Impacts of root sulfate deprivation on growth and elements concentration of globe amaranth ( globosa L.) under hydroponic condition

M.Y. Wang1,2, L.H. Wu1,2, J. Zhang3

1Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, P.R. China 2Zhejiang Provincial Key Laboratory of Subtropic Soil and Nutrition, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, P.R. China 3School of Environmental Science and Technology, Zhejiang Forestry University, Lin’an, P.R. China

ABSTRACT

Sulfur (S) regarded as the fourth key element is mainly taken by the plant roots. However, some can also absorb atmospheric sulfides, which may be of great importance for ameliorating the environment and for farming as a green organic S fertilizer used to balance insufficient soil S content for intensive cultivation in China; H2S and mainly SO2 are emitted to air as a result of the rapid industrialized and economic development. Globe amaranth (Gomphrena globosa L.) might be one of the plants that can use atmospheric sulfides for its growth. Therefore the effects of sulfate deprivation from root on its growth, S status and other elements concentration under hydroponic culture were explored firstly. Based on measurements of plant growth, biomass, nitrogen (N), phosphorus (P), po- tassium (K), calcium (Ca), magnesium (Mg), S, iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (B), and molybdenum (Mo) concentration, the results showed that S concentration in flower, shoot and root of plant without root sulfate supplied was increased with plant growth and development, symptoms of S deficiency disappeared and other elements concentration in plant tended to be nearly the same as the root sulfate-supplied plants. The interest- ing results might imply that globe amaranth may be able to live on the atmospheric sulfides as sulfur source.

Keywords: globe amaranth (Gomphrena globosa L.); atmospheric sulfur; growth condition; biomass; elements con- centration

Sulfur (S) is one of the essential macro elements (vegetative growth, seed production) and com- of plant and is regarded as the fourth key element monly ranges from 0.03 to 2 mmol/g dry weight next to N, P and K (Morris 1988). However, it is (Tabatabai 1986, Pedersen et al. 1998, Hawkesford attributed rather catalytic and regulatory than and De Kok 2006). structural functions are attributed to sulfur be- S is usually taken up as sulfate (Nikiforova et al. cause it is much less abundant than other macro 2006). Generally, plants utilize sulfate taken up elements (Lewandowska and Sirko 2008). For ex- by the roots as an S source for growth and sulfur- ample, there is on average about 30-fold more N, deficient plants generate a lower yield and quality 8-fold more K and 2-fold more P than S in plant (Lunde et al. 2008). Plants are also able to take up shoot dry matter (Marshner 2005). Its content sulfate from atmosphere and metabolize the sulfur strongly varies between species and may be de- dioxide (SO2) and/or hydrogen sulfur (H2S) as the pendent upon the developmental stage of the plant sole source for growth upon sulfate deprivation of

Supported by the National Natural Science Foundation of China, Project No. 30871595, and by the Science and Tech- nology Cooperation Project of Hangzhou, China, Project No. 2004532I33.

484 PLANT SOIL ENVIRON., 55, 2009 (11): 484–493 the root, as a result of SO2/H2S release from hu- summer until frost. The tiny, white true flowers man technology (Hawkesford 2000, Hawkesford within the flower heads are rather inconspicuous and De Kok 2006). The early studies believed that and insignificant. The narrow green leaves are atmospheric S could not replace root sulfate, and opposite and oblong, 10–15 cm in length, and it only takes up 10–20% S of the total S in plant woolly-white when young, becoming sparsely (Cowling et al. 1973). However, several plants, such white-hairy as they grow up. as Brassica oleracea and Allium cepa L., were found This plant might fulfill its growth stage by ab- to absorb atmospheric S that completely replaced sorbing atmospheric sulfides without root sulfate sulfate taken up by the roots as an S source for supply. However, information available in the lit- plant growth (Maas et al. 1987, De Kok et al. 1997, erature on the primary nutrition status of the globe 2002a, Westerman et al. 2000a, b, Tausz et al. 2003, amaranth under root sulfate deprivation is little, Durenkamp and De Kok 2004, Yang et al. 2006). especially on the S nutrition status. So the aim of However, the plants still need additional atmos- the experiment was to investigate the plant growth pheric S supplied for their growth. Atmospheric and its primary nutrition conditions response to S is usually taken up via the stomata, turned into root sulfate deprivation including growth status, sulfate, metabolized with high affinity into cysteine, biomass production and elements concentration catalyzed by O-acetylserine (thiol)lyase, and then under hydroponic condition in order to further subsequently into other S metabolites (De Kok et study its S metabolism physiology. al. 1997, De Kok and Tausz 2001, Hawkesford and De Kok 2007). Sulfate needs to be reduced to sulfid before it is metabolized into organic S compounds MATERIALS AND METHODS and the chloroplast appears to be the primary site for the reduction of sulfate to sulfide (Brunold 1990, Plant materials and pre-culture. Globe ama- 1993, Davidian et al. 2000). ranth variety used in the experiment was cv. Gnome

