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Salicylic acid (SA) acts as an endogenous signal molecule responsible for inducing abiotic stress tolerance in plants. In this study, the role of SA in improving drought tolerance in two maize cultivars (Zea mays L.) differing in their tolerance to drought was evaluated. The plants were regularly watered per pot and grown until the grain filling stage (R2) under a rainout shelter. At stage R2, parts of the plants were treated with SA, after which drought stress was applied. Leaf samples were harvested on the 10th and 17th days of the drought. Some antioxidant enzyme activity, such as the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), hydrogen peroxide (H 2 O 2 ) and malondialdehyde (MDA) content, was measured during the drought period. Exogenous SA prevented water loss and delayed leaf rolling in comparison with control leaves in both cultivars. As a consequence of drought stress, lipid peroxidation, measured in terms of malondialdehyde content, was prevented by SA. SA pretreatment induced all antioxidant enzyme activities, and to a greater extent than the control leaves, during drought. SA also caused a reduction in the ascorbate (ASC) and glutathione (GSH) content in two maize cultivars. The H 2 O 2 level was higher in SA pretreated plants than the controls in both cultivars. Pretreatment with SA further enhanced the activities of antioxidant enzymes and the concentrations of non-enzymatic antioxidants in the tolerant cultivar compared with the sensitive cultivar. Results suggested that exogenous SA could help reduce the adverse effects of drought stress and might have a key role in providing tolerance to stress by decreasing water loss and inducing the antioxidant system in plants with leaf rolling, an alternative drought protection mechanism.

Salicylic acid (SA) is one of the important signal molecules modulating plant responses to environmental stress. In this study, the effects of exogenous SA on leaf rolling, one of drought avoidance mechanisms, and antioxidant system were investigated in Ctenanthe setosa during long term drought stress. The plants were subjected to 38-day drought period and they were treated with or without SA (10 -6 M) on the 25th, 27th and 29th days of the period. Leaf samples were harvested on the 30th, 34th and 38th days. Some antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase), reactive oxygen species (hydrogen peroxide and superoxide) and lipid peroxidation were determined during the drought period. Treatment with SA prevented water loss and delayed leaf rolling in comparison with control leaves. Exogenous SA induced all antioxidant enzyme activities more than control leaves during the drought. Ascorbate and glutathione, a-tocopherol, carotenoid and endogenous SA level were induced by the SA treatment. Levels of reactive oxygen species were higher in SA treated plants than control ones on the 34th day. Their levels on the 38th day, however, fastly decreased in SA treated plants. SA treatment prevented lipid peroxidation while the peroxidation increased in control plants. The results showed that exogenous SA can alleviate the damaging effect of long term drought stress by decreasing water loss and inducing the antioxidant system in the plant having leaf rolling, alternative protection mechanism to drought.

