Search

Plant hormones play an important role in plant adaptation to abiotic stress, but hormonal responses of cool-season turfgrass species to salt stress are not well documented. This study was carried out to investigate the responses of hormones to salt stress and examine if salt stress-induced injury was associated with hormonal alteration in kentucky bluegrass (KBG, Poa pratensis L.). The grass was grown in a growth chamber for 6 weeks and then subjected to salt stress (170 mm NaCl) for 28 days. Salt stress caused cell membrane damage, resulting in photosynthetic rate (Pn), chlorophyll (Chl), and turf quality decline in KBG. Salt stress increased leaf abscisic acid (ABA) and ABA/cytokinin (CK) ratio; reduced trans-zeatin riboside (ZR), isopentenyl adenosine (iPA), and indole-3-acetic acid (IAA), but did not affect gibberellin A4 (GA4). On average, salt stress reduced ZR by 67.4% and IAA by 58.6%, whereas it increased ABA by 398.5%. At the end of the experiment (day 28), turf quality, Pn, and stomatal conductance (gs) were negatively correlated with ABA and ABA/CK ratio, but positively correlated with ZR, iPA, and IAA. Electrolyte leakage (EL) was positively correlated with ABA and ABA/CK and negatively correlated with ZR, iPA, IAA, and GA4. GA4 was also positively correlated with turf quality and gs. The results of this study suggest that salt stress-induced injury of the cell membrane and photosynthetic function may be associated with hormonal alteration and imbalance in KBG.

Plant hormones play an important role in plant adaptation to abiotic stress, but hormonal responses of cool-season turfgrass species to drought stress are not well documented. This study was to investigate responses of hormones and photosynthesis to drought stress and examine if drought stress – induced hormone alteration is associated with stress tolerance in kentucky bluegrass (KBG, Poa pratensis L.). The grass was grown in a growth chamber for 6 weeks and then subjected to drought stress [40%-50% evapotranspiration (ET) replacement)] for 28 d. Drought stress caused cell membrane damage, resulting in decline in photosynthetic rate (Pn), chlorophyll content, and visual quality in KBG. Drought stressed grass had higher leaf abscisic acid (ABA), lower leaf trans-zeatin riboside (ZR), isopentenyl adenosine (iPA), and indole-3-acetic acid (IAA), but similar level of leaf gibberellin A4 (GA4) when compared to the control (well-watered). On average, drought stress treatment reduced leaf ZR by 59.1%, iPA by 50.4%, IAA by 26.7%, while increased ABA by 108.5% when compared to the control at the end of drought stress (28 d). The turf quality and photosynthetic rate was positively correlated with cytokinins and IAA, but negatively correlated with ABA and ABA/cytokinins (CK) ratio under drought stress. The results of this study suggest drought stress-induced injury to Kentucky bluegrass may be associated with hormonal alteration, and the plants with higher cytokinins and IAA and less ABA under drought stress may have better photosynthetic function and performance.

Soil salinization is a major factor limiting crop growth and development in many areas. Switchgrass (Panicum virgatum L.) is an important warm-season grass species used for biofuel production. The objective of this study was to investigate antioxidant metabolism, proline,and protein variation associated with alkali-salt tolerance among 30 switchgrass lines and identify metabolic markers for evaluating alkali-salt tolerance of switchgrass lines. The grass lines were transplanted into plastic pots containing fine sand. When the plants reached E5 developmental stage, they were subjected to either alkali-salt stress treatment (150 mM Na+ and pH of 9.5) or control (no alkali-salt stress) for 20 d. The 30 switchgrass lines differed in alkali-salt tolerance as determined by the level of leaf malondialdehyde (MDA), antioxidant enzyme activity [(superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX)], proline and protein. Alkali-salt stress increased MDA, proline, SOD, reduced CAT activity, but its effect on protein and APX varied depending on lines. Wide variations in the five parameters existed among the 30 lines. In general, the lines with higher CAT activity and lower proline content under alkali-salt stress had less MDA, exhibiting better alkali-salt tolerance. Among the five parameters, CAT can be considered as valuable metabolic markers for assessment of switchgrass tolerance to alkali-salt stress.

