Interaction between Signal Pathways upon Formation of Plant Defense in Response to Environmental Stress Factors

In the course of evolution, plants have developed numerous specific regulatory signal pathways, which are hormonal for the most part. Phytohormones comprise not only such generally recognized endogenous growth regulators as abscisic acid, auxins, cytokinins, gibberellins, brassinosteroids (BS), ethylene, salicylic acid (SA), and jasmonates but also recently described derivatives of apocarotenoids—strigolactones (SL). Signal pathways interact at the level of biosynthesis of messengers and their translocation as well as upon activation of target genes. Since abiotic and biotic environmental stressors negatively influence plant productivity, understanding of molecular mechanisms of regulation induced by stress agents may help researchers to produce stress-resistant and high-yielding plants using molecular techniques. This paper is a review of present-day literature dealing with the interaction and interference of nonhormonal and hormonal signals regulating growth and development of plants under ever-changing environmental conditions.

Glutathione Status in the Roots of Tomato Plants Transgenic by Genes psl and rapA1 in the Presence of Rhizobium leguminosarum

The level of glutathione was investigated in the roots of tomato (Solanum lycopersicum L.) plants transgenic by genes psl and rapA1 in the presence of a microsymbiont of leguminous plants Rhizobium leguminosarum VSy3. The plants transformed with gene psl showed a greater bacterial adhesion than the plants transformed with gene rapA1, which positively correlated with growth parameters of plants. Treatment with rhizobia elevated the content of glutathione in the roots of wild type plants three times, 4.7 times in the roots of plants transformed with gene rapA1, and more than five times in the plants transgenic by gene psl. The obtained results suggest that the level of glutathione in the roots may serve as a marker of efficiency of artificial symbiotic systems produced de novo.

Thermal Stress, Aggregation of Chlorophyll-Protein Complexes, and Light-Dependent Recovery of PSII activity in Wheat Seedlings

The dynamics of changes in the photochemical activity of photosystem II (PSII) and low-temperature spectra at 77 K in the first leaves of 11-day winter wheat plants Triticum aestivum L., as well as structural changes in chlorophyll-protein complexes (CPC) of thylakoid membranes during recovery after a short-term (20 min) heating at a temperature of 42°C, were studied. Changes in the Fv/Fm, F735/F695, and F735/F685 ratios indicate inhibition of PSII immediately after heating. Using nondenaturing electrophoresis, it was shown that the light-harvesting Chl a/b complex of PSII does not aggregate immediately after heating but after several hours, after 6 h the desagregation of CPC was observed, which was consistent with an increase in the Fv/Fm ratio upon recovery. The influence of temperature, intensity, and quality of light (white, blue, and red light) on the recovery of PSII activity and low-temperature fluorescence spectra was studied. It was concluded that the recovery is a photo-activated low-energy process, independent of photosynthesis, and the most effective in blue light.