Strategies of a potential cash crop halophyte (Beta vulgaris ssp. maritima) to avoid salt injury

摘要

Salt stress effects were studied on Beta vulgaris ssp. marítima plants cultivated in defined nutrient solution in a gravel/hydroponic quick check system (QCS) with flow irrigation. We compared plants grown with 0, 125, 250, 375 and 500 mol m~(-3) NaCl-salinity. The salinity tolerance was measured on the basis of three parameters: a) The maximum yield of Beta vulgaris ssp. marítima was reduced by 50% (Cso-value) at 375 mol m~(-3) NaCl-salinity. b) The salinity threshold was reached at 125 mol m~(-3)NaCl-salinity. c) Gas exchange parameters such as net photosynthesis (mu mol m~(-2) s~(-1)), stomatal conductance (mol m~(-2) s~(-1)) and transpiration (mol m~(-2) s~(-1)) were highest at 250 mol m~(-3) NaCl-salinity. At salinities above the Cso-value the ratio of intercellular (Ci) to atmospheric (Ca) CCVconcentrations (Ci/Ca ratios), transpiration and stomatal conductance showed a distinct reduction and there was a steep rise in water use efficiency. The strategies employed by the seabeet for avoiding salt injury depend on adaptation to low water potential and high Na and Cl concentrations. The seabeet was able to balance out low external water potential and to generate turgor by accumulating high internal Na aád Cl concentrations in the leaf and of sucrose and proline in the taproot. However, the speeifity for the uptake of K, Mg and Ca was insufficient to prevent dilution of these ions at tissue and cellular level, supporting the hypothesis that the major reason for the particular threshold of salinity tolerance in the seabeet is ion-deficiency. The biennial seabeet survives NaCl in the range of seawater salinity because of a division of labour between leaf and taproot. It can be concluded that the mechanisms in the leaf are effective only until the taproot provides sufficient conditions for completion of a second vegetation period.