Systemic irradiance signalling in tobacco

Summary • We report the influence of a systemic irradiance signal, from mature leaves, on the anatomical characteristics of developing leaves. • A systemic signal of reduced irradiance was induced by growing tobacco (Nicotiana tabaccum) plants at high irradiance and then measuring the effect of shading mature leaves on the development of new leaves. The reverse, a systemic signal of increased irradiance was induced by growing plants at low irradiance and then measuring the effect of increasing the irradiance of mature leaves. • Stomatal pore length, stomatal density and index, epidermal cell shape, epidermal cell size and developing leaf size were all influenced by the irradiance signal. These responses were reversible with changing irradiance, except for stomatal pore length.