Physiological acclimation of seashore paspalum and bermudagrass to low light

Scientia Horticulturae 105 (2005) 101–115 www.elsevier.com/locate/scihorti

Physiological acclimation of seashore paspalum and bermudagrass to low light Yiwei Jiang a,1, Robert N. Carrow a,*, Ronny R. Duncan b a

Department of Crop and Soil Sciences, University of Georgia at Experiment Station, 1109 Experiment Street, Griffin, GA 30223-1797, USA b Turf Ecosystems, LLC, P.O. Box 781482, San Antonio, TX 78278-1482, USA Accepted 11 November 2004

Abstract Physiological responses play an important role in low light tolerance in plants. The acclimations of photosynthetic activities, total soluble protein, and antioxidant enzyme were characterized in low light-tolerant ‘Sea Isle 1’ seashore paspalum (Paspalum vaginatum Swartz) and intolerant ‘TifSport’ hybrid bermudagrass (Cynodon dactylon L.  Cynodon transvaalensis Burtt-Davy) grown under high light control (HL, 500–900 mmol m 2 s 1), low light (LL, 60–100 mmol m 2 s 1), and LL to HL transfer in the greenhouse. Shade cloth was used to create the LL treatment. Sea Isle 1 maintained higher turf quality and normalized difference vegetation index (NDVI) than that of TifSport under LL. Chlorophyll a (Chl a) and chlorophyll b (Chl b) content were reduced by 34–36% in Sea Isle 1 and by 51–63% in TifSport at day 35 of LL, respectively, relative to their HL levels. Chlorophyll a/b ratio (Chl a/b) generally was not affected by LL for Sea Isle 1, but the values under LL increased to above HL level in TifSport. Photochemical efficiency (Fv/Fm) remained constant under LL in both species. Total soluble protein content (SPC), water-soluble carbohydrate content (WSC), catalase (CAT) activity, and ascorbate peroxidase (APX) activity decreased 22% and 55%, 52% and 66%, 68% and 77%, and 40% and 66% under LL for Sea Isle 1 and TifSport, respectively. After grasses were transferred from LL to HL, Chl a, Chl b, SPC, WSC, and CAT activity increased, but to a higher extent in Sea Isle 1. A short-term reduction in Fv/Fm was exhibited in both species after light transfer but a further decrease was found in TifSport. The results indicated that the relative higher levels of Chl, SPC, WSC, and antioxidant enzyme activities under LL contributed to better LL tolerance in grass species. More rapid recovery of these parameters from LL to HL was a

* Corresponding author. Tel.: +1 770 228 7277; fax: +1 770 412 4734. E-mail address: [email protected] (R.N. Carrow). 1 Present address: Department of Agronomy, Purdue University, West Lafayette, IN 47907-2054, USA. 0304-4238/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2004.11.004

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characteristic of the tolerant Sea Isle 1 seashore paspalum relative to the intolerant TifSport bermudagrass. # 2004 Elsevier B.V. All rights reserved. Keywords: Turfgrass; Low light tolerance; Physiological mechanisms

