Photosynthesis and transpiration of in vitro cultured asparagus plantlets

Nodal sections of asparagus (Asparagus officinalis L.) were cultured and rooted on a modified Murashige and Skoog (MS) medium for 10 weeks. These plants were then acclimatized for 5 weeks. Photosynthesis and transpiration of in vitro plantlets, acclimatized plantlets and control seedlings were measured with an open gas exchange system. Rates of photosynthesis of in vitro-cultured plantlets were as high as those of seedlings grown in a greenhouse, while their rates of transpiration were much higher. Photosynthetic capacity of in vitro-cultured asparagus plantlets was sufficiently high to support autotrophic growth during the period of acclimatization. Photosynthesis of acclimatized plantlets was always considerably lower than that of in vitro plantlets except at high concentrations of CO2. Evaportranspiration of acclimatized plantlets was comparable to that of seedlings. These results suggest that high water loss incurred by in vitro shoots imposes severe limitations on newly formed shoots in acclimatization thus reducing whole plant photosynthesis. Protecting in vitro plantlets from water stress is the most important factor to consider in order to ensure their survival during the acclimatization period.