Environmental conditions, specifically heat stress, are important factors in asparagus crop production. Arbuscular mycorrhizal fungi (AMF) have been shown to increase plant growth. Effects of heat stress on nutrient uptake have rarely been examined in intact plants, but the limited results indicate that heat stress will decrease uptake; no studies have examined heat stress effects on asparagus nutrient uptake. We examined the effects of AMF, Glomus intraradices, on the growth, nutrient uptake, heat stress responses, and antioxidative activity in asparagus (Asparagus officinalis L.). We grew AMF-inoculated or non–AMF-inoculated asparagus plants in sand culture at 20 to 25 °C for 14 weeks in a greenhouse and subsequently subjected to three temperature conditions (control = 20 °C/25 °C night/day, mild heating = 30 °C/35 °C night/day, and severe heating = 37 °C/42 °C night/day) in growth chambers. Morphological and physiological growth parameters were compared between AMF-inoculated and non–AMF-inoculated plants. The mycorrhizal symbiosis markedly enhanced biomass production and heat stress responses negatively in plants compared with that in the non–AMF-inoculated plants. Plants grown under non–AMF-inoculated treatment had severe rate of leaf browning (80% to 100%), whereas the mycorrhizal plants showed a minimum rate of leaf browning under heat stress conditions. The results indicated mycorrhizal-inoculated plants showed an increase activity of antioxidative enzymes, such as superoxide dismutase and ascorbate peroxidase. The 2,2-diphenyl-1picrylhydrazyl radical scavenging activity also showed a greater response in mycorrhizal plants than in the control plants under each temperature treatment. Application of AMF enhanced plant growth and mineral nutrients and alleviated heat stress damage through an increased antioxidative activity and the mycorrhizal symbiosis significantly enhanced heat stress tolerance of asparagus.
Rumana Yeasmin, Stephen P. Bonser, Satoru Motoki and Eiji Nishihara
Tomoo Maeda, Hideo Kakuta, Takahiro Sonoda, Satoru Motoki, Reiichiro Ueno, Takashi Suzuki and Katsuji Oosawa
The antioxidation capacities of green `Welcome', green and white `Gijnlim', and purple `Purple passion' asparagus spears were evaluated. Analyses of rutin and total polyphenols, and assays of DPPH radical absorbing and low-density lipoprotein (LDL) antioxidation were conducted. Varietal differences associated with the colors of spears were observed both in the amounts of rutin, total polyphenols and in DPPH radical absorbing activities, although not in LDL antioxidation activities. DPPH radical absorbing activities seemed to be affected by both rutin and other polyphenolic compounds. However, LDL antioxidation activities were likely to be influenced more by other polyphenolic compounds than by rutin. Total polyphenol content showed a fairly close relationship with rutin content, DPPH radical absorbing activity and LDL antioxidation activity. To determinate total polyphenol content using the Folin–Denis' method seemed to be useful for selecting the breeding lines that show high antioxidative capacities.
Satoru Motoki, Hiroaki Kitazawa, Tomonori Kawabata, Hiroaki Sakai, Ken-ichi Matsushima and Yasunori Hamauzu
Head tightness, soluble solid content (SSC), and rutin level were investigated in asparagus spears harvested at different lengths. We found no correlation between spear length and SSC per dry weight (DW) in spearheads. Spearheads became looser and the rutin content of the spearhead increased as spear length at harvest increased, although appearance quality decreased. These findings revealed that spears previously discarded, because their length did not meet the length specifications, contained abundant rutin. Therefore, spears for which the optimum harvesting time has been missed are a useful rutin source.