HORTSCIENCE 45(4):650–653. 2010. center (Peng and Gilmore, 2003; Taiz and Zeiger, 1998). When the absorption of light radiation exceeds the capacity of photosyn- Pigment Concentrations among thesis, excess excitation energy can result in the formation of triplet excited chlorophyll 3 1 Heat-tolerant Turfgrasses ( Chl) and reactive singlet oxygen ( O2). 1 Carotenoid pigments protect photosynthetic Mark G. Lefsrud structures by quenching excited 3Chl to dis- Bioresource Engineering Department, McGill University, 21 111 Lakeshore sipate excess energy (Tracewell et al., 2001) 1 Boulevard, Ste-Anne-de-Bellevue, Quebec H9X 3V9, Canada and binding O2 to inhibit oxidative damage (Demmig-Adams et al., 1996; Tracewell John C. Sorochan and Dean A. Kopsell et al., 2001). The carotenoid molecule then Plant Sciences Department, The University of Tennessee, 2431 Joe Johnson slowly releases this excess energy as heat and Dr., Knoxville, TN 37996-4561 inhibits further oxidative damage. Caroten- oids are also integral constituents of mem- J. Scott McElroy branes (Peng and Gilmore, 2003; Taiz and Department of Agronomy and Soils, Auburn University, 202 Funchess Hall, Zeiger, 1998) and may be involved in struc- Auburn, AL 36849-5412 tural stabilization of membranes and reduc- tion of lipid peroxidation (Frank and Cogdell, Additional index words. b-carotene, carotenoids, chlorophyll a and b, HPLC, lutein, 1996). seasonality, Poa pratensis L., Festuca arundinacea Schreb Carotenoid accumulation appears to be shaped by a plant species’ physiological, Abstract. Heat-tolerant bluegrass varieties were developed to resist dormancy and retain genetic, and biochemical attributes as well pigmentation during heat stress events. The objective of this study was to investigate the as environmental growth factors such as influence of grass species, nitrogen (N) fertilization, and seasonality on the accumulation light, temperature, and fertility (Kopsell patterns of lutein, b-carotene, and chlorophyll a and b in the leaf tissues of turfgrass. The et al., 2004; Kurilich et al., 1999; Lefsrud heat-tolerant bluegrass cultivars Dura Blue and Thermal Blue (Poa pratensis L. · Poa et al., 2005, 2006). Kurilich et al. (1999) arachnifera Torr.), Apollo kentucky bluegrass (Poa pratensis L.), and Kentucky 31 tall reported genotypic differences among sub- fescue (Festuca arundinacea Schreb.) were compared for the accumulation of plant species of Brassica oleracea L. (broccoli) pigments. Evaluations were conducted over 2 consecutive years (Years 4 and 5 after accounted for 79% of the variance of establishment) during two different seasons (spring and summer) and under varying N b-carotene concentration, 82% of the vari- fertilization. Fertilizer applications of 5, 14, and 27 g N/m2/year resulted in a significant ance of a-tocopherol (vitamin E), and 55% of positive correlation for the accumulation of leaf blade lutein and chlorophyll a and b, but the variance of ascorbate (vitamin C). There- not for b-carotene. The accumulation of the four measured plant pigments among the fore, it is critical to consider both genetic and grasses was significantly different with ‘Apollo’ having the largest concentration of environmental influences when determining pigments followed by ‘Dura Blue’, ‘Thermal Blue’, and finally ‘Kentucky 31’. Specif- plant carotenoid accumulation. ically, when comparing the cultivars Apollo and Kentucky 31, the pigment levels Nitrogen (N) is critical in plant growth decreased 27%, 26%, 26%, and 23% for lutein, b-carotene, and chlorophyll a and b, and development and is an essential compo- respectively. The interesting observation of the analysis of the grass pigment concentra- nent of amino acids, proteins, nucleic acids, tions was that the least reported heat-tolerant cultivar in our study (‘Apollo’) had the and many enzymes. Plants grown under largest measured pigment concentrations. limited N levels have reduced Chl a and Chl b pigments, resulting in stunted plants and characteristic leaf chlorosis (Marschner, Kentucky bluegrass (Poa pratensis L.) as kentucky bluegrass and, with higher tem- 1995). Increased additions of N usually result and tall fescue (Festuca arundinacea perature tolerance, can be grown as a sub- in increased yield of crop plants (Hochmuth Schreb.; syn., Lolium arundinaceum Darby- stitute for kentucky bluegrass in warmer et al., 1999; Mills and Jones, 1996). How- ever, toxicity from overapplication of N shire) are cool-season grasses commonly climatic regions but