## 3 Results
### PAS-Reactive Elements and Tissue Structure Analysis after Cd Treatment  
The localisation and amount of the PAS-reactive elements were analysed during the experiment (Figures 2-6). The PAS reaction resulted in purple staining of starch and the cell wall polysaccharides. Figure 2 shows the cross-sections of the leaves of control, 50, and 200 \(\upmu\)M Cd-treated plants 7 days after treatment (Figure 2A-C) and the cross-sections of young leaves (Figure 2D-F) and old leaves (Figure 2G-I) 28 days after treatment. The number of PAS-positive deposits was highest in the leaves 28 days after Cd treatment (Figure 2D-I) followed by those after 7 days of treatment (Figure 2A-C). Figure 1: Cd accumulation in roots (**A**) and shoots (**B**), translocation factor, and tolerance index (**C**) of Cd after 28 days in _P. sativum_ of the plants treated with Cd (10, 50, 100 and 200 \(\upmu\)M CdSO\({}_{4}\)). Each value is the mean of three replicates \(\pm\) SD. Different letters represent significant differences (\(p<0.05\)). Figure 2: Cross-sections of the leaves of control (**A1,A2,D1,D2,G1,G2**), 50 (**B1,B2,E1,E2,H1,H2**) and 200 \(\upmu\)M CdS\({}_{4}\) (**C1,C2,F1,F2,I1,I2**) treated _P. sativum_ plants. Images show leaves 7 days after Cd-treatment (**A1,A2,B1,B2,C1,C2**), young leaves (**D1,D2,E1,E2,F1,F2**) and older leaves 28 days after Cd treatment. The upper and lower parts of the leaf cross-section are denoted by “1” and “2”, respectively. The purple colour shows the PAS-reactive elements, arrows indicate starch grains. The dotted arrows show plasmolysis. Abbreviations: st—stomata, pm—palisade mesophyll, sm—spongy mesophyll, vb—vascular bundle, we—upper epidermis, le—lower epidermis. Scale bar 10 \(\upmu\)m.  
The distribution of the starch grains in the leaves and stems of _P. sativum_ during the experiment was depicted in Table 1. Many starch grains were observed in the young leaves (Figure 2D,E) but not in the old leaves of the control plants and those treated with 50 \(\upmu\)M Cd (Figure 2G,H). In contrast to this, the number of starch grains in the leaf mesophyll of 200 \(\upmu\)M Cd-treated plants was higher in old leaves than in young ones (Figure 2L,F, accordingly). The distribution scheme of PAS-positive cell wall polysaccharides was similar. Moreover, excessive plasmolysis in the cells of the young leaves (Figure 2(F1)--dotted arrows) and alteration of the phloem in the old leaves of 200 \(\upmu\)M Cd-treated plants (Figures 2I and 3--arrows, dotted arrows) compared to control plants were observed. The cell walls of both the sieve tubes (dotted arrows) and companion cells (arrows) of these leaves were folded when compared to the other analysed variants of the experiment (Figure 3). \begin{table}
\begin{tabular}{c c c c c c c} \hline  & & \multicolumn{2}{c}{**LEAVES**} & \multicolumn{2}{c}{**STEM**} \\ \cline{2-7}  & 0 \(\upmu\)M CdSO\({}_{4}\) & 50 \(\upmu\)M & 200 \(\upmu\)M & 0 \(\upmu\)M CdSO\({}_{4}\) & 50 \(\upmu\)M & 200 \(\upmu\)M \\  & & CdSO\({}_{4}\) & CdSO\({}_{4}\) & CdSO\({}_{4}\) & CdSO\({}_{4}\) & CdSO\({}_{4}\) \\ \hline \multicolumn{7}{c}{1 week after} \\ \multicolumn{7}{c}{Cd-treatment} & + & + & + & + & + & – \\ \hline \multicolumn{7}{c}{4 weeks after} \\ \multicolumn{7}{c}{Cd-treatment} & Young leaves & + & + & – & & \\ \cline{2-7} \multicolumn{7}{c}{Cd-treatment} & Old leaves & – & – & + & + \\ \hline \end{tabular} \({}^{\ast}\)+\({}^{\ast}\) starch grains: present, \({}^{\ast}\)–\({}^{\ast}\) starch grains: low number or absent.  
\end{table} 
Table 1: Distribution of starch grains in the tissues of _P. sativum_. Figure 3: Cross-sections of the leaves of control (**A**,**D**) 50 (**B**,**E**) and 200 \(\upmu\)M CdSO\({}_{4}\) (**C**,**F**)-treated _P. sativum_ plants. Images show a vascular bundle structure (arrow—companion cell, dotted arrow—sieve tube). Abbreviations: x—xylem, ph—phloem, pm—palisade mesophyll, sm—spongy mesophyll. Scale bar 10 \(\upmu\)m.  
After 7 days of 50 and 200 uM Cd treatment, the cells of the stem parenchyma were damaged (Figure 4B,C--dashed arrows).