The review deals with objective reasons that limit the use of chlorophyll fluorescence induction kinetics (Chl FIK) method in plant ecology. Based on the ontogenetic approach (analysis and comparison of the dynamics of the Chl fluorescence ratio F p /F s and physiological characteristics of plant leaves in ontogeny) possible criteria for the estimation of general plant resistance of photosynthetic apparatus (PSA) to prolonged stress affects are proposed. One of these criteria is the presence or absence of a steady-state phase in the dynamics of Chl fluorescence ratio F p /F s (or R fd ) of plant leaves after they stop growing. We also propose to use the duration of the steady-state phase and variability of Chl fluorescence ratios R fd and F p /F s in this period for quantitative assessment of plant PSA resistance to prolonged stress during plant leaf ontogeny.Additional key words: leaf age; photosystems 1 and 2; radiation colour; specific leaf growth rate.

Uniaxially oriented commercial films of isotactic polypropylene were strained with ends keeping fixed and subjected to the heat treatment at temperatures from 50 to 2008C. The rigidity of annealed samples was characterized by the value of tangent modulus, E t , determined graphically at the initial portions of stress-strain curves. The structural changes in the samples were studied with the help of the IR and low-frequency Raman spectroscopies. The smallest E t values were obtained for the low-strained films, while the tangent moduli measured for highly strained samples exceeded the value for the original (untreated) film. The most prominent positive effect was achieved after annealing the samples at 908C.

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The deformational rigidity increases due to relaxation of stresses in oriented PP fibres. Elongation of PP fibres is accompanied by mechanical failure in all stages, which is a distinctive feature of deformation processes in these materials. Ordering of the structure of amorphous regions, manifested by an increase in the deformational rigidity of these fibres, is the result of stress relaxation in oriented PP fibres.Isotactic polypropylene is widely used for manufacturing industrial fibres, and the high strength at relatively low density should be noted above all [1][2][3]. The manufacturing process for polypropylene (PP) fibres is a multistage process, and the fibre undergoes temperature and deformation treatment in different stages [4,5]. To improve product quality and optimize industrial orientation of PP fibre, it is necessary to understand the structural processes that take place in fixing the fibre in the stitched state, i.e., as a result of stress relaxation [6].The relaxation processes that take place in stitched (loaded) fibres and yarns in many cases significantly alter their performance properties. There is currently no complete representation of the structural processes that cause such changes in the deformation properties of fibres and yarns. The change in the deformation characteristics of fibres in the stretched state must undoubtedly be taken into account for reliable prediction of the deformation properties of synthetic fibres and the articles made from them, which is not always done in practice.We established the character of the change in the rigidity of stretched film PP fibres during stress relaxation and elucidated the structural nature of these changes. We investigated PP film fibre (manufactured by Tverkhimvolokno OJSC) with a linear density of 130 tex and draw ratio of λ = 6, tensile strength of σ t = 580 MPa, and elongation at break of ε b = 22%.The deformation-strength properties in the stress relaxation and active stretching regime and the structural rearrangements that take place in stitched fibers and yarns were investigated. The studies of the mechanical properties of the fibres in active stretching (obtaining the stress-strain diagrams) and stress relaxation regimes were conducted on an Instron-1122. The tests in conditions of stopping stretching and then stretching again were performed on the same setup. IR spectroscopy was used to reveal the moleculardecomposition processes that take place in stretched oriented samples. The valence bond breaks in the macromolecules were recorded with this method based on the newly formed stable terminal groups formed as a result of decomposition. The data were obtained by frustrated total internal reflection on a Spectrum One Fourier IR spectrometer. The absorption bands at 1742 and 1650 cm -1 were considered the molecular-decomposition bands in the IR spectrum of PP [7]. Low-frequency Raman spectroscopy, which is sensitive to the regular segments of macromolecules of any type regardless of their localization both in amorphous and in crystalline ...