Emil Páldi

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.

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 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.

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.

Influence of arbuscular mycorrhizae and Rhizobium on free polyamines and proline levels in water-stressed alfalfa

Summary The objective of this research was to study the effect of drought on polyamine and proline levels in alfalfa ( Medicago sativa L. cv. Aragon) plants inoculated with a mycorrhizal fungus and/or Rhizobium compared with non-inoculated ones. The four treatments were: a) plants inoculated with Glomus fasciculatum (Taxter sensu Gerd.) Gerdemann and Trappe and Rhizobium meliloti 102 F51 strain (MR), b) plants inoculated with Rhizobium only (R), c) plants inoculated with Glomus only (M), and d) non-inoculated plants (N). Plants were drought stressed during two cycles of moisture stress and recovery. Although proline concentrations increased and free polyamine (spermidine and spermine) contents decreased in leaves and roots of alfalfa under water stress, symbiotic R, M and MR plants maintained higher free polyamine concentrations than non-symbiotic N ones. Results suggest that symbiotic alfalfa plants are better adapted than non-symbiotic ones to cope with water deficit.

Role of light in the development of post-chilling symptoms in maize

Summary The effect of light (250 μmol m -2 s -1 ) on the appearance of post-chilling symptoms was investigated in cold-treated maize ( Zea mays L. hybrid Furio) seedlings using electrolyte leakage and chlorophyll fluorescence induction measurements as indicators. The longer the cold pretreatment (0.5 °C) in complete darkness, the more rapid the decrease in F v /F m and the increase in electrolyte leakage during cold treatment in the light. The most important difference in the changes in these two parameters is that the changes in F v /F m occur much earlier if the cold treatment is carried out in the light. These findings suggest that chilling stress in cold sensitive maize plants led to an increased susceptibility to photoinhibition at low temperatures. F v /F m and electrolyte leakage changed not only at low temperatures but also after a certain cold pretreatment period at normal temperature. When the seedlings were returned to 25 °C after various chilling periods in the dark both parameters showed that post-chilling symptoms appeared much more rapidly in the light than in the dark. By contrast to the change in F v /F m , where plants chilled for only two days exhibited differences in post-chilling changes in the light and dark, a substantial increase in electrolyte leakage was only observed after four days of cold pretreatment. These results suggest that photoinhibition has a role not only during the chilling period, but also in the appearance of post-chilling symptoms.

Effect of short-term and long-term low temperature stress on polyamine biosynthesis in wheat genotypes with varying degrees of frost tolerance

Summary Two series of experiments were carried out to examine the short- and long-tetm effects of low temperature on polyamine biosynthesis in wheat. In the first series, studies were made on the polyamine accumulation in the leaves, crowns and roots of winter wheat varieties with varying degrees of frost toletance subjected to short-term low temperature stress (6h, -2 °C). A marked accumulation of Put was observed. Agm accumulation was also examined and found comparable to that of Put. This suggests that Agm, which is an intermediate product of Put synthesis only in higher plants, may play an important role during short-term cold treatment. The second series of experiments was aimed at discovering the effect of wheat chromosomes 5A and 7A, which contain major genes responsible for frost resistance, on the polyamine synthesis taking place in various parts of the seedlings during long periods of cold treatment, and especially on the alternative metabolic pathway present only in higher plants.

S-methylmethionine reduces cell membrane damage in higher plants exposed to low-temperature stress

S-methylmethionine (SMM), an important intermediate compound in the sulphur metabolism, can be found in various quantities in majority of plants. The experiments were designed to determine the extent to which SMM is able to preserve cell membrane integrity or reduce the degree of membrane damage in the course of low-temperature stress. By measuring electrolyte leakage (EL), it was proved that SMM treatment reduced cell membrane damage, and thus EL, during low-temperature stress in both the leaves and roots of peas, maize, soy beans and eight winter wheat varieties with different levels of frost resistance. Investigations on the interaction between SMM and polyamine biosynthesis revealed that SMM increased the quantities of agmatine (Agm) and putrescine (Put) as well as that of spermidine (Spd), while it had no effect on the quantity of spermine (Spn). Using a specific inhibitor, methylglyoxal-bis-guanyl hydrazone (MGBG), it was proved that the polyamine metabolic pathway starting from methionine played no role in the synthesis of Spd or Spn, so there must be an alternative pathway for the synthesis of SMM-induced polyamines.