Tryptophan is one of the 22 essential amino acids and serves as a building block for protein synthesis. Tryptophan also is a known precursor for auxin in plants. Previous research has shown that applying fertilizers amended with auxin coming from tryptophan may enhance plant defense chemical responses during limited soil moisture conditions. This occurs through increases in root production, as well as changes in endogenous hormone levels, resulting in plant growth regulating activity. Tryptophan is produced industrially through fermentation, and following that process, a byproduct remains. Tryptophan byproduct (TRP-B) is currently considered a waste product. However, the trace amounts of tryptophan and nitrogen containing compounds remaining in the byproduct following fermentation make it an intriguing subject for use as a growth promoter for turfgrasses. The objective of this research was to determine whether applications of TRP-B improve Penn A-4 creeping bentgrass (Agrostis stolonifera L.) performance more than applications of pure tryptophan and/or urea.

Water deficit is a major limiting factor for grass culture in many regions with physiological mechanisms of tolerance not yet well understood. Antioxidant isozymes and hormones may play important roles in plant tolerance to water deficit. This study was designed to investigate antioxidant enzymes, isozymes, abscisic acid (ABA), and indole-3-acetic acid (IAA) responses to deficit irrigation in two perennial ryegrass (Lolium perenne L.) cultivars contrasting in drought tolerance. The plants were subjected to well-watered {100% container capacity, 34.4% ± 0.21% volumetric moisture content (VWC), or deficit irrigation [30% evapotranspiration (ET) replacement; 28.6% ± 0.15% to 7.5% ± 0.12% VWC]} conditions for up to 8 days and rewatering for 4 days for recovery in growth chambers. Deficit irrigation increased leaf malondialdehyde (MDA) content in both cultivars, but drought-tolerant Manhattan-5 exhibited lower levels relative to drought-sensitive Silver Dollar. Superoxide dismutase (SOD) activity declined and then increased during water-deficit treatment. ‘Manhattan-5’ had higher SOD activity and greater abundance of SOD1 isozyme than ‘Silver Dollar’ under water deficit. Deficit irrigation increased catalase (CAT) and ascorbate peroxidase (APX) activity in ‘Manhattan-5’, but not in ‘Silver Dollar’. ‘Manhattan-5’ had higher CAT, APX, and peroxidase (POD) activity than ‘Silver Dollar’ during water limitation. Deficit irrigation increased mRNA accumulation of cytosolic cupper/zinc SOD (Cyt Cu/Zn SOD), whereas gene expression of manganese SOD (Mn SOD) and peroxisome APX (pAPX) were not significantly altered in response to deficit irrigation. No differences in Cyt Cu/Zn SOD, Mn SOD, and pAPX gene expression were found between the two cultivars under deficit irrigation. Water limitation increased leaf ABA and IAA contents in both cultivars, with Silver Dollar having a higher ABA content than Manhattan-5. Change in ABA level may regulate stomatal opening and oxidative stress, which may trigger antioxidant defense responses. These results indicate that accumulation of antioxidant enzymes and ABA are associated with perennial ryegrass drought tolerance. Activity and isozyme assays of key antioxidant enzymes under soil moisture limitation can be a practical screening approach to improve perennial ryegrass drought tolerance and quality.

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.

Heat stress reduces creeping bentgrass performance in temperate to sub-tropical climates. The research objective was to characterize effects of nitrogen (N) and cytokinin (CK) on creeping bentgrass under heat stress. In a 38°C/28°C chamber, grasses were treated with two nitrogen (2.5 and 7.5 kg N ha−1) and three CK rates (0, 10 and 100 μM) biweekly. Grass grown at high N had better turf quality, higher photochemical efficiency (Fv/Fm), normalized difference vegetation index (NDVI), and chlorophyll concentration at d15 and 28 than low N. CK increased NDVI at d15, with Fv/Fm of the CK100 treatment being 18% higher than that of CK0 at d28. Under high N with 100 μM CK, root trans-zeatin riboside (tZR) and isopentenyl adenosine (iPA) were 160% and 97% higher than under low N without CK, respectively. These results demonstrate positive impacts of N and CK on creeping bentgrass under heat, with N playing a dominant role.

