitrate rates (no N-0, low N-2.5, medium N-7.5, and high N-12.5 kg N ha−1) applied biweekly. Visual turfgrass quality (TQ), normalized difference vegetation index (NDVI), photochemical efficiency of photosystem II (Fv/Fm), shoot electrolyte leakage (ShEL), and root viability (RV) were monitored, along with the expression pattern of HSPs. There was no difference in measured parameters between treatments until week seven, except TQ at week five. At week seven, grass at medium N had better TQ, NDVI, and Fv/Fm accompanied by lower ShEL and higher RV, suggesting a major role in improved heat tolerance. All the investigated HSPs (HSP101, HSP90, HSP70, and sHSPs) were up-regulated by heat stress. Their expression patterns indicated cooperation between different HSPs and their roles in bentgrass thermotolerance. In addition, their production seems to be resource dependent. This study could further improve our understanding about how different N levels affect bentgrass thermotolerance. Published version

This study was conducted to determine whether the plant endogenous antioxidant concentration is responsive to exogenous hormone-containing products (HCPs) in two turfgrass species subjected to drought. Two-week-old seedlings of tall fescue (Festuca arundinacea Schreb.) and creeping bentgrass (Agrostis palustris Huds. A.) were treated with two HCPs , seaweed extract (SWE) at 326 g ha-1 or humic acid (HA, 25% a.i.) at 5 L ha-1, applied alone or in combination and grown under either -0.03 or -0.5 MP a soil moisture for 5 wk. Growth and antioxidant status of leaves were determined subsequently. The HCP treatments significantly improved leaf water status (LWS) and shoot and root growth of the grasses grown under high (-0.03 MPa) and low (-0.5 MPa) soil moisture. alpha-Tocopherol concentration increased significantly and ascorbic acid concentration remained unchanged for drought-stressed compared with nonstressed turfgrass. The HCP treatments significantly increased alpha-tocopherol and ascorbic acid concentration of the grasses grown under high and low soil moisture. Positive correlation between antioxidants and shoot or root growth was found in the two grass species. Improvement of growth and LWS of turfgrass treated with HCPs may be related to its high antioxidant concentration.

Plants possess various constitutive and inducible defense mechanisms such as pigment and antioxidant systems for protection against stresses such as ultraviolet-B (UV-B; 290 to 320 nm) radiation. Our previous research has indicated that higher chlorophyll, carotenoid, and anthocyanin concentrations were associated with greater tolerance of UV-B stress by `Georgetown' kentucky bluegrass (Poa pratensis L.). The objectives of this study were to determine if kentucky bluegrass cultivars with darker leaf color possessed greater pigment and antioxidant defense systems and if such increases were associated with greater resistance to UV-B. Eight cultivars exhibiting a range of green color intensity (`Apollo', `Brilliant', `Julius', Limerick', `Midnight', `Moonlight', `Nuglade', and `Total Eclipse') were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m-2·s-1). UV-B irradiation reduced turf quality (55% to 62%) and photochemical efficiency (37% to 70%) when measured 5 days after initiation of UV-B exposure. Significant differences in turf color, photochemical efficiency, chlorophyll a, chlorophyll b, chlorophyll a+b, and carotenoids were found among the cultivars. `Moonlight' had greatest photochemical efficiency, chlorophyll, carotenoids, and turf quality. Positive correlations of pigment concentration with photochemical efficiency and turf color were observed under UV-B radiation stress, with correlation coefficients ranging from 0.49 to 0.62. The results of this study suggests that selecting cultivars with higher concentrations of chlorophyll and carotenoids and photochemical efficiency may be an effective way for turfgrass managers and sod producers to improve sod establishment and quality in environments with higher UV-B radiation.

