Soil contamination with heavy metals has become a worldwide problem, leading to the loss in agricultural productivity. Plants have a remarkable ability to take up and accumulate heavy metals from their external environment and it is well known that high levels of heavy metals affect different physiological and metabolic processes. Brassinosteroids are considered as the sixth class of plant hormones and they are essential for plant growth and development. These compounds are able of inducing abiotic stress tolerance in plants. In this paper, information about brassinosteroids and plant responses to heavy metal stress is reviewed.

We evaluated the effects of foliar application of 24-epibrassinolide (EBL) on growth, oxidative metabolism and water relations of rice seedlings cv. J-104, stressed with 100 mmol L -1 NaCl for 7 days and recovered without NaCl in the nutrient solution during the next 15 days. Measurements were made at the beginning, at the end and after recovery from salt stress. Salinity decreased growth but the effects were observed during the recovery period. Foliar application of EBL restored growth in salt stressed seedlings. Water relations were affected by salt stress but spraying EBL only restored turgor potential. Proline concentration increased after recovery in salt stressed seedlings and application of EBL reverted this effect by 35 %. Lipid peroxidation and protein oxidation increased with salt stress and seedlings sprayed with EBL showed lower damage to membranes and proteins than salt stressed plants without EBL application. Antioxidant enzymes responded variably to salt stress, peroxidases and SOD either decreased or were little affected by salt stress, whereas catalase activity increased with salinity. The effect of EBL on antioxidant enzymes was in general to increase activities of catalase, ascorbate peroxidase and SOD. The protective effects of EBL of salt stressed rice seedlings may be associated with a decrease of oxidative stress probably modulated by proline accumulation via catalase and SOD, evidenced by a reduction of lipid peroxidation and proteins oxidation, and maintenance of chlorophylls concentration.

Soil salinity is one of the abiotic stresses, which reduces plant growth and limits crop productivity. Brassinosteroids are considered as the sixth class of plant hormones and they have pleiotropic effects on plants, among them, they can protect plants under abiotic stresses and especially under salt stress. This paper reviews the information published during the last sixteen years related to the effects of brassinosteroids and their spirostanic analogs in plants submitted to saline stress when they are used by means of seed treatments, through the application of foliar sprays or by rooting media. Brassinosteroids stimulated salt stress tolerance in plants is associated to a decrease of oxidative damage generated by this stress and the interaction between brassinosteroids and other plant hormones, for example: abscisic acid, ethylene and salicylic acid.

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