Do brassinosteroids mediate the water stress response?

Abstract

Brassinosteroids (BRs) have been suggested to increase the resistance of plants to a variety of stresses, including water stress. This is based on application studies, where exogenously applied bioactive BRs have been shown to improve various aspects of plant growth under water stress conditions. However, it is not known whether changes in endogenous BR levels are normally involved in mediating the plant's response to stress. We have utilized BR mutants in pea (Pisum sativum L.) to determine whether changes in endogenous BR levels are part of the plant's response to water stress and whether low endogenous BR levels alter the plant's ability to cope with water stress. In wild-type (WT) plants, we show that while water stress causes a significant increase in ABA levels, it does not result in altered BR levels in either apical, internode or leaf tissue. Furthermore, the plant's ability to increase ABA levels in response to water stress is not affected by BR deficiency, as there was no significant difference in ABA levels between WT, lkb (a BR-deficient mutant) and lka (a BR-perception mutant) plants before or 14 days after the cessation of watering. In addition, the effect of water stress on traits such as height, leaf size and water potential in lkb and lka was similar to that observed in WT plants. Therefore, it appears that, at least in pea, changes in endogenous BR levels are not normally part of the plant's response to water stress.

Reactive Oxygen Species Are Involved in Brassinosteroid-Induced Stress Tolerance in Cucumber

“…These studies support the involvement of BR in plant responses to various environmental stresses (Krishna, 2003;Nakashita et al, 2003;Kagale et al, 2007). There were significant increases in several intermetabolite levels in the BR biosynthesis pathway after Tobacco mosaic virus inoculation in tobacco leaves (Nakashita et al, 2003), whereas there were no consistent changes in the intermetabolite levels in leaves of pea in response to water stress (Jager et al, 2008). Accordingly, BR biosynthesis may be induced in some but not all types of stress conditions.…”

“…Most recently, we also found that EBR application to wild-type and BR-deficient mutant all increased their resistance to Cladosporium fulvum in tomato (data not shown). There was, however, no significant difference in the tolerance of wild-type and BR-deficient mutant to water stress in pea (Jager et al, 2008). Thus, BR may be involved in plant responses to some but not all types of plant stress conditions.…”

“…However, it is difficult to analyze genetically the role and action mechanisms of BR in plant stress tolerance because of the strong and pleiotropic phenotypes of BR biosynthesis and signaling mutants, including extreme dwarfism, dark green and epinastic leaves, and delayed development (Khripach et al, 2000;Bishop and Koncz 2002;Mü ssig et al, 2002;Cao et al, 2005). Moreover, current techniques allow for measurement of stress-induced changes in the levels of only intermediates in the BR biosynthesis pathway but not of the bioactive brassinolide (Nakashita et al, 2003;Jager et al, 2008). As a result, application of Brz, a specific and potent inhibitor of BR biosynthesis (Asami et al, 2000(Asami et al, , 2001, has been used to study the role of BR in plant stress responses.…”

Brassinosteroids Confer Stress Tolerance

“…Studies in pea have shown that while water stress causes a significant increase in ABA levels, it does not result in altered BR levels in either apical, internode or leaf tissue. Also, the plant's ability to increase ABA levels in response to water stress is not affected by BR deficiency in lkb (BR-deficient) and lka (BR-perception) mutant plants [68]. On the basis of these results it is argued that in pea changes in endogenous BR levels are not part of the plant's response to water stress.…”

24-epibrassinolide increases growth, grain yield and β-ODAP production in seeds of well-watered and moderately water-stressed grass pea

“…In contrast, exogenous ABA applied to soil was shown to enhance endogenous ABA accumulation, decrease the grain yield, but increase the transpiration efficiency for grain in wheat (Du et al 2013). Jager et al (2008) found, however, no significant differences in endogenous ABA concentration among wild-type plants, a brassinosteroid-deficient mutant (Ikb) and a brassinosteroid-perceptive mutant (Ika) of pea (Pisum sativum L.) subjected to water stress, suggesting that EBL and ABA may function along two different pathways in plants. While BRs have increased growth in several species, their effect on grass pea has not been reported as far as the authors are aware.…”