modern research physics

---

Aluminum toxicity is one of the most important limiting factors for plant growth and development in acidic soil (pH <5.5). Soil acidity and consequently availability of Al in the soil can be accelerated by some farming practices and acid rain. The mechanisms of Aluminum toxicity have not been elucidated yet. The first response of the plant to aluminium toxicity is the inhibition of root elongation, that is apparently resulted from increasing of cell wall cross links. Therefore, the effect of aluminium on activity and gene expression of enzymes involved in phenolic compounds biosynthesis such as phenylalanine ammonialyase and peroxidase was investigated in this research.To this end, the flax seeds grown in Hoagland’s solution were treated with 0, 50 and 100 &muM aluminium (as AlCl3. 6H2O). The results showed that aluminium decreased root growth but increased wall bound phenolics content, compared with those of the control plants. Increase of the activity of peroxidase especially in ionically and covalently fractions in Al-treated roots was consisted with reducing root growth.  Increased activity, PAL expression and lignin contents were observed in higher concentrations of aluminum. The investigation of the expression of peroxidase isozymes, Flxper1 and Flxper3 suggested that Flxper3 is the isozyme which is more involved in aluminium toxicity in flax roots.  

---

Manganese (Mn) is a micronutrient that is essential for plant growth and develop-ment. Meanwhile, an excess amount of Mn is one of the most important growth limiting factors in acid soils. The present study was undertaken to identify the effects of excessive Mn on the physiological aspects of tea plant. To this end, 2-year old rooted cuttings of tea (Camellia sinensis L. assamica × sinensis) were grown in a modified Hoagland solution with pH=4.2 for 1 month with aeration in green house, with temperature of 27 ± 3 ˚C and photosynthetic photon flux of 101.5 µmol. m-2 s-1 (400-700 nm) at the plant level. After emergence of new, white roots with 5 to 10 cm in length, the plants were treated for 1 week with excessive Mn to a final concentration of 0.9 mM. After 1 week, the white roots were harvested and frozen in liquid N2 and kept at -80 ˚C until used for determination of PO activity, lignin and sugar as well as chlorophyll content. The activities of soluble peroxidase (SPO), covalently wall-bound peroxidase (CPO) and lignin content decreased by Mn treatment. On the other hand, the activities of ionically wall-bound peroxidase (IPO), sugar and chlorophyll contents increased by Mn treatment. These results suggest that excessive Mn may have beneficial effects on tea plant via lowering lignin content and increasing extensibility of the walls.