is poorly adapted for concentrations is possible but is not very used for lawns in temperate regions of North temperate and transition regions (Read et al., common in turfgrass. Therefore, proper N America. However, these grasses can be 1994). The resultant hybrid heat-tolerant management is critical for optimum plant exposed to heat stress during the growing bluegrass (P. pratensis · P. arachnifera)is season in temperate regions. During high performance. reported to have the ability to survive heat Seasonality effects caused by increases in stress events, kentucky bluegrass can become stress events (Su et al., 2007) and, from visual dormant and lose pigmentation (Beard, 1973; irradiance, photoperiod, temperature, and comparison, may be able to maintain tissue rainfall can directly influence the growth Su et al., 2007). Tall fescue has increased pigmentation [carotenoids and chlorophylls heat and drought tolerance, but it is usually and photosynthetic rate of plants, resulting (Chl)] throughout the growing season (Su in increased production of carbohydrates and not selected over the finer textured kentucky et al., 2007; Teuton et al., 2007). However, bluegrass. Researchers have been develop- total biomass (Mills and Jones, 1996). Summer- nothing in the literature has been reported on grown kale (Brassica oleracea L. var. ace- ing heat-tolerant bluegrasses through hybrid- the pigment concentration independent of the ization of kentucky bluegrass and texas phala D.C.) had higher lutein and b-carotene stress events and during the stress events. concentrations than kale grown during winter bluegrass (Poa arachnifera Torr.). Texas Carotenoids are lipid-soluble yellow, or- bluegrass has similar visual characteristics months when light levels and photoperiod ange, and red pigments synthesized in higher were reduced (de Azevedo and Rodriguez- plants, fungi, algae, and bacteria. Caroten- Amaya, 2005). oids function to help harvest light energy Kentucky bluegrass is the major temper- Received for publication 13 Jan. 2010. Accepted during photosynthesis and to dissipate excess ate weather turfgrass, but it becomes dormant for publication 19 Feb. 2010. energy before damage occurs. Within the and loses pigmentation during either individ- This material is based on work supported by the thylakoid membranes of chloroplast organ- Tennessee Turfgrass Association, the Scotts Com- ual or combined drought and heat stress pany (Marysville, Ohio), and the University of elles, carotenoids are found bound to specific events (Su et al., 2007; Teuton et al., 2007). Tennessee Agricultural Experiment Station. protein complexes of the photosystems. Ca- With the development of heat-tolerant blue- 1To whom reprint requests should be addressed; rotenoids are located in both the antenna grass cultivars, dormancy has become less of e-mail [email protected]. pigments and the photosynthetic reaction an issue and the grass is able to better retain

650 HORTSCIENCE VOL. 45(4) APRIL 2010 j TURF MANAGEMENT more of its visual quality during stress con- which is based on the method of Khachik et al. integrated using 1100 HPLC ChemStation ditions. However, it is unclear whether tradi- (1986). A frozen 0.25-g subsample was placed Software (Agilent Technologies). Peak as- tional and heat-tolerant turfgrasses are able to into a Potter-Elvehjem tissue grinder tube signment was performed by comparing re- accumulate plant pigments (lutein, b-carotene, (Kontes, Vineland, NJ). A 0.8-mL volume of tention times and line spectra obtained from and Chls) over the growing season to allow the internal standard, ethyl-b-apo-8#-carote- the photodiode array detection with authentic the turfgrass to tolerate stress events. There- noate (Sigma Chemical Co., St. Louis, MO) standards (lutein from Carotenature, Lupsin- fore, the objective of this study was to de- and 2.5 mL of tetrahydrofuran stabilized with gen, Switzerland; b-carotene, Chl a, and Chl termine the accumulation patterns of lutein, 25 mgL–1 2,6-Di-tert-butyl-4-methoxyphenol b from Sigma Chemical Co.). Recovery rates b-carotene, Chl a, and Chl b in the leaf tissues were added to the grinding tube. The sample of ethyl-b-apo-8#-carotenoate during extrac- of heat-tolerant and nonheat-tolerant turf- was homogenized in the tube with 25 in- tion were above 90%. grass between turfgrass species, N fertility, sertions of the grinder pestle attached to a drill Statistical analysis. The experimental and sampling time (during the spring and press (Model Craftsman 