Abstract

In this study, the effects of different nitrogen sources on lentil (Lens clunaris) and barley (Hordeum vulgare) plants, exposed to 5 and 10 mM boron stress previously, were studied. After ten-day germination, the lentil (native) and barley (Tokak157/37) were incubated 16 h light and 8 h dark per day for 7-day growth cycle under the conditions of boron stress via different nitrogen sources (10 mM nitrogen in NH₄ Cl, KNO₃ and urea). As a result of the changes in the nitrogen sources of the plants, there were determined decreases in the relative growth rate (%) and total chlorophyll content related to boron stress, (p < 0.05) and (p < 0.01), respectively. The changes in the lentil were obtained much more than those in the barley. In addition, the changes in the groups in which NH₄⁺ was used as nitrogen source were obtained at lowest levels. The concentrations of MDA, H₂O₂ and proline showed increases under boron stress (p < 0.05). The effect of boron toxicity on the activities of SOD, GPX and LOX was similar in the two species but the levels of CAT and APX activities were different in both species under 5 and 10 mM boron stress (p < 0.01). SOD, GPX and LOX activities increased in the roots and shoots of boron treated plants as compared with the controls (p < 0.01). Although, lentil CAT and APX, activities decreased; in barley, CAT and APX, activities increased under boron toxicity. In conclusion, the fertilizers which contain NH₄⁺ should be used in the boron stressed farmlands.

Key words: Boron toxicity, antioxidant enzymes, nitrate, ammonium, urea, lentil, barley.

Abbreviation

SOD, Superoxide dismutase; CAT, catalase; APX, ascorbate peroxidase; GPX, guaiacol peroxidase; PEG, polyethylene glycol; AOS, active oxygen species; NBT, nitroblue tetrazolium; EDTA, ethylenediamine-N,N,N0,N0-tetraacetic acid; MDA, malondialdehyde; DAB, diamino-benzidine tetrahydrochloride; DW, dry weight; FW, fresh weight.