Tibor Janda

Hydroponic treatment with salicylic acid decreases the effects of chilling injury in maize (Zea mays L.) plants

Abstract. The addition of 0.5 mM salicylic acid (SA) to the hydroponic growth solution of young maize (Zea mays L.) plants under normal growth conditions provided protection against subsequent low-temperature stress. This observation was confirmed by chlorophyll fluorescence parameters and electrolyte leakage measurements. In addition, 1 d of 0.5 mM SA pre-treatment decreased net photosynthesis, stomatal conductivity and transpiration at the growth temperature (22/20 °C). Since there was only a slight decrease in the ratio of variable to maximal fluorescence (Fv/Fm) the decrease in photosynthetic activity is not due to a depression in photosystem II. The analysis of antioxidant enzymes showed that whereas SA treatment did not cause any change in ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1.15.1.1) activities, there was a decrease in catalase (EC 1.11.1.6) activity, and an increase in guaiacol peroxidase (EC 1.11.1.7) and glutathione reductase (EC 1.6.4.2) activities after the 1-d SA treatment at 22/20 °C. In native polyacrylamide gels there was, among the peroxidase isoenzymes, a band which could be seen only in SA-treated plants. It is suggested that the pre-treatment of maize plants with SA at normal growth temperature may induce antioxidant enzymes which lead to increased chilling tolerance.

Induction of Abiotic Stress Tolerance by Salicylic Acid Signaling

The role of salicylic acid (SA) as a key molecule in the signal transduction pathway of biotic stress responses has already been well described. Recent studies indicate that it also participates in the signaling of abiotic stresses. The application of exogenous SA could provide protection against several types of stresses such as high or low temperature, heavy metals, and so on. Although SA may also cause oxidative stress to plants, partially through the accumulation of hydrogen peroxide, the results published so far show that the preliminary treatment of plants with low concentrations of SA might have an acclimation-like effect, causing enhanced tolerance toward most kinds of abiotic stresses due primarily to enhanced antioxidative capacity. The effect of exogenous SA depends on numerous factors such as the species and developmental stage of the plant, the mode of application, and the concentration of SA and its endogenous level in the given plant. Recent results show that not only does exogenous SA application moderate stress effects, but abiotic stress factors may also alter the endogenous SA levels in the plant cells. This review compares the roles of SA during different abiotic stresses.

Exogenous salicylic acid increases polyamine content but may decrease drought tolerance in maize

Abstract It was shown in a previous work that 0.5 mM salicylic acid (SA) added in the hydroponic solution of maize increased its tolerance to low temperature stress [Planta 208 (1999) 175]. The effect of SA and cold treatments on polyamine content in the leaves was investigated using the HPLC technique in this work. Both 0.5 mM SA and cold treatment caused a significant increase in putrescine content. Spermidine increased only when the addition of SA was followed by low temperature stress. The spermine content decreased after both SA and low temperature treatments. The parallel use of 0.5 mM SA and 15% PEG caused a dramatic increase in the electrolyte leakage and a decrease in certain photosynthetic parameters in maize and wheat. It is concluded that the 0.5 mM SA pre-treatment, which increased the chilling tolerance, caused an increased sensitivity to drought.

Exogenous treatment with salicylic acid attenuates cadmium toxicity in pea seedlings

