Physiological Responses under Nutrient Stresses and Gene Expression under Phosphorus Deficiency in Phalaenopsis Sogo Yukidian ‘V3’
Date Issued
2014
Date
2014
Author(s)
Luo, Miao-Zhen
Abstract
Phalaenopsis spp., an epiphytic orchid, is tolerant to nutrient stresses. The nutrient deficient symptoms usually develop very slowly. To understand how Phalaenopsis survives under nutrient starvation, we examined the effect of nitrogen (N), phosphorus (P) or potassium (K) deficiency on Phalaenopsis from the aspects of physiology, anatomy, and gene expression, respectively. To investigate the symptoms and growth responses of Phalaenopsis under nutrient deficiency, Phal. Sogo Yukidian ‘V3’ plants were supplied with fertilizer containing different concentrations of N (0, 0.71, 7.14 mM), P (0, 0.16, 6.14 mM), or K (0, 0.64, 6.4mM). Plants were grown in a 30/25 oC phytotron, and no significant differences in plant appearance and growth were observed during 4, 8, or 12 weeks of starvation. When plants were kept at vegetative growth and straved for 32 weeks, N deficiency resulted in reduced whole-plant fresh weight, total leaf area, and leaf number and P deficiency aggravated leaf falling. However, no effects were observed under K deficiency. The 8-week nutrient-straved plants were further subjected to low temperature (25/20 oC) to provoke flowering. At 32 weeks of nutrient deficiency, N deficient plants showed early spiking, reduced dry weight, and appearance of yellow leaves; P deficiency caused decreased spiking rate along with the increase of falling leaves and the development of purple pigment. However, the growth were not affected by K deficiency except for delayed spiking. Besides, photosynthesis efficiency decreased significantly after 12 weeks of N deficiency but was not affected by K deficiency even after 32 weeks of deficiency. While low-P treatment reduced the net carbon dioxide exchange rate, it did not affect chlorophyll fluorescence (Fv/Fm), suggesting photosystem II was not impaired. There are two cell layers of velamen at the outermost of Phal. Sogo Yukidian ‘V3’ roots. There are long cells with O-shaped walls and U-shaped walls in endodermis and exodermis, repectively. Passage cells were among endodermis and exodermis and opposite to the xylem in endodermis. These structures may be beneficial for water and nutrient uptake and retention. Anatomical analyses revealed that P deficiency did not signigicantly affect cell morphology of roots and leaves but decreased the size of stele and the number of vascular bundle in roots. Furthermore, several P starvation-responsive genes identified from a previous microarray analysis were selected for validation by reverse transcription polymerase chain reaction analysis. I was able to validate the up-regulated expression for most of genes in leaf but unable to confirm the down-regulated expression of several genes. Among them, the expression of PATC128122, encoding a RING domain-containing protein, was highly up-regulated in the leaves and roots subjected to 12-week P deficient treatment but didn’t respond to N or K deficient treatment. Results of in situ RNA hybridization indicated its expression in the root cortex and leaf phloem. Transgenic Arabidopsis thaliana overexpressing PTAC128122 driven by 35S promoter of Cauliflower mosaic virus displayed no differences in fresh weight, inorganic phosphate concentration, and visible appearance in comparison with wild-type plants grown under various phosphate supplies, 250, 50, and 10 μM phosphate. In summary, in spite of no noticeable changes during vegetative growth, the expression of a subset of genes and vascular pattern of Phalaenopsis are altered, likely as adaptative responses to cope with limited P. Of note, the long term nutrient starvation during the vegetative growth severly affects the flowering of Phalaenopsis at the later stage.
Subjects
Phalaenopsis
Nutrient Stress
Phosphorus Deficiency
Anatomy
Gene expression validation
SDGs
Type
thesis
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