Influence of plant growth regulators on turfgrass polar lipid composition, tolerance to drought and salinity stresses, and nutrient efficiency

Two groups of plant growth regulators (PGRs), seaweed extract and triazole chemical, have been used in turfgrass management for improving turf quality and strengthening turfgrass tolerance to environmental stress. In order to understand the physiological functions and stress-tolerance mechanisms of the PGRs on turfgrass, a series of studies were conducted with perennial ryegrass (Lolium perenne L.).

Ryegrass was treated with or without propiconazole (PPC) (1-( (2-(2,4- dichlorophenyl)-4-propyl-l,3-dioxolan-2yl)methyl) IH-l,2,4-triazole) and a proprietary fortified seaweed extract (FSE), which were combined with or without drought and salinity stress treatment. Total lipids, fatty acid composition of polar lipids, and total free and conjugated sterols were determined by the thin layer chromatograph, gas chromatograph, and scanner densitometer. This study indicates that ppe and FSE affected the unsaturation of polar lipid fatty acids and concentration of free sterols, which are major factors in changing cell membrane fluidity and permeability. The PGR-induced alteration of cell membrane lipid composition could be an adaptive process to protect plant membrane function under drought and salinity stresses. However, the metabolic effects of PPC and FSE may be different. It was found that PPC had a strong inl1uence on unsaturation of polar lipid fatty acids, whereas FSE had a strong effect on free sterol concentration. Furthermore, a radish cotyledon expansion bioassay analysis showed that the FSE had cytokinin or cytokinin-like activity and could stimulate endogenous cytokinins in ryegrass, whereas an inhibition of cell expansion was seen in PPC-treated plants.

The possibility of using the PGRs to reduce fertilizer requirements was also studied. A higher uptake efficiency of most essential elements was found in PPC and FSE-treated Kentucky bluegrass (Poa pratensis L.) than in the control (without PGR treatments). This effect was greater at lower than at higher fertilization levels. The utilization efficiency of some major nutrient elements also was higher in PPC and FSE-treated bluegrass than in the control. The possibility of reducing fertilization by PGR application is positive.