CROP PRODUCTION HORTSCIENCE 42(6):1337–1340. 2007. synthesis or storage of indole glucosinolates (Chong and Bible, 1974; Ju et al., 1980). The cabbage looper (Trichoplusia ni Changes in Gluconasturtiin Hu¨bner) is a generalist insect native to the United States. It has been extensively used Concentration in Chinese Cabbage with in controlled feeding trials and it was chosen for the present study because of its voracity, Increasing Cabbage Looper Density lower susceptibility to pesticides, and espe- cially because cabbage plants have been Fernando A. De Villena shown to tolerate moderate defoliation before Department of Horticultural Science, University of Minnesota, 1970 Folwell a significant reduction in plant weight occurs Avenue, St. Paul, MN 55108 (Andaloro and Shelton, 1981). Changes in leaf nutrients incited by herbivory depend on Vincent A. Fritz1 the timing and intensity of feeding (Rosta´s Department of Horticultural Science, University of Minnesota, 1970 Folwell et al., 2002). However, little has been done to correlate the concentration of glucosinolates Avenue, St. Paul, MN 55108; and the Southern Research and Outreach with the level of insect pressure. Center, University of Minnesota, 35838 120th Street, Waseca, MN 56093 The possibility of manipulating the metabolism of cruciferous plants to modify Jerry D. Cohen its glucosinolate content has generated con- Department of Horticultural Science, University of Minnesota, 1970 Folwell siderable interest. The potential impact this Avenue, St. Paul, MN 55108 will have on both consumers and producers will depend on the plant’s ability to offer William D. Hutchison improved nutritional quality, less suscepti- Department of Entomology, University of Minnesota, 1980 Folwell Avenue, bility to herbivores/pathogens, increased St. Paul, MN 55108 therapeutic properties, and desirable agro- nomic, storage, and sensory characteristics Additional index words. glucosinolate, herbivory, insect feeding, stress-induced (Rosa et al., 1997). Abstract. Changes in the levels of gluconasturtiin (2-phenylethyl glucosinolate), an Our objectives were to: 1) determine if aromatic glucosinolate, was used to evaluate the response of ‘Green Rocket’ Chinese there was an effect of cabbage looper larvae cabbage (Brassica campestris ssp. pekinensis L.) to the feeding of three and five cabbage feeding on gluconasturtiin concentration in looper (Trichoplusia ni Hu¨bner) larvae per plant. Plants were harvested 0, 10, and Chinese cabbage by correlating it with the 17 days after infestation. The change in gluconasturtiin concentration resulting from insect pressure imposed on the plant; 2) decreased light capture from diminished leaf area was also studied. All samples were evaluate the effect after the larvae were assayed for gluconasturtiin concentration using high-performance liquid chromatogra- removed; and 3) determine if reduced light phy. The gluconasturtiin concentration of plants subjected to five larvae per plant conditions had an effect on gluconasturtiin showed a 59% increase 10 days after infestation compared with noninfested plants. concentration. Difference in gluconasturtiin concentration between three and five larvae per plant was nonsignificant. Seventeen days after initial infestation and 7 days after larvae were Materials and Methods removed (final harvest), gluconasturtiin concentration did not decrease compared with the previous harvest. Reduced light or leaf area removal did not significantly affect Two greenhouse experiments were con- gluconasturtiin concentration. ducted to evaluate the effect of cabbage looper larval feeding on gluconasturtiin con- centration in ‘Green Rocket’ Chinese cab- In recent years, the consumption of cru- The hydrolysis of the aromatic glucosino- bage plants. This cultivar was used to model ciferous vegetables with increased recogni- late gluconasturtiin releases phenethyl iso- the response of cruciferous vegetables to tion of their nutraceutical properties has thiocyanate (PEITC). Isothiocyanates are insect herbivory because of its relatively high become very important because of the asso- known to induce phase II detoxification gluconasturtiin concentration compared with ciated benefit of reducing the incidence of enzymes (Wattenberg, 1990). Previous stud- other cultivars (V.A. Fritz, personal commu- cancer and other chronic diseases (Talalay ies have shown that PEITC provides signif- nication). A preliminary study was con- and Fahey, 2001; Wargovich, 2000). A group icant chemoprevention, especially against ducted in 2002 to determine the effect of of secondary compounds, called glucosino- human prostate cancer (Powolny et al., larval feeding of two densities of cabbage lates, is widely present in crucifers. On 2003; Wargovich, 2000; Xiao et al., 