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.

The presence of biologically active substances (BAS) in biosolids may enhance plant stress tolerance and growth, but the underlying mechanisms are not well understood. This greenhouse study investigated the effects of two biosolids: Alexandria (anaerobically digested; Class A product from the Alexandria Sanitation Authority Wastewater Treatment Facility in Alexandria, VA) and Blue Plains (lime-stabilized; Class B product from Washington, DC, Water and Sewer Authority) on tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] antioxidant enzyme activity associated with drought resistance. Treatments included a fertilizer control, Alexandria (11.9 g·kg−1 soil) and Blue Plains (17.6 g·kg−1 soil) biosolids to match the nitrogen in the control. Tall fescue physiological responses were measured under well-watered or drought-stressed conditions. Drought stress reduced turfgrass quality, photochemical efficiency (PE), and catalase (CAT) activity while increasing superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD) activities. The two biosolids improved turfgrass quality and root mass under both soil moisture regimes and delayed leaf wilting during moisture stress. The biosolids also improved PE, SOD, and APX activities relative to the control under both soil moisture regimes. The data suggest that biosolids application may improve antioxidant enzyme activity and subsequent drought resistance.

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.

Sustainable irrigation of turfgrass grown on coarse-textured soils with reclaimed water must avoid detrimental effects of soluble salts on plant growth and soil quality and groundwater enrichment of nitrogen (N) and phosphorus (P). The purpose of this study was (1) to investigate the effects of irrigating with municipal reclaimed water containing higher concentrations of soluble salts than potable water on turfgrass growth and quality and (2) to compare the effects of reclaimed and potable water on turfgrass assimilation and leaching of N and P. A sand-based medium plumbed to supply potable and reclaimed water and instrumented with lysimeters to collect leachate was planted with hybrid bermudagrass (Cynodon dactylon x Cynodon transvaalensis var. Tifsport) and creeping bentgrass (Agrostis stolonifera var. L-93). Both species produced high quality turfgrass with the reclaimed water. Although both grasses are moderately or highly salt tolerant when fully established, the bermudagrass growth and quality were reduced by the reclaimed water upon breaking dormancy, and its N use during this period was reduced. Continuous use of reclaimed water of the quality used in the study poses a potential soil Na accumulation problem. Both turfgrasses assimilated high amounts of N and P with minimal potential losses to groundwater. Published version

Field research was conducted to assess the effects of organic and inorganic soil amendments on soil humified carbon content and plant physiological properties. Long term applications of various types and rates of compost, poultry litter and inorganic fertilizer were assessed for their effects on corn [Zea mays (L.) Pioneer 31G20] and soybean [Glycine max (l.) Delta Pine 4933RR] grown in a Virginia (United States) Piedmont soil in 2004 and 2005. Treatment differences in leaf antioxidant activity were only observed in the corn plots. Corn fertilized with amendments supplying the crop's nitrogen needs, regardless of the source, had greater leaf nitrogen (+29%), chlorophyll (+33%), and protein contents (+37%), lower superoxide dismutase (−29%) and ascorbate peroxidase (−17%) activities, and lower malondialdehyde (−33%) contents than the control and low nitrogen treatments. Yield was strongly related to midseason leaf nitrogen contents (R2=0.87, p

Seaweed (Ascophyllum nodosum Jol.) extract-based cytokinins (SWEC) have been used to improve turfgrass stress tolerance, but optimum dosages for improving creeping bentgrass (Agrostis stolonifera L.) heat tolerance are lacking. This study was designed to examine effects of SWEC at various dosages on creeping bentgrass heat tolerance and to compare their effects to a trans-zeatin riboside (t-ZR)-standard in a growth chamber. The SWEC and t-ZR were applied to the foliage of 'L-93' creeping bentgrass four times (14-d interval) at 1, 10, and 100 μM. After the second application, the grass was subjected to heat stress for 49 d at 35/25°C (day/ night) in the initial experiment or 38/28°C (day/ night) in the second experiment. The SWEC and t-ZR treatments at 10 and 100 μM alleviated the decline of turfgrass quality and chlorophyll content. They also increased leaf t-ZR content and nitrate reductase (NR) activity, relative to the control, especially under 38/28°C (day/night). These data indicate that improvements under heat stress may be associated with an increase in plant t-ZR levels and NR activity due to SWEC or t-ZR application. Results suggest that repeated foliar application of SWEC at 10 μM may be an effective approach for improving turfgrass performance and heat stress tolerance.

