Kappaphycus alvarezii is a seaweed of great economic importance for the extraction of kappa carrageenan from its cell walls. The most common strains are dark red, brown, yellow, and different gradations of green. It is known that ultraviolet radiation (UVR) affects macroalgae in many important ways, including reduced growth rate, reduction of primary productivity, and changes in cell biology and ultrastructure. Therefore, we examined the brown strain of K. alvarezii exposed to ultraviolet-B radiaton (UVBR) for 3 h per day during 28 days of cultivation. The control plants showed growth rates of 7.27% d-1, while plants exposed to UVBR grew only 4.0% d-1. Significant differences in growth rates and in phycobiliproteins between control and exposed plants were also found. Compared with control plants, phycobiliprotein contents were observed to decrease after UV-B exposure. Furthermore, the chlorophyll a (Chl a) contents decreased and showed significant differences. UVBR also caused changes in the ultrastructure of cortical and subcortical cells, which included increased thickness of the cell wall and number of plastoglobuli, reduced intracellular spaces, changes in the cell contour, and destruction of chloroplast internal organization. Reaction with Toluidine Blue showed an increase in the thickness of the cell wall, and Periodic Acid-Schiff stain showed a decrease in the number of starch grains. By the significant changes in growth rates, photosynthetic contents and ultrastructual changes observed, it is clear that UVBR negatively affects intertidal macroalgae and, by extension, their economic viability. and É. C. Schmidt ... [et al.].
Measurement of the chlorophyll (Chl) a fluorescence rise (FR) under higher exciting irradiance (EI), the O-J-I-P transient, or under lower irradiance, the O-I-P transient, is a routinely used method to access photosystem 2 function in thylakoid membranes of chloroplasts. Our measurements with a suspension of pea thylakoid membranes showed that the relative heights of the J and I steps in the FR depended not only on EI but also on the concentration and thickness of the sample. We explain this effect as a consequence of the gradient of EI within the sample. We tested this suggestion by theoretical simulations of the FR based on the model that was previously used for simulation of the FR considering in addition the gradient of EI within the sample. Our theoretical results correspond well with the experiments. The irradiance gradient effect may influence measured FR significantly and this fact should be taken into consideration in the interpretation of measured FRs. and P. Sušila ... [et al.].