15 inch Drill Press; design was a randomized complete block summer seasons). Sears Co., Hoffman Estates, IL) at 540 rpm design repeated in time with analysis using while immersed in ice. The tube was placed the multivariate generalized linear model Material and Methods into a clinical centrifuge for 3 min at 500 gn. procedure using SPSS (Chicago, IL. Multi- The supernatant was removed with a Pasteur variate analysis of variance determined sig- Turfgrass culture. The turfgrass cultivars pipette, placed into a conical 15-mL test tube, nificance of the main effects of treatments, were field-grown in Knoxville, TN (lat. capped, and held on ice. The sample pellet was cultivar, sample time, and their interactions 35.49N, long. 83.56W) with seeding oc- resuspended in 2 mL of tetrahydrofuran and and post hoc tests were complete using curring on 23 Oct. 2002. Establishment and homogenized with 25 insertions of the grind- Tukey’s honestly significant difference. maintenance was performed as outlined by ing pestle. The tube was centrifuged for 3 min Teuton et al. (2007) with only one tall fescue at 500 gn and the supernatant was collected analyzed for this experiment. Kentucky blue- and combined with the first extracted super- Results and Discussion grass and tall fescue varieties were seeded at natant. The extraction procedure was repeated 100 and 300 kgha–1, respectively. Nitrogen twice more until the supernatant was colorless. Turfgrass fresh mass pigment accumula- was applied as urea and occurred as reported The pellet was discarded and the combined tion was significantly influenced by grass by Teuton et al. (2007). Turfgrasses were four supernatants were placed in a 40 C water cultivar, N treatment concentrations, and fertilized at the time of seeding and monthly bath and reduced to 0.5 mL using N gas time of sampling with no significant interac- thereafter until December with N applied at (N-EVAP 111; Organomatic Inc., Berlin, tion effect expressed from the statistical 2.4 gm–2 to ensure adequate turfgrass den- MA). A total of 2.5 mL MeOH and 2 mL tetra- analysis. The four grass cultivars varied sity. Fertilization started in April of each year hydrofuran were added to the sample, which significantly in pigment accumulation for and included N applied at 5, 14, 27 g N/m2/ was then vortexed and filtered through a 0.2-mm lutein (P # 0.001), b-carotene (P # 0.001), year. The 5-g N/m2 treatments were applied polytetrafluoroethylene filter (Econofilter Chl a (P # 0.001), and Chl b (P # 0.001). as 2.5 g N/m2 in April and September. The PTFE 25/20; Agilent Technologies, Wilming- When the turfgrass cultivars were compared, 14-g N/m2 treatments were applied as 2.3 g ton, DE) using a 5-mL syringe (Becton, Dick- ‘Apollo’ and ‘Dura Blue’ always had more of N/m2 in April and May and 4.7 g N/m2 in inson and Company, Franklin Lakes, NJ) the four plant pigments than did ‘Kentucky September and December. The 27-g N/m2 before high-performance liquid chromatogra- 31’, and ‘Apollo’ always had more of all four treatments were applied as 6 g N/m2 in April, phy (HPLC) analysis. of the plant pigments than ‘Thermal Blue’ May, June, July, September, and December. High-performance liquid chromatogra- (Table 1). The grass cultivars tested included a tall phy analysis. An HPLC unit with photodiode Differences among turfgrass cultivars fescue, ‘Kentucky 31’, a kentucky bluegrass, array detector (Agilent 1100; Agilent Tech- resulted in varying accumulation levels of ‘Apollo’, and two F1 hybrids, ‘Thermal Blue’ nologies, Palo Alto, CA) was used for pig- tissue lutein, b-carotene, and both Chls. Re- (formerly HB-129) and ‘Dura Blue’ (for- ment separation. All samples were analyzed search by Bremer et al. (2003) showed that merly HB-329) (Scotts Company Inc., Mar- for carotenoid compounds using a Pronto SIL the tall fescue ‘Dynasty’ had the highest ysville, OH). The most heat-tolerant turfgrass 5.0 mm 250 · 4.6-mm column (200-5-C30; visual quality rating (National Turfgrass in our study was ‘Kentucky 31’ and then Bischoff Chromatography, Leonberg, Ger- Evaluation Program) followed by the hybrid ‘Thermal Blue’, ‘Dura Blue’, and finally many) fitted with a 4 · 3.0 mm, 7.0-mm guard ‘Thermal Blue’, kentucky bluegrass ‘Apollo’ based on previous research by Su column compartment. The column was main- ‘Apollo’, and finally the hybrid ‘Dura Blue’. et al. (2007) and Teuton et al. (2007). The tained at 30 C using a thermostatic column Under an irrigation treatment of 40% re- turfgrass and N treatment were separated into compartment. The eluent was 11% methyl- placement of evapotransportation (severe randomized complete blocks with three rep- tert butyl ether, 89% methanol, 0.1% triethy- drought), the top-rated grass for visual qual- lications. Plots were not irrigated and stan- amine in water (v/v). The flow rate was 1.0 ity was still ‘Dynasty’ followed by ‘Thermal dard mowing (7.5-cm mowing height) was mLmin–1 for 55 min. Eluted compounds Blue’, ‘Dura Blue’, and finally ‘Apollo’. performed once a week over the growing from a 10.0-mL injection were detected at However, Bremer et al. (2006) reported season. 