Information about micronutrient concentrations of plants in general can be found in botany and plant physiology textbooks, but micronutrient concentrations in field-grown lettuce is hard to find and so are concentrations of heavy metals. Lettuce consumers may be concerned with heavy metal concentrations and information about heavy metal concentrations may help consumers make a choice. This study examined the concentrations of eight micronutrients and five heavy metals in field-grown lettuce with different fertilization programs. Under the field conditions, different NPK fertilizers and fertilization rates did not differ in the leaf concentrations of micronutrients and heavy metals. The overall means of Fe, Na, Mo, and Ni concentrations in the lettuce were 663, 710, 0.9, and 1.9 μg·g–1 of dry leaves, respectively. These values were significantly higher (over 500% greater) than the values found in textbooks for plants in general. Mean Mn, Cu, B, and Zn concentrations were 55.5, 7.3, 23.7, and 28.4 μg·g–1 of dry leaves, respectively, which are in general agreement with textbook values. Mean concentrations of heavy metals Cd, Co, Cr, and Pb were 1.5, 1.0, 2.9, and 4.5 μg·g–1 of dry leaves, respectively, whereas mean Al concentration was 498.5 micrograms per gram of dry leaves. These results indicate that concentrations of some elements in lettuce leaves can be high under certain field conditions. It would be beneficial for lettuce growers and consumers to have this information.
Nutrient concentrations in lettuce leaves are an important factor that affects lettuce quality, particularly the nutritional value of lettuce. When lettuce is grown hydroponically, tissue nutrient concentrations may be regulated through adjustments of the nutrients in the solution in which the lettuce is grown. However, when lettuce is grown in the field, the levels of tissue nutrients can be affected by many factors, such as soil conditions, fertilizer applications, and weather conditions. The objective of this study was to ascertain the variability of leaf and root tissue nutrients in loose-leaf lettuce grown in the field. An organic fertilizer that had an analysis of 4-6-6 as well as 3% Ca, 0.5% Mg, and 5% S derived from dehydrated manure, crab meal, cocoa meal, and other materials was applied at the time of planting and also side dressed after planting. There were significant differences in the concentrations of some elements between leaf tissues and root tissues. Leaf K, Ca, and Mg concentrations were significantly higher than those in the roots while leaf P concentration was lower than that in the roots. Leaf N concentration was similar to root N concentration. Micronutrients, such as Fe, MN Cu, Zn, and Mo, had lower concentrations in the leaves than in the roots. Leaf B concentration was similar to that in the roots. In addition, leaves accumulated lower concentrations of Al and Na than did the roots. No significant differences in the concentrations of these elements were observed between the fertilized plots and the unfertilized plots, which suggested that the field might have a sufficient fertility level and/or that the organic fertilizer might be slow in releasing its nutrients for the lettuce.
Kai Zhou, Weiming Guo, and Zhongchun Jiang*
The autointoxication of chrysanthemum was studied using water extract of Dendranthema morifolium's rhizospheric soil. Results of bioassays showed that the water extract inhibited chrysanthemum seed germination and the activities of some important root enzymes. The seedling nitrate reductase activity was decreased linearly with increasing concentration of the extract. The activity of root dehydrogenase was inhibited only at the highest concentration tested [3.2 g·mL-1, dry weight (DW)], but was stimulated at a lower concentration tested (1.6 g·mL-1, DW). Malondialdehyde content increased at higher than 1.6 g·mL-1, DW concentrations of the extract. The autointoxication phenomenon might be related to the difficulties in continuous plantings of chrysanthemum at the same location.
Zhongchun Jiang, Chenping Xu, and Bingru Huang
Low nitrogen (N) rates are recommended for creeping bentgrass (Agrostis stolonifera) putting greens to prevent excessive shoot growth and potential nitrate leaching, but low N rates could lead to N deficiency, which induces leaf senescence. This study was conducted to examine the effects of N deficiency on two enzymes involved in organic N metabolism as well as amino acid (AA) and soluble protein (SP) contents in both young and old leaves and roots of creeping bentgrass. Creeping bentgrass plants (cv. Penncross) were grown in a nutrient solution containing either 6 mm nitrate (+N plants) or zero N (−N plants), and each of the two treatments had four replicate pots. Young leaves on upper portions of the stolons and old leaves on lower portions of the stolons were separated and sampled at 14, 21, and 28 days of treatment, and roots were sampled at 28 days. Nitrogen deficiency increased glutamine synthetase (GS) transferase activity in all three tissues and at all three dates and GS biosynthetic activity in young leaves at all three dates. Prolonged N deficiency at 21 and 28 days increased glutamate dehydrogenase (GDH) deamination and amination activities in old leaves. In the roots, N deficiency at 28 days increased GS transferase activity but decreased GDH deamination activity. The N deficiency decreased AA content in all three tissues and at all three dates and SP content in young leaves at all three dates and in old leaves at 21 and 28 days. Decreasing organic N reserves in AA and SP and increasing GS and GDH activities in senescing leaves may be adaptive responses to N deficiency.