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.

The presence of biologically active substances (BAS) in biosolids may enhance plant stress tolerance and growth, but the underlying mechanisms are not well understood. This greenhouse study investigated the effects of untreated biosolids, containing 2.1 μg indole-3-acetic acid (IAA) g -1 , and tryptophan-treated biosolids, containing 15.4 μg IAA g -1 , on tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] drought resistance. Treatments included a fertilizer control, indole-3-butyric acid (IBA) at 2 μM (hormone control), treated biosolids (2.95 g kg -1 soil), and untreated biosolids (2.97 g kg -1 soil). Nitrogen availability was equalized among treatments, and tall fescue physiological responses were measured under well-watered or moisture stress conditions. Treated biosolids improved turfgrass quality and root mass under both soil moisture regimes and delayed leaf wilting under moisture stress. At the end of the second drought cycle (2 February), treated biosolids improved quality and photochemical efficiency by 18 and 26% relative to the control. Treated biosolids increased leaf IAA by 122 and 52%, respectively, and trans-zeatin riboside by 100 and 189%, respectively, during each of two maximum drought periods. Leaf tissue increases of IAA and cytokinin were associated with greater content of these hormones in the soil. The data suggest that biosolids application may alter growth hormone (IAA and cytokinin) content and improve plant drought resistance.

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.O estresse hídrico é um dos mais importantes fatores ambientais que induz mudanças fisiológicas, como diminuição do potencial de água na célula, o fechamento dos estômatos e o desenvolvimento de processos oxidativos mediante a formação das espécies reativas de oxigênio (ROS). As enzimas antioxidantes superóxido dismutase (SOD), catalase (CAT) e ascorbato peroxidase (APX) são eficientes eliminadores das ROS. O objetivo deste estudo foi examinar como a aplicação de bioestimulantes com substâncias húmicas e aminoácidos em sua composição afeta os níveis de SOD, CAT e APX nos tecidos das folhas de plantas de milho e de soja cultivadas com ou sem estresse hídrico. Amostras de um Argissolo foram colocadas em vasos (4,5 L) onde foram adicionadas as doses dos bioestimulantes. Foram retiradas amostras de folhas para análise da atividade da SOD, CAT e APX nas plantas. A SOD e APX aumentaram nas plantas de milho com a aplicação do bioestimulante 1. A atividade da CAT não aumentou nas plantas com a aplicação dos bioestimulantes. As composições dos bioestimulantes não possibilitaram aumento na resistência ao estresse hídrico em plantas de milho e de soja submetidas ao estresse hídrico

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.

Trinexapac-ethyl (TE) is a popular plant growth regulator in the turfgrass industry not only for its effectiveness in reducing mowing requirements but for its positive effects on turf density and appearance. We hypothesized that reported side effects of TE such as increases in color, photochemical efficiency (PE) of photosystem II, tillering, and chlorophyll, may be related to changes in leaf cytokinin content. Our objective was to determine if TE influences leaf transzeatin riboside (t-ZR) content of three common turfgrass species. Sods of Kentucky bluegrass (Poa pratensis L.), creeping bentgrass (Agrostis stolonifera L.), and hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) were transplanted and grown in flats under a greenhouse mist system. Label-rate TE treatments were applied every 2 wk for 2 mo. Canopy PE, leaf color, canopy height, and leaf t-ZR contents were measured every 2 wk in 2003, with leaf total nonstructural carbohydrates (TNC) measurements added in 2004. A significant increase in tZR content was measured following sequential TE treatment in all three species in both years. Leaf TNC was consistently increased following the second TE application in creeping bentgrass and hybrid bermudagrass. While our data are nonspecific as to how TE increases leaf t-ZR, it appears that a shift in assimilate partitioning to basal organs could be a contributing factor. Whatever the mechanism, increased leaf t-ZR is likely to confer aesthetic, as well as functional, advantages to treated turfgrasses.