Water stress is one of the most important environmental factors inducing physiological changes in plants, such as decrease in the water potential of the cells, the stomatal closure; and the development of oxidative processes mediated by reactive oxygen species (ROS). Antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) are efficient scavengers of ROS. The aim of this research was to examine how the application of biostimulant based on humic substances and aminoacids may affect activity levels of SOD, CAT, and APX of maize and soybean plants under well-watered or drought stress conditions. Pots (4.5 L) were filled with a Typic Hapludult soil where the biostimulants doses were applied. It was taken leaf samples in order to analyze SOD, CAT, and APX activities in plants. SOD and APX activity levels were increased by application of biostimulant 1 in maize subjected to stress. Catalase activity was not enhanced in plants by using the biostimulants. The composition of the biostimulants was not able to enhance stress tolerance in maize and soybean plants subjected to water stress.

Seaweed (Ascophyllum nodosum) is a known source of plant growth regulators, and application to turfgrasses has increased activity of the antioxidant superoxide dismutase (SOD) and specific vitamin precursors. Increased antioxidant activity in both plants and animals diminishes oxidative stress. Two pasture experiments investigated effects of Tasco-Forage (a proprietary seaweed-based product) applied to tall fescue (Festuca arundinacea) on antioxidant activity in plants and in ruminants that grazed the forage. In Exp. 1, fescue was 70 to 100% infected with the endophyte fungus Neotyphodium coenophialum ([Morgan-Jones and Gams] Glenn, Bacon, and Hanlin). Twenty-four wether lambs (initial BW 41 kg; SD = 5) grazed fescue treated with 0, 1.7, or 3.4 kg Tasco/ha applied in April and July, 1994, with four replications per treatment. Grazing occurred for 26 d beginning April 21 and for 22 d beginning July 19. In July, there was a linear increase in daily gains (P < 0.05), and serum vitamin A (P < 0.13) and whole-blood Se (P < 0.10) tended to increase in lambs grazing Tasco-treated fescue. In Exp. 2, 48 Angus and Angus x Hereford steers (initial BW 245 kg; SD = 20) grazed infected or uninfected tall fescue in Virginia that was treated (3.4 kg/ ha) or untreated with Tasco in April and July, 1995. Steers that grazed infected tall fescue had lower (P < 0.02) serum vitamin A and E and tended (P < 0.07) to have lower whole-blood Se in September compared with steers that grazed uninfected tall fescue. Tasco decreased (P < 0.06) serum vitamin E but tended to increase whole-blood Se (P < 0.10) in September and serum vitamin A in July (P < 0.12). During 1996 and 1997, the experiment was repeated in Virginia with Angus steers and was replicated at Prairie, MS, where 1/4 Brahman x 3/4 Angus steers were used. Forty-eight steers were included at each location in each year (n = 192 total steers for 1996 and 1997). Steers that grazed infected tall fescue in Mississippi had lower (P < 0.05) serum vitamin E by the end of the grazing season. At both locations Tasco increased (P < 0.05) activity of superoxide dismutase in both infected and uninfected fescue. The endophyte in tall fescue seemed to decrease antioxidant activity in grazing steers, whereas Tasco seemed to increase antioxidant activity in both the forage and the grazing ruminant. Tasco may provide opportunities to reduce oxidative stress in plants and animals.

Little is known about the effects of NaCl stress on perennial ryegrass (Lolium perenne L.) photosynthesis and carbohydrate flux. The objective of this study was to understand the carbohydrate metabolism and identify the gene expression affected by salinity stress. Seventy-four days old seedlings of two perennial ryegrass accessions (salt-sensitive ‘PI 538976’ and salt-tolerant ‘Overdrive’) were subjected to three levels of salinity stress for 5 days. Turf quality in all tissues (leaves, stems and roots) of both grass accessions negatively and significantly correlated with GFS (Glu+Fru+Suc) content, except for ‘Overdrive’ stems. Relative growth rate (RGR) in leaves negatively and significantly correlated with GFS content in ‘Overdrive’ (P0.05 for turf quality). A greater up-regulation in the expression of SPS, SS, SI, 6-SFT gene was observed in ‘Overdrive’ than ‘PI 538976’. A higher level of SPS and SS expression in leaves was found in ‘PI 538976’ relative to ‘Overdrive’. Accumulation of hexoses in roots, stems and leaves can induce a feedback repression to photosynthesis in salt-stressed perennial ryegrass and the salt tolerance may be changed with the carbohydrate allocation in leaves and stems. Published version