Hirano et al. [26] observed acceleration of the rates of O2 evolution as well as synthesis of sugar during photosynthesis in Spirulina platensis when exposed to 10 mT geomagnetic field. They opined that the treatment using magnetic field increased the phycocyanin content in S. platensis, which plays an important role in the activation of photosystem II to help the ac­tivation of electron transfer reactions during photosynthesis. Their results also suggested that the magnetic fields accelerate the light excitation of chlorophyll radical pair.

Li et al. [27] subjected the same cyanobacterium S. platensis, to a range of static magnetic field intensities among which some stimulated its growth, uptake of carbon and light energy utilization. They observed that the levels of micro and trace elements (Ni, Sr, Cu, Mg, Fe, Mn, Ca, Co and V) and essential amino acids such as histidine improved at 250 mT magnetic field treatments. Also, chlorophyll a content of the magneti­cally treated sample was higher than the control, suggesting better light harvesting for photosynthesis. However there was slight decrease in lipid synthesis.

In Dunaliella salina, P-carotene content could be raised when treated with 10-23 mT of static magnetic field and the maximum was obtained at 10 mT with addition of 1 mg L-1 of Fe-EDTA. It also showed higher accumulation of the heavy metals viz. Co, Cd, Cu and Ni in the magneti­cally treated cultures, indicating its potential for bioremediation of heavy metals [32].

Singh et al. [29] investigated the use of permanent magnets and found that the physiological response of a cyanobacterium Anabaena doliolum, was dependent on exposure time and magnetic pole orientation. They reported that N, S and N+S poles from 0.3 T permanent magnets produced different ef­fects depending on the exposure time from 1 to 6 h. The effect was significant on a two hour exposure with combined N+S poles, where one culture was exposed to only N pole, which was then mixed with another culture exposed to S pole only. Treated cultures recorded 150, 110, 38, 34 and 20% increase in phycocyanin, chlorophyll a, carbohydrates, carotenoid and protein content, respectively and 55% increase in optical density over the control.

5.3.1.3 OTHER PHYSIOLOGICAL PROCESSES