In many developing countries, such as in China, Pink. The seeds were sterilized in 10% (v/v) H2O2 S in soil has been decreasing without proper S for 5 min, rinsed thoroughly with deionized water, fertilizer use. SO2 and H2S pollution are of great and germinated in vermiculite in a climate-control- significance as they are result of the rapid eco- led room for 30 days. Day and night temperatures nomic growth, industrialization and urbanization were 29 and 22°C, respectively, with a relative (Feng 2000). For example, volume of China SO2 humidity of 60–70%. The photoperiod was 14 h emissions, totaled 24.68 million tons in 2007, at a photon fluence rate of 200 ± 25 µmol/m2 s was still the highest in the world, though they (PAR 400–700 nm). 30-day-old uniform seedlings were decreased by 4.66% compared to 2006 (EPM were used for the further experiment. 2008). It is well known that SO2 emissions and the Experimental sites and design. Pot experiments resulting acid deposition have adverse impacts on were conducted in a naturally-lit glasshouse from forests, freshwaters and soils, killing insect and April 5 to October 31, 2007 at Zhejiang University, aquatic life-forms as well as causing damage to Hangzhou, China. The change trend of sulfides buildings and having impacts on human health. concentration in atmosphere in the experimental Thus, growing plants with high efficiency of ab- site in 2007 is shown in Figure 1 (EPM 2007). sorbing atmospheric S would be very useful and important in China for sulfide pollution control and emission reduction. 3.5 Among S deprivation studies of many horticul- 3 tural flower plants under soilless culture (Wang et 2.5 ) al. 2008), a , named globe amaranth 3 2 (Gomphrena globosa L.), was found to have espe- 1.5

cially high ability to absorb atmospheric S. Globe (µmol/m 1 amaranth, belonging to the family 0.5 is an annual plant that can grow up to 60 cm in 0 height. The true species has colorful scalelike sulfides conc.Atomopheric 1 2 3 4 5 6 7 8 9 10 11 12 perianths and may have white, red, purple, carmine Month and different shades of pink round, papery clover- like flowers. The flower heads are about 3–4 cm Figure 1. Atmospheric sulfides change trend in the in length, and are borne on upright spikes from experimental site in 2007

