Interactive Effects of Polylactic Acid with Different Aluminum Concentrations on Growth, Pigment Concentrations, and Carbohydrate Accumulation of Azolla

Abstract

The interactive effects of 1 pLg 1-1 polylactic acid (PLA) with aluminum concentrations of 2, 4, 8, and 16 mg 1-~ on Azolla caroliniana growth, chlorophyll, carotenoid, anthocyanin, and carbohydrate accumulation were examined. Azolla growth was decreased with increases in alu- minum concentration. Furthermore, the growth reduction was less pronounced when PLA was present. Chlorophyll a and b concentrations were decreased in plants grown at Al concentrations of 4 mg 1-1 and higher. Polylactic acid reduced the influence of Al concentrations of 4, 8, and 16 mg 1-1 on chlorophyll a and b. Similarly, carotenoid concentrations were decreased as Al concen- trations increased in the growth media. Anthocyanin concentration was increased at 4.0 mg 1-1 Al without PLA and at higher Al concentrations with or without PLA. In general, carbohydrate accumulation increased as Al concentration increased. However, this increase in carbohydrates was less pronounced in the presence of PLA. In the absence of Al from the growth media, treat- ment with 1 iLg 1-1 PLA resulted in an increase in plant growth, chlorophyll, and carotenoid concentration and a decrease in carbohydrate accumulation. Aluminum (Al) toxicity is an important component of the damaging effects of acid rain in rivers and lakes. Rueter et al. (1987) reported that acid rain not only increased total soluble Al concentration, but also changed the affinity of organic and inorganic complexes with metals. Sprenger and McIntosh (1989) showed that Al concentrations were elevated in both water and submerged aquatic macrophytes (Ranunculus ololeucos J. Lloyd, Luronium natans Raf.) in acidified waters. According to Stanley (1974), an addition of 92 ,L.mol 1-1 Al to well-buffered medium inhibited 50% of the root growth of Myriophyllum spicatum L. The toxicity of Al depends upon a number of factors, including pH and organic matter content (Tan and Binger, 1986). Aluminum toxicity increases at a pH below 5 because its solubility increases considerably. Of the different species of Al, A13+ is the only significant one that is found in freshwater at a pH of 4 or less (Poleo, 1995). In general, Al has been shown to interfere with cell division, decrease respiration rates, interfere with enzymes governing the deposition of polysaccharide in cell walls, increase cell wall rigidity, and de- crease the uptake and transport of water and several elements including Ca, Mg, P, and K in plants (Foy et al., 1978). The earliest recorded use of lactic acid as a plant growth regulator was by