Plant efficiency analyser

The maximum photochemical efficiency of PSII was estimated in dark-adapted samples by the F_v/F_m ratio. After 12 days of transplanting, F_v/F_m ratio were measured during mid-photoperiod using the Plant Efficiency Analyser (Hansatech Instruments, UK) according to He et al. [32 (link)].

F_v/F_m ratios (maximum potential quantum efficiency of PSII) of dark-adapted attached leaves were measured using the Plant Efficiency Analyser (Hansatech Instruments Ltd, England) during mid-photoperiod. The ETR, ΔF/F_m’, qP and NPQ were determined from detached leaf using the IMAGING PAM MAXI (Walz, Effeltrich, Germany) at 25°C in the laboratory. The details of F_v/F_m ratio, ETR, ΔF/F_m′, qP and NPQ measurements were described by He et al. (2011) (link).

F_v/F_m ratio were measured from the dark-adapted leaves (15 min in the darkness) during midday (1200 to 1300 h) using the Plant Efficiency Analyser (Hansatech Instruments Ltd., King’s Lynn, England). The initial fluorescence, F_o, was recorded before assessing the maximum fluorescence, F_m, by 0.8 s of saturated pulse (>6000 μmquol∙m⁻² s⁻¹). Variable fluorescence, F_v, was calculated as F_v = F_m − F_o.

The maximal efficiency of PS II photochemistry was measured by the fluorescence F_v/F_m ratio from the dark-adapted leaves (15 min in darkness) using a Plant Efficiency Analyser (Hansatech Instruments Ltd., England) during the mid-photoperiod [48 (link)]. The initial fluorescence, F_o, was first recorded. F_m, maximum fluorescence, was assessed by 0.8 s of saturated pulse (>6000 μmquol∙m⁻² s⁻¹, which completely reduces all primary acceptors for PS II). Variable fluorescence, F_v, was calculated as F_v = F_m − F_o.

Simultaneous gas exchange and chlorophyll fluorescence parameters were measured in leaves of control and 24 h stress treated WT and transgenic tobacco using LI-6400XT portable photosynthesis system (LICOR, Lincoln, NE, USA). Plants were dark-adapted for 45 min and fluorescence parameters were recorded. Steady state fluorescence yield was achieved by exposing plants to ambient light (1,200 μmol m⁻²s⁻¹) for 60 min in a plant growth chamber (PGC-105, Percival Scientific, US). The gas exchange measurement conditions were 1,200 μmol m⁻² s⁻¹ PPFD, ambient atmospheric CO₂ (380 μmol⁻¹ mol⁻¹) and RH (60–65%) and 26°C block temperature. The net photosynthetic rate (P_N; μmol m⁻²s⁻¹), stomatal conductance (g_s; mmol H₂O m⁻²s⁻¹), intercellular CO₂ (C_i) concentration (μmol m⁻²s⁻¹), transpiration rate (E; mmol m⁻²s⁻¹), PSII operating efficiency (ΦPSII), electron transport rate (ETR), photochemical quenching (qP), non-photochemical quenching (NPQ) were determined.
Chlorophyll a fluorescence transient (Strasser and Strasser, 1995 ) in leaves was measured on dark adapted stressed and unstressed plant using plant efficiency analyser (Hansatech Instruments Ltd., England). Chlorophyll fluorescence was recorded thrice (sub-replicate) at different regions of 03rd leaf of 03 plants (biological replicate) from each treatment (n = 9).

Chl fluorescence induction (FI) measurements were carried out at room temperature using Plant Efficiency Analyser (Hansatech, Kings Lynn, Norfolk, UK). The assay medium contained 20 mM MES-NaOH (pH 6.2), 15 mM NaCl, 10 mM MgCl₂, 400 mM sucrose, PSII submembrane fractions at 25 μg Chl.ml^-1 and the specified concentrations of Al³⁺. Samples were adapted for 1 min in the dark and then excited with saturating red actinic light (peaking at 655 nm and intensity of 3000 μmol photons m^-2 s^-1) provided by light emitting diodes. As the fluorescence signal during the first 40 μs is ascribed to artifacts due to delay in response time of the instrument, these data were not included in the analysis of FI traces. The signal at 40 μs is taken as F₀, the initial fluorescence intensity. Variable fluorescence, F_v (the difference between F₀ and the maximal fluorescence, F_m in dark adapted samples) was used to calculate the F_v/F_m and F_v/F₀ ratios.