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.

Introduction

The role of salicylic acid (SA) in defense mechanisms against pathogen attack has been known for several years [2], [3]. In recent years its role has been widely investigated in both biotic and abiotic stresses. It was also reported that SA accumulated during exposure to ozone or UV light [4], [5]. SA ameliorated the damaging effects of heavy metals on membranes in rice [6] and improved the heat-shock tolerance of mustard (Sinapis alba L.) [7], [8] and tobacco plants [9]. Acetyl SA (aspirin) induced heat tolerance in potato microplants [10] and decreased the inhibitory effect of drought [11] and salt stress [12] in wheat. It has already been shown that salicylic acid may alter the synthesis of the plant hormone ethylene in maize [13]. The addition of salicylic acid [1] or certain related compounds [14] to the hydroponic solution of maize plants (Zea mays L.) reduces the effect of low temperature stress.

Polyamines are essential components of living organisms and their role in the physiological and biochemical processes has long been studied [15]. It was shown in several cases that stress tolerance is associated with changes in the polyamine metabolism [16]. An increase in the endogenous polyamine content was reported during low temperature stress [17], especially when chilling was accompanied by light stress [18]. The role of polyamines in osmotic and salinity stresses [19], [20] and in frost hardening [21] is also well documented.

Besides low temperature, drought is one of the most important limiting factors of crop production all over the world. The aims of the present work were: (1) to investigate the effect of SA pre-treatment on the polyamine content in maize; (2) to discover whether SA was able to induce drought tolerance in maize and wheat plants under the same conditions where it induces chilling tolerance.