Nitric oxide is involved in integration of UV‐B absorbing compounds among parts of clonal plants under a heterogeneous UV‐B environment

In nature, ultraviolet‐B (UV‐B) radiation is highly heterogeneous, both spatially and temporally. Plants exposed to UV‐B radiation produce UV‐B absorbing compounds that function as a protective filter. For clonal plants under heterogeneous UV‐B radiation conditions, integration among ramets can allow irradiated ramets to benefit un‐irradiated ramets by causing them to increase their UV‐B absorbing compounds content. In this study, we evaluated integration between pairs of clonal ramets of Glechoma longituba under heterogeneous or homogeneous UV‐B conditions. We determined the levels of UV‐B absorbing compounds, nitric oxide (NO) and hydrogen peroxide (H₂O₂) and measured the activity of phenylalanine ammonia‐lyase (PAL) in connected ramet pairs under homogeneous or heterogeneous UV‐B conditions. Under heterogeneous UV‐B conditions, the UV‐B absorbing compounds content increased in leaves of irradiated and un‐irradiated ramets, but not in the connecting stolons. The NO content increased in irradiated and un‐irradiated leaves and stolons, but the H₂O₂ content did not. Application of NO synthesis inhibitors and an NO blocker to irradiated ramets blocked the increase in UV‐B absorbing compounds and PAL activity in un‐irradiated ramets. These results suggested that NO is involved in the integration process for UV‐B absorbing compounds among ramets. Our findings suggested that a UV‐B‐induced increase in NO transmits a signal to un‐irradiated ramets via the stolon, leading to an increase in PAL activity and UV‐B absorbing compounds content. The internal translocation of signal enables members of clonal networks to function as a whole unit and to mount an efficient defensive response to localized UV‐B radiation.