[Analysis of photosynthetic characteristics and its influencing factors of medicinal plant Mirabilis himalaica].

To study photosynthetic characteristics and its influencing factors in leaves of medicinal plant Mirabilis himalaica, and provide an evidence for guiding artificial planting and improving the quantity. The light-response and diurnal photosynthesis course of leaves at the booting stages of 1-3 year old M. himalaica were measured with LI-6400 system. The Results showed that the light response curves were fitted well by non rectangle hyperbola equation (R2 > or = 0.98). The values of the maximum photosynthetic rate (Pmax) and light use efficiency of three-year old M. himalaica leaves were higher than those of 1-2 year old individuals. The diurnal variation of net photosynthetic rate (Pn) and stomatal conductance (Gs) of 2-3 year old M. himalaica were typical double-peak curves determinately regulated by stomatal conductance. However, transpiration rate (Tr) of 1-3 year old plants leaves were single-peak curve, which was self-protection of harm reduction caused by the higher temperature at noontime. Correlation analysis showed that the changes between photosynthetic active radiation (PFD), air temperature (T ) and Pn, were significant positive related. Therefore, M. himalaica is a typical sun plant, which should be planted under the sufficient sunshine field and prolong the growing ages suitably in order to improve the yield.

Growth responses and cadmium accumulation of Mirabilis jalapa L. under interaction between cadmium and phosphorus.

Based on the identification of Mirabilis jalapa L. as a new Cd-hyperaccumulating ornamental, the growth response of the plant to interaction between cadmium (Cd) and phosphorus (P), its effect on the Cd accumulation in the species and relevant mechanisms were further investigated by the pot-culture experiment with chemical analyses and the X-ray absorption near edge structure spectra (XANES). It showed that the leaf, shoot and root biomass (as dry matter) increased with an increase in P supplies from 20 to 100 mg kg(-1) at various tested Cd levels except 10 mg kg(-1). The Cd accumulation in the leaves and shoots significantly decreased with increasing P concentrations from 20 to 500 mg kg(-1) at the Cd concentrations from 10 to 50 mg kg(-1), except the Cd level at 100 mg kg(-1). It was also found that the translocation factor of Cd in M. jalapa L. reached the maximum at different tested Cd levels when the concentration of added P was 100 mg kg(-1), but the bioaccumulation factor of Cd decreased with increasing P. This changing law may be responsible for the mechanism of P immobilizing Cd. The investigation using the P-K edge XANES showed the spectra of adsorbed phosphate in the shoots exhibited a stronger white-line peak than that in the leaves and roots, and the oscillation near 2165eV was more intense. Besides, the P-K edge XANES spectra for M. jalapa L. indicated P may exist as Cd-phosphate. Thus, it can be inferred that the addition of P at appropriate contents may be a useful approach to enhance the plant growth and to immobilize Cd in the Cd-contaminated soil. Furthermore, P and Cd may form a deposit in plants to tolerate Cd toxicity for reducing the degree of the structural damage of the plant.

Genes associated with opening and senescence of Mirabilis jalapa flowers.

A modest ethylene climacteric accompanies flower senescence in Mirabilis jalapa L., and exogenous ethylene accelerates the process. However, inhibitors of ethylene action and synthesis have little effect on the life-span of these ephemeral flowers. Treatment with alpha-amanitin, an inhibitor of DNA-dependent RNA synthesis, substantially delays the onset of senescence. This effect falls linearly between 7 h and 8 h after the start of flower opening. Subtractive hybridization was used to isolate transcripts that were up- and down-regulated during this critical period. Eighty-two up-regulated and 65 down-regulated transcripts were isolated. The genes identified encode homologues of a range of transcription factors, and of proteins involved in protein turnover and degradation. Real-time quantitative RT-PCR was used to examine expression patterns of these genes during flower opening and senescence. Genes that were identified as being down-regulated during senescence showed a common pattern of very high expression during floral opening. These genes included a homologue of CCA1, a 'clock' gene identified in Arabidopsis thaliana and an aspartyl protease. Up-regulated genes commonly showed a pattern of increase during the critical period (4-9 h after opening), and some showed very strong up-regulation. For example, the abundance of transcripts encoding a RING zinc finger protein increased >40 000 fold during the critical period.