The activities of photosystem 2 (PS2) and whole chain electron transport declined in high temperature treated cells at the room temperature beyond 35 °C, while photosystem 1 (PS1) showed increased activity. Thylakoid membrane studies did not exhibit increase in PS1 activity indicating that the enhancement of PS1 activity is due to permeability change of cell membranes. However, the electron transport activity measured from reduced duroquinone to methylviologen which involves intersystem electron transport was extremely sensitive to high temperature. The activity of PS2 at different irradiance, which was accompanied by alterations in absorption and fluorescence emission properties, indicated changes in the energy transfer processes within phycobilisomes. Thus high temperature has multiple target sites in photosynthetic electron transport system of Spirulina platensis. and V. Venkataramanaiah, P. Sudhir, S. D. S. Murthy.
Salt stress causes decrease in plant growth and productivity by disrupting physiological processes, especially photosynthesis. The accumulation of intracellular sodium ions at salt stress changes the ratio of K : Na, which seems to affect the bioenergetic processes of photosynthesis. Both multiple inhibitory effects of salt stress on photosynthesis and possible salt stress tolerance mechanisms in cyanobacteria and plants are reviewed. and P. Sudhir, S. D. S. Murthy.
Exposure of intact cells of Spirulina to high temperature (HT) stress (40-60 °C) caused decrease in absorption spectrum and fluorescence emission spectrum. Low temperature emission spectra were altered at phycocyanin (PC) level. Room and low temperature emission spectra of intact phycobilisomes showed that PC was the main target in this cyanobacterium for the altered energy transfer under HT. and S .D. S. Murthy, V. V. Ramanaiah, P. Sudhir.
Effect of UV-B (1.9 W m-2) alone or in combination with supplemental "white light". WL (20 W m-2) exposure was studied on the energy transfer process of intact phycobilisomes isolated from Spirulina platensis. Exposure of UV-B or supplemental irradiation induced a decrease in room temperature fluorescence intensity and caused a shift towards shorter wavelengths. The low temperature fluorescence measurements showed that UV-B impairs energy transfer from phycocyanin to allophycocyanin B and the extent of damage may be reduced by the exposure to supplemental WL. and S. Rajagopal, Prasanna Mohanty, S. D. S. Murthy.
Al3+ significantly delayed the loss of chlorophyll (Chl), protein, and carotenoids when compared to K+ and Mg2+ during dark-induced senescence of detached primary leaves of Triticum aestivum. Thylakoid membranes isolated from Al3+ - treated leaves showed a better retention of photosystem (PS) 2, PS1, and whole chain electron transport activities than thylakoids of K+- or Mg2+-treated leaves. These ions protected the electron transport activities and restored the DCMU-dependent fluorescence increase of thylakoid membranes in a valency-dependent manner. Al3+ also delayed the change of excitation energy distribution during senescence. and D. Subhan, S. D. S. Murthy.
Al3+ in combination with kinetin showed more protection against degradation of chlorophyll (Chl) and protein than Al3+ or kinetin alone during dark-induced senescence in wheat primary leaf segments. MV-dependent whole chain electron transport, photosystem (PS) 2 mediated oxygen evolution, and PS1 activities were also delayed to a greater extent. Absorbed excitation energy distribution was more in favour of PS1 in Al3+ plus kinetin-treated leaf thylakoids at 72 h. and D. Subhan, S. D. S. Murthy.