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.
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.
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.
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.
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.
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.
Xi-Lin Hou, Shou-Chun Caq, and Zhong-Chun Jiang*
It reviewed the research and development on genetic resources in non-heading Chinese cabbage (Brassica campestris L. ssp.chinensis Makino var. communis Tsen et Lee) achieved during the past 50 years. Researches were carried out on the methodology and classification of horticultural crops, investigation and collection of the genetic resources and development of new cultivars. Further studies were conducted on the morphological and biological characteristics, identification and analysis of disease resistance and genetic model of main economic characteristics. On these bases, 13 new cultivars were selected and spread to 800,000 hm2.
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.
W. Michael Sullivan, Zhongchun Jiang, and Richard J. Hull
Efficient use of nitrogen by turfgrasses depends on the ability of roots to absorb and assimilate nitrate. If a larger amount of nitrate is assimilated in the roots than in the shoots and organic N is transported to shoots as needed, nitrogen loss through clipping removal would be reduced. However, the ability of roots to assimilate nitrate depends on carbohydrate supply from the shoots. Our study examined the relationship between nitrate assimilation and photosynthate partitioning between shoots and roots of tall fescue grown in nutrient solution. To alter the pattern of nitrate reduction and photosynthate partitioning, we treated the plants as follows: 1) nutrient solution was aerated and nitrate was supplied to the roots, 2) nutrient solution was not aerated and nitrate was supplied to the roots, 3) nutrient solution was aerated and nitrogen was supplied to the leaves as nitrate, and 4) nutrient solution was aerated, and nitrogen was supplied to the leaves as urea. Photosynthate partitioning was assessed using carbon-14 as a tracer. Nitrate and nitrite reductase activities were determined by in vivo methods. Fortyeight hours after the grass leaves were exposed to carbon-14, >60% of the fixed carbon was translocated to stems and >15% to roots. Foliar application of urea resulted in less export of fixed carbon from leaves and lower leaf nitrite reductase activity than when nitrate was supplied to leaves. Less than 5% of the plant total nitrate reduction was attributed to root based activity. Root aeration decreased root nitrate reductase activity. Our results suggest that root-zone aeration and foliar N application could affect total nitrate assimilation and photosynthate partitioning to roots.