Root growth of somatic plants of hybrid Pinus strobus (L.) and P. wallichiana (A. B. Jacks.) is affected by the nitrogen composition of the somatic embryo germination medium

Abstract

This paper describes improvement in root growth of hybrid white pine somatic plants on a somatic embryo germination medium containing solely organic nitrogen sources. Mature somatic embryos of F2 hybrid Pinus strobus × Pinus wallichiana backcrossed with P. strobus converted to plants but survival of the somatic plants was not satisfactory prompting the present study on somatic seedling root growth on germination media varying in nitrogen (N) composition. The media were modifications of Litvay’s (Litvay et al. in Plant Cell Rep 4:325–328, 1985) which included two main groups: G1, G2, G3, G4 all contained inorganic N with or without glutamine (Gln) or casein hydrolysate (CH) and G5, G6, G7 contained solely glutamine and/or CH. In addition, G8 was half-strength G1 (with organic N) and G9 was half-strength CD (Campbell and Durzan in Can J Bot 53:1652–1657, 1975) without organic N. The roots of plants growing on media containing solely organic N grew about 2.55 times longer than on those containing solely inorganic N or both inorganic and organic N. The longest roots grew on G7 supplemented with CH and on G5 with both CH and Gln. Microarray analysis of somatic plants germinated on G1 versus G7 revealed that depending on the N source the somatic plants displayed changes in the transcriptome resulting in the differential expression of a range of genes involved in essential processes for plant growth and development. Roots grown in the absence of inorganic N were capable of rapid uptake of labelled inorganic 15N during the 2 h incubation in the nutrient solution. The somatic plants from G5 medium acclimatized at the rate twice as high as those from G1 (with both inorganic and organic N) and G2 (solely inorganic N) under standard fertilization regime.