R. 2000. Water stress effects on the content of low molecular weight carbohydrates and phenolic acids in Ctenanthe setosa (Rosc.) Eichler. Can. J. Plant Sci. 80: 373-378. Morphological and biochemical changes in plant cells are known as important events for adaptation to stress. In this study, changes in carbohydrate and phenolic acid concentrations during leaf rolling under water stress were investigated. Leaves of vegetatively propagated Ctenanthe setosa (Rosc.) Eichler plants started to roll after a 28-d water deficit. After approximately 33-35 d, the leaves were tightly rolled. Water stress significantly increased the dry weight of rolled leaves. Low molecular dry weight carbohydrate components identified in unrolled and rolled leaves were fructose, glucose, inositol and sucrose. Leaves of stressed plants tended to accumulate more carbohydrates of low molecular weight. The same sugars (except inositol) were also identified in liquid and crystal forms of exudates, which appeared on the abaxial surface of the leaves during leaf rolling. The phenolic acids identified in unrolled and rolled leaves were from the benzoic group (benzoic, salicylic, 4-hydroxybenzoic, vanillic, 3,4-dihydroxybenzoic, syringic acids), and the cinnamic group (ferulic and caffeic acids both in free and methyl ester form and cis-and trans-p-coumaric acids). All phenolic acid concentrations (except for salicylic acid) in the phenolic group increased in rolled leaves in comparison with unrolled leaves. In the cinnamic group, the amounts of cis-and trans-p-coumaric and caffeic acids were greater in rolled leaves than in unrolled leaves. Water deficit stress is one of the major factors limiting the growth of land plants (Levitt 1980). During water stress in plants, some adaptive response such as leaf movements are observed (Begg 1980;Ehleringer and Forseth 1980). Among the leaf movements, leaf rolling has been identified as one of the most frequent responses to water deficit in some plants (Townley-Smith and Hurd 1979;Begg 1980;Blum 1988). Leaf rolling is induced by a reduction in pressure potential as a consequence of water loss from the bulliform cells in the upper epidermis of the leaf. Leaf rolling reduces indicent irradiation, leaf temperature and transpiration (O'Toole et al. 1979;Begg 1980;Ehleringer and Forseth 1980;Hsiao et al. 1984), and has been investigated especially in grasses (Clarke 1986;Ekanayake et al. 1993); rice (Omarova et al. 1995;Turner et al 1986) and maize (Loresto et al. 1976;O'Toole and Garrity 1984;Premachandra et al. 1993) also show leaf rolling behavior.Ctenanthe setosa, a species that shows a leaf rolling response to drought, is a member of a small family of tropical herbaceous perennials, and is cultivated as a greenhouse ornamental and houseplant (Heywood 1978 For personal use only. CANADIAN JOURNAL OF PLANT SCIENCErolling (Turgut and Kadioglu 1998). Kadioglu and Turgut (1999) reported that upon irrigation of Ctenanthe setosa that have rolled leaves, many exudates can be observed on the abaxial surface of the...

Hydrogen peroxide (H 2 O 2 ) functions as a signal molecule in plants under abiotic and biotic stresses. Leaves of detached maize (Zea mays L.) seedlings were used to study the function of H 2 O 2 pretreatment in osmotic stress resistance. Low H 2 O 2 concentration (10 mM) which did not cause a visual symptom of water deficit (leaf rolling) was applied to the seedlings. Exogenous H 2 O 2 alone increased leaf water potential, endogenous H 2 O 2 content, abscisic acid (ABA) concentration, and metabolite levels including soluble sugars, proline, and polyamines while it decreased lipid peroxidation and stomatal conductance. Osmotic stress induced by polyethylene glycol (PEG 6000) decreased leaf water potential and stomatal conductance but enhanced lipid peroxidation, endogenous H 2 O 2 content, the metabolite levels, and ABA content. H 2 O 2 pretreatment also induced the metabolite accumulation and improved water status, stomatal conductance, lipid peroxidation, ABA, and H 2 O 2 levels under osmotic stress. These results indicated that H 2 O 2 pretreatment may alleviate water loss and induce osmotic stress resistance by increasing the levels of soluble sugars, proline, and polyamines thus ABA and H 2 O 2 production slightly decrease in maize seedlings under osmotic stress.

Photochemical efficiency of PSII of Ctenanthe setosa was investigated to understand the photosynthetic adaptation mechanism under drought stress causing leaf rolling. Stomatal conductance (g s ), the levels of photosynthetic pigments and chlorophyll (Chl) fluorescence parameters were determined in leaves that had four different visual leaf rolling scores from 1 to 4, opened after re-watering and mechanically opened at score 4. g s value gradually decreased in adaxial and abaxial surfaces in relation to scores of leaf rolling. Pigment contents decreased until score 3 but approached score 1 level at score 4. No significant variations in effective quantum yield of PSII (Ф PSII ), and photochemical quenching (q p ) were found until score 3, while they significantly decreased at score 4. Non-photochemical quenching (NPQ) increased at score 2 but then decreased. After re-watering, the Chl fluorescence and other physiological parameters reached to approximately score 1 value, again. As for mechanically opened leaves, g s decreased during drought period. The decrease in adaxial surface was higher than that of the rolled leaves. NPQ was higher than that of the rolled leaves. Ф PSII and q p significantly declined and the decreases were more than those of the rolled leaves. In conclusion, the results indicate that leaf rolling protects PSII functionality from damage induced by drought stress.