Chlorophyll fluorescence as an indicator of age-dependent changes in photosynthetic apparatus of wheat leaves

Wheat (Triticum sativus L.) seedlings of various ages (2- to 16-day-old plants) were used to study age-dependent changes in the chlorophyll fluorescence induction (CFI) at various light intensities during flu- orescence measurements. Plants were raised in a growth chamber using hydroponics with expanded clay, controlled environmental conditions, and 690 A mu mol/(m(2) s) photon flux density (PFD) of photosynthetically active radiation (PAR). Parameters of CFI were determined under actinic PFD of 380, 580, 820, and 1340 A mu mol/(m(2) s) PAR. The fifth leaf from the stem base, exposed to uniform lighting, was sampled for measurements. This leaf emerged at the plant age of 16 days. Based on fluorescence data, we calculated the maximal photochemical quantum yield of photosystem II (F (v)/F (m)), the effective photochemical quantum yield of PSII (Yield), parameters of photochemical (qP) and non-photochemical (qN and NPQ) quenching of chlorophyll fluorescence, the F (p)/F (t) ratio, and the "vitality index" (fluorescence decrease ratio, R (fd)). At moderate actinic PFD, applied commonly in PAM fluorometers (about 380 A mu mol/(m(2) s)), age-dependent changes in NPQ, F (p)/F (t), and R (fd) were observed. Analysis of CFI parameters in wheat leaves of different ages at PFD increasing from 380 to 820 A mu mol/(m(2) s) revealed that R (fd), NPQ, and qN are the most sensitive markers of the leaf age among all parameters tested. These suitable indicators can be used for rapid assessment of the leaf age.