Feb. 1 st, 2011 B4730/5730 Plant Physiological Ecology Photosynthesis I

Filled crop, open broadleaf, crosses conifers Medlyn et al. PCE 2002

Light Dependent Reactions Three fates of photon striking reaction center –Heat, fluorescence, photochemistry Linear electron flux (LEF) goes from PSII to PSI to drive H+ pmf, –Cyclic flux around PSI Low light, efficiency maximized High light, energy dissipation maximized

Baker et al. PCE 2007

Chlorophyll Fluorescence Absorption (photochemistry), heat, and fluorescence all occur in competition with incoming light –Light absorbed different wavelength than light fluorescing Light always lost, so all measurements relative –Add to 1 Measurements made with modulated light –Allows measurement in the field with background light levels Kautsky effect is rise in fluorescence when leaves go from dark to light conditions –Electrons from PSII to Q A, –if Q A reduced; reaction center closed –fluorescence when reaction center closed Quenching causes fluorescence to fall after initial burst –Photochemical quenching-light induction –Nonphotochemical quenching (NPQ)-heat and zeaxanthin cycle

Measuring Fluorescence F rate of fluoresce –’ indicates light acclimated (“adapted”) measurements F o background fluorescence in dark, F o ’ in light F m maximal rate in dark or F m ’ in light –Occurs when Q A is maximally reduced F v variable fluorescence from dark, Fv’ light –Demonstrates primary photochemistry

Interpreting Fluorescence F v /F m intrinsic quantum yield of PSII F v ’ = F’-F m ’ Quantum yield of PSII –Φ PSII = F v ’/F m ’ Photochemical (qP) and nonphotochemical quenching (NPQ) –qP = (F’ m – F’ o )/(F m – F o ) –NPQ = 1 – (F’ m – F’ o )/(F m – F o ) J = Φ PSII · I abs · β · PPFD –β = 0.5 equal distribution PSII & PSI –Relative without I abs

Nicotiana tabacum; Kramer et al Photo. Res q p puddle model PSII open q L lake model PSII open

Wang & Kellomaki New Phyt. 1997, Pinus sylvestris a)Control N & amb CO2, b) Control N & elev CO2, c) High N & amb CO2, d) High N & elev CO2 ΔF=Fq’

F s is steady state Fluorescence (F’) Closed circle F’ m amb CO2 Closed triangle F s amb CO2 Open circle F’ m elev CO2 Open triangle F s elev CO2

Leipner et al Env. Exp. Bot Maize

Mesophyll conductance Flux of CO 2 to stroma (C c ) limited by g s, g m and g b Recent work has shown g m to be variable and important –Low g m reduces C C underestimate V Cmax C c =C i -A/g m –Estimate g m with curve fitting Estime g m with fluorescence and A

Hedera helix; Pons et al J Exp Bot 2009

Many species; S c = surface area of chloroplasts exposed to intercellular airspace; Evans et al J Exp Bot 2009

Limitations to the Farquhar/Fluorescence model of Photosynthesis No gene expression controls –Connection to hormones, whole plant controls –Longer time scales Stomatal physiology almost a black box Scale of leaf patchiness violates homogeneity Light dynamics problematic Respiration models are crude