Abscisic acid and transpiration rate are involved in the response to boron toxicity in Arabidopsis plants

Abstract

Boron (B) is an essential microelement for vascular plant development, but its toxicity is a major problem affecting crop yields in arid and semi-arid areas of the world. In the literature, several genes involved in abscisic acid (ABA) signalling and responses are upregulated in Arabidopsis roots after treatment with excess B. It is known that the AtNCED3 gene, which encodes a crucial enzyme for ABA biosynthesis, plays a key role in the plant response to drought stress. In this study, root AtNCED3 expression and shoot ABA content were rapidly increased in wild-type plants upon B-toxicity treatment. The Arabidopsis ABA-deficient nced3-2 mutant had higher transpiration rate, stomatal conductance and accumulated more B in their shoots than wild-type plants, facts that were associated with the lower levels of ABA in this mutant. However, in wild-type plants, B toxicity caused a significant reduction in stomatal conductance, resulting in a decreased transpiration rate. This response could be a mechanism to limit the transport of excess B from the roots to the leaves under B toxicity. In agreement with the higher transpiration rate of the nced3-2 mutant, this genotype showed an increased leaf B concentration and damage upon exposure to 5 mM B. Under B toxicity, ABA application decreased B accumulation in wild-type and nced3-2 plants. In summary, this work shows that excess B applied to the roots leads to rapid changes in AtNCED3 expression and gas exchange parameters that would contribute to restrain the B entry into the leaves, this effect being mediated by ABA.

Boron toxicity in higher plants: an update

“…Papadakis et al (2014) demonstrated that B excess prevalently affects transpiration rate and detected severe stomata limitations induced by B excess. These findings were in agreement with other authors who observed, in association with the reduction of transpiration rate, a severe increment of the abscisic acid metabolism (Macho-Rivero et al 2017, the major player in stomata closure, for example in case of reduced water availability. However, some authors proposed that there is no evidence to support the hypothesis of the generation of B toxicity effects in leaves due to osmotic stress induced by accumulation of borate or boric acid (Reid et al 2004).…”

Boron Excess Imbalances Root/Shoot Allometry, Photosynthetic and Chlorophyll Fluorescence Parameters and Sugar Metabolism in Apple Plants

“…The reduction of photosynthetic rate in top leaves was partially attributable to stomatal limitation (severe reduction of g s ) which impair the diffusion of CO 2 to carboxylation sites. Most available reports highlight that B is directly or indirectly responsible for stomata closures given that stomatal limitations were reported in some cases [53][54][55][56], whilst this stomata reaction has not been observed in others [57]. This suggests that this stomatal reaction to B excess is a species-specific responsive trait and/or a characteristic which depends to specific experimental conditions (which affect B accumulation/transport) and leaf age (reviewed by [45]).…”

Increased transpiration is correlated with reduced boron deficiency symptoms in the maize tassel‐less1 mutant

“…B has been proposed to interact with multiple hormonal signaling pathways in plants (Blevins and Lukaszewski , Martin‐Rejano et al , Abreu et al , Li et al ) although further research is needed to determine if hormones are mediating any of the processes described in this paper. In particular, ABA, which is directly involved in stomatal closure (Jones and Mansfield ) has been shown to interact with B (Zhou et al , Macho‐Rivero et al ). Both B and ABA accumulate in shoot tissue upon B toxicity treatment, which in turn results in a decrease in transpiration rate, suggesting a possible role of ABA in the control of leaf B content (Macho‐Rivero et al ).…”

“…In particular, ABA, which is directly involved in stomatal closure (Jones and Mansfield 1970) has been shown to interact with B (Zhou et al 2016, Macho-Rivero et al 2017. Both B and ABA accumulate in shoot tissue upon B toxicity treatment, which in turn results in a decrease in transpiration rate, suggesting a possible role of ABA in the control of leaf B content (Macho-Rivero et al 2017). Moreover, ABA biosynthesis genes as well as other hormone pathways are transcriptionally regulated under B deficiency (Zhou et al 2016).…”