1. Introduction Low light (LL) is a major problem that influences turfgrass quality, and the estimated turfgrass area under shade conditions in the U.S. is about 25% (Beard, 1973). Information is limited regarding mechanisms of shade acclimation of turfgrass species, especially for those differing in LL tolerance. Seashore paspalum (Paspalum vaginatum Swartz) is a relatively new warm-season turfgrass, and the hybrid bermudagrasses (Cynodon dactylon L.  Cynodon transvaalensis Burtt-Davy) has been widely used throughout the warm climate regions. Although both grasses have similar uses in turf areas, their comparative physiological mechanisms under LL and recoverability from LL to high light (HL) conditions are not known. Understanding of physiological mechanisms that contribute to LL tolerance would benefit turfgrass management and breeding programs. Previous studies in woody species and agronomic crops have indicated that physiological mechanisms exhibit complex patterns during shade acclimation and results are often conflicting. Concerning photosynthetic activities, LL increases (Zhao and Oosterhuis, 1998; Khan et al., 2000), decreases (Hashemi-Dezfouli and Herbert, 1992; Logan et al., 1998) or causes no changes in chlorophyll content (Olsen et al., 2002) in different plant species. The ratio of chlorophyll a to chlorophyll b (Chl a/b) of leaves remains stable (Chow et al., 1991; Maxwell et al., 1999) or is lower (Schwanz et al., 1994; Grace and Logan, 1996; Zhao and Oosterhuis, 1998) under LL, compared to HL. Photochemical efficiency (Fv/Fm) is an indicator of the maximum quantum efficiency of photosystem II photochemistry (Bjo¨ rkmann and Demmig, 1987). This trait declined in conifer species (Khan et al., 2000), increased in woody species (Groninger et al., 1996), or did not change in Socratea exorrhiza (Mart.) Wendl. (Araus and Hogan, 1994) under LL. Soluble proteins, the major constituents of the chloroplast stroma important for the photosynthetic carbon reduction cycle, are also affected by LL. LL reduces soluble protein content (SPC) in some plant species (Besford, 1986; Eckardt et al., 1997; Logan et al., 1998). In contrast, Maxwell et al. (1999) found that the total soluble protein content, expressed on fresh weight basis, was higher in LL-acclimated than HL-acclimated Guzmania monostachia L., but when expressed on a chlorophyll basis, the amount of soluble protein was constant for LL-acclimated and HL-acclimated plants. In addition to relative long-term shade effects, many plant species including turfgrasses often experience fluctuating irradiance due to influences of tree canopy, buildings or different weather patterns. Shaded plants exposed to HL are more susceptible to photoinhibition than plants grown under full sunlight (Anderson and Osmond, 1987; Osmond, 1994). The absorption of excess light can potentially lead to an enhanced production of singlet oxygen and reactive oxygen species (Elstner and Osswald, 1994; Allen, 1995). Hydrogen peroxide (H2O2) is one of the toxic oxygen species that can attack

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membranes and proteins, resulting in lipid peroxidation. Plants have evolved antioxidant enzyme systems to scavenge H2O2. In the peroxisome and mitochondria, H2O2 is detoxified by catalase (CAT) (Scandalios, 1994), and by ascorbate peroxidase (APX) in chloroplasts (Gillham and Dodge, 1986). Logan et al. (1998) found that CAT and APX activities increase with increasing photosynthetic photon flux densities (PPFDs). Burritt and Mackenzie (2003) reported that LL to full sunlight transfer caused a rapid increase in CAT activity and H2O2 content in Begonia  erythrophylla J. Neuman, however, decreased CAT activity was observed in Norway spruce (Picea abies L.) when transferred from LL to HL (Schittenhelm et al., 1994). These investigations indicated that physiological acclimation of leaves to variable light conditions was closely associated with acclimation of photoprotective mechanisms. Collectively, variations in the physiological mechanisms discussed above suggest a complex situation for plant species in response to variable light environments with different mechanisms important for different species. Although physiological mechanisms vary with plant species under LL conditions, we speculate that a combination of physiological adjustments to changing light situations may be a characteristic in LLtolerant turfgrass species. Better LL tolerance has been observed in seashore paspalum compared to bermudagrass in a field study (Jiang et al., 2004), but physiological mechanisms associated with LL tolerance in these two species have not been determined. Therefore, the objectives of this study were to investigate shade acclimation of photosynthetic activities, soluble protein, and antioxidant enzymes in ‘Sea Isle 1’ LLtolerant seashore paspalum and hybrid ‘TifSport’ LL-intolerant bermudagrass; and to examine performance of two grass species when shifting from LL to HL conditions.

2. Materials and methods 2.1. Plant material and growth conditions Sods of Sea Isle 1 seashore paspalum (P. vaginatum Swartz) (LL-tolerant) and TifSport hybrid bermudagrass (C. dactylon L.  C. transvaalensis Burtt-Davy) (intolerant) were collected from field plots at The University of Georgia Experiment Station in Griffin. These two grasses were chosen based on their LL performance in a field study (Jiang et al., 2004) and their similar uses in turf area. Grasses were grown in pots (24 cm diameter and 23 cm depth) containing Earthgro Organic Fertilizer/Compost (N–P–K, 0.05:0.05:0.05) and sand (1:1) in greenhouse for 32 days before a LL treatment was initiated in October 2002. The temperature in the greenhouse was 25  2/18  2 8C (day/night) and the photoperiod was 10 h. The grasses were fertilized twice monthly with water-soluble fertilizer (N–P–K, 15:0:15) and were mowed at 1.3 cm twice weekly using a hand clipper with clippings removed. The pots were irrigated twice weekly with tap water to well-watered conditions. Two irradiance treatments, high light (HL, control) and low light (LL), were used. HL refers to a light intensity in the range of 500–900 mmol m 2 s 1 corresponding to midday maximum photosynthetically active radiation (PAR) during the period of the experiment. LL was imposed by reducing irradiance with one layer of black shade cloth (Hummert

