Improvement ofex vitroacclimatization of mulberry plantlets by supplement of abscisic acid to the last subculture medium

Abstract

Mulberry (Morus sp.) of the family Moraceae is very economically important in Asian countries including Korea, because its leaf and fruit have been commercially used in sericulture and horticultural industries. Therefore it is necessary to develop the optimal production system for rapid and cost-effective propagation of mulberry. Our studies focused on establishing an acclimatization method for the successful plantlet production of new cultivar 'Cheongsu' which was transferred ex vitro after in vitro culture. In particular, effect of abscisic acid (ABA) addition into the last subculture medium on plantlet response to subsequent ex vitro transfer and its growth was investigated. During acclimatization, stomatal conductance and transpiration rate of ABA-pretreated plantlets were significantly lower than those of non-treated plantlets. Net photosynthetic rate of ABA-pretreated plantlets decreased after ex vitro transfer but increased after 14 days, and it was mostly higher than that of non-treated plantlets. Moreover, relative water content as well as chlorophyll contents and its ratio were also higher in ABA-pretreated plantlets. On the other hand, proline was considerably higher than in control plantlets. After 1 month of ex vitro transfer, survival rate of ABA-pretreated plantlets was 85.6%, which increased by 29.1% in comparison with control (56.5%). More vigorous growth was also observed in ABA-pretreated plantlets. From these results, it was found that application of ABA to the last subculture medium could improve acclimatization and promote survival of mulberry plantlets after ex vitro transfer, inducing water stress tolerance and alleviating abiotic stresses.Keywords Mulberry, Abscisic acid, Ex vitro transfer, Acclimatization, Water stress Introduction Mulberry (Morus sp.) is an economically important tree grown in India, China, Korea and several Asian countries where its foliage is used as food for silkworms in sericulture industry (Vijayan et al. 2012). It is also commercially valuable in the horticulture, food and cosmetic industries, in particular, its phytochemical and medicinal properties such as antioxidants (Yen et al. 1996) and hypoglycemia compounds (Kelkar et al. 1996) have been widely used as healthcare products. These days it is cultivated for fruit production, which is used for human consumption including jam, jelly, frozen desserts, pulp, juice and wine (Koyuncu 2004). Mulberry fruit is regarded as a traditional medicine for dysentery, constipation and avulsed teeth due to rich phenolic acids and flavonoids (Arfan et al. 2012; Lee and Bae 2011).Plant micropropagation has been widely applied to agriculture industry for large scale production of economically important and valuable species. But its commercial use is limited in many species due to the low plantlet survival rates during the acclimatization (Pospisilova et al. 2009a, b), which are known to be related to an abnormal morphology, anatomy and physiology under in vitro culture conditions (Dias et al. 2013a). Poor functioning of...

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