Effects of calcium on antioxidant activities and water relations associated with heat tolerance in two cool-season grasses.
Calcium (Ca2+) may be involved in plant tolerance to heat stress by regulating antioxidant metabolism or/and water relations. This study was designed to examine whether external Ca2+ treatment would improve heat tolerance in two C(3), cool-season grass species, tall fescue (Festuca arundinacea L.) and Kentucky bluegrass (Poa pratensis L.), and to determine the physiological mechanisms of Ca2+ effects on grass tolerance to heat stress. Grasses were treated with CaCl(2) (10 mM) or H(2)O by foliar application and then exposed to heat stress (35/30 degrees C) in growth chambers. Some of the Ca2+ -untreated plants were maintained at 20/15 degrees C as the temperature control. Heat stress reduced grass quality, relative water content (RWC), and chlorophyll (Chl) content of leaves in both species, but Ca2+ treatment increased all three factors under heat stress. The Ca2+ concentration in cell saps increased with heat stress and with external Ca2+ treatment in both species. Osmotic potential increased with heat stress, but external Ca2+ treatment had no effect. Osmotic adjustment increased during short-term heat stress, but then decreased with a prolonged period of stress; it was not influenced by Ca2+ treatment. The activity of superoxide dismutase (SOD) in both species increased transiently at 12 d of heat stress and then remained at a level similar to that of the control. External Ca2+ treatment had no effect on SOD activity. The activities of catalase (CAT), ascorbate peroxidase (AP), and glutathione reductase (GR) of both species decreased during heat stress. Plants treated with Ca2+ under heat stress had higher CAT, GR and AP activities than untreated plants. Lesser amounts of malondialdehyde (MDA) accumulated in Ca2+ -treated plants than in untreated plants during extended periods of heat stress. The results suggested that exogenous Ca2+ treatment enhanced heat tolerance in both tall fescue and Kentucky bluegrass. This enhancement was related to the maintenance of antioxidant activities and a decrease in membrane lipid peroxidation, but not to the regulation of osmotic potential and osmotic adjustment.
Department of Horticulture, Forestry and Recreational Resources, Kansas State University, Manhattan, KS 66506, USA.
Y
Y
Jiang
B
B
Huang
D000975:Antioxidants / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002122:Calcium Chloride / Q000494:pharmacology; D002374:Catalase / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D005980:Glutathione Reductase / Q000378:metabolism; D006358:Hot Temperature / Q000009:adverse effects*; D008315:Malondialdehyde / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D009997:Osmotic Pressure; D018384:Oxidative Stress; D010088:Oxidoreductases / Q000378:metabolism*; D009195:Peroxidase / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D006109:Poaceae / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D013482:Superoxide Dismutase / Q000187:drug effects / Q000378:metabolism; D014867:Water / Q000502:physiology*
D000975:Antioxidants; D008563:Membrane Lipids; D014867:Water; D002734:Chlorophyll; D008315:Malondialdehyde; D010088:Oxidoreductases; D002374:Catalase; D009195:Peroxidase; D013482:Superoxide Dismutase; D005980:Glutathione Reductase; D002122:Calcium Chloride; D002118:Calcium