Water-Stress-Induced Changes in the Growth and Metabolism of Growing and Non-Growing Root Zones of Barley Seedlings

Abstract

Experiments were conducted on 7-day-old barley (Hordeurn vulgare L. cv. KN 16) seedlings using polyethylene glycol (PEG-6000) to induce water stress. Growth, amount of PEG absorbed, and glucose, sucrose, free proline and organic acid contents were measured in growing (non-vacuolated) and non-growing (vacuolated) root tissues and shoots. Relative water content (RWC) and water potential were used to indicate the degree of stress. Lowering of RWC reduced growth and decreased the root : shoot ratio. Sugar content of the non-growing root zone changed with a pattern almost the reverse of that occurring in the growing root zone. The glucose level changed much more than the sucrose level in both growing and non-growing roots and shoots. Stress-induced proline accumulation was greater in the growing than in the non-growing root zones. The citric and malic acid contents increased in growing roots only above stress levels of -0.6 MPa. In growing roots, citric and malic acid concentrations began to decrease at - 0.35 MPa and - 0.8 MPa or lower stress levels, respectively. High water potential (-0.35 MPa) caused a decrease in malic acid concentration but low water potential (- 0.80 to - 0.89 MPa) caused a decrease in citric acid concentration in shoots.