PLANT SOIL ENVIRON., 55, 2009 (11): 484–493 485 Uniform seedlings were transplanted to black first in 2.0 ml HNO3 and 0.5 ml H2O2, and diges- plastic pots (30.0 cm in height and 25.5 cm in di- tion solutions were then allowed to cool to room ameter, with a suitable plastic cover, 4 seedlings temperature (25°C) and adjusted to a final volume planted per pot). Two treatments, one was root of 25 ml with doubly deionized water (Zhang et sulfate deprivation (minus S) and the other was root al. 2008). All these elements in the solutions were sulfate supply (plus S), were set in the experiment. determined by inductively coupled plasma mass The plants were grown to maturity in hydroponic spectrometry (ICP-MS, model Agilent 7500a, culture and laid out in a completely randomized USA). design with three repetitions per treatment. In root Leaf chlorophyll content was determined on May sulfate deprivation treatment, 30-day-old seedlings 20 and June 25 by Chlorophyll Meter (5M/HT4- were transferred to a 50% modified Hoagland nutrient SPAD-502, Japan). solution with 2.50mM/l Ca(NO3)2·4H2O, 0.26mM/l All data statistical analyses were performed us- KH2PO4, 2.50mM/l KNO3, 23.20µM/l H3BO3, 4.57µM/ ing Statistica (v. 5.5). Each value represented the l MnCl2·4H2O, 0.96µM/l Zn(CH3COO)·2H2O, average of three repetitions. Data were subjected to 0.16µM/l CuCl2·5H2O, 0.26µM/l Na2MoO4·2H2O. the analysis of variance (ANOVA) and significant MgSO4 replaced MgCl2 in the modified Hoagland differences in mean values were separated using nutrient solution in root sulfate supply treatment. the Duncan’s Multiple Range Test (P ≤ 0.05). Nutrient solutions were refreshed once a week. Plant sampling and analysis. One plant was removed from each pot for analyses on May 5, RESULTS 31 days after transplanting. The second one was sampled on July 2 (the early flowering time), and Growth status. After root sulfate deprivation the third one was taken on October 31(the end treatment for one and a half month (on May 20), of flowering). After being rinsed with 0.01M HCl the SPAD value of the leaves of globe amaranth was (AR) and then with deionized water in order to 13.08, and was significantly different from the root clean thoroughly the samples, the plants were sulfate-supplied plants (28.12). All leaves of sulfate- separated into three parts: the shoot, the flower deprived plants were greenish yellow, whereas all and the root. All parts of the plant were dried at leaves of sulfate-supplied plants were green. The 70°C to constant weight. All samples were then symptoms of S deficiency were not very specific and ground to powder within a sample grinder (model just like other chlorosis in plants. However, when Retsch MM301, Germany). buds formed and were ready to bloom (on June 25), For N and P concentration determination, the the SPAD value of leaves of plants under root sulfate powder of different tissues was digested firstly by deficiency treatment increased to 29.81, and there boiling in concentrated H2SO4-H2O2. Total N was was no significant difference to the treatment of determined by the Kjeldahl method, and total P root sulfate supply (Table 1). concentration was determined by molybdenum The plants with sulfate supply started flowering antimony blue colorimetry (Lu 2000). on June 21, while sulfate-deprived plants bloomed Total S in different parts of the plant was digested on July 2. Due to the fadelessness of the plant, to sulfate by dissolving in 3 ml HNO3, 2 ml HClO4 flowers of all the plants weighed much more than and 1 ml HCl, and the turbidity of the samples was their shoots in the late flowering time. The sul- measured on a spectrophotometer at 450 nm after ad- fate-deprived plants had even more flowers than dition of BaCl2 (Durenkamp and De Kok 2002b). the Plus S ones (Figure 2). To determine the concentration of K, Ca, Mg Biomass production. Without S supply for and trace elements, the tissue powder was digested 1 month (on May 5), above- and underground dry

Table 1. The third leaf SPAD values of globe amaranth

Treatments May 20 June 25 Plus sulfate 28.12a 31.25a Minus sulfate 13.08b 29.81a

Means with the same letter within a column are not significantly different by the Duncan’s Multiple Range Test at P ≤ 0.05 level (r = 3); plus sulfate (plus S), the treatment of sulfate supply in hydroponic culture; minus sulfate (minus S), the treatment of sulfate deprivation in hydroponic culture

486 PLANT SOIL ENVIRON., 55, 2009 (11): 484–493 5 root weight (Figure 2). Globe amaranth shoot a 4.5 Flower growth was affected more than root growth upon 4 2– SO4 deprivation; more prolonged sulfate depri- 3.5 b vation generally results in changes of shoot/root 3 biomass ratio in favor of root production (Stuiver 2.5 et al. 1997, Yang et al. 2003, 2006, Buchner et al. 2 2004) and root morphology by increasing the to-

Dry (g)weight 1.5 a tal absorptive surface of the root system (Kutz et 1 al. 2002, López-Bucio et al. 2003). However, the 0.5 b 0 sulfate-deprived plants seemed to have a rapid growth when they were in bloom; their above- plus S minus S plus S minus S plus S minus S and underground dry weights were much higher than those of sulfate-supplied plants at the end of 05-May 02-Jul 31-Oct flowering sampling on October 31. The average 4 a dry weights of flower, shoot and root with sulfate 3.5 Shoot deprivation treatment were increased significantly 3 by 36.9, 68.2 and 46.7% respectively, as compared 2.5 with the respective parts of the sulfate-supplied 2 b plants (Figure 2). 1.5

