Abstract
Plants respond to salinity by altering their physiological parameters in order to maintain their water balance. The reduction in root hydraulic conductivity is one of the first responses of plants to the presence of salt in order to minimize water stress. Although its regulation has been commonly attributed to aquaporins activity, osmotic adjustment and the toxic effect of Na+ and Cl− have also a main role in the whole process. We studied the effects of 30 mM NaCl on Phaseolus vulgaris plants after 9 days and found different responses in root hydraulic conductivity over-time. An initial and final reduction of root hydraulic conductivity, stomatal conductance, and leaf water potential in response to NaCl was attributed to an initial osmotic shock after 1 day of treatment, and to the initial symptoms of salt accumulation within the plant tissues after 9 days of treatment. After 6 days of NaCl treatment, the increase in root hydraulic conductivity to the levels of control plants was accompanied by an increase in root fructose content, and with the intracellular localization of root plasma membrane aquaporins (PIP) to cortex cells close to the epidermis and to cells surrounding xylem vessels. Thus, the different responses of bean plants to mild salt stress over time may be connected with root fructose accumulation, and intracellular localization of PIP aquaporins.
Highlights
Soil salinity is a major problem in many areas around the world as it affects plant establishment, development and productivity [1]
The regulation of root hydraulic conductivity (L) in plants under stress has been mainly attributed to cell-to-cell pathway and in particular to the expression and abundance of transmembrane aquaporins, with the apoplastic water flow limited by the presence of suberized barriers as the exo- and/or the endodermis [12], [13] and Casparian strips [14]
Stomatal conductance significantly decreased in NaCl treated plants after 1 and 9 days of treatment compared with their respective control plants
Summary
Soil salinity is a major problem in many areas around the world as it affects plant establishment, development and productivity [1]. Plants are primarily affected by salt due to its osmotic effect since the osmotic water potential of the soil decreases with increasing salt concentration [2]. Plants respond to the reduced water availability in the soil by reducing their leaf transpiration [3], stomatal conductance [4], and by adjusting their root water uptake [5]. The regulation of root hydraulic conductivity (L) in plants under stress has been mainly attributed to cell-to-cell pathway and in particular to the expression and abundance of transmembrane aquaporins, with the apoplastic water flow limited by the presence of suberized barriers as the exo- and/or the endodermis [12], [13] and Casparian strips [14]. Under prolonged periods of exposure to salt, a partial recovery of L could take place [19], and this could be mainly caused by the accumulation of compatible solutes within the plant roots [5]
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