Effect of abscisic acid on the resistance of cucumber seedlings to combined exposure to high temperature and chloride

The effect of abscisic acid (ABA) on heat and salt resistance of cucumber seedlings exposed (consecutively or simultaneously) to high temperature and chloride was studied. Exogenous ABA proved to additionally increase the heat and salt resistance after both consecutive and simultaneous exposure of cucumber seedlings to 38∞N and NaCl. The involvement of this hormone in the common (nonspecific) mechanisms increasing plant resistance to the studied environmental factors is concluded.     

The effect of α-factor on the rate of cell-cycle initiation in Saccharomyces cerevisiae : α-Factor modulates transition probability in yeast

The rate of cell-cycle initiation was studied in a-cells of S. cerevisiae in the presence of the synthetic analogue of α-factor [N-Trp, Arg⁷]-α-factor (TA-αF). It was shown that TA-αF lowers the rate constant of cell-cycle initiation (or transition probability) for each separate cell. It was concluded on the basis of these results that the term ‘arrest’ in G1 by α-factor should be interpreted in a quantitative sense as the decrease in the probability of the emergence from ‘start’ per unit time and not as being equivalent to an ‘all-or-none’ response. The dependence of the rate constant of the cell-cycle initiation on the concentration of TA-αF can be described by the Hill equation where n = 1.01 + 0.05 and K = 14.5 ± 2.5 nM (±S.E.). It is demonstrated that after transfer of cells into the medium with a higher or a lower concentration of TA-αF, the rate constant of cell-cycle initiation changes abruptly from one value to another after a lag-period of 30 and 40 min respectively. This suggests a multistep mechanism of action for α-factor. The difference in the lag-periods allows us to suggest that α-factor exerts its action by two independent pathways. Since the Hill coefficient is practically equal to unit, no cooperative interactions are likely to be involved at least in one of these pathways. The inhibition of cell-cycle initiation can be used as a more adequate and sensitive test for biological activity of α-factor as compared to morphological measurements.     

Structural and functional reorganization of the photosynthetic apparatus in adaptation to cold of wheat plants

In seedlings of a cold-resistant wheat variety, the dynamics was studied of the main structural-functional parameters of the photosynthetic apparatus (PSA) and of cold resistance of leaf cells in low-temperature plant adaptation. It has been established that a complex of structural-functional PSA changes takes place in seedling leaves under the influence of cold. As a result, as early as in the first hours of hardening, the formation of chloroplasts begins to occur in mesophyll cells of larger sizes and with a thylakoid system of the “sun type.” Owing to structural and functional readjustment (a change of content of pigments, stabilization of pigment-protein complexes, and enhancement of nonphotochemical quenching of excess energy) in the process of cold adaptation, the rate of photosynthesis stabilizes. It is suggested that the observed structural-functional PSA rearrangement is a necessary condition for formation of increased cold resistance of leaf cells; this, alongside with other physiological-biochemical changes occurring in parallel in cells and tissues of the plants, provides their survival under conditions of low temperatures.     

Continuous wavelet analysis: A new method for studying nonstationary oscillations in the cardiac rhythm

Continuous wavelet analysis can be used to quantitatively describe local changes in cardiac rhythm oscillations. The following new indices of the wave structure of the cardiac rhythm were suggested: the rate of changes in the frequency of the oscillatory component within a given time interval, the lengths of the fading periods for specific frequency oscillations detected on the cardiointervalogram, and the changes in the instantaneous frequency-amplitude ratios during the observation period. These indices allow a deeper insight into sympathetic and parasympathetic oscillators that affect the cardiac rhythm.