The presence of biologically active substances such as plant hormones in certain biosolids may enhance plant stress resistance by providing hormones directly or by stimulating the activity of microbes that supply substrates and hormones. This study was conducted to investigate if auxinboosted biosolids increase physiological fitness and drought stress resistance of Kentucky bluegrass (KBG; Poa pratensis L.) under greenhouse conditions. Calcined clay-filled containers were amended with auxin-boosted biosolids, non-treated biosolids, and indole butyric acid (IBA) at three rates. The control received inorganic N (202 kg ha -1 ) only. The KBG subjected to each treatment was grown under well-watered (80-90% field capacity (FC)) and drought stress (4050% FC) conditions. Root and shoot growth, visual quality, visual estimates of leaf wilting, canopy photochemical efficiency (PEc), leaf proline, cytokinin, and antioxidant enzyme activities were measured. The grass treated with auxin-boosted biosolids or IBA had greater root mass under drought stress compared to either the control or non-dosed biosolids treatments. Auxin-boosted biosolids improved turfgrass quality and delayed leaf wilting. The KBG amended with auxin boosted biosolids or IBA had greater PEc, leaf proline content, cytokinin trans-zeatin riboside (t-ZR) content, and antioxidant superoxide dismutase (SOD) activity under drought stress conditions when compared to the control. These data suggest that auxin-boosted biosolids may enhance defense chemical responses during limited soil moisture conditions, improving drought resistance. The beneficial effects of auxin-boosted biosolids may be closely associated with their increased activity of hormones such as auxin.

Background Switchgrass (Panicum virgatum L.) is a warm-season C4 grass that is a target lignocellulosic biofuel species. In many regions, drought stress is one of the major limiting factors for switchgrass growth. The objective of this study was to evaluate the drought tolerance of 49 switchgrass genotypes. The relative drought stress tolerance was determined based on a set of parameters including plant height, leaf length, leaf width, leaf sheath length, leaf relative water content (RWC), electrolyte leakage (EL), photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), intercellular CO2 concentration (Ci), and water use efficiency (WUE). Results SRAP marker analysis determined that the selected 49 switchgrass genotypes represent a diverse genetic pool of switchgrass germplasm. Principal component analysis (PCA) and drought stress indexes (DSI) of each physiological parameter showed significant differences in the drought stress tolerance among the 49 genotypes. Heatmap and PCA data revealed that physiological parameters are more sensitive than morphological parameters in distinguishing the control and drought treatments. Metabolite profiling data found that under drought stress, the five best drought-tolerant genotypes tended to have higher levels of abscisic acid (ABA), spermine, trehalose, and fructose in comparison to the five most drought-sensitive genotypes. Conclusion Based on PCA ranking value, the genotypes TEM-SEC, TEM-LoDorm, BN-13645-64, Alamo, BN-10860-61, BN-12323-69, TEM-SLC, T-2086, T-2100, T-2101, Caddo, and Blackwell-1 had relatively higher ranking values, indicating that they are more tolerant to drought. In contrast, the genotypes Grif Nebraska 28, Grenville-2, Central Iowa Germplasm, Cave-in-Rock, Dacotah, and Nebraska 28 were found to be relatively sensitive to drought stress. By analyzing physiological response parameters and different metabolic profiles, the methods utilized in this study identified drought-tolerant and drought-sensitive switchgrass genotypes. These results provide a foundation for future research directed at understanding the molecular mechanisms underlying switchgrass tolerance to drought. Electronic supplementary material The online version of this article (doi:10.1186/s13068-015-0342-8) contains supplementary material, which is available to authorized users.