453 nm (carotenoids and internal standard) similar responses in the overall growth Turfgrass was sampled on 10 Mar. and 31 and 652 nm (Chls) with data collected and among the three turfgrasses, ‘Thermal Blue’, July 2006 and 12 Mar. and 22 July 2007. These dates were chosen for measurement during the spring and summer seasons and Table 1. Tissue lutein, b-carotene, and chlorophyll a and b pigments expressed on a fresh mass (FM) basis replicated as close as possible for days after for the kentucky bluegrass ‘Apollo’, two hybrid heat-tolerant bluegrass ‘Thermal Blue’ and ‘Dura mowing (5 d). At sampling, the turfgrass was Blue’, and tall fescue ‘Kentucky 31’.z hand-cut with scissors, separated for only Pigment concn (mg/100 g FM) green tissue samples, and weighed for each of the three N treatments, four cultivars, and Cultivar Lutein b-carotene Chlorophyll a Chlorophyll b three replication combinations. Turfgrass Apollo 55.5 ± 2.5 a 24.0 ± 1.3 a 514.7 ± 25.0 a 168.4 ± 6.9 a Dura Blue 52.6 ± 1.7 a 22.5 ± 1.1 ab 478.8 ± 22.0 ab 162.1 ± 6.3 a samples were stored at –80 C before Thermal Blue 44.2 ± 2.2 b 20.2 ± 1.3 bc 432.5 ± 28.2 bc 139.9 ± 8.8 b high-performance liquid chromatography Kentucky 31 40.5 ± 2.1 b 17.8 ± 1.2 c 377.9 ± 29.5 c 129.6 ± 8.2 b analysis. zData were combined over 2 years from three replications of three nitrogen treatments (5, 14, and 27 g/m2/ Carotenoid and chlorophyll determination. year) and two seasons (spring and summer). The turfgrass pigments were extracted and Mean values ± SE. separated according to Kopsell et al. (2004), Tukey’s HSD significance at P # 0.05.

HORTSCIENCE VOL. 45(4) APRIL 2010 651 ‘Dura Blue’, and ‘Apollo’, in a Kansas field levels resulting in less pigment accumulation reported that increased temperatures resulted study. Genetic variation for carotenoid accu- (Lefsrud et al., 2007). Under limited N, these in a decrease in Chl accumulation in two tall mulation can be found in a number of plants, pigments are reduced, resulting in leaf tissue fescue cultivars. However, temperature was including spinach (Spinacia oleracea L.) chlorosis (Marschner, 1995). Previously, not considered a significant influencing fac- (Lefsrud et al., 2007), broccoli (Brassica Lefsrud et al. (2007) reported a maximum tor with the average temperature 10 d before oleracea L. var. italica Plenck) (Almela lutein, b-carotene, and Chl accumulation sampling being virtually identical in the et al., 1991; Daood et al., 1996), and kale occurring on hydroponically grown spinach spring at 10 C for both years (maximum (Kopsell et al., 2004). Zhang et al. (2005) at 52 mg N/L for one cultivar but continuing temperature was 24 C in 2006 and 21 Cin reported that when kentucky bluegrass was to increase for the other reported cultivar. In 2007, minimum was –3 C both years) and exposed to ultraviolet B irradiation, some a field study with winter wheat (Triticum in the summer at 25 C in 2006 and 24 Cin cultivars accumulated Chls and carotenoids aestivum L.), Follett et al. (1992) reported 2007 (maximum/minimum was 35 C/18 C at a greater rate than others. The bluegrass a 19% increase in Chl with an increase in N and 33 C/17 C, respectively). Research by cultivars that accumulated Chls at the great- leaf concentration from 28 to 38 gkg–1. Jiang and Carrow (2005) on seashore paspa- est rate (darkest color) resulted in an im- Mangiafico and Guillard (2007) showed that lum (Paspalum vaginatum Swartz) and hy- proved tolerance to ultraviolet B light. In our increases in leaf N resulted in increased brid bermudagrass (Cynodon dactylon L. · C. current study, the level of ultraviolet light pigmentation for kentucky bluegrass. The transvaalensis Burtt Davy) cultivars showed was not measured. Zhang et al. (2005) highest levels of pigment accumulation (ex- that increased drought stress resulted in de- showed that genetics and cultivar can have cluding