Dry (g)weight 1 Macro- and medium elements concentration. a a b Compared to the sulfate-supplied plant, where 0.5 b 30.2% of N was accumulated in the root, it was 0 55.1% of N in sulfate-deprived plant (Table 2). plus S minus S plus S minus S plus S minus S There was the highest Mg concentration in the shoot of sulfate-deprived plant and the lowest 05-May 02-Jul 31-Oct concentration in the root of sulfate-supplied plant. 1.2 Deprivation of S caused a significant decrease in Root a 1 the concentration of total P, K, Ca, S both in shoot 0.8 b and root (Table 2). In addition, shoots had higher concentration of those four elements than roots in 0.6 both sulfate supply and deprivation treatments. At a a 0.4 a this sampling time, S concentration in the shoot Dry (g)weight b 0.2 and root of sulfate-deprived decreased by 71.8% and 78.9%, respectively, as compared to the sulfate- 0 supplied plant. When plants starved for sulfate, the plus S minus S plus S minus S plus S minus S decreased sulfate uptake led to reduced assimila- tion activity and affected many different metabolic 05-May 02-Jul 31-Oct processes (Hirai and Saito 2004). Eventually, the limited supplies of S in plants resulted in decreased plant tissue S content. Decreases in S content Figure 2. Biomass of globe amaranth with and without resulted in the inhibition of sulfate assimilation, root sulfate added reduced amounts of chlorophyll and imbalance of nitrogen as well as of other elements (Nikiforova et al. 2003, 2005, Schachtman and Shin 2007). weight of the plants were decreased significantly Overall, these changes led to a reduced rate of by 45.3% and 36.4%, respectively, as compared metabolism and growth of plant. with the root sulfate supply treatment (Figure 2). At early flowering time (on July 2), N concentra- At early flowering time (on July 2), shoot with the tion did not differ largely among the three plant sulfate deprivation treatment was 0.37 g and flower parts in sulfate-supplied plant, whereas the value was 0.24 g, whereas the sulfate supply treatment was significantly much higher in the flower of resulted in the values of 0.51 g (shoot) and 1.10 g sulfate-deprived plant than in its shoot and root (flower). The aboveground dry matter under sulfate (Table 2). S concentration in the corresponding deprivation treatment was decreased significantly three parts of the plant was increased markedly 2– by 62.1%, while SO4 deprivation did not reduce whether it was the deprived of sulfate or not when

PLANT SOIL ENVIRON., 55, 2009 (11): 484–493 487 Table 2. Macro- and medium elements concentration and N/S value in different organs in globe amaranth with and without root sulfate supply

N P K Ca Mg S N/S Treatments (%) May 5 Plus sulfate Shoot 1.39b 0.39a 1.00a 0.95a 0.67b 0.39a 3.56c Root 1.16c 0.12b 0.56b 0.13c 0.14d 0.19b 6.11b Minus sulfate Shoot 0.85d 0.08c 0.56b 0.39b 0.73a 0.11c 7.73b Root 1.70a 0.07c 0.28c 0.10c 0.21c 0.04d 42.50a July 2 Plus sulfate Flower 1.28b 0.27b 0.96a 0.58c 0.31b 0.26cd 4.92c Shoot 1.07b 0.08c 1.05a 1.63a 0.78a 0.54a 1.98d Root 0.83b 0.06c 0.52b 0.22d 0.16b 0.39b 2.13d Minus sulfate Flower 2.62a 0.33a 0.94a 0.63c 0.33b 0.18de 14.56a Shoot 0.86b 0.08c 0.97a 1.35b 0.77a 0.32bc 2.69cd Root 1.15b 0.05c 0.46b 0.35d 0.22b 0.10e 11.50b October 31 Plus sulfate Flower 0.95ab 0.27a 0.84b 0.82c 0.25d 0.23ab 4.13b Shoot 1.01ab 0.10bc 1.12a 2.01a 0.84a 0.34a 2.97c Root 1.01ab 0.07c 0.49c 0.44d 0.34cd 0.25ab 4.04b Minus sulfate Flower 1.18a 0.24a 0.78b 0.69c 0.22d 0.20b 5.90a Shoot 0.78b 0.10bc 0.76b 1.67b 0.62b 0.28ab 2.79c Root 0.80b 0.06c 0.45c 0.83c 0.49bc 0.23ab 3.48bc

