Acclimatization and subsequent gas exchange, water relations, survival and growth of microcultured apple plantlets after transplanting them in soil

Abstract

Previous findings indicated that leaf conductance and net photosynthesis were positively correlated with water status (relative water content) of tissue‐cultured shoots and plantlets, and that acclimatization was associated with a reduction in leaf conductance and transpiration. In the present study, the effect of acclimatization on plant water status after plants were removed from culture and transplanted in soil, as well as the relation of water status with survival and growth after acclimatization were determined. Tissue‐cultured plantlets (Malus pumila cv. Greensleaves) were acclimatized by exposure to a 4‐day gradual reduction in humidity before they were transplanted. Once plants were transplanted, acclimatized plants maintained a higher relative water content than nonacclimatized plants, probably because of a lower initial stomatal conductance and less transpiration. High plant water status, as indicated by high relative water content, appeared to be an important factor for both plant survival and growth after the plants were transplanted. Higher water status was associated with higher growth rates and net assimilation rates. The differences in gas exchange, water relations and growth characteristics between plantlets in vitro and at 4 weeks after they were transplanted were also studied. Compared to in vitro plants, transplanted plants had a higher water status and higher leaf conductance and net photosynthesis. There was also an increase in the leaf area ratio (leaf area to plant biomass ratio) after they were transplanted which might have contributed to the higher net assimilation rate in transplanted compared to in vitro plants.