b-carotene) in the current study creases of 12% to 27% in turf quality a significant effect on pigment accumulation. occurred at the highest N treatment concen- expressed mainly as a reduction in plant McElroy et al. (2006) reported that for tration (Table 2). pigmentation. This study investigated differ- creeping bentgrass (Agrostis stolonifera L.), Sampling time had a significant effect on ent species and varieties than our article, but levels of b-carotene decreased with no the accumulation of lutein (P # 0.001), the research by Jiang and Carrow (2005) change in lutein as irradiance increased. b-carotene (P # 0.001), Chl a (P # 0.001), support our explanation that a decrease of However, other carotenoids (zeaxanthin, and Chl b (P # 0.001). The sampling time rainfall of 40% between the 2 years of the antheraxanthin, and violaxanthin) increased and year of sampling had a significant impact study could explain the significant decrease in response to increased irradiance, which on the accumulation rate of the pigments in plant pigmentation in our turfgrass varie- may be potentially attributable to selection within the turfgrass (Table 3). However, no ties measured between years. efforts of more stress-tolerant varieties. An direct conclusions could be made because interesting observation of the analysis of the data from Year 1 resulted in an increase in grass pigment concentrations in the current pigments from the spring to the summer, Conclusion study was that the least reported heat-tolerant whereas in Year 2, a decrease in pigmenta- Four turfgrasses (kentucky bluegrass cultivar in our study, ‘Apollo’, had the high- tion resulted. An observation between the 2 ‘Apollo’, two hybrid heat-tolerant bluegrass est measured pigment concentrations. years of data was that Year 1 had higher ‘Thermal Blue’ and ‘Dura Blue’, and tall The N treatments also had a significant rainfall, resulting in drought-stressed grass in fescue ‘Kentucky 31’) were analyzed for the impact on pigment accumulation for lutein Year 2. Year 1 had 78.9 mm of rainfall, pigment carotenoids lutein, b-carotene, and (P = 0.019), Chl a (P = 0.036), and Chl b (P = whereas Year 2 had 46.2 mm of rainfall for the two Chl a and b to determine the impact 0.021), but not for b-carotene (P = 0.051). 21 d before sampling with an expected that genetics and environment have on pig- When the N treatment levels were compared, average rainfall of 100.8 mm for the month ment accumulation. Increasing N fertilization 27 g N/m2/year consistently had the highest of July (www.powellweather.com). from 5 to 27 g N/m2/year resulted in a signif- levels of measured pigments with a reduction The impact of temperature on the quality icant increase in lutein and Chl a and b, but for 14 g N/m2/year and then for 5 g N/m2/year of turfgrass has been reported by Su et al. had no impact on the accumulation of b- (Table 2). Nitrogen has been correlated to (2007) and in carotenoid accumulation by carotene. A result of the analysis of the grass lutein, b-carotene, and Chl with lower N McCurdy et al. (2008). Cui et al. (2006) pigment concentrations is that the most heat- tolerant turfgrass in our study was the tall fescue ‘Kentucky 31’ and decreasing to Table 2. Tissue carotenoid and chlorophyll pigments expressed on a fresh mass (FM) basis from three different nitrogen treatment levels (5, 14, and 27 g/m2/year).z ‘Thermal Blue’, ‘Dura Blue’, and finally ‘Apollo’. However, the grasses with the Nitrogen treatment Pigment concn (mg/100 g FM) highest pigmentation were the reverse with (g/m2/year) Lutein b-carotene Chlorophyll a Chlorophyll b ‘Apollo’ having the largest concentration of 5 45.2 ± 2.2 a 19.7 ± 1.0 427.6 ± 23.0 a 140.0 ± 7.0 a pigments then ‘Dura Blue’, ‘Thermal Blue’, 14 48.9 ± 2.0 ab 21.8 ± 1.1 458.0 ± 21.8 ab 152.7 ± 6.8 ab and finally ‘Kentucky 31’. This result sug- 27 50.4 ± 2.1 b 22.0 ± 1.2 467.4 ± 27.7 b 157.3 ± 7.3 b z gests that having elevated levels of lutein, Data were combined from three replications of four grass cultivars (kentucky bluegrass ‘Apollo’, two b-carotene, and Chl a and b may actually hybrid heat-tolerant bluegrass ‘Thermal Blue’ and ‘Dura Blue’, and tall fescue ‘Kentucky 31’) with samples taken during the spring (March) and summer (July), repeated over 2 years. result in less heat stress tolerance, possible as Mean values ± SE. a result of increased partitioning of photo- Tukey’s HSD significance at P # 0.05. synthates to pigment production.

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