The effect of light on the biosynthesis of leaf‐specific thionins in barley, Hordeum vulgare

Abstract

In barley seedlings grown in the dark large amounts of thionin‐specific mRNAs are present, the concentration of which rapidly declines once the seedling is exposed to light. This rapid light effect is mediated by a complex interaction of possibly two photoreceptors, phytochrome and a blue‐light‐absorbing photoreceptor. Parallel to the decline in mRNA content, the de novo synthesis of leaf‐specific thionins ceases rapidly upon illumination of etiolated seedlings. However, thionins which have accumulated before the onset of illumination remain stable within the seedling at high concentrations. In younger leaves of mature, nonstressed barley plants grown under a 16‐h‐light/8‐h‐dark cycle thionins are still present, although at much lower concentrations. In these plants, synthesis and accumulation of thionins occur predominantly in the meristematic zone at the leaf basis, which is shielded from light through the sheath of the preceding leaf. In mature light‐adapted barley plants, mRNA encoding leaf‐specific thionins may reaccumulate if these plants are exposed to pathogens or other stresses. Thus, the inhibitory effect of light on the biosynthesis of thionins may be overruled by stress‐ and pathogen‐induced signals.

Low Temperature Induces the Accumulation of Phenylalanine Ammonia-Lyase and Chalcone Synthase mRNAs of Arabidopsis thaliana in a Light-Dependent Manner

“…Although it has been reported that the basal levels of other defense-related genes are modulated by light (Reimann-Philipp et al, 1989), it is unexpected that light appears to be a requirement for the induction of a defense gene by bacterial infiltration. Similarly, other genes involved in plant adaptive responses, like a desiccation-inducible gene of Craterostigma plantagineum, k ave been shown to be regulated by light (Bartels et al, 1932).…”

Characterization and Analysis of Thionin Genes

“…Steady state messenger levéis seemed to be higher in the lower 1/3 of the leaf (younger cells) than in the upper 2/3 (older cells) and to decline sharply upon illumination (Gausing, 1987). The effect of light has been further investigated by Reimann-Philipp et al (1989a), who have postulated the mediation of two photoreceptors, phytochrome and a blue-light-absorbing photoreceptor. Synthesis of thionins concomitantly ceased upon illumination, but the previously accumulated thionin was rather stable (Reiman-Philipp et al, 1989a).…”

An Arabidopsis thaliana Thionin Gene Is Inducible via a Signal Transduction Pathway Different from That for Pathogenesis-Related Proteins

“…* Corresponding author; e-mail bohlmann8ipw.agrl.ethz.ch; fax 41-1-632-1081. 81 3 concentrations of thionins (Reimann-Philipp et al, 1989a). Thionins that were isolated from leaves or the endosperm of barley were both toxic to plant pathogenic fungi and bacteria in vitro (Bohlmann et al, 1988;Florack et al, 1993;Molina et al, 1993;Terras et al, 1993).…”