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International, Earth City, MO, USA) above the benches, which provided a light intensity in the range of 60–100 mmol m 2 s 1. Light intensity (PAR) was measured with a LI-250 light meter (LI-Cor Inc., Lincoln, NE, USA). Supplementary lighting was provided to grasses when an overcast or rainy day occurred during the experiment. An additional fan was used to adjust temperature and humidity inside the shade environment to levels similar to the area with HL. After 35 days of LL treatment, turf quality of both tolerant and intolerant grass declined to unacceptable levels, and thus were transferred to HL for reacclimation. 2.2. Turf quality and canopy reflectance Turf quality was rated visually based on color, shoot density and uniformity, where 1 = brown, dead turf and 9 = ideal dark green, best density and uniformity for the species. The minimum acceptable level for quality was 6. Canopy spectral reflectance was collected between 400 and 1100 nm wavelengths at 3 nm intervals with a Unispec Spectral Analysis System (PP Systems, Haverhill, MA, USA). Normalized difference vegetation index (NDVI) was calculated by using the canopy reflectance formula (R750 R705)/ (R750 + R705) (Gamon and Surfus, 1999). The highest NDVI value is best for green cover. 2.3. Chlorophyll content and chlorophyll fluorescence Leaf chlorophyll content was measured according to the methods of Inskeep and Bloom (1985). Leaf chlorophyll was extracted by soaking 50 mg leaf samples in 5 ml dimethylformamide in the dark for 48 h. The absorbance of the supernatant was read at 665 and 647 nm, and the chlorophyll a and chlorophyll b content were determined. Chlorophyll fluorescence was measured between 1:30 and 2:00 p.m. on randomly selected leaves after 30 min dark adaptation with a Fim 1500 fluorescence induction monitor (Dynamax Inc., Houston, TX, USA). 2.4. Water-soluble carbohydrate content For analysis of water-soluble carbohydrate (WSC) content, 15 mg dried leaves were extracted three times for 15 min in 10 ml boiling water. After centrifugation at 3500  g for 10 min, supernatants were collected and pooled; and the final volume was adjusted to 25 ml. The WSC content was determined using the method of Dubois et al. (1956) modified by Buysse and Merckx (1993). Briefly, 1 ml supernatant was put into a glass tube, and 1 ml of 18% phenol solution and 5 ml concentrated sulfuric acid were added. The mixture was shaken, and absorbance was read at 490 nm using a spectrophotometer (Beckman Instrument Inc., Fullerton, CA, USA). 2.5. Soluble protein content and antioxidant enzyme activities Soluble protein and enzymes were extracted from leaves at 4 8C. Leaf tissue (0.5 g fresh weight) was ground in 10 ml solution containing 50 mM phosphate buffer (pH 7.0), 1% (w/v) polyvinylpyrrolidone, and 0.2 mM ascorbic acid (AsA). The homogenate was

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centrifuged at 6000  g for 20 min, and the supernatant was collected and used for protein and enzyme assays. Total soluble protein content was determined by the method of Bradford (1976). One hundred microliters of protein sample was mixed with 5 ml of protein regent (Sigma, St. Louis, MO, USA), and the absorbance was measured at 595 nm after 15 min using a DU 640B spectrophotometer (Beckman Instrument Inc.). Bovine serum albumin was used as a standard (Sigma). The activity of CAT was determined as a decrease in absorbance at 240 nm for 1 min following the decomposition of H2O2 (Change and Maehly, 1955). The reaction mixture contained 50 mM phosphate buffer (pH 7.0) and 15 mM H2O2. The activity of APX was measured as a decrease in absorbance at 290 nm for 1 min (Nakano and Asada, 1981). The assay mixture consisted of 0.5 mM AsA, 0.1 mM H2O2, 0.1 mM EDTA, 50 mM sodium phosphate buffer (pH 7.0), and 0.15 ml enzyme extract. 2.6. Experimental design The experiment was a randomized completely block design. Each light regime was replicated four times in the greenhouse, and the grass species (pots) were arranged randomly within each light regime. Leaves (from clippings) were used for various measurements.

