## 3 Results and Discussion
### Changes in OJIP Transients after Drought and Recovery  
Prompt Chl fluorescence transients (Figure 1) between drought-stressed and -recovered _Brassica_ crops revealed obvious \(\Delta\)V\({}_{\text{OP}}\) differences among varieties. Chinese cabbage showed a positive \(\Delta\)V\({}_{\text{OP}}\) amplitude after drought. Upon re-watering, the amplitude turned negative, with noticeable J and I bands (Figure 1a). White cabbage showed positive amplitudes (Figure 1f) after drought and recovery, with higher amplitudes observed in drought-stressed seedlings. In kale, both transients were negative (Figure 1k), with more pronounced curves observed after recovery. The OJ phase reflects the reduction in Q\({}_{\text{A}}\) and the partial reoxidation of Q\({}_{\text{A}}\)\({}^{-}\)[64]. Positive \(\Delta\)V\({}_{\text{OP}}\) amplitudes are usually reported for various species, such as maize [38], barley [34], sorghum [33], perennial ryegrass [65], and linden trees [37], exposed to drought, and they are often reported in genotypes/cultivars described as sensitive ones. The \(\Delta\)V\({}_{\text{OP}}\) curve reveals additional inflections which correspond to L, K, H, and G bands that describe specific events of primary photochemistry [66]. The L band (\(\Delta\)V\({}_{\text{OK}}\)) was shown to be a reliable parameter describing the energetic connectivity between photosynthetic units [61, 67], while the K band was recognized as a great indicator of stress in plants, especially drought [33, 34, 36, 38, 50, 63, 68, 69]. All three _Brassica_ crops revealed similar results for both L and K bands. In Chinese cabbage, there were positive band amplitudes (Figure 1b,c), while after recovery, the amplitude was similar to the control one. White cabbage showed positive amplitudes (Figure 1g,h), while kale revealed negative amplitudes (Figure 1l,m) of L and K bands in both drought-stressed and re-watered seedlings. Positive L bands were reported frequently in drought-stressed plants [34, 38, 50, 68], and they are a sign of low energetic connectivity and lower system stability [61]. Connectivity and PSII stability could be disturbed in water-deprived plants due to the degradation of PSII proteins, causing the reorganization of and reduction in thylakoid membranes' stability [70, 71]. The negative L band is associated with the efficient utilization of excitation energy, since PSII units are more connected, forming a better stability of the system [61]. The positive K band is connected with decoupling the oxygen-evolving complex (OEC) and/or an increased size of functional antennae [37, 61], while a negative amplitude usually indicates tolerance to stressful conditions of the investigated genotype [33, 34, 50] as well as increased adaptability [72], suggesting the tolerance of kale seedlings to drought. Drought-stressed Chinese cabbage showed a higher K band amplitude compared to white cabbage. However, white cabbage showed that the inactivation of OEC was severe, and it could not recover for running functional reactions. Similar behavior was reported for the sensitive barley genotype after re-watering [33, 50]. The negative K band amplitude in Chinese cabbage after recovery suggested that the accessibility of proline [9], as an alternative electron donor to OEC, replaced a sufficient number of electrons to drive efficient photosynthetic reactions. The H band is related to the reduction in and oxidation of the plastoquinone (PQ) pool, and it is used to describe multiple-turnover events [65, 73, 74, 75]. Slower reoxidation causes an increased accumulation of reduced electron carriers that form a positive H band [67, 76]. In Chinese cabbage (Figure 1d) as well as in kale (Figure 1h), drought stress induced the appearance of positive H band inflection. Upon recovery, the H band revealed a higher positive amplitude compared to that in stressed Chinese cabbage, while in kale, the recovery curve was more similar to the control, with almost no visible inflections.