2003). looper on gluconasturtiin concentration. A cellular damage or disruption, hydrolysis of Gluconasturtiin is present in several crucifers second experiment was designed to evaluate glucosinolates, through the enzyme myrosi- such as watercress (Nasturtium officinale L.) the level of gluconasturtiin over time and was nase, produces isothiocyanates, which may, and Chinese cabbage (Brassica campestris conducted twice in 2003. Greenhouse con- in part, account for the chemopreventive ssp. pekinensis L.). Because of the chemo- ditions were maintained constant throughout properties associated with these vegetables. preventive properties of PEITC, it is desir- all experiments (20 ± 2 °C with natural able to characterize gluconasturtiin (precursor photoperiod at 45° latitude). of PEITC) concentration and explore the Effect of cabbage looper density. On Received for publication 20 Feb. 2007. Accepted potential of plants to produce increased 15 Oct. 2002, two seeds of ‘Green Rocket’ for publication 21 May 2007. amounts of this compound. Chinese cabbage (American Takii, Salinas, We thank Mr. Greg Holden and Ms. Lynette Wong The variation in total and individual CA) were planted 2.5 cm deep in each cell of for their technical assistance with high-perfor- glucosinolate concentration in a plant is the a53· 27-cm germination tray (Dillen Prod- mance liquid chromatography analysis. result of several factors, both abiotic and ucts, Middlefield, OH) filled with Metro-Mix Mention of a trademark, proprietary product, or biotic (Rosa et al., 1997; Smith et al., 2003). 200 potting mix (60% horticultural vermicu- vendor does not constitute a guarantee or warranty Research has also shown that glucosinolate of the product by the University of Minnesota and lite, 40% Canadian sphagnum peatmoss, does not imply its approval to the exclusion of other levels are not constant throughout the phenol- horticultural perlite, and washed sand; Scotts products or vendors that also may be suitable. ogy of a plant, particularly in early growth Co., Marysville, OH) and watered as needed. 1To whom reprint requests should be addressed; stages. Young photosynthetically active tis- On germination, plants were thinned to one e-mail [email protected]. sues are believed to be the major sites of per cell. After thinning, 100 mgÁL–1 of a HORTSCIENCE VOL. 42(6) OCTOBER 2007 1337 20N–8.7P–16.6K soluble fertilizer (JR Peters, described. The statistical model used was a Samples were analyzed using an Ultra Aque- Allentown, PA) was used to fertilize plants split-plot design with five replicates with ous C18 analytical column (4.6 mm · 15 cm, twice a week for the first 2 weeks. From the netting treatment being the main plots and 5 mm; Restek USA, Bellefonte, PA) at 30 °C third week after thinning until the end of the larval densities comprising the subplots. with a flow rate of 1.0 mLÁmin–1. Solvent A experiment, plants received a weekly applica- Each treatment was comprised of six plants was 0.1 M ammonium acetate and solvent B tion of 200 mgÁL–1 of the same 20N–8.7P– per replicate located at each corner of a 76 · was 30% methanol with 0.1 M ammonium 16.6K fertilizer. Three weeks after sowing, 56-cm rectangle with three plants equally acetate. The elution protocol was 0 to 6 min, plants were transplanted to greenhouse distributed on the longer edge of the rectan- 100% A; 6 to 21 min, a linear gradient to 70% benches, filled with a mixture of 1 sterilized gle. Treatments were separated from each B; and 21 to 24 min, a linear gradient to 100% sandy loam soil:3 SB 300 (55% bark, 45% other by six nontreated plants arranged in a B. The solvent was then held at 100% B for horticultural vermiculite, Canadian sphagnum similar manner. Three sequential harvests 11 min. After the analytical sequence, a linear peatmoss, horticultural perlite, dolomitic lime- were conducted and gluconasturtiin concen- gradient to starting conditions (35 to 37 min, stone, and gypsum; Sungro Horticulture Can- tration at each of them was determined to linear gradient to 100% A) followed by a 13- ada Ltd., Vancouver, BC) by volume. observe temporal distribution. The first har- min postrun hold at 100% solvent A recon- The statistical model used was a split-plot vest was performed on 12 Oct. 2003 before ditioned the column for the next injection. design with four replicates. Half the plants in infestation and the second harvest was con- Samples were analyzed in duplicate. each replicate were covered [photosynthetic ducted 10 d after infestation. On this date, The external standards used to identify photon flux (PPF): 240 mmolsÁm–2Ás–1] with all larvae were manually removed from all chromatogram peaks were prepared using a antiaphid netting (Kaplan-Simon Co., Brain- plants. Finally, the third harvest was per-