The present study investigated the possible mediatory role of salicylic acid (SA) in protecting plants from cadmium (Cd) toxicity. The exposure of pea plants to increasing Cd concentrations (0.5, 1.0, 2.0 and 5.0 microM) during early stages of their establishment, caused a gradual decrease in shoot and root fresh weight accumulation, the rate of CO2 fixation and the activity of ribulose-1,5-bisphosphate carboxylase (RuBPC, E.C. 4.1.1.39), the effect being most expressed at higher Cd concentrations. In vivo the excess of Cd-induced alterations in the redox cycling of oxygen-evolving centers and the assimilatory capacity of the pea leaves as revealed by changes in thermoluminescence emission after flash illumination. The levels of some important parameters associated with oxidative stress, namely lipid peroxidation, electrolyte leakage and proline production were increased. Seed pretreatment with SA alleviated the negative effect of Cd on growth, photosynthesis, carboxylation reactions, thermoluminescence characteristics and chlorophyll content, and led to decrease in oxidative injuries caused by Cd. The data suggest that the beneficial effect of SA during an earlier growth period could be related to avoidance of cumulative damage upon exposure to cadmium thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity. In addition, the observed high endogenous levels of SA after treatment with Cd suggests that SA may act directly as an antioxidant to scavenge the reactive oxygen species and/or indirectly modulate redox balance through activation of antioxidant responses. Taken together these evidences could explain at some extend the protective role of SA on photochemical activity of chloroplast membranes and photosynthetic carboxylation reactions in Cd-stressed pea plants.

Exogenous 4-hydroxybenzoic acid and salicylic acid modulate the effect of short-term drought and freezing stress on wheat plants

Exogenous salicylic acid has been shown to confer tolerance against biotic and abiotic stresses. In the present work the ability of its analogue, 4-hydroxybenzoic acid to increase abiotic stress tolerance was demonstrated: it improved the drought tolerance of the winter wheat (Triticum aestivum L.) cv. Cheyenne and the freezing tolerance of the spring wheat cv. Chinese Spring. Salicylic acid, however, reduced the freezing tolerance of Cheyenne and the drought tolerance of Chinese Spring, in spite of an increase in the guaiacol peroxidase and ascorbate peroxidase activity. The induction of cross tolerance between drought and freezing stress was observed: drought acclimation increased the freezing tolerance of Cheyenne plants and cold acclimation enhanced the drought tolerance. The induction of drought tolerance in Cheyenne was correlated with an increase in catalase activity.

Complex phytohormone responses during the cold acclimation of two wheat cultivars differing in cold tolerance, winter Samanta and spring Sandra

Hormonal changes accompanying the cold stress (4°C) response that are related to the level of frost tolerance (FT; measured as LT50) and the content of the most abundant dehydrin, WCS120, were compared in the leaves and crowns of the winter wheat (Triticum aestivum L.) cv. Samanta and the spring wheat cv. Sandra. The characteristic feature of the alarm phase (1 day) response was a rapid elevation of abscisic acid (ABA) and an increase of protective proteins (dehydrin WCS120). This response was faster and stronger in winter wheat, where it coincided with the downregulation of bioactive cytokinins and auxin as well as enhanced deactivation of gibberellins, indicating rapid suppression of growth. Next, the ethylene precursor aminocyclopropane carboxylic acid was quickly upregulated. After 3-7 days of cold exposure, plant adaptation to the low temperature was correlated with a decrease in ABA and elevation of growth-promoting hormones (cytokinins, auxin and gibberellins). The content of other stress hormones, i.e., salicylic acid and jasmonic acid, also began to increase. After prolonged cold exposure (21 days), a resistance phase occurred. The winter cultivar exhibited substantially enhanced FT, which was associated with a decline in bioactive cytokinins and auxin. The inability of the spring cultivar to further increase its FT was correlated with maintenance of a relatively higher cytokinin and auxin content, which was achieved during the acclimation period.

In vitro salicylic acid inhibition of catalase activity in maize: differences between the isozymes and a possible role in the induction of chilling tolerance

