Comparative analysis of stress-induced calcium signals in the crop species barley and the model plant Arabidopsis thaliana

Background Plants are continuously exposed to changing environmental conditions and biotic attacks that affect plant growth. In crops, the inability to respond appropriately to stress has strong detrimental effects on agricultural production and yield. Ca2+ signalling plays a fundamental role in the response of plants to most abiotic and biotic stresses. However, research on stimulus-specific Ca2+ signals has mostly been pursued in Arabidopsis thaliana, while in other species these events are little investigated . Results In this study, we introduced the Ca2+ reporter-encoding gene APOAEQUORIN into the crop species barley (Hordeum vulgare). Measurements of the dynamic changes in [Ca2+](cyt) in response to various stimuli such as NaCl, mannitol, H2O2, and flagellin 22 (flg22) revealed the occurrence of dose- as well as tissue-dependent [Ca2+](cyt) transients. Moreover, the Ca2+ signatures were unique for each stimulus, suggesting the involvement of different Ca2+ signalling components in the corresponding stress response. Alongside, the barley Ca2+ signatures were compared to those produced by the phylogenetically distant model plant Arabidopsis. Notable differences in temporal kinetics and dose responses were observed, implying species-specific differences in stress response mechanisms. The plasma membrane Ca2+ channel blocker La3+ strongly inhibited the [Ca2+](cyt) response to all tested stimuli, indicating a critical role of extracellular Ca2+ in the induction of stress-associated Ca2+ signatures in barley. Moreover, by analysing spatio-temporal dynamics of the [Ca2+](cyt) transients along the developmental gradient of the barley leaf blade we demonstrate that different parts of the barley leaf show quantitative differences in [Ca2+](cyt) transients in response to NaCl and H2O2. There were only marginal differences in the response to flg22, indicative of developmental stage-dependent Ca2+ responses specifically to NaCl and H2O2. Conclusion This study reveals tissue-specific Ca2+ signals with stimulus-specific kinetics in the crop species barley, as well as quantitative differences along the barley leaf blade. A number of notable differences to the model plants Arabidopsis may be linked to different stimulus sensitivity. These transgenic barley reporter lines thus present a valuable tool to further analyse mechanisms of Ca2+ signalling in this crop and to gain insights into the variation of Ca2+-dependent stress responses between stress-susceptible and -resistant species.