Low temperature storage of plants under dim light

In the production of quality plantlets by micropropagation, there is a crucial need to store plantlets for a short term if production facilities and labor are to be used efficiently and a flexible production schedule is intended. For this type of storage, not only plant growth but also the plant quality needs to be preserved. For the storage of plantlets in the middle of the multiplication stage, photosynthetic and growth abilities of explants produced from the stored plantlets is an important quality index, while visual quality in addition to the photosynthetic and growth abilities is important for stored plantlets ready to be sold as transplants. Dark storage (storing plantlets under darkness) has been utilized in commercial operations, but there are problems such as rapid deterioration of plantlets during storage, and thus the number of species storable under darkness is limited. The positive effects of dim light in low temperature storage have been shown for seedlings of several species by Heins et al. (1992). Similar effects were observed in photoautotrophically f micropropagated plantlets (e.g., Kubota and Kozai, 1994). Through the investigation on optimizing storage environment for photoautotrophically cultured plantlets, the optimum conditions for storing plantlets, and later for seedlings or transplants in general, were shown to be the combinations of low temperature with PPF close to the light compensation point (in case of broccoli (Brassica oleracea L. Botrytis Group) plantlets, the combination of 5 C and 2 μmol m^-2 s^-1 PPF gave the best result). These findings contributed to discovering a theory to optimize plantlet storage environment based on mass balance of the vessels and plantlets under various environmental conditions, a new area of controlled environment in plant production system. In this chapter, factors affecting low temperature storage will be summarized with emphasis on tissue culture and especially applications in photoautotrophic culture conditions. Information on storing seedlings (transplants) is also added when necessary. Principles and applications of low temperature storage a of transplants are also discussed in Kubota (2003).