2017 ASHS Annual Conference

Phalaenopsis plant has great nitrogen (N) storage capability, hence it is not easy to study its reaction to N deficiency stress and the development of deficiency symptoms in mature plants. Therefore, tissue-cultured plantlets from intermediate cultures of Phalaenopsis Sogo Yukidian ‘V3’ (V3) and Phalaenopsis amabilis (AMA) were used as plant materials in this study. The plantlets were subcultured on half-strength Murashige and Skoog medium containing 0 mM N in N deficiency treatment or 30 mM N in control. Three months after culture, the plantlets were subcultured on the same medium. After 3 months of N deficiency treatment, the main symptom in V3 compared with control was longer roots that grew almost vertically downwards so that the shoot was elevated from the medium. Lower leaf yellowing began to occur after 3.5 months of N deficiency treatment and became more severe after 6 months of treatment. Leaf growth was markedly reduced in V3 after 6 months of N deficiency treatment, with progressively smaller new leaves becoming evident and a shoot dry weight of only 110 mg being found in the N deficiency treatment group, in contrast to 179 mg in control. However, 6 months of N deficiency treatment to V3 significantly increased root growth (135 mg dry weight vs. 99 mg in control), root diameter (5.7 mm vs. 4.4 mm), and root hardness (5.7 N vs. 4.8 N). The response of AMA to N deficiency was largely similar to that of V3, differing in the slightly later occurrence and the lower severity of lower leaf yellowing, as well as the greater changes in shoot and root dry weights relative to control. After 6 months of N deficiency treatment, shoot dry weights of AMA were reduced by 52% compared with control, which was greater than the 39% reduction found in V3. In conclusion, under N deficiency Phalaenopsis plants exhibit lower leaf yellowing, reduced shoot growth, but increased root growth, so that the shoot/root ratio decreased to 17%-26% that of control. In other words, greater biomass is allocated to the roots, presumably to increase the N absorption capability of the plant.