Abstract It has been suggested that the inhibition of catalase (CAT) (EC 1.11.1.6) by salicylic acid (SA) plays a role in mediating stress responses. In this work, it is proposed that CAT-1 and CAT-2 isozymes of maize (Zea mays L.) might differ in the nature of SA inhibition, as it was shown for 0 and 9 dpi (days postimbibition) scutellum preparations, containing mainly CAT-1 and CAT-2 isozymes, respectively. In the case of 9 dpi extract, only a weak, competitive inhibition of CAT activity was observed upon treatment with SA or several other phenolic compounds. On the other hand, CAT activity of the 0 dpi extract was inhibited to a significantly greater extent and in a non-competitive manner by SA and its analogues, except for p-hydroxybenzoic acid (pHBA), which showed the same kinetics of inhibition as for 9 dpi samples. All of the phenolic compounds but pHBA, were found to significantly increase chilling tolerance when added hydroponically to young maize seedlings. According to these results, CAT-1 might be a candidate for mediating the effect of SA on the induction of chilling tolerance in maize. Maize genotypes with varying degrees of chilling tolerance were compared: chilling-tolerant maize lines showed significant inhibition by SA, while chilling-sensitive lines were not uniform in this respect, as in the case of Mo17, catalase activity was hardly inhibited by SA, while Penjalinan showed the same rate of inhibition as the chilling-tolerant genotypes.

Effects of cold acclimation and salicylic acid on changes in ACC and MACC contents in maize during chilling

The effect of 0.5 mM salicylic acid (SA) pretreatment and of growing at hardening temperatures on chilling-induced changes in 1-aminocyclopropane-1-carboxylic acid (ACC) and malonyl 1-aminocyclopropane-1-carboxylic acid (MACC) was investigated in young maize (Zea mays L.) plants grown in hydroponic solution at 22/20 °C. Chilling at 5 °C caused an increase in ACC content;however, this increase was less pronounced in plants cold acclimated at 13/11 °C 4 d before the chilling treatment, and in those which were pretreated with SA for 1 d before the cold stress. Changes in MACC at low temperature showed no correlation with chilling tolerance in maize.

Role of Salicylic Acid in the Induction of Abiotic Stress Tolerance

Investigations on compounds capable of reducing the stress sensitivity of crops are of great importance from both the theoretical and the practical point of view. In terms of stress physiology, salicylic acid was first demonstrated to play a role in responses to biotic stress. However, it was gradually found to have more and more effects that could be of importance for other stress factors, and a great deal of evidence has accumulated in recent years suggesting that salicylic acid also plays a role in responses to abiotic stress effects (such as low and high temperature, UV-B irradiation, ozone, heavy metals, etc.). Most papers, on this subject, have reported on the protective effect of exogenous salicylic acid against abiotic stress. When applied in satisfactory concentrations salicylic acid may cause a temporary low level of oxidative stress in plants, which acts as a hardening process, improving the antioxidative capacity of the plants and helping to induce the synthesis of protective compounds such as polyamines. Numerous mutant or transgenic plants are now available in which the salicylic acid metabolism has been modified in some way. These allow us to obtain a more accurate picture of the endogenous effect and role of salicylic acid. Evidence now suggests the existence of a regulatory defence mechanism in which salicylic acid plays an important role, but which is not stress-specific, apparently functioning against many different stress factors. This chapter provides a review of the effects exerted by salicylic acid and related compounds in relation to abiotic stress tolerance.

Speculation: Polyamines are important in abiotic stress signaling

The main role of polyamines was originally assumed to be as direct protective compounds important under stress conditions. Although in some cases a correlation was found between the endogenous polyamine content and stress tolerance, this relationship cannot be generalized. Polyamines should no longer be considered simply as protective molecules, but rather as compounds that are involved in a complex signaling system and have a key role in the regulation of stress tolerance. The major links in polyamine signaling may be H2O2 and NO, which are not only produced in the course of the polyamine metabolism, but also transmit signals that influence gene expression via an increase in the cytoplasmic Ca(2+) level. Polyamines can also influence Ca(2+) influx independently of the H2O2- and/or NO-mediated pathways. Furthermore, these pathways may converge. In addition, several protein kinases have been shown to be influenced at the transcriptional or post-translational level by polyamines. Individual polyamines can be converted into each other in the polyamine cycle. In addition, their metabolism is linked with other hormones or signaling molecules. However, as individual polyamines trigger different transcriptional responses, other mechanisms and the existence of polyamine-responsive elements and the corresponding transacting protein factors are also involved in polyamine-related signaling pathways.