3. Results and discussion 3.1. Turf quality and NDVI Turf quality was reduced by LL for both turfgrass species (Table 1). At day 21 of LL treatment, Sea Isle 1 seashore paspalum had an acceptable quality value of 6.7, while the turf quality of TifSport bermudagrass dropped to 5.3, below the minimum acceptable level of 6. NDVI is correlated with turf quality and density under wear stress (Trenholm et al., 1999; Jiang et al., 2003). In this study, NDVI decreased 21% and 44% for Sea Isle 1 and TifSport at day 21 of LL, respectively, compared to HL. These variations in turf quality were consistent to those observed under 70% and 90% LL in a field study (Jiang et al., 2004), which demonstrated that Sea Isle 1 had higher turf quality and better LL tolerance than TifSport. Table 1 Turf quality and normalized difference vegetation index (NDVI) at day 21 of high light (HL) and low light (LL) in Sea Isle 1 seashore paspalum and TifSport bermudagrass Grass

Turf quality HL

LL

HL

LL

Sea Isle 1 (SP)a TifSport (BD)

8.2  0.30b 8.0  0.17

6.7  0.13 5.3  0.15

0.67  0.02 0.64  0.02

0.53  0.01 0.36  0.02

a b

SP: seashore paspalum; BD: bermudagrass. Values represent means  standard deviations.

NDVI

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3.2. Chlorophyll content and chlorophyll a/b ratio Chlorophyll a (Chl a) content generally remained constant during HL, but was reduced by LL for both species (Fig. 1). After 35 days of LL, Chl a was reduced by 34% in Sea Isle 1 and by 51% in TifSport, relative to HL. After 21 days of LL–HL transfer, Chl a recovered to 93% and 84% of HL level in Sea Isle 1 and TifSport, respectively. Chlorophyll b (Chl b) content also remained relatively constant during HL, but was reduced by 36% and 63% after 35 days in LL in Sea Isle 1 and TifSport, respectively (Fig. 2). TifSport exhibited greater reductions in Chl b than in Chl a during LL treatments. For Sea Isle 1, Chl b recovered to 95% of HL level, which was similar to that of Chl a, but only 59% of HL level in Chl b was observed in TifSport after 21 days of LL–HL transfer. Our results agree with Hashemi-Dezfouli and Herbert (1992) who found in corn (Zea mays L.) that LL decreased Chl content. Short-term LL (7 days) did not cause reductions in Chl a and Chl b in TifSport, but dramatic and greater decreases in Chl a and Chl b were observed after 7 days of LL, compared to Sea Isle 1. The result indicated that the extended period of LL was an important factor influencing Chl content in LL-intolerant bermudagrass. Burritt and Mackenzie (2003) found that leaves transferred from LL to full sunlight had lower Chl (a + b) than shade leaves. In this study, LL–HL transfer resulted in increases in Chl a and Chl b content in both species. Chl a and Chl b in Sea Isle 1

Fig. 1. Chlorophyll a (Chl a) content of Sea Isle 1 seashore paspalum and TifSport bermudagrass under high light (HL), low light (LL), and LL to HL transfer. Arrow indicates the transfer from LL to HL. Error bars represent standard deviations.

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Fig. 2. Chlorophyll b (Chl b) content of Sea Isle 1 seashore paspalum and TifSport bermudagrass under high light (HL), low light (LL), and LL to HL transfer. Arrow indicates the transfer from LL to HL. Error bars represent standard deviations.

recovered to more than 90% of HL level after LL–HL transfer, which was much higher than that of TifSport. Adaptation to variable light conditions is particularly important for grasses to capture light and use it efficiently. The quick recovery and flexible light response of Chl in Sea Isle 1 should contribute to its good LL tolerance. The Chl a/b ratio is one of the most important characteristics for sun/shade response (Anderson and Osmond, 1987). No changes in Chl a/b were observed between LL-grown and HL-grown grass for Sea Isle 1 (Fig. 3). Only shortly after LL–HL transfer (7 days), a slightly higher Chl a/b ratio was shown in Sea Isle 1. In contrast, Chl a/b levels in TifSport were found much higher under both LL and LL–HL transfer than under HL. At day 35, Chl a/b ratio was 3.3 under HL and 4.3 under LL in TifSport. After 21 days of LL–HL transfer, the ratio was about 39% higher than that of HL in TifSport. The large increases in Chl a/b in TifSport were due to a greater reduction and a slower recovery of Chl b compared to Chl a. Chow et al. (1991) reported that the stable Chl a/b ratios of Tradescentia albiflora (Kunth) under variable light conditions are consistent with the lack of acclimation of chlorophyll-proteins, which suggested that the photosynthetic unit size of both photosystems is unchanged by growth irradiance. It has been reported that variations in Chl a/b ratio occur as plants respond to changing irradiance during growth, which may imply a size differential for photosystem I and II in the thylakoid membrane (Leong and Anderson, 1986; Smith et al., 1990). Changes in Chl content accompanied with stable Chl

