A bacterial consortium alleviated a low-dose gamma-irradiation effect in Kalanchoe plantlets

The ability of plants to protect themselves against ionizing radiation is limited. One of the way how to alleviate irradiation consequences in plants is to use plant-associated bacteria for inoculation. Two defined plant growth promoting bacterial strains were used for inoculation Kalanchoe daigremontiana (Hamet & Perrier) plantlets before acute irradiation with gamma-quanta (Co-60). Lethal doses of the 7-rays for Klebsiella oxytoca IMBG26 was 3,0 kGy, and for Paenibacillus sp. IMBG156 it was 500 Gy. Bacteria expressed enhanced the pelX promoter activity after sublethal dose irradiation. The pelX promoter activity that measured as activity of beta-galactosidase of the pelX::lacZ fusion in K oxytoca (pGalP) was 0,88 mkM/ml.min after exposure to 2,0 kGy, e.a. 80% of control (untreated) bacterial activity, although the irradiated bacterial population comprised 1,25% from control one. Integrated index of plantlets development which relied on both a root number and root length reflected fluctuations in metabolic processes in irradiated plantlets without treatment with bacteria. Stabilizing stress reactions occurred 10 days post irradiation at different doses (30, 50, 70. Gy), however, index of growth (IG) remained at the level of 30-60% to control plantlets. The effect of irradiation on kalanchoe plantlets was relieved by bacteria at doses of 30 and 50 Gy, moreover, IG was observed at levels of 500 and 200%, respectively. A 30 Gy dose was obviously stimulating for K daigremontiana plantlets. Intense root elongation, instead of development of new coronal roots, led to fast adaptation to stressful conditions and normalization of metabolic processes in kalanchoe plantlets.