Boric acid and salinity effects on maize roots. Response of aquaporins ZmPIP1 and ZmPIP2, and plasma membrane H⁺‐ATPase, in relation to water and nutrient uptake

Abstract

Under saline conditions, an optimal cell water balance, possibly mediated by aquaporins, is important to maintain the whole-plant water status. Furthermore, excessive accumulation of boric acid in the soil solution can be observed in saline soils. In this work, the interaction between salinity and excess boron with respect to the root hydraulic conductance (L(0)), abundance of aquaporins (ZmPIP1 and ZmPIP2), ATPase activity and root sap nutrient content, in the highly boron- and salt-tolerant Zea mays L. cv. amylacea, was evaluated. A downregulation of root ZmPIP1 and ZmPIP2 aquaporin contents were observed in NaCl-treated plants in agreement with the L(0) measurements. However, in the H3BO3-treated plants differences in the ZmPIP1 and ZmPIP2 abundance were observed. The ATPase activity was related directly to the amount of ATPase protein and Na+ concentration in the roots, for which an increase in NaCl- and H3BO3+ NaCl-treated plants was observed with respect to untreated and H3BO3-treated plants. Although nutrient imbalance may result from the effect of salinity or H3BO3 alone, an ameliorative effect was observed when both treatments were applied together. In conclusion, our results suggest that under salt stress, the activity of specific membrane components can be influenced directly by boric acid, regulating the functions of certain aquaporin isoforms and ATPase as possible components of the salinity tolerance mechanism.

The effects of the combination of salinity and excess boron on the water relations of tolerant tomato (Solanum lycopersicum L.) cv. Poncho Negro, in relation to aquaporin functionality

“…Also recently, two different aquaporins (HvPIP1;3 and HvPIP1;4) have been described as B transporters although their expression has not responded to B nutritional status, but expressed under toxicity conditions (Fitzpatrick and Reid, 2009). Thus, B uptake across the plasma membrane, by permeation through the lipid membrane and aquaporins, may be influenced greatly by the plant tolerance to salinity, through the associated changes in L 0 (Bastías et al, 2004b;Martínez-Ballesta et al, 2008). The observed decrease in L 0 caused by salinity would have then, as a consequence, coupled effects on root B uptake and B transport from root to shoot (Martínez-Ballesta et al, 2008).…”

“…The fact that L 0 was slightly affected by HgCl 2 , a reagent commonly used to inhibit aquaporin-mediated water transport (Chrispeels and Maurel, 1994;Wan and Zwiazek, 1999;Javot and Maurel, 2002) in all the treatments suggests that in these plants changes in L 0 were not mainly an aquaporin-mediated response or were mediated by Hg 2+ -insensitive aquaporins. In addition, the greater inhibition by Hg 2+ in treated plants, compared with control plants, could be an indication that different aquaporin isoforms may operate under different environmental conditions (Qi et al, 2009) or that in treated plants the expression or number of aquaporins was modified compared with the non-treated plants (Bastías et al, 2004a;Martínez-Ballesta et al, 2008).…”

“…One of these tolerant crops, that can be exposed to both salinity and B toxicity stress, simultaneously, is the variety of tomato, Solanum lycopersicum L., called 'Poncho Negro' by farmers (Díaz, 2008). Its behaviour, according to studies conducted to date, is similar in some characteristics to that of the ecotype Zea mays L. amylacea 'Lluteño' (Bastías et al, 2004a,b;Martínez-Ballesta et al, 2008).…”

Interactive effects of excess boron and salinity on response curves of gas exchange to increase in the intensity of light of Zea mays amylacea from the Lluta Valley (Arica-Chile)

“…This the case in the Lluta valley of northern Chile, where elevated levels of B in soils and irrigation water limit local agricultural production to a few landrace crops of this region, which has less than 1 mm annual precipitation (Bastías et al, 2004b). Zea mays L. amylacea is a sweet maize variety well adapted to the agro-ecological characteristics of the Lluta Valley; the physiological mechanisms of tolerance to high levels of NaCl and B in amylacea maize have been studied previously with respect to the salt accumulation capacity of tissues, photosynthetic assimilation and water relations (Bastías et al, 2004b), as well as root hydraulic conductance (Lo), abundance of aquaporins and ATPase activity (Bastías et al 2004a, Martínez-Ballesta et al, 2008. Additionally, other studies at the leaf and root levels have been published (Bastias et al, 2013a, Bastias et al, 2013b showing the degree of tolerance to salinity and excess B.…”

Leaf micromorphology in Zea mays L. amylacea from the Lluta Valley (Arica-Chile) with excess boron and salinity

“…Similar conditions occur naturally in many parts of world (Smith et al, 2013). Zea mays L. amylacea is a sweet maize variety well-adapted to the agro-ecological characteristics of the Lluta Valley; the physiological mechanisms of tolerance to high levels of NaCl and B in amylacea maize have been studied previously with respect to the salt accumulation capacity of tissues, photosynthetic assimilation and water relations (Bastías et al, 2004b), as well as root hydraulic conductance (Lo), abundance of aquaporins and ATPase activity (Bastías et al, 2004a;Martínez-Ballesta et al, 2008). Very few studies have examined micromorphological changes induced by salts and B in the leaf epidermis and xylem vessel in the flow and transport of water during abiotic stresses.…”