Iryna Tartachnyk

Effect of mechanically-simulated hail on photosynthesis, dark respiration and transpiration of apple leaves

Abstract Mechanical hail injury, as a source of abiotic stress, was examined using non-destructive in-situ gas exchange measurements and stomatal imprints of affected apple leaves. Apple leaves closed their stomata, as shown by stomatal imprints, within 3 min after induced damage. Water vapour efflux (evaporation) increased in the light, in spite of stomatal closure, by 16% from 3.9 to 4.5 mmol H2O m−2 s−1 for approximately 10 min after injury due to evaporation from ruptured tissue, with a subsequent decrease to 2.3 mmol H2O m−2 s−1 after 2.5 h. After 3 h, hail-damaged leaves re-opened their stomata to a certain extent and recovered in terms of transpiration. Photosynthesis decreased from 13.5 μmol CO2 m−2 s−1 to 9.1 μmol CO2 m−2 s−1 15 min after hail damage with a concomitant increase in intercellular CO2 from approximately 250 to 340 ppm CO2 and recovered to 73% of its control within 5 h. No difference in dark respiration was observed between control and hail-damaged leaves. Water loss, measured in the dark to separate stomatal transpiration from hail-induced (non-stomatal) evaporation, of apple leaves also increased in the dark after simulated hail damage within 10 min from 1 to 1.3 mmol H2O m−2 s−1 and then declined slowly from 1.3 to 0.9 mmol H2O m−2 s−1 within 1 h. It is concluded that approximately 0.27 mmol H2O m−2 s−1 or 20–27% of the recorded water loss after the hail damage was evaporation from ruptured tissue.

Detection of Heterodera schachtii infestation in sugar beet by means of laser-induced and pulse amplitude modulated chlorophyll fluorescence

Two glasshouse experiments with sugar beet cvs Penta and Macarena inoculated, respectively, with 0 or 1500 and 0, 500, 1000 or 1500 juveniles of Heterodera schachtii, were conducted to estimate the capability of laser-induced chlorophyll fluorescence (LIF) and pulse amplitude modulated (PAM) chlorophyll fluorescence techniques to detect H. schachtii infestation and to differentiate between infestation levels. Fluorescence and gas exchange parameters, nitrogen and chlorophyll content of sugar beet leaves were measured weekly after nematode inoculation. Sugar beet plants responded to H. schachtii infestation initially with a decrease in photosynthesis rate and later with a reduction in nitrogen uptake and chlorophyll concentration. At the early stages of nematode infestation, before visual symptoms were evident, infested sugar beet plants displayed increased fluorescence (F680, F740). Later stages of infection were accompanied by an increase in the F686/F740 ratio, ground fluorescence (Fo) and a decrease in photochemical efficiency (Fv/Fm) induced by degradation of leaf chlorophyll. Sugar beet plants infested with 500, 1000 or 1500 juveniles per 100 cm3 of soil did not differ either in their nitrogen and chlorophyll content or in photosynthesis and transpiration rate. The linear discrimination analysis based on the combination of PAM and LIF parameters resulted in 100% correct classification of control plants and high classification rates (60-100%) of the infested treatments on all the sampling dates. Whether the fluorescence technique will differentiate nematode densities under field conditions needs further study.

Temperature, evapotranspiration and primary photochemical responses of apple leaves to hail

The objective of this work was to examine immediate physiological plant responses to hail and subsequent recovery in terms of evapotranspiration, leaf temperature and primary photochemical processes using apple as a model crop. Thermal emission pictures were taken in darkness to avoid interference from stomatal movements; temperature gradients were identified in concentric rings around sites of hail injury, with a distinct drop in temperature of up to 2.3 degrees C in the center immediately after the induced hail injury. This was due to enhanced evapotranspiration from the injured tissue. Six to twelve minutes after hail injury, the initial decrease in leaf temperature partially reversed. Chlorophyll fluorescence kinetics of light-adapted leaves showed a dramatic decrease in effective photosynthetic electron transport rate (ETR), from 20.5 to 9.0 micromol electron m(-2)s(-1) within 5 min from hail injury, and a rapid recovery to 14.1 micromol electron m(-2)s(-1) within the next 5 min. After 7h, ETR partially recovered to 17.4 micromol electron m(-2)s(-1). An initial drop in non-photochemical efficiency (NPQ) from 1.07 to 0.90 units within 5 min after hail injury was followed by a sharp increase to 1.67 units after another 5 min. During the next hour, NPQ gradually decreased to the initial level. This indicates increased thermal dissipation in photosystem II (PS II) as a protective mechanism against incident excessive energy in the leaves with closed stomata for 1h after hail injury. In contrast to the fluorescence kinetics of light-adapted leaves, maximum quantum yield Fv/Fm of PSII in the dark-adapted state remained unchanged at 0.79-0.81 relative units for the first 5 min after hail injury. Thereafter, Fv/Fm slowly declined to 0.75 within 1h, and to a trough of 0.73 at 3h. Seven hours after hail injury, Fv/Fm values were at 0.76, indicating partial recovery of PS II efficiency. The discrepancy in the dynamics of ETR and Fv/Fm responses may be explained by the formation of alternative electron sinks such as reactive oxygen species, particularly superoxides, which withdraw electrons from the photosynthetic transport, resulting in apparently higher values of calculated ETR.