Direct CAT Effects on Root Growth and Morphology

In the Arabidopsis model species, neither germination rate nor germination time was changed by the presence of CAT (data not shown). Conversely, the fresh weight of the maize plants after 14 days of exposure to CAT was reduced, as compared to untreated plants (Table 10.2). Such reduction was considerable for both roots and shoots, being larger in the former, and directly correlated to CAT concentration in the medium (Fig. 10.18). At the larger CAT concentrations (9 and 27 mM), the shoot/root ratio was significantly altered in comparison to control

Table 10.2 Effect of varying concentrations of the CAT iron-porphyrin (mM) on fresh weight (FW, mg) allocation in Arabidopsis seedlings

CAT

Whole plant FW

Leaf FW (1)

Root FW (2)

(1)/(2)

0

18.44 ± 1.16a

13.24 ± 0.68a

5.20 ± 0.58a

2.71 ± 0.26a

3

11.07 ± 1.12b

7.41 ± 0.69b

3.66 ± 0.64b

2.43 ± 0.30a

9

5.74 ± 0.68c

4.43 ± 0.53c

1.31 ± 0.19c

3.73 ± 0.44b

27

2.69 ± 0.38d

2.00 ± 0.25d

0.69 ± 0.14d

3.37 ± 0.34b

Different letters denote statistically significant differences (p < 0.05) respect to control

Different letters denote statistically significant differences (p < 0.05) respect to control

Fig. 10.18 Arabidopsis plants exposed for 14 days to different concentrations of CAT iron-porphyrin

OfiM 3 yjT.1 9 pM 27 jAfl

Fig. 10.18 Arabidopsis plants exposed for 14 days to different concentrations of CAT iron-porphyrin

(Table 10.2), thus suggesting a biomass redistribution, following probable changes in internal translocation and availability of nutrients taken up by the roots.

The analysis of the root morphology showed a negative CAT effect on the total root length (primary + laterals) after 8 days of growth, at all concentrations (Fig.10.19). In particular, treatments with 3 and 9 p.M CAT caused a 17% and a 75% root length inhibition, respectively, while at a CAT concentration of 27 p.M the root length reduction reached up to 85%, as compared to control. The length of the primary root was not affected by 3 p.M CAT, whereas it decreased by 50% in plants

Fig. 10.19 Total root length in Arabidopsis plants of Fig. 10.18

Days

Fig. 10.19 Total root length in Arabidopsis plants of Fig. 10.18

Days

Fig. 10.20 Primary root length in Arabidopsis plants of Fig. 10.18

Days

Fig. 10.20 Primary root length in Arabidopsis plants of Fig. 10.18

grown with 9 p.M CAT and its growth was totally arrested after 14 days with 27 p.M CAT in the medium (Fig. 10.20).

It was however the growth of lateral roots, rather than primary ones, to be most inhibited by CAT (see Fig. 10.20 versus Fig. 10.21). However, despite such growth inhibition, 9 and 27 p.M CAT caused an anticipated emergence of lateral roots, which became already visible after 5 days from germination, whereas 8 days were required for lateral root emergence in control plants and for those exposed to only 3 mM CAT (data not shown).

Days

Fig. 10.21 Length of lateral roots in Arabidopsis plants of Fig. 10.18

Days

Fig. 10.21 Length of lateral roots in Arabidopsis plants of Fig. 10.18

Days

Fig. 10.22 Number of lateral roots in Arabidopsis plants of Fig. 10.18

Days

Fig. 10.22 Number of lateral roots in Arabidopsis plants of Fig. 10.18

An inhibitory action of CAT was also observed on the number of lateral roots, though less substantial than on their length (Fig. 10.22). This affected the root density, i.e., the ratio of the number of lateral roots over the length of primary roots, that appeared to be larger in plants treated with 9 and 27 p.M CAT than in control (Fig. 10.23).

1412-

Days

Fig. 10.23 Root density (ratio of number of lateral roots over length of primary root) in Arabidopsis plants of Fig. 10.18

Days

Fig. 10.23 Root density (ratio of number of lateral roots over length of primary root) in Arabidopsis plants of Fig. 10.18

F-IF mm

IK t

%KA

»»■4M

^^^^^ »te

MMi

C»n«T

■ pM

M.<

N>I>M .m

HCMJUH

Fig. 10.24 Primary root of Arabidopsis after 8 days of growth at different concentrations of CAT iron-porphyrin

Table 10.3 Root hairs development in Arabidopsis seedlings as affected by varying CAT iron-porphyrin concentrations (|iM)

CAT

Elongation zone

Hairs number

Hairs length (mm)

1°mm

2°mm

3°mm

1 ° mm

2°mm

3°mm

0

1.76 ± 0.64a

0

15 ± 1.29

14.50 ± 2.33

0

40.43 ± 3.09

40.43 ± 3.09

3

1.24 ± 0.08c

0

19.67 ± 4.37

21.33 ± 2.03

0

50.95 ± 5.35

80.30 ± 10.04

9

1.61 ± 0.31a

0

5 ± 2.89

5.67 ± 0.33

0

78.65 ± 3.80

103.55 ± 6.16

Different letters denote statistically significant differences (p < 0.05) respect to control

Different letters denote statistically significant differences (p < 0.05) respect to control i

Fig. 10.25 Rosettes of Arabidopsis plants exposed to varying concentrations of CAT iron-porphyrin for 14 days

Microscopic analysis (Fig. 10.24 and Table 10.3) revealed that, even at 3 p.M CAT, the elongation zone between the primary root apex and the point of emerging root hairs was significantly shorter, and root hairs were more numerous and longer than in control. Conversely, exposure to 9 p.M CAT caused a reduction in the number of root hairs, but they were longer than for both control plants and those treated with 3 mM CAT. After 8 days in the presence of 27 p.M CAT, the development of the primary root was so strongly inhibited that evaluation of root hairs was not feasible. All together, the above results suggest that comparatively low concentrations of CAT affect the pattern of root hair growth, rather than arresting their growth.

Moreover, we found that CAT induced changes in the root architecture of Arabidopsis seedlings, at all tested concentrations. This is considered a general adaptive plants response vis-a-vis the changes occurring in their growth environment. The formation of lateral roots from primary root increases the plant capacity for soil exploration, and root hairs are directly involved in the uptake of water and nutrients. Both processes are influenced by several factors and this dynamic root development (plasticity) represents the main survival strategy for non-motile organisms such as plants.

However, a negative CAT effect was observed on the shoot development of A. thaliana seedlings (Fig. 10.25). This may have been either the consequence of inhibitory effects on the root system or a specific CAT effect on the aerial part, following possible absorption and translocation of the iron-porphyrin molecule. With 9 and 27 mM CAT, the number of leaves was reduced by 58 and 51%, respectively, as compared to control. The rosette diameter was lowered by 35% with 3 mM CAT and by 70-80% at larger concentrations. This indicates that CAT

Table 10.4 Rosette morphology in Arabidopsis seedlings as affected by varying CAT iron-porphyrin concentrations (mM)

CAT

Mean number of leaves in each rosette

Mean rosette diameter (mm)

0

7.55 ± 0.17a

20.77 ± 0.74a

3

6.91 ± 0.21a

13.27 ± 0.75b

9

4.40 ± 0.27b

7.90 ± 0.43c

27

3.82 ± 0.12b

6.73 ± 0.38d

Different letters denote statistically significant differences (p < 0.05) respect to control

Different letters denote statistically significant differences (p < 0.05) respect to control mainly affected leaf extension, rather than leaf number, as suggested by values of the rosette diameter reported in Table 10.4.

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment