Focus Issue on Roots: Plant Nutrition: Root Transporters on the Move

Nutrient and water uptake from the soil is essential for plant growth and development. In the root, absorption and radial transport of nutrients and water toward the vascular tissues is achieved by a battery of specialized transporters and channels. Modulating the amount and the localization of these membrane transport proteins appears as a way to drive their activity and is essential to maintain nutrient homeostasis in plants. This control first involves the delivery of newly synthesized proteins to the plasma membrane by establishing check points along the secretory pathway, especially during the export from the endoplasmic reticulum. Plasma membrane-localized transport proteins are internalized through endocytosis followed by recycling to the cell surface or targeting to the vacuole for degradation, hence constituting another layer of control. These intricate mechanisms are often regulated by nutrient availability, stresses, and endogenous cues, allowing plants to rapidly adjust to their environment and adapt their development.Plants take up nutrients and water from the soil and transport them to the leaves to support photosynthesis and plant growth. However, most soils around the world do not provide optimal conditions for plant colonization. Consequently, plants have evolved sophisticated mechanisms to adjust to deficiency or excess of nutrients and water supply. Membrane transport proteins, including channels and transporters, play crucial roles in the uptake of nutrients and water from the soil and in their radial transport to the root vasculature. Newly synthesized membrane transport proteins have to be properly targeted to a defined compartment, usually the plasma membrane, to efficiently ensure their function. The trafficking of membrane transport proteins along the secretory pathway is tightly controlled and involves the recognition of exit signals by gatekeeper protein complexes. After reaching the plasma membrane, membrane transport proteins can be endocytosed and subsequently recycled to the cell surface or targeted to the vacuole for degradation. Because the subcellular localization of proteins directly influences their activity, modulating the localization of membrane transport proteins constitutes a powerful way to control nutrient and water uptake in plants. This review discusses the fundamental mechanisms at stake in membrane protein secretion and endocytosis, with a specific focus on membrane transport proteins, and how endogenous and exogenous cues affect their dynamics to integrate uptake of nutrients and water to plant growth conditions.     

Trichodermin: Effects on plants

Trichodermin, 4ß-acetoxy-12,13-epoxy-⁹ -trichothecene,a fungal metabolite from Trichoderma viride, is a potent inhibitorof plant growth and produces other phytotoxic effects. It inhibitswheat coleoptile growth, is phytotoxic to tobacco at high concentrationsand inhibits growth at lower concentrations. Bean and corn plantsare also affected by the metabolite. (Received June 22, 1977; )     

Notes on Technic: Pkotargol: Old and New

Stocks of protargol of foreign origin are becoming exhausted, and since such protargol is no longer available, the American-made product must be used for histologic staining. Some of the earlier domestic protargol seems not to have given satisfaction in neurohistology; therefore it seemed desirable to compare the staining qualities of the pre-war material with several lots furnished recently by Winthrop-Stearns, Inc., New York City.     

Notes on Technic: Pkotargol: Old and New

Stocks of protargol of foreign origin are becoming exhausted, and since such protargol is no longer available, the American-made product must be used for histologic staining. Some of the earlier domestic protargol seems not to have given satisfaction in neurohistology; therefore it seemed desirable to compare the staining qualities of the pre-war material with several lots furnished recently by Winthrop-Stearns, Inc., New York City.