Abstract
Possible use of integral characteristics of slow stage of chlorophyll fluorescence induction (CFI) for monitoring of physiological state of plants in phytocenoses was studied in the leaves of wheat Triticum aestivum L. and radish Raphanus sativus var. radicula Pers., cv. Virovskii belyi, grown in artificial-light culture. Investigation concerned the behavior of T-0.5 (half-time of fluorescence intensity decrease from its peak to a steady-state level), R-fd (fluorescence decrease ratio also known as vitality index), parameter (V) over bar (max) (maximum possible average rate of induction transient), and (alpha) over bar (average efficiency of PSA in the induction period) during leaf ontogenesis. Plant material was the discs cut from uniformly illuminated wheat leaves of different age from the top (sixth) storey of plants and the disks from the second (in the order of emergence) true leaves of radish at the age from 3 to 24 days. The plants were grown in controlled-climate chambers in hydroponic culture on claydite at irradiance of 100 W/m(2) of photosynthetically active radiation (PAR). CFI curves were recorded using a single-beam unit. Values of parameter T-0.5 slightly changed during leaves' ontogenesis up to the time of senescence (the age of 26 days). Relative changes in the values of CFI parameters (Delta rel., %) at the age from 2 to 24 days were 28% for (alpha) over bar and 30% for T-0.5. For (V) over bar (max) and R-fd, the values were 67 and 70%, respectively. Upon more advanced ageing and comparison of parameters for 24- and 26-day-old leaves, more pronounced changes were observed for T-0.5 (by 37.6%) and (V) over bar (max )(by 36.0%) and less pronounced for (alpha) over bar (by 23.0%) and R-fd (by 13.0%). Thus, the pattern of parameter T-0.5 behavior observed in the course of wheat leaves' ontogenesis distinguished it from other fluorescence parameters of CFI slow stage (R-fd, (alpha) over bar, and (V) over bar (max)); this gives grounds for a potential use of T-0.5 as one of the simplest integral indicators of physiological state and pathophysiological (irreversible) changes occurring in plant leaves within a wide age interval and upon senescence. Unambiguous interpretation of the data obtained by means of parameter T-0.5 under stress conditions for estimation of irreversibility of the observed changes in PSA requires more detailed investigations.
NSTL
Pleiades Publishing Inc