Chenping Xu, Zhongchun Jiang, and Bingru Huang
Nitrogen (N) deficiency inhibits plant growth and induces leaf senescence through regulating various metabolic processes. The objectives of this study were to examine protein changes in response to N deficiency in immature and mature leaves of a perennial grass species and determine major metabolic processes affected by N deficiency through proteomic profiling. Creeping bentgrass (Agrostis stolonifera cv. Penncross) plants were originally fertilized with a diluted 36N–2.6P–5K fertilizer. After 14 days acclimation in a growth chamber, plants were grown in a nutrient solution containing 6 mm nitrate (control) or without N (N deficiency). Immature leaves (upper first and second not yet fully expanded leaves) and mature leaves (lower fully expanded leaves) were separated at 28 days of treatment for protein analysis. Two-dimensional electrophoresis and mass spectrometry analysis were used to identify protein changes in immature and mature leaves in response to N deficiency. The abundance of many proteins in both immature and mature leaves decreased with N deficiency, including those involved in photosynthesis, photorespiration, and amino acid metabolism (hydroxypyruvate reductase, serine hydroxymethyltransferase, alanine aminotransferase, glycine decarboxylase complex, glycolate oxidase), protein protection [heat shock protein (HSP)/HSP 70, chaperonin 60 and FtsH-like protein], and RNA stability (RNA binding protein). The reduction in protein abundance under N deficiency was greater in mature leaves than in immature leaves. The abundance of small HSP and metalloendopeptidase increased under N deficiency only in immature leaves. These results suggest that N deficiency accelerated protein degradation in immature and mature leaves of creeping bentgrass, particularly those proteins associated with energy and metabolism, but to a lesser extent in immature leaves. Immature leaves were also able to accumulate proteins with chaperone functions and for N reutilization, which could protect leaves from senescence under N deficiency.
Wenting He, Weiming Guo, and Zhongchun Jiang*
Effects of two pretreatments, i.e., ultrasonic wave (UW) and ultrasonic wave plus preservative solution (UW+PS), on water conditions of flower stem and membrane stability of petals in Nymphaea tetragona during 6-d cold wet storage. Compared with no pretreatment control, the two pretreatments prolonged the vase life and improved water conditions of the cut flower during cold storage to different degrees. Fresh weight of flower stems and relative water content of petals increased during cold storage. The water utilization efficiency of flower stem and water potential in different parts of flower stem were improved significantly as a result of the pretreatments. Although both pretreatments helped the cut flowers maintain favorable water relations, the effects of UW + PS combined pretreatment were better than UW pretreatment alone. In addition, UW and UW+PS inhibited the increase in the contents of lipid peroxidation product malondialdehyde (MDA) and superoxide anion in petals. UW + PS promoted superoxide dismutase (SOD) and catalase (CAT) activities in petals during cold storage to a greater degree than did UW.
Zhongchun Jiang, W. Michael Sullivan, and Richard J. Hull
Efficient utilization of fertilizer-nitrogen (N) by turfgrasses is probably related to N uptake efficiency of roots and metabolic efficiency of absorbed N in roots and shoots. This study evaluated Kentucky bluegrass (Poa pratensis L.) cultivars for potential differences in nitrate uptake rate (NUR), temporal variation in NUR, and the relationship between NUR and N use efficiency (NUE), defined as grams dry matter per gram N. Six cultivars were propagated from tillers of seeded plants, grown in silica sand, mowed weekly, and watered daily with a complete nutrient solution containing 1.0 mm nitrate. A nutrient depletion method from an initial nitrate concentration of 0.5 mm was used to determine NUR of 5-month-old plants. NUR (μmol·h-1 per plant) of the six cultivars ranked as follows: `Blacksburg' > `Conni' > `Dawn' > `Eclipse' = `Barzan' > `Gnome'. When NUR was based on root weight, `Conni' ranked highest; when NUR was based on root length, surface, or volume, `Eclipse' ranked highest. Averaged across cultivars, NUR on the second day was greater than NUR for the first day of nitrate exposure. Temporal variation was greatest in `Blacksburg', while none was noted in `Conni' or `Eclipse'. Cultivar differences in NUE were significant in fibrous roots, rhizomes, and leaf sheaths, but not in leaf blades and thatch. Total nitrate uptake was positively related to total N recovered and total plant dry matter, but NUR based on root weight was negatively correlated with NUE of the whole plant.
