Psychrometric Pressure-Volume Analysis of Osmoregulation in Roots, Shoots, and Whole Sporophytes of Salinized Ceratopteris

Osmotic and turgor adjustment in roots, shoots, and whole sporophytes of a NaCl-tolerant mutant and a NaCl-sensitive wild-type strain of the fern Ceratopteris richardii Brongn. were characterized following exposure to 60 millimolar NaCl, using a psychrometric approach to pressure-volume analysis. Water potential components of whole plants and shoots at full or ambient hydration were similar between strains. Roots of the mutant, however, had osmotic potentials at full turgor and water potentials at zero turgor which were lower (0.32 and 0.46 megapascal, respectively) than those in roots of the wild type after salinization. Although compromised in the absence of NaCl, sporophytes of the mutant strain were larger and much less necrotic in 60 millimolar NaCl after 17 days, compared to the wild type. Root growth in the mutant strain was unaffected by salinization and far exceeded root growth in the wild type. Correlation coefficients of the linear regression and the general consistency and precision of the pressure-volume data demonstrated the feasibility of using PV curves for estimating water potential components of roots. The technique should also provide a means of studying osmoregulation in a variety of other rapidly equilibrating plant tissues.