Growth and solute accumulation in 3‐week‐old seedlings of Agropyron elongatiun stressed with sodium and potassium salts

Abstract

Agropyron elongatum [Host. (Beauv.)] [cv. Arizona Glendale, was grown in liquid medium salinized with either NaCl, KCI, or a 50:50 mixture of these two salts at osmotic potentials ranging from 0 to –1.6 MPa. The amount of growth in 21 days was measured, and extracts were made of the shoots at this time. The extracts were assayed for low‐molecular‐weight organic compounds (glucose, fructose, sucrose, be‐taine, proline) and inorganic solutes (Na+, K+, Cl−, P.). The purpose was to determine if there was any correlation between the harmful effect of salinity on growth and the concentrations of solutes in tissues. Growth inhibition of A. elongatum was roughly proportional to the osmotic potential of the growth medium and was independent of the ionic composition of the salinizing salts. Total monovalent cation (the sum of Na+ and K+) concentrations and the ratio of these two cations in leaves were mainly a function of the ionic compostion of the salt in growth media, and, to a lesser degree, of osmotic potentials. F At an osmotic potential of –0.2 MPa, total monovalent cation in leaves was the same as in non‐stressed plants. However, if the salinizing salt contained NaCl, there was an increase in foliar Na+ with a balancing decrease in K+. At stress levels between –0.4 and –1,6 MPa, and, if the media were salinized with either 100% NaCl or a 50:50 mixture of NaCl and KCI, total monovalent cation concentrations remained constant at a value that was twice that in non‐stressed plants. Although total monovalent cation concentrations were equal in plants grown under these two salinity conditions, the K+/Na+ ratios shifted from a value of 1:2 in plants grown in 100% NaCl to 3:1 in plants subjected to the 50:50 mixture. If 100% KCI was used to salinize media, total monovalent cation was 80% of its concentration in NaCl‐treated plants in the range of –0.4 to ‐1.2 MPa. At –1.6 MPa due to 100% KCI, total monovalent cation was double that in plants subjected to ‐0.4 MPa. In the range of osmotic potentials from–0.2 to –1.2 MPa, the chloride:cation ratio was 1:2. At –1.6 MPa the ratio changed to 3:4. Proline started accumulating in leaves of A. elongatum when the tissue concentration of total monovalent cation exceeded 200 μ (g fresh weight)−1. Above this threshold value of total monovalent cation, the proline concentration of leaves was 6% of the amount of total monovalent cation that exceeded 200 umol (g fresh weight)1.