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Fig. 3. Chlorophyll a to chlorophyll b ratio (Chl a/b) of Sea Isle 1 seashore paspalum and TifSport bermudagrass under high light (HL), low light (LL), and LL to HL transfer. Arrow indicates the transfer from LL to HL. Error bars represent standard deviations.

a/b ratio in seashore paspalum and large increases in Chl a/b ratio in bermudagrass might represent different acclimation strategies of chlorophyll-protein or/and photosystem concentration under LL or after LL–HL transfer. However, both components deserve further investigations for the two grass species. 3.3. Photochemical efficiency Photochemical efficiency, expressed as chlorophyll fluorescence ratio of Fv/Fm, exhibited some variation but generally was not affected by HL or LL (Fig. 4). After 7 days of LL–HL transfer, Sea Isle 1 and TifSport remained similar patterns of Fv/Fm, which were 6.0% lower than their HL levels. However, after 21 days of LL–HL, Sea Isle 1 maintained constant Fv/Fm but a further decrease in Fv/Fm was observed in TifSport. The value of Fv/Fm has been used to understand photosynthesis affected by shade, but the results are inconsistent (Groninger et al., 1996; Khan et al., 2000; Burritt and Mackenzie, 2003). The constant Fv/Fm observed in Sea Isle 1 and TifSport indicated that tolerant and intolerant grass species could maintain similar quantum yields under HL and LL. Large reductions in Chl but not Fv/Fm suggested that an adaptation of photochemical efficiency to LL environment was not affected by Chl molecule degradation in both tolerant and intolerant grass species. Araus and Hogan (1994) also found that Fv/Fm was

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Fig. 4. Photochemical efficiency (Fv/Fm) of Sea Isle 1 seashore paspalum and TifSport bermudagrass under high light (HL), low light (LL), and LL to HL transfer. Arrow indicates the transfer from LL to HL. Error bars represent standard deviations.

stable in S. exorrhiza (Mart.) Wendl. and Scheelea zonensis L. under LL, but was lower in HL-leaves for both species. They proposed that the lower Fv/Fm in HL-plants was due to photoinhibition. Grasses grown under heavy shade might suffer photoinhibition when they were removed to HL, indicating by temporarily but lower Fv/Fm in both Sea Isle 1 and TifSport. 3.4. Water-soluble carbohydrate content and total soluble protein content The level of WSC decreased under LL for both species (Fig. 5). Compared to levels at HL, WSC was reduced 44% and 52% for Sea Isle 1 and 65% and 66% for TifSport at days 14 and 35 of LL, respectively. After 14 days of LL–HL, Sea Isle 1 exhibited 73% of WSC to that HL level. Although WSC in TifSport increased after LL–HL transfer, only 65% of HL level in WSC was observed. The patterns of decline in WSC were consistent with changes in leaf SPC in both species (Fig. 6). Compared to HL level, SPC decreased 22% in Sea Isle 1 and 55% in TifSport at day 35 of LL. After 14 days of LL–HL transfer, SPC recovered to 95% and 74% of HL level in Sea Isle 1 and TifSport, respectively. The reduced soluble protein content under LL was also noted in other species (Besford, 1986; Eckardt et al., 1997; Logan et al., 1998), however, in this study, the tolerant grass species exhibited higher SPC content than in tolerant one

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Fig. 5. Water-soluble carbohydrate (WSC) content of Sea Isle 1 seashore paspalum and ‘TifSport’ bermudagrass under high light (HL), low light (LL), and LL to HL transfer (LL–HL). 14R represents 14 days after LL to HL transfer.

