12942 - Molecular Physiology of Plants

Learning outcomes

At the end of the course, the student assimilates with critical insight and in depth analysis, the main themes of plant physiology and their molecular basis (transport, photosynthesis, metabolism, mineral nutrition, hormonal regulation and photomorphogenesis).

Course contents

Module 1 - Prof. Paolo Trost
Introduction: Arabidopsis thaliana as a model species in molecular plant physiology.

Membrane transport. Proton pumps of the plant cell. The proton-ATPase of the plasma membrane: structure, mechanism of action, regulation. The membrane potential: diffusive component and electrogenic component. Electrochemical potential. Thermodynamic basis of the stoichiometry of proton ATPase of the plasma membrane and tonoplast. Permease: bioenergetics of apoplastic loading of sucrose in the phloem. Channels: Shaker family of potassium channels. Membrane potential and potassium balance. Role of ion transport systems in stomata movements.

Cell water relationships. Aquaporins. Forces that affect the movement of water at the cellular level: hydrostatic pressure (P) and osmotic pressure (π). Water (Ψw), pressure (Ψp) and osmotic (Ψs) potential. Relationships between chemical potential and water. Calculation of intracellular Ψp knowing the internal and external concentrations of solutes. Opening/closing of stomata and variations of Ψs. Cell expansion and change of Ψp. Acid growth theory. Cell wall weakening by  ROS (redox theory of cell expansion).

Water relationships in the whole plant. Soil-plant-atmosphere continuum. Water potential in the soil, water uptake by roots and ΔΨw. Root pressure and guttation. Movement of xylem sap and ΔΨp. Transpiration and ΔCwv. Effect of temperature on ΔCwv. Transpiration rate, stomata resistance (rs) and boundary layer resistance (rb).

Mineral nutrition and assimilation (N and Fe). Essential nutrients. Mineral nutrition in agriculture. Mycorrhizae. Strategies of iron absorption in grasses versus dicots and non-grasses monocots. Nitrogen: deficiency and excess. Absorption and reduction of nitrate to ammonium. Assimilation of ammonium (GS-GOGAT). Aromatic amino acid biosynthesis: glyphosate and transgenic plants.

Photosynthesis (light phase). Light, solar emission and atmospheric absorption, PAR light, light energy. Anatomy of chloroplasts. Photosynthetic pigments: chlorophylls and carotenoids. Light-chlorophyll interaction and modes of excitation energy dissipation. Concept of photosystem. Structure of photosystem II reaction center, internal antenna, external antenna, a oxygen evolving complex, supramolecular organization. Functioning of the PS-II. Relationship between redox potential and energy of light. Photolysis of water. Reduction of quinones. Cytochrome b6f. Q-cycle Structure and function of photosystem I. Similarities between PS-II and PS-I. ATPsynthase of chloroplasts. Bioenergetics of photo-phosphorylation. Scheme Z. Photosynthetic electron transport: non-cyclic (linear), cyclic and pseudo-cyclic. Distribution of photosystems in thylakoids. Sate I-state II transition. Stoichiometric ratios of absorbed photons, oxygen evolved, protons accumulated in the lumen, NADPH and ATP products. Quantum yield of cyclic and linear electron transport.

Module 2 - Dr. Francesca Sparla

Photosynthesis (metabolism). Carbon metabolism. Rubisco: structure, reactions, regulation. Calvin cycle and its light/dark regulation. Thioredoxins. Regulation of GAPDH and PRK using CP12. Relationship between Rubisco oxygenase and carboxylase activities. Photorespiration. Calculation of the energy cost of photorespiration. Gross and net photosynthesis. Compensation point for CO2 and internal concentration of CO2. Mechanisms of concentration of CO2. C4 plants: metabolic outline, general anatomy and differentiation of chloroplasts. Energy cost of CO2 concentration, compared with C3 plants. CO2 compensation point in C4 plants. Effect of temperature on net photosynthesis in C3 and C4 plants. Water use efficiency. CAM plants. Metabolic relationships between starch and sucrose. Biosynthesis of sucrose, amylose and amylopectin. Architecture of the starch granule. Role of inorganic phosphate in the metabolic relationship between sucrose and starch synthesis. Sink/source relationships. Degradation of primary starch in the dark. Phloem: anatomy and cytology. Composition of the phloem sap. Apoplastic and symplastic phloem loading. Raffinose and sugar alcohols. Phloem transport. Water relations between phloem and xylem.

Respiration. Functions of respiration in plants. Conversion of sucrose into hexoses. Plastid and cytosolic glycolysis. Bypasses of cytosolic glycolysis. Pentose phosphate pathway and differences in regulation between cytosolic and chloroplastic pathway. Krebs cycle. Respiratory chain: external and internal NAD(P)H dehydrogenases, alternative oxidase, uncoupling protein. Stoichiometry ATP / H + of the mitochondrial ATP synthase.

Photomorphogenesis. Scoto- and photo-morphogenesis. Classes of plant photoreceptors. Phytochrome: molecular structure, photoconversion, absorption spectrum, photostationary state, action spectrum. Nuclear translocation of Pfr and modification of gene expression. Family of PHY genes and multiplicity of responses: VLFR, LFR, HIR. Concepts of fluence, irradiance, reciprocity, photoreversibility. Shade avoidance response. Cryptochromes CRY. De-etiolation and hypocotyl elongation inhibition: the role of CRY1 and PHY. Structure of critpocromi. Fototropine.    

Hormones. General concepts. Auxins, natural and synthetic. IAA biosynthesis and conjugation. Polar auxin transport and transport in the phloem. Role of IAA role in cell expansion. IAA and phototropism. IAA and positive gravitropism of the root. Regulation  of gene expression mediated by IAA. Gibberellins, effects on germination and plants height. Regulation of gene expression mediated by GA. Germination in cereals: GA signaling pathway. Cytokinins: biosynthesis and signaling. CK, IAA and cell cycle. Agrobacterium tumefaciens. 

Readings/Bibliography

Rascio N, Carfagna S, Esposito S, La Rocca N, Lo Gullo MA, Trost P, Vona V (2012) Elementi di Fisiologia vegetale. EdiSES

Teaching methods

The course will consist of lectures accompanied by the projection of pictures and diagrams (power point). Questions and requests of further explanation from the students are always welcome, both during and after the lesson.

Assessment methods

Verification will be performed by oral examination, but the student will be asked to show on paper the structure of biochemical formulas, metabolic pathways, reactions, etc..

Teaching tools

The course will take place in classrooms with PC projection. All lectures will be given with power point presentations. The files of power point presentations will be made ​​available to students at the end of the course (downloadable files from AMSCAMPUS).

Office hours

See the website of Paolo Bernardo Trost

See the website of Francesca Sparla