The impact of heat stress targeting on the hormonal and transcriptomic response in Arabidopsis.

Targeting of the heat stress (HS, 40°C) to shoots, roots or whole plants substantially affects Arabidopsis physiological responses. Effective stress targeting was proved by determination of the expression of HS markers, HsfA2 and HSA32, which were quickly stimulated in the targeted organ(s), but remained low in non-stressed tissues for at least 2h. When shoots or whole plants were subjected to HS, a transient decrease in abscisic acid, accompanied by a small increase in active cytokinin levels, was observed in leaves, consistent with stimulation of transpiration, the main cooling mechanism in leaves. HS application targeted to part of plant resulted in a rapid stimulation of expression of components of cytokinin signaling pathway (especially of receptor genes) in the non-exposed tissues, which indicated fast inter-organ communication. Under all HS treatments, shoot apices responded by transient elevation of active cytokinin contents and stimulation of transcription of genes involved in photosynthesis and carbohydrate metabolism. Duration of this stimulation was negatively correlated with stress strength. The impact of targeted HS on the expression of 63 selected genes, including those coding regulatory 14-3-3 proteins, was compared. Stimulation of GRF9 (GRF14μ) in stressed organs after 2-6h may be associated with plant stress adaptation.