The effects of moderate soil drought on phytohormonal balance of Triticum aestivum L. and Triticum spelta L.

Soil drought, which is one of the most threatening abiotic plant stressors, negatively impacts plant growth and yields. Plant phytohormones play a key role in the formation of plant responses to stress. We investigated the effect of moderate soil drought, created in controlled laboratory conditions on plant growth and peculiarities of endogenous abscisic (ABA), indole-3-acetic (IAA), gibberellic (GA3) and salicylic (SA) acids and cytokinins (CKs) accumulation in organs of two closely related wheat species: Triticum aestivum and T. spelta. We demonstrated that following the cessation of watering (within four days), shoots and roots of 18-day-old plants of both species accumulated ABA and SA, while the level of GA3 and IAA decreased. Pool of CKs significantly increased in roots and decreased in shoots. On day 21 following recovery, an increase in ABA content occurred in wheat shoots and roots and spelt shoots. IAA level increased in both species, but not to the levels measured in control plants. The highest level of GA3 was present in wheat roots. While the content of SA in wheat was at control level, spelt SA levels significantly exceeded the controls. There were complex changes in CKs pool, the nature of which depended on the species and plant organ. We propose that specific alterations in the nature of accumulation, localization, and balance between certain classes of phytohormones in wheat and spelt organs under the action of moderate soil drought are one of the main factors in systemic response to stress and the formation of an adaptation strategy.