under LL or LL–HL transfer. The decrease in soluble protein caused by LL also resulted in low photosynthetic rate and capacity (Krall et al., 1995). The patterns of alterations in soluble protein content under LL or after LL–HL transfer were parallel to changes of Chl and WSC content in the two grasses, which were consistent with their different LL tolerance. Coupled with slow recovery of WSC, Chl and Fv/Fm, the slow recovery of SPC indicated a characteristic of intolerant TifSport bermudagrass in response to light variations. 3.5. Antioxidant enzyme activities The activities of CAT and APX decreased under LL, and the greater declines in CAT activities than APX activities were observed in both species at day 35 of LL (Figs. 7 and 8). The CAT activities decreased 68% and 77%, and APX activities decreased 41% and 56% in Sea Isle 1 and TifSport, respectively, relative to their HL levels. After LL–HL transfer, CAT and APX activities increased in both species. At day 14 of LL–HL, CAT activity exceeded the HL level in Sea Isle 1 and remained 67% of HL level in TifSport, while APX activities remained 79% and 76% of HL level in Sea Isle 1 and TifSport, respectively.

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Fig. 6. Total soluble protein content (SPC) of Sea Isle 1 seashore paspalum and TifSport bermudagrass under high light (HL), low light (LL), and LL to HL transfer (LL–HL). 14R represents 14 days after LL to HL transfer.

Grace and Logan (1996) found that CAT activity responses to growth PPFDs vary with species. In their study, CAT activities of Vinca major L. and Schefflera arboricola (Hayata) Merrill did not exhibit strong relations to growth PPFD, but increased twofold in the high-PPFD treatment in Mahonia repens (Lindley) Don. Our results demonstrated that CAT activity was light-responsive in both grass species with observation of lower activity under LL and increased activity after LL–HL transfer, but the tolerant Sea Isle 1 exhibited less reduction in CAT activities under LL than intolerant TifSport. The activity of CAT is mainly concentrated within the peroxisome (Volk and Feierabend, 1989) with a function in removing H2O2 generated during photorespiration. The less reduction in CAT activity observed in Sea Isle 1 might suggest a greater photoprotection of CAT in seashore paspalum. The enhanced CAT activity after LL–HL transfer may play a role in detoxification of H2O2 during photorespiration in response to increasing light intensity in both species, particularly for tolerant seashore paspalum. LL to HL transfer increased CAT and APX activities in both grass species. In contrast to this observation, Schittenhelm et al. (1994) found that transfer of Norway spruce (P. abies L.) seedlings from LL to HL resulted in significant decreases in CAT activities. These

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Fig. 7. CAT activity of Sea Isle 1 seashore paspalum and TifSport bermudagrass under high light (HL), low light (LL), and LL to HL transfer (LL–HL). 14R represents 14 days after LL to HL transfer.

results demonstrated that the acclimation of CAT activity from LL to HL varies with plant species, and activity of CAT is regulated by light in a complex manner (Scandalios, 1994). The activity of APX did not respond to LL as rapidly as CAT although both enzyme activities were reduced by LL in this study. The similar degree of APX activity relative to their HL was also noted in both species at day 21 of LL to HL transfer. These results suggested that APX activity was relatively stable under LL, compared to CAT, and might present a pattern of chloroplast-based enzymatic removal of H2O2 since over 90% of total leaf APX activity is localized in the chloroplast (Gillham and Dodge, 1986). Less reduction in APX activity in Sea Isle 1 under LL would contribute its LL tolerance. In summary, LL caused decreases in turf quality, NDVI, Chl a, Chl b, SPC, CAT and APX activities and WSC in both Sea Isle 1 seashore paspalum and TifSport bermudagrass, but greater reductions occurred in LL-intolerant TifSport than in tolerant Sea Isle 1. Chl a/b ratio was not affected by LL in Sea Isle 1 but increased to exceed the HL level in TifSport. Fv/Fm was generally not affected by LL in both Sea Isle 1 and TifSport. The results indicated that relative higher levels of Chl, SPC, WSC, and antioxidant enzyme activities under LL contributed to better LL tolerance in grass species. More rapid recovery of these parameters from LL to HL was a characteristic of the tolerant seashore paspalum relative to the intolerant bermudagrass.

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Fig. 8. APX activity of Sea Isle 1 seashore paspalum and TifSport bermudagrass under high light (HL), low light (LL), and LL to HL transfer (LL–HL). 14R represents 14 days after LL to HL transfer.

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