Effect of pre-sowing priming of seeds with exogenous abscisic acid on endogenous hormonal balance of spelt wheat under heat stress

Pre-sowing priming of seeds with exogenous phytohormones affects plant growth, development and resistance. However, it remains unclear, whether the effect of exogenous hormones on growth is direct, or whether it is associated with changes in the level and distribution of endogenous hormones. The dynamics and distribution of endogenous abscisic (ABA), indole-3-acetic (IAA), gibberellic (GA(3)) and salicylic (SA) acids in spelt wheat (Triticum spelta L., 'Frankenkorn') plants grown from seeds primed with ABA (10(-6) M) were analysed. Fourteen-day-old, water-germinated and ABA-primed plants that had been exposed to a heat stress (2 h at +40 degrees C) and 21-day-old plants after recovery were studied. Endogenous ABA, IAA, GA 3 and SA were found to dominate in shoots of 14-day-old plants. On the 21st day, the pattern of distribution of all phytohormones, except GA(3), remained unchanged. However, most of the endogenous GA(3) was transferred to the roots. Pre-sowing priming of seeds with exogenous ABA induced changes in the balance of endogenous hormones. In shoots and roots of 14-day-old water-germinated, heat-stressed plants, accumulation of endogenous ABA and SA was enhanced, and the content endogenous of IAA and GA(3) decreased. In the recovery period, the amount of SA in 21-day-old plants increased, and the ABA content was reduced; endogenous GA(3) and IAA accumulated in the roots. In 14-day-old, exogenous ABA-primed plants, after heat stress maximal concentrations of endogenous ABA were recorded in shoots (46.8 +/- 2.3 ng g(-1) FW) and roots (32.3 +/- 1.6 ng g(-1) FW). In roots of 14-day-old exogenous ABA-primed, unstressed plants, the content of endogenous IAA reached a maximum (53.9 +/- 2.7 ng g(-1) FW). The maximum concentration (39.7 +/- 2.0 ng g(-1) FW) of endogenous GA 3 was recorded on the 21st day after recovery in roots of exogenous ABA-primed plants. The SA content in shoots and roots of exogenous ABA-primed, heat-stressed plants increased by 31% and 44.7%, respectively, while in non-primed ones - by 15.9% and 12.8%. In summary, the pre-sowing priming of spelt wheat seeds with exogenous ABA induced differentiated prolonged changes in the dynamics and distribution of endogenous ABA, IAA, GA(3) and SA in shoots and roots of 14- and 21-day-old water-germinated plants (controls) and high temperature (heat stress) conditions. This suggests that the response to heat stress is associated with changes in the level and distribution of endogenous hormones in young spelt wheat plants caused by pre-sowing priming of seeds with exogenous ABA.