Means within a column on the same sampling time with the same letter are not significantly different by Duncan’s Multiple Range Test at P ≤ 0.05 level (r = 3). Plus sulfate, the treatment of sulfate supply in hydroponic culture; minus sulfate, the treatment of sulfate deprivation in hydroponic culture it was in the bloom (Table 2). However, compared responding parts of sulfate-supplied plant (Table to the sulfate-supplied plant, S concentrations in 2), that was in coincidence with the SPAD valued the flower, shoot and root of the sulfate-deprived on June 25 (Table 1). plant were decreased significantly by 30.8%, 40.7% At the end of flowering (on October 31), there and 74.4%, respectively. The flower of sulfate-de- was still the highest Ca, Mg and S in the shoot of prived plant tended to have the highest N, P and sulfate-supplied plant and the highest N and P K concentration, and the highest Ca, Mg and S concentration in the flower of sulfate-deprived appeared in the shoot of sulfate-supplied plant plant. The root accumulated extra percentages of (Table 2). At this sampling time, Mg concentration Ca and Mg after flowering, and their values were in the organs of sulfate-deprived plants showed almost twice as high as that at the early flowering no significant difference compared to the cor- time. Concentration of other elements had simi-

488 PLANT SOIL ENVIRON., 55, 2009 (11): 484–493 lar values to those from July 2. Strange enough, ground part of globe amaranth (Figure 3). After the S concentration declined in the tissues of the flowering, the ratio of S in flower to the whole plant sulfate-supplied plant since flowering, but kept was generally increasing; however, S ratio in the unchanged in flower and shoot of sulfate-deprived flower of sulfate-deprived plant was lower than that plant and this accumulation in its root just went of the sulfate-supplied plant (Figure 3). on. S concentration in the organs of sulfate-de- Trace elements concentrations. Generally, dep- 2– prived plant showed no significant difference to rivation of SO4 for one month depressed the trace the corresponding parts of sulfate-supplied plant at elements concentration in plant (Table 3). But we this time (Table 2, Figure 3). The results at whole could also find that Fe concentration in the sulfate- plant level showed that the demand of sulfate and deprived root was similar to that in the sulfate-sup- its distribution in the plant were driven presum- plied root, and Mn concentration in the root and ably by the S demand for growth at any specific Mo concentration in the shoot were even increased developmental stage. significantly by 72.7% and 167.0%, respectively, com- N/S as affected by sulfate supply. On the first pared to their counterparts in sulfate-supplied plant. sampling (May 5), the highest N/S was obtained Higher Fe and Cu concentration was found in root in the root of sulfate-deprived plant, i.e. 42.50, than in shoot, and higher Mn, Zn and B concentra- and was about 7 times higher than in the root of tion in shoot. Fe concentration was much higher sulfate-supplied plant. However, once the plant than other elements, the values being from ten to was in the bloom, the highest N/S appeared in the hundred times higher. flower of the sulfate-deprived plant. In the early At early flowering time (Table 3), however, Fe flowering time, the ration of N to S was 14.56 in concentration decreased markedly in all parts the flower of sulfate-deprived plant; it was about of the plant whether sulfate was added or not. 3 times higher than in the flower of the sulfate- Similarly Mo concentration decreased markedly supplied plant; however, it declined to 5.90 at the in the shoot and root of sulfate-supplied plant. end of flowering time sampling (Table 2). Sulfate deprivation did not cause a decrease in As to the whole plant, N/S of the sulfate-deprived the proportion of trace elements allocated to the plant was 5.2 times higher than that of the sulfate- plant tissues at this time, but even raised Zn, B supplied plant on May 5. In bloom, N/S of the sul- and especially Mo concentration (Table 3). fate-deprived plant declined to be 3.2-fold higher At the end of flowering time, Fe concentration than in the sulfate-supplied plant; towards the end in shoot continued to decrease, whereas the values of flowering, no significant difference of the N to in flower and root began to increase whether the S ratio between the two treatments of plants was sulfate was supplied or not in hydroponic solu- observed (Table 2). However, in a study on wheat tions. Zn and Mo concentration decreased a lot in by Gilbert et al. (1997), the optimal ratio of N/S was flower of the sulfate-deprived plant compared to 15.00; similarly, in corn, Wang et al. (2003) found sampling at the early flowering time (Table 3). the ratio of total N/S in root of 10.70 with the sulfate S occurs in the environment in a variety of oxidative supply, and 48.70 without the sulfate supply. states that range from –2 in its most reduced form Whether sulfate was supplied in root or not, more (sulfide -S2–) to +6 in its most oxidized form (sulfate 2+ than 80% S was accumulated mainly in the above- -SO4 ). Though inorganic sulfate is the primary

