Abstract
The medium pH level of plant tissue culture has been shown to be essential to many aspects of explant development and growth. Sensitivity or tolerance of medium pH change in vitro varies accordingly to specific requirements of individual species. The objectives of this study are to 1) determine medium pH change over time in storage conditions and with presence of explants, 2) evaluate the effects of medium pH change and explant growth performance and 3) assess the effects of adding a pH stabilizer, 2-(N-morpholino)ethanesulfonic acid (MES) to Douglas-fir micropropagation medium. Spring buds, collected before breaking dormancy from juvenile and mature donor trees were utilized for these evaluations. Medium with or without MES, each at five medium pH levels was pre-adjusted before adding MES, agar and autoclaving. Medium pH changes and explant growth parameters were measured at eight different incubation times. In general, medium with MES provided a more stable medium pH compared to pre-adjusted pH values under two storage conditions as well as with presence of explants over time. A general trend of decreasing medium pH over time was found comparing explants from juvenile and mature donor genotypes. Explant height and weight growth increased over time, but differ among explants from juvenile and mature donor genotypes. MES may help to maintain stable medium pH for bulk medium preparation. Our findings suggested a 21-day subculture practice may facilitate to sustain medium freshness, medium pH level and desirable explant growth.
Highlights
The Christmas tree industry plays an important role within Pennsylvania agriculture as well as across the nation
The medium pH of plant tissue culture has been shown to be very important to many aspects of explant development and growth
Storage of medium in the dark resulted in less medium pH fluctuation than storage under light
Summary
The Christmas tree industry plays an important role within Pennsylvania agriculture as well as across the nation. The goal of this micropropagation project was to develop a true-to-type clonal propagation system to alleviate the cost of tree-to-tree variation by conventional seedling propagation. The medium pH of plant tissue culture has been shown to be very important to many aspects of explant development and growth. Similar to soil pH, medium pH level may influence nutrient uptake (Ramage & Williams, 2002), cellular pH adjustment (Ballarin-Denti & Antoniotti, 1991), rooting and cellular growth (Leifert et al, 1992; de Klerk et al, 2008), plant gene expression and transcriptional pH responses in roots (Lager et al, 2010), and the efficiency of Agrobacteriummediated transformation (Ogaki et al, 2008; Rai et al, 2012). Medium pH can act to facilitate or inhibit nutrient availability in the medium such as ammonium uptake in vitro can be facilitated with a stable pH of 5.5 (Thorpe et al, 2008)
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