A computer‐operated routine of gas exchange and optical measurements to diagnose photosynthetic apparatus in leaves

Abstract

Photosynthesis is a complex process whose rate is affected by many biochemical and biophysical factors. Fortunately, it is possible to determine, or at least estimate, many of the most important parameters using a combination of optical methods and gas transient analyses. We describe here a computer-operated routine that has been developed to make detailed assessments of photosynthesis at a comprehensive level. The routine comprised the following measurements: steady-state light and CO 2 response curves of net CO 2 assimilation at 21 and 2 kPa O 2 ; transients from limiting to different saturating CO 2 concentrations at 2 kPa O 2 ; post-illumination CO 2 fixation transient; dark-light induction of O 2 evolution; O 2 yield from one saturating single-turnover flash; chlorophyll fluorescence F 0 , F s and F m during the light and CO 2 response curves; leaf transmission at 820 nm (P700 + ) during the light and CO 2 response curves; post-illumination re-reduction time of P700 + . The routine was executed on a two-channel fast-response gas exchange measurement system (A. Laisk and V. Oja: Dynamic Gas Exchange of Leaf Photosynthesis. CSIRO, Canberra, Australia). Thirty-six intrinsic characteristics of the photosynthetic machinery were derived, including quantum yield of CO 2 fixation ( Y CO2 Key-words : Betula pendula Roth; leaf; methods; photosynthesis.)Abbreviations : A , net CO 2 assimilation rate; AC, assimilatory charge; a II , a I , a 0 , relative optical cross-sections of PSII and PSI antenna and of non-photosynthetic absorption; C a , C i , C w , C c , CO 2 concentrations: ambient, intercellular space, cell wall liquid and carboxylation site, respectively; CRC, carbon reduction cycle; Cyt, b 6 f, cytochrome b 6 f; DCMU, dichlorophenol-dimethyl urea; ETR, and J , electron transport rate; F 0 , F s , F m , F md , fluorescence yields, minimum, steady state, maximum (all in the light) and maximum F m in the dark, respectively; FRL, far-red light; Γ , CO 2 compensation point; K s , Rubisco CO 2 /O 2 specificity; k N , relative rate constant for regulatory non-photochemical excitation quenching; k P0 , relative rate constant for photochemical excitation quenching at open PSII centres; P s , P m , P o , 820 nm signal difference from the dark level, steady state, maximum and corresponding to oxidizable P700; PAD, ( I in equations), PFD, photon flux density, absorbed and incident, respectively; PC, plastocyanin; PGA, 3-phosphoglyceric acid; P i , inorganic phosphate; PSI, PSII, photosystems I and II; PQ, plastoquinone; P700, donor pigment of PSI; q E , q I , non-photochemical quenching, energy dependent and inhibitory; R d , R K , Krebs cycle CO 2 evolution rate in the dark and in the light, respectively; r gw , r m , r md , leaf diffusion resistances, in gas phase, mesophyll total and mesophyll diffusional; RuBP, ribulose 1,5-bisphosphate; Rubisco, ribulose 1,5-bisphosphate carboxylase-oxygenase; SCE, specific carboxylation efficiency; VPD, water

Evidence for a Role for NAD(P)H Dehydrogenase in Concentration of CO2 in the Bundle Sheath Cell of Zea mays

“…Mean G values ranged from 0.008 mM to 0.023 mM CO 2 and 2-way ANOVA indicated no significant effect of O 2 . Conversely, normal and NDHO-deficient Arabidopsis leaves showed highly significant, and identical, linear increases in G with an O 2 level similar to that commonly observed in C 3 plants (Laisk and Oja 1998).…”

“…We employed a K sp value of 75 at 30°C based on unpublished measurements in this laboratory of the temperature-and O 2 -dependencies of G in C 3 Arabidopsis and Nicotiana benthamiana (see Laisk and Oja, 1998). We emphasize that results obtained using the ZmNDHN/ZmNdhn pair were similar to the results obtained for ZmNDHO/ ZmNdho (Fig.…”

“…Minimum (F o ), steady state (F s ), maximal (F m ), and variable (F v = F m -F o ) fluorescence yields were measured at each combination of CO 2 and O 2 . Conductances to diffusion of CO 2 (expressed as dissolved liquid phase molarity, mM) across the stomatal [g s = A/(C o -C m ), mm s 21 ] and mesophyll liquid phase plus enzymic (g m = A/C m at rate-limiting C m , mm s 21 ) barriers were assessed according to Laisk et al (2002). Leaf absorbance of white light was measured on a 2.0-cm 2 disc from each test leaf using an integrating sphere.…”

Feedback limitation of photosynthesis at high CO2 acts by modulating the activity of the chloroplast ATP synthase

“…A small air space (3-mm thickness) was left on the lower side of the leaf, and gas with known humidity, O 2 and CO 2 content (mixed with the FastEst system, Tartu, Estonia; Laisk et al 2002) was constantly passed over the lower leaf surface at a rate of 10 cm 3 s -1 . The window was illuminated by actinic diffuse red light-emitting diode (LED) light.…”

“…Leaf gas exchange and fluorescence yield measurements Gas exchange and chlorophyll a fluorescence analyses were made under the same conditions as above on equivalent leaf material using a FastEst gas exchange system (Tartu, Estonia), which is described in detail in (Laisk et al 2002). The system was equipped with a CO 2 analyser (Li-Cor 6251, Lincoln, Nebraska, USA), and O 2 analyser (S-3A; Applied Electrochemistry Inc., Sunnyvale, California, USA).…”