Plant Cell, Tissue and Organ Culture 78: 209–216, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 209 The effect of ventilation on in vitro response of seedlings of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii to salt stress David Mills 1,∗ & Moshe Tal 2 1 Institutes for Applied Research, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel; 2 Department of Life Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel ( ∗ requests for offprints: Fax: +972-8-6472984; E-mail: mills@bgumail.bgu.ac.il) Received 18 June 2003; accepted in revised form 10 December 2003 Key words: hyperhydricity, salt stress, salt tolerance, tomato species, ventilation, vitrification Abstract Organs or plants grown in vitro do not always exhibit the same responses to salinity as the whole plant of same spe- cies grown ex vitro. The response to salinity (100 mM NaCl) of seedlings of the wild tomato species Lycopersicon pennellii acc. Atico (Lpa) and of the cultivated tomato L. esculentum cv. M82 (Lem), the former is known as salt tolerant and the second as relatively salt sensitive under ex vitro conditions, was compared under in vitro conditions with three different ventilation regimes. It was found that under salinity shoots of the wild species accumulated the same or even more dry biomass than the control (roots somewhat less) under all ventilation levels. Growth of shoots and roots of the cultivated species was inhibited under the same conditions especially under the high ventilation. Ventilation reduced some abnormalities of leaf development related to hyperhydricity and consequently ventilated leaves exhibited a more compounded structure, increased area, increased resistance to water loss and stomata functioning. Ventilation increased K + , Na + and Cl - accumulation in shoots of both tomato species. This was more pronounced under salinity and in Lpa. This work indicates that differences that characterize whole plants of these species in response to salinity under ex vitro conditions are exhibited also in whole plants grown in vitro under high ventilation. It is suggested that ventilation is needed to evaluate well the response of whole plants to salt stress applied in vitro. Abbreviations: Lem – Lycopersicon esculentum cv. M82; Lpa – L. pennellii acc. Atico Introduction Cell or tissue in vitro cultures have been used for se- lecting for stress resistance and to examine for the existence of a correlation between the mechanisms operating in cultured cells and in cells of the whole plant (Tal, 1990). Tal (1990) listed all possible cor- relations between the responses to salt of the whole plant and those of tissues and cells developed from that plant. A positive correlation, where both the whole plant and cultured cells are tolerant or sensitive to salt was interpreted, respectively, as an indication for the operation or lack of cellular mechanisms of salt tolerance in the whole plant. A negative correlation where the whole plant is salt tolerant but the iso- lated cells are sensitive, was regarded as an indica- tion for mechanisms that depend for their operation on the organization of the cells in tissues or organs in the whole plant. Another negative correlation, where the plant is sensitive to salt but the isolated cells are tolerant, was interpreted as due to the differences in environment surrounding the cells in culture and in the leaf tissue (Gale and Boll, 1978; Flowers et al., 1985). Although effective salt exclusion at the cellular level can be advantageous in vitro (where carbohydrate supply should be unlimited) it can be disadvanta- geous for leaf cells in vivo for which the carbon sup- ply is not unlimited and ions excluded from leaf cells and accumulated in the apoplast may induce water deficit and loss of turgor (Oertli, 1968). This case