Soil salt-alkalization is a major limiting factor for crop production in many regions. Switchgrass (Panicum virgatum L.) is a warm-season C4 perennial rhizomatous bunchgrass and a target lignocellulosic biofuel species. The objective of this study was to evaluate relative alkali-salt tolerance among 30 switchgrass lines. Tillers of each switchgrass line were transplanted into pots filled with fine sand. Two months after transplanting, plants at E5 developmental stage were grown in either half strength Hoagland’s nutrient solution with 0 mM Na+ (control) or half strength Hoagland’s nutrient solution with 150 mM Na+ and pH of 9.5 (alkali-salt stress treatment) for 20 d. Alkali-salt stress damaged cell membranes [higher electrolyte leakage (EL) ], reduced leaf relative water content (RWC), net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr). An alkali-salt stress tolerance trait index (ASTTI) for each parameter was calculated based on the ratio of the value under alkali-salt stress and the value under non-stress conditions for each parameter of each line. Relative alkali-salt tolerance was determined based on principal components analysis and cluster analysis of the physiological parameters and their ASTTI values. Significant differences in alkali-salt stress tolerance were found among the 30 lines. Lowland lines TEM-SEC, Alamo, TEM-SLC and Kanlow were classified as alkali-salt tolerant. In contrast, three lowland lines (AM-314/MS-155, BN-13645-64) and two upland lines (Caddo and Blackwell-1) were classified as alkali-salt sensitive. The results suggest wide variations exist in alkali-salt stress tolerance among the 30 switchgrass lines. The approach of using a combination of principal components and cluster analysis of the physiological parameters and related ASTTI is feasible for evaluating alkali-salt tolerance in switchgrass. Published version

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.

The fatty acid composition of warm‐season turfgrasses is physiologically regulated by environmental changes, particularly temperature. Species or cultivars, which have increased degree of unsaturation, usually have a greater freeze resistance. Quantifying fatty acid composition not only can help understand the freeze‐resistant mechanism of warm‐season turfgrasses but also in practice develop a management strategy for better turf. A high‐performance liquid chromatography (HPLC) method was developed for this purpose. The method is based on the bromophenacyl reaction of fatty acids and separation on a C8 column with gradient elution. Information on limit of identification, linearity of quantification, response factor, and derivatization conditions is presented and discussed. The method presented is simple to apply and provides an alternative to the traditional gas chromatography (GC) method. The results of fatty acid composition from a field freezing‐resistance experiment are discussed.

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.

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.

A primary economic concern of sod producers is loss of sod quality during the transportation and storage phases of a sale. Previous research and field experience indicate that soil and plant respiration rates, and thus the rate of pallet heating, may be reduced by harvesting in the morning, lowering mowing heights and removing clippings, and minimizing tissue nitrogen and soil moisture before harvest. However, even when proper cultural guidelines are followed, excessive sod heating and tissue damage often occurs. Various pre- and post-harvest chemical treatments aimed at protecting leaf tissue integrity during and after supraoptimal heating have shown promise for increasing transplant success. One of these compounds is the natural plant growth regulator salicylic acid (SA). This study was conducted to investigate the influence of pre-harvest foliar application of SA on transplant injury and root strength of tall fescue (TF; Festuca arundinacea Schreb.) and Kentucky bluegrass (KBG; Poa pratensis L.) sod following supraoptimal heating. Salicylic acid was applied at 0.5 kg ha -1 to the turfgrass 10 d before harvest and canopy photochemical efficiency was measured 1 d before harvest. Harvested and rolled sod was subjected to high temperature stress (38-40°C for 72 or 96 h), transplanted into the field, and injury and root strength were determined. Application of SA enhanced the pre-harvest canopy photochemical efficiency of KBG and TF sod in both years. Averaged over years and heat duration, SA increased canopy photochemical efficiency by 12% for KBG and 14% for TF. Salicylic acid reduced visual injury and enhanced post-harvest root strength in both years. Averaged over years and heat duration, SA increased transplant root strength by 26% for KBG and 9% for TF. These data suggest that pre-harvest foliar SA application may improve shelf life and transplant success of supraoptimally heated cool-season sod.

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.