Heat Stress Targeting Individual Organs Reveals the Central Role of Roots and Crowns in Rice Stress Responses.

Inter-organ communication and the heat stress (HS; 45°C, 6 h) responses of organs exposed and not directly exposed to HS were evaluated in rice () by comparing the impact of HS applied either to whole plants, or only to shoots or roots. Whole-plant HS reduced photosynthetic activity (F /F and QY ), but this effect was alleviated by prior acclimation (37°C, 2 h). Dynamics of , , , and expression revealed high protection of crowns and roots. Additionally, was strongly expressed in leaves. Whole-plant HS increased levels of jasmonic acid (JA) and cytokinin -zeatin in leaves, while up-regulating auxin indole-3-acetic acid and down-regulating -zeatin in leaves and crowns. Ascorbate peroxidase activity and expression of alternative oxidases () increased in leaves and crowns. HS targeted to leaves elevated levels of JA in roots, -zeatin in crowns, and ascorbate peroxidase activity in crowns and roots. HS targeted to roots increased levels of abscisic acid and auxin in leaves and crowns, -zeatin in leaves, and JA in crowns, while reducing -zeatin levels. The weaker protection of leaves reflects the growth strategy of rice. HS treatment of individual organs induced changes in phytohormone levels and antioxidant enzyme activity in non-exposed organs, in order to enhance plant stress tolerance.