scholarly journals The Action Spectrum of Photosynthesis in Euglena Gracilis at Different Stages of Chloroplast Development

1970 ◽  
Vol 23 (1) ◽  
pp. 33 ◽  
Author(s):  
JT O Kirk ◽  
JA Reade
Keyword(s):  
Oxygen Evolution ◽  
Euglena Gracilis ◽  
Chloroplast Development ◽  
Platinum Electrode ◽  
Action Spectrum ◽  
Thin Strip ◽  
Agarose Gel ◽  
Photosynthetic Oxygen Evolution ◽  
Unicellular Algae ◽  
Photosynthetic Oxygen

A method for measuring the action spectra of photosynthetic oxygen evolution in unicellular algae is described. This involves embedding the cells in a thin strip of agarose gel. These gel strips can then be used for action spectrum measurements, with a bare platinum electrode of the Haxo and Blinks type in the same way as measure� ments are made with a piece of multicellular algal thallus.

Light-induced inhibition of respiration in DCMU-poisoned Chlorella caused by photosystem I activity

1972 ◽  
Vol 50 (1) ◽  
pp. 13-21 ◽  
Author(s):  
D. F. Sargent ◽  
C. P. S. Taylor
Keyword(s):  
Oxygen Uptake ◽  
Chlorophyll A ◽  
Oxygen Evolution ◽  
Photosystem I ◽  
Action Spectrum ◽  
Photosynthetic Oxygen Evolution ◽  
Intracellular Atp ◽  
Respiratory Inhibition ◽  
Cyclic Photophosphorylation ◽  
Photosynthetic Oxygen

We have demonstrated that the reduced net rate of oxygen uptake observed when DCMU-poisoned Chlorella are illuminated is a result of an inhibition of respiration rather than residual photosynthetic oxygen evolution. The action spectrum of the effect demonstrates that chlorophyll a is the main photoreceptor, implicating system I of photosynthesis. Studies using PMS, which is known to stimulate cyclic photophosphorylation by photosystem I, show that the respiratory inhibition is caused by a change in the intracellular ATP/ADP balance as a result of cyclic photophosphorylation.

scholarly journals TIP family aquaporins play role in chloroplast osmoregulation and photosynthesis

2020 ◽  
Author(s):  
Azeez Beebo ◽  
Ahmad Zia ◽  
Christopher R. Kinzel ◽  
Andrei Herdean ◽  
Karim Bouhidel ◽  
...  
Keyword(s):  
Electron Transport ◽  
Oxygen Evolution ◽  
Photosynthetic Electron Transport ◽  
Chloroplast Envelope ◽  
Photosynthetic Oxygen Evolution ◽  
Wild Type ◽  
Thylakoid Lumen ◽  
Photosynthetic Oxygen ◽  
Osmotic Treatment ◽  
Envelope Membranes

SUMMARYPhotosynthetic oxygen evolution by photosystem II requires water supply into the chloroplast to reach the thylakoid lumen. A rapid water flow is also required into the chloroplast for optimal oxygen evolution and to overcome osmotic stress. The mechanisms governing water transport in chloroplasts are largely unexplored. Previous proteomics indicated the presence of three aquaporins from the tonoplast intrinsic protein (TIP) family, TIP1;1, TIP1;2 and TIP2;1, in chloroplast membranes of Arabidopsis thaliana. Here we revisited their location and studied their role in chloroplasts. Localization experiments indicated that TIP2;1 resides in the thylakoid, whereas TIP1;2 is present in both thylakoid and envelope membranes. Mutants lacking TIP1;2 and/or TIP2;1 did not display a macroscopic phenotype when grown under standard conditions. The mutant chloroplasts and thylakoids underwent less volume changes than the corresponding wild type preparations upon osmotic treatment and in the light. Significantly reduced rates of photosynthetic electron transport were obtained in the mutant leaves, with implications on the CO2 fixation rates. However, electron transport rates did not significantly differ between mutants and wild type when isolated thylakoids were examined. Less acidification of the thylakoid lumen was measured in mutants thylakoids, resulting in a slower induction of delta pH-dependent photoprotective mechanisms. These results identify TIP1;2 and TIP2;1 as chloroplast proteins and highlight their importance for osmoregulation and optimal photosynthesis. A third aquaporin, TIP1;1, is present in the chloroplast envelope, and may play role in photosynthesis under excessive light conditions, as based on the weak photosynthetic phenotype of its mutant.

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