Effects of Water Stress on Germination and Growth of Linseed Seedlings (Linum usitatissimum L), Photosynthetic Efficiency and Accumulation of Metabolites

Drought is a serious problem in many nations, adversely affecting both crop growth and yield. Here, we investigate the effects of water stress on growth, photosynthesis, physiology and germination in seedlings of linseed (Linum usitatissimum L). Water stress was imposed by exposing the sand-grown roots to irrigation with a range of concentrations of polyethylene glycol-6000 (PEG). Both relative growth rate (RGR) and water content (WC) decreased with increasing PEG concentration with the reductions being greatest for 20% PEG (water potential -0.58 MPa). The results show that as PEG concentration increased, the fluorescent chlorophyll and chloroplast pigments decreased but the ratio of Chl a/Chl b gradually increased. Meanwhile, shoot carbohydrate content increased slightly with increasing PEG concentration while that in the roots peaked at 5% PEG (-0.09 MPa) before decreasing at higher PEG concentrations. The content of proline in shoots and roots increased with increasing PEG concentration. With increasing PEG concentration, betaine showed a slight tendency to rise in the root, but to rise and then fall in the shoot. The results indicate that PEG-induced water stress increased the accumulations of carbohydrate, proline and betaine. These may help the linseed seedlings to survive periods of osmotic stress induced by drought and may be involved in the perception and transmission a drought signal, also playing a role in osmotic adjustment. Under water stress, the main inorganic ions involved in osmotic adjustment were K+, Na+, Ca2+ and Cl- likely thereby increasing drought resistance. The germination percentage of the seeds was severely reduced by increasing PEG concentrations, ceasing altogether at 15% PEG. Many of the seeds that remained dormant in the higher PEG concentrations germinated satisfactorily when afterwards placed in pure water. The research provides useful leads in the planned development of linseed cultivars having increased drought tolerance.