100%100

80%80

60% 60

40%40 Flower Shoot Root to the plant (%) 20% Ration of S in organs 20 Ratio of S in organs to the plant the to Ratio of S in organs

0%0 plusPlus S Smin Minusus SSplus Plus SSmin Minusus S Splus Plus SSmin Minusus S Figure 3. Ratio of S in organs in globe ama- ranth with and without root sulfate added

PLANT SOIL ENVIRON., 55, 2009 (11): 484–493 489 Table 3. Trace elements concentration in different organs in globe amaranth with and without root sulfate supply

Fe Mn Cu Zn B Mo (mg/kg) May 5 Plus sulfate Shoot 650.07b 7.84a 24.01b 28.81a 27.60a 11.88d Root 1040.11a 4.90b 31.21a 19.21b 13.80c 19.26b Minus sulfate Shoot 390.07c 8.46a 12.90d 15.08c 16.11b 31.72a Root 975.17a 8.46a 15.49c 6.56d 9.47d 13.88c July 2 Plus sulfate Flower 107.2d 9.17b 34.93b 52.27e 38.45cd 2.35f Shoot 287.01b 14.62a 33.21b 113.57c 76.04a 8.73e Root 467.56a 8.89b 45.34a 71.07d 34.35cd 13.48d Minus sulfate Flower 105.99d 4.63c 35.13b 168.46b 41.32c 17.73c Shoot 209.34c 10.69b 37.9b 189.45a 53.97b 56.99a Root 504.96a 9.55b 44.5a 81.62d 31.05d 24.52b October 31 Plus sulfate Flower 175.53c 8.81c 41.37ab 68.82cd 32.66bc 3.04c Shoot 141.84d 26.53b 34.34b 165.53a 51.31a 10.9b Root 724.81a 24.2b 43.26ab 72.23c 27.9c 12.48b Minus sulfate Flower 122.34d 7.97c 38.91b 59.75d 32.07c 3.81c Shoot 172.3c 39.63a 43.26ab 171.34a 47.33ab 20.73a Root 641.18b 41.34a 54.12a 112.86b 32.34bc 12.39b

Means with the same letter within a column on the same sampling day are not significantly different by the Duncan’s Multiple Range Test at P ≤ 0.05 level (r = 3); plus sulfate (plus S), the treatment of sulfate supply in hydroponic culture; minus sulfate (minus S), the treatment of sulfate deprivation in hydroponic culture

2− source of S used by plant, S may be taken up from Due to prolonged SO4 deprivation from root, S the atmosphere as well, as H2S and mainly SO2 are deficiency symptoms of globe amaranth gradually emitted to the atmosphere as a result of volcanic disappeared (Table 1). Why did this phenomenon activity, decomposition of biological tissues and appear? It might be caused by a capacity of the plant anthropogenic activities (Hawkesford 2000, Maathuis to capture atmospheric sulfides. 2– 2009). Atmospheric SO4 derived form industry Up to the early flowering stage, the growth of 2− and coal burning frequently reaches levels of over the plant aboveground part was affected by SO4 100 µg/m3 (Maathuis 2009). It has been proved that deprivation more than root growth, which resulted atmospheric levels of ≥ 0.1 µl/l of these S gases should in a decrease in the shoot/root ratio (Figure 2). That be sufficient to cover the organic S need for growth was in coincidence with the previous studies which of most plant species (Durenkamp and De Kok 2004). reported that the prolonged sulfate deprivation

