Oxygen exchange activity in whole chain (H₂O to FeCN, A), PSII (H₂O to <i>p</i>BQ, B) and PSI (DCIPH₂ to MV, C) catalyzed electron flow in thylakoids isolated from leaves of control (DMSO) and artemisinin-treated (Artemisinin) rice plants.

<p>The measuring cuvette contained 20 µg Chl. equivalent thylakoids suspension in 1 ml of the reaction medium. The numbers in parenthesis denote the electron transport rate, expressed as µmol O₂ evolved (A and B) or consumed (C) mg Chl.⁻¹ h⁻¹. Arrow up, light on; arrow down, light off.</p

Kinetics of <i>p</i>BQ concentration dependent electron transport rate in thylakoids prepared from control (DMSO) and Artemisinin-treated (Artemisinin) leaves.

<p>The electron transport rate obtained from the control and treated samples (A) was further analysed for Michaelis-Menten type enzymatic reaction kinetics (B and C). The intersection of the line with the ordinate and the abscissa denotes the inverse values of V_max and K_m respectively. The values calculated for the respective K_m and V_max has been shown in the inset table. The <i>p</i>BQ titration experiments were carried out in thylakoids isolated both from spinach and rice leaves following similar <i>in vivo</i> treatments with artemisinin and the results shown here are from spinach.</p

Kinetics of DQ supported electron transport rate in thylakoids prepared from control (DMSO) and Artemisinin-treated (Artemisinin) leaves.

<p>The reciprocal plot of the velocity-versus-concentration is shown as inset. The intersection lines with ordinate and abscissa respectively represents the inverse of V_max and K_m.</p

The characteristic room temperature Chl. <i>a</i> fluorescence transient of control (DMSO) and artemisinin-treated (Artemisinin) rice leaves.

<p>The leaves were washed and dark adapted for 20 min. before subjected for fluorescence measurements. The sequence of light used to evoke the various fluorescence transients are as follows. Minimal fluorescence (F<i>_O</i>) was obtained with low intensity modulated light. Saturating pulse (SP, ≤1 s duration, 18,000 µmol photons m⁻² s⁻¹) was used to give F<i>_m</i> level of fluorescence in darkness and F<i>_m′</i> in light. Actinic light (300 min duration, 615 µmol photons m⁻² s⁻¹) was applied to drive photosynthesis and gives the transient F<i>_P</i>. and F<i>_t</i> level of fluorescence. A short pulse of far–red light was used to get F<i>_O′</i> fluorescence. Each tracing is the average plot of five individual readings. The R_fd (fluorescence decline ratio from ‘<i>p</i>’ to ‘<i>t</i>’ level) value for control and treated sample was noted to be 1.98±0.04 and 0.08±0.006 respectively.</p

Effect of increasing concentration of artemisinin on FeCN supported O₂ evolution activity of spinach thylakoids.

<p>The concentration of artemisinin used in µM is shown in parenthesis. The inset depicts the increase in percent inhibition of electron transfer rate relative to control with increase in artemisinin concentration. Arrow up, light on; arrow down, light off.</p

Inhibition of FeCN supported electron transport activity of spinach thylakoid incubated with the supernatant (A) and resuspended pellet (B) obtained following ultracentrifugation.

<p>Hundred µg Chl. equivalent control thylakoids suspension were incubated with both the fractions (A, supernatant; B, pelleted fraction) for two different time frames of 30 and 60 min (mentioned below the tracings). FeCN supported electron transport activity was assayed in 1 ml of reaction mixture containing thylakoid suspension equivalent to 20 µg Chl. The number in parenthesis denotes the electron transport rates in µmol O₂ evolved mg Chl⁻¹ h⁻¹. Arrow up, light on; arrow down, light off.</p

The room temperature Chl. <i>a O-J-I-P</i> fluorescence transient of control (DMSO) and artemisinin-treated (Artemisinin) leaves (A), and the effect of DCMU (B).

<p>Leaves were floated in DCMU (20 µM) solution for 1 h in complete dark to evaluate its effect in DMSO and artemisinin sprayed leaves. The minor difference in F<i>₀</i> (<i>O</i>) and F<i>_p</i> (<i>P</i>) obtained was double normalized at F<i>_O</i> and F<i>_m</i> level using biolyzerhp3 software. Each tracing is average plot of nine individual readings. The SD for F<i>_O</i> and F<i>_m</i> in control leaves was 358±9 and 1784±13 and for treated leaves was 368±11 and 1757±19.</p

Alteration in the electron transport activity in thylakoids prepared from control (DMSO) and artemisinin-treated (Artemisinin) rice leaves under basal and uncoupled conditions.

<p>Thylakoids isolated from leaves of control and treated plants were assayed for alteration in basal and uncoupled (NH₄Cl or GS) electron transport activities with FeCN as terminal electron acceptor. Measuring cuvette contained 20 µg Chl. equivalent thylakoids suspension in 1 ml of the reaction medium. The number in parenthesis denotes the electron transport rates in µmol O₂ evolved mg Chl⁻¹ h⁻¹. Arrow up, light on; arrow down, light off. The error bars indicate ±SD of electron transport (n=3).</p