Abstract
Although salinity inhibits plant growth, application of appropriate rhizosphere bacteria can diminish this negative effect. We studied one possible mechanism that may underlie this beneficial response. Wheat plants were inoculated with Bacillus subtilis IB-22 and Pseudomonas mandelii IB-Ki14 and their consequences for growth, water relations, and concentrations of the hormone abscisic acid (ABA) were followed in the presence of soil salinity. Salinity alone increased ABA concentration in wheat leaves and roots and this was associated with decreased stomatal conductance, but also with chlorophyll loss. Bacterial treatment raised ABA concentrations in roots, suppressed accumulation of leaf ABA, decreased chlorophyll loss, and promoted leaf area and transpiration. However, water balance was maintained due to increased water uptake by inoculated plants, brought about in part by a larger root system. The effect may be the outcome of ABA action since the hormone is known to maintain root extension in stressed plants. Root ABA concentration was highest in salt-stressed plants inoculated with B. subtilis and this contributed to greater root hydraulic conductivity. We conclude that bacteria can raise salt resistance in wheat by increasing root ABA, resulting in larger root systems that can also possess enhanced hydraulic conductivity thereby supporting better-hydrated leaves.
Highlights
High salt concentration in the soil solution is widespread, and the area of saline land makes up to 6% of arable land
Bacterial inoculates for seeds treatments were obtained by cultivating B. subtilis IB-22 on K1G medium as described in [34], while King B medium [35] was used for cultivation of bacteria of P. mandelii IB-Ki14
In plants inoculated with B. subtilis IB-22, water flow was facilitated by increased hydraulic conductivity
Summary
High salt concentration in the soil solution is widespread, and the area of saline land makes up to 6% of arable land. In the case of salinity, the protective action of bacteria is due to an increase in the activity of the antioxidant system [5], accumulation of osmotically active substances and osmoprotectors [6], maintenance of ionic homeostasis [7], and direct action of bacteria on plant growth explained by their ability to produce growth stimulating plant hormones [4]. Along with these mechanisms, the bacteria-induced increase
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