John W. Pote, Chhandak Basu, Zhongchun Jiang, and W. Michael Sullivan
Leaching-induced N losses have been shown to be minimal under turfgrasses. This is likely due to superior ability of turfgrasses to absorb nitrate. No direct evidence for this theory has been reported. The present study quantified nitrate leaching under miniature turf and nitrate uptake by individual turfgrass plants, and established the relationship between nitrate leaching loss and nitrate uptake rate. Seedlings of six Kentucky bluegrass (Poa pratensis L.) cultivars, `Blacksburg', `Barzan', `Connie', `Dawn', `Eclipse', and `Gnome', were planted individually in polystyrene containers filled with silica sand. The plants were irrigated with tap water or a nutrient solution containing 1 mm nitrate on alternate days and mowed to a 5-cm height once each week for 25 weeks. Nitrate leaching potential was then determined by applying 15 to 52 mL of nutrient solutions containing 7 to 70 mg·L-1 nitrate-N into the containers and collecting leachate. After the leaching experiment, plants were excavated, roots were washed to remove sand, and the plants were grown individually in containers filled with 125 mL of a nutrient solution containing 8.4 mg·L-1 nitrate-N. Nitrate uptake rate was determined by monitoring nitrate depletion at 24-hour intervals. Leachate nitrate-N concentration ranged from 0.5 to 6 mg·L-1 depending on cultivar, initial nitrate-N concentration, irrigation volume, and timing of nitrate-N application. Significant intraspecific difference in nitrate uptake rate on a root length basis was observed. Nitrate uptake rate on a per plant basis was significantly (P ≤ 0.05) and negatively correlated (r = -0.65) with nitrate leaching loss. The results provide strong evidence that superior nitrate uptake ability of turfgrass roots could reduce leaching-induced nitrate-N losses.
Yuexia Wang, Chhandak Basu, Zhongchun Jiang, and W. Michael Sullivan
It has been suggested that shoot demand for nitrogen controls nitrate uptake in plant roots. In turfgrasses, shoots are partly removed by regular mowing, which may severely alter nitrate uptake ability. However, reported groundwater nitrate concentrations under intensively managed turf are well below the USEPA maximum contaminant limit of 10 mg·L-1 nitrate-N in potable water. We hypothesize that the turfgrass root can also exert significant control over its nitrate uptake ability. The present study was to test this hypothesis by comparing nitrate uptake rates of excised roots and intact, whole plants of six Kentucky bluegrass (Poa pratensis L.) cultivars. Three replications or cultures of each cultivar were grown in sand for 15 months. For whole-plant nitrate uptake, the roots were placed in a flask filled with 200 mL of a nutrient solution containing 0.125 mm nitrate. Nitrate depletion was monitored at 20-minute intervals over an 8-hour period under ≈600 μmol·m-2·s-1 photosynthetic photon flux density. After the whole-plant experiment, the plants were placed in an N-free nutrient solution for 15 hours, and the roots were then excised. The excised roots were placed in a beaker containing 60 mL of the 0.125-mm nitrate nutrient solution and nitrate depletion was monitored at 20-minute intervals over a 6-hour period. Whole-plant nitrate uptake rate differed significantly (P ≤ 0.05) among cultivars and was twice that of excised roots. Excised root nitrate uptake rate exhibited no cultivar difference but was positively and significantly (P ≤ 0.05) correlated with whole-plant nitrate uptake rate. Our results indicate that turfgrass roots exert substantial control over nitrate uptake.
Changling Zhao, Weiming Guo, Junyu Chen, and Zhongchun Jiang*
Mei (Prunus mume Sieb. et Zucc.) flower is one of the candidates for the national flower of the People's Republic of China. Several major anthocyanins from the flowers of P. mume Sieb. et Zucc. were isolated with MeOH-HOAc-water (10:1:9, v/v), and purified by paper chromatography and subsequent column chromatography. Specific chemical reactions, chromatographic and spectroscopic analyses indicated that the anthocyanins in `Nanjing Hongxu' (Nanjing red-bearded) were cyanidin 3-O-(6'-O-α-rhamnopyranosyl-β-glucopyranoside) and cyanidin 3-O-(6'-O-galloyl-3'-O-β-glucopyranosyl-β-glucopyranoside). Anthocyanins in `Nanjing Hong' (Nanjing red) were cyanidin 3-O-(6'-O-α-rhamnopyranosyl-β-glucopyranoside), cyanidin 3-O-(6'-O-galloyl-β-glucopyranoside) and cyanidin 3-O-(6'-O-E-feruloyl-βglucopyranoside). In addition to contributing to the blue flower color, the anthocyanins may improve the ability of the two cultivars to survive at low temperatures.