Converging Light, Energy and Hormonal Signaling Control Meristem Activity, Leaf Initiation, and Growth.

The development of leaf primordia is subject to light control of meristematic activity. Light regulates the expression of thousands of genes with roles in cell proliferation, organ development, and differentiation of photosynthetic cells. Previous work has highlighted roles for hormone homeostasis and the energy-dependent Target of Rapamycin (TOR) kinase in meristematic activity, yet a picture of how these two regulatory mechanisms depend on light perception and interact with each other has yet to emerge. Their relevance beyond leaf initiation also is unclear. Here, we report the discovery that the dark-arrested meristematic region of Arabidopsis (Arabidopsis thaliana) experiences a local energy deprivation state and confirm previous findings that the PIN1 auxin transporter is diffusely localized in the dark. Light triggers a rapid removal of the starvation state and the establishment of PIN1 polar membrane localization consistent with auxin export, both preceding the induction of cell cycle- and cytoplasmic growth-associated genes. We demonstrate that shoot meristematic activity can occur in the dark through the manipulation of auxin and cytokinin activity as well as through the activation of energy signaling, both targets of photomorphogenesis action, but the organ developmental outcomes differ: while TOR-dependent energy signals alone stimulate cell proliferation, the development of a normal leaf lamina requires photomorphogenesis-like hormonal responses. We further show that energy signaling adjusts the extent of cell cycle activity and growth of young leaves non-cellautonomously to available photosynthates and leads to organs constituted of a greater number of cells developing under higher irradiance. This makes energy signaling perhaps the most important biomass growth determinant under natural, unstressed conditions.

Application of an enzyme digestion method reveals microlitter in Mytilus trossulus at a wastewater discharge area.

The ingestion of microlitter by blue mussels (450) was studied at a wastewater recipient area in the Baltic Sea. The mussel soft tissues were digested using enzymatic detergents and the detected litter particles characterized with FT-IR imaging spectroscopy. Microlitter concentration in seawater and WWTP effluent were also measured. Microlitter was found in 66% of the mussels. Mussels from the WWTP recipient had higher microlitter content compared to those collected at the reference site. Plastics made up 8% of all the analysed microlitter particles. The dominating litter types were fibres (~90% of all microlitter), 42% of which were cotton, 17% linen, 17% viscose and 4% polyester. The risk of airborne contamination during laboratory work was lowered when mussels were digested with their shells on instead of dissecting them first. The approach was found applicable and gentle to both non-synthetic and synthetic materials including fragile fibres.