490 PLANT SOIL ENVIRON., 55, 2009 (11): 484–493 would generally result in changes of shoot/root N/S in plants of the sulfate deprivation treatment biomass ratio in favor of root production (Stuiver was higher than in the sulfate-supplied plants. et al. 1997, Yang et al. 2003, 2006, Buchner et al. Whether the sulfate was supplied to the plant or 2004) and root morphology by increasing the total not, the highest root N/S was before the plant was absorptive surface of the root system (Kutz et al. in bloom; during the blooming period, the flower 2002, López-Bucio et al. 2003). However, at the end N/S was higher than that in roots and shoots (Tables of flowering period, all of the three organs weighted 2 and 4). It was suggested that for S deficiency significantly more than the corresponding parts of diagnosis of globe amaranth, the root could be the sulfate-supplied plant when root sulfate depri- an optional organ to estimate plant S deficiency vation was prolonged (Figure 2). It seems that the symptom before flowering; in bloom, the flower activated root production and root morphology at would be a better organ. That was not always in prolonged sulfate deprivation could activate the accordance with the findings of Wang et al. (2003) growth of the aboveground parts of globe amaranth. who reported that the root N/S of corn could be The results confirmed that this species had a rather a diagnosis index to determine whether S supply low root sulfate need for growth in normal atmos- was deficient. pheric sulfides condition (Figure 1) and showed To globe amaranth, S content per seed was gen- that the effect of S was primarily on the number of erally only about 5 µg, and it could be recognized grains per ear, indicating that S deficiency either that no sulfate was imported into the aqueous reduces the initiation of spikelet and/or floret, or culture solutions for the deionized water and increased the mortality of floret. It was in com- analyzed reagents used during the hydroponic pliance with the conclusions of Archer (1974) on experiment. However, towards the end of flowering wheat and Scott et al. (1984) on barley. Recent data time, S content in the sulfate-deprived plants was also suggested that when Brassica was grown at a 18.95 mg per plant on average. Where did S come maintained 5µM sulfate concentration (the sulfate from in the sulfate-deprived plant? S deficiency concentration in Hoagland nutrient solution is symptoms of globe amaranth gradually disap- 2000µM), plant growth was quite normal although peared with prolonged S deprivation from root the sulfate content of the shoots was somewhat and the plant did fulfill its whole growth stage lower compared to plants grown at 100 or 500µM without root sulfate supply. A rational hypothesis (Hawkesford and De Kok 2006). was that globe amaranth (Gomphrena globosa L.) 2− Yang (2006) proved that SO4 deprivation did could efficiently utilize the atmospheric sulfides not affect total N content of shoot and root of as its S source for plant growth. But up to now, cv. Kasumi, whereas David et al. (1951) reported there was no direct evidence that could prove that the percentage of total N was always greater the phenomena shown in the case of globe ama- 2– when the SO4 supply was limited in cotton. The ranth (Gomphrena globosa L.); to explore the plant findings of our experiment were similar to Yang atmospheric sulfides utilization characteristics (2006). S concentration of plants under sulfate directly with the physiological and biological ap- deprivation was less than 30% of that in sulfate- proaches was thus certainly what should be done supplied plants on May 5, and it led to decreases of next, for sulfate starvation of plants led to a series P, K, Ca concentration excluding Mg. S concentra- of metabolic and physiological responses aiming at tion in sulfate-deprived plants increased with the adopting plant metabolism to the available nutrient plant’s growth, and P, K, Ca, and Mg concentration supply and to acquire a new homeostatic balance turned to be similar to those in the sulfate-sup- (Nikiforova et al. 2005). After all, the primary tar- plied plant. A similar trend occurred in the trace get site for effects of sulfate deprivation were the elements concentration as well. The S demand S containing metabolites, the amino acids cysteine might be dependent upon the developmental stage and methionine and their immediate derived me- of the plant. In the perspective of whole plant S tabolites such as GSH and SAM (Nikiforova et al. metabolism, the requirement was the provision of 2006). Amino acid content in plants was usually adequate S to optimize vegetative plant growth, balanced in a delicate way (Hofgen et al. 1995). and hence reproductive potential, and ultimately Yet, environmental conditions were affecting plant to provide S for seed tissues to maximize fecun- amino acid compositions. dity. It was unclear to what extent the external or Nevertheless, the plant having high effective internal sulfate concentration in the root itself assimilation of atmospheric sulfides may be of was the sensing factor in the modulation of the great use in ameliorating the environment and for sulfate efficiency in general. farming as a green organic S fertilizer.

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Corresponding author:

Lianghuan Wu, PhD., Ministry of Education Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, 268 Kaixuan Road, P.O. Box 310029, Hangzhou, P.R. China phone: + 865 718 697 1921, fax: + 865 718 604 9815, e-mail: [email protected]

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