engleski

Monitoring standard deviations of chlorophyll a fluorescence parameter Fv/Fm of JIP-test during increasing water deficit

Chlorophyll fluorescence (ChlF) parameters of JIP-test are considered as early indicators of stress in photosynthetic tissues. The JIP-test is particularly useful for crop plants when applied in vivo under mild drought stress under control and field conditions. However, due to increasing intrinsic photosynthetic heterogeneity affected by increasing drought stress severity, the usefulness of the classical ChlF parameters is in question. Objective of this study was to monitor changes in values of the maximum efficiency of photosystem II (Fv/Fm) parameter and its corresponding standard deviations during increasing water deficit in barley measured in 25 replications and conducted in three independent pot experiments. After ten days of growing, drought stress was induced by withholding water and monitored for the next ten days. During the 10-days interval, Fv/Fm values decreased from 0.80 to 0.48, 0.53 and 0.54 in three experiments, respectively. However, standard deviations of Fv/Fm values increased successively being from 0.005 on the day 1 to 0.18, 0.19 and 0.26 on the day 10 in the respective three experiments. The consistent sharp increase of the corresponding standard deviation of about 0.02 occurred at the Fv/Fm value of 0.75 indicating considerable increasing of photosynthetic heterogeneity. Therefore, we propose a threshold Fv/Fm level of 0.75 that would reflect a point at which the spatio-temporal heterogeneity of Fv/Fm should be considered since it represents a boundary value for fully functional photosystem II. In our studies in the field environments in maize though, we found that even under moderate drought stress, Fv/Fm values were rarely lower than 0.75 with small standard deviations corroborating the use of classical ChlF parameters.

barley ; Chlorophyll a fluorescence ; Fv/Fm values ; JIP-test ; maize ; standard deviation

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