Maize
Genetics Cooperation Newsletter 80. 2006.
Institute of Plant Physiology and Biochemistry
Glycolysis, as the best studied respiration enzyme system, was selected for the present investigation of metabolic regulation mechanisms in the cell at lower temperatures. Potential activity of three major enzymes of glycolysis was identified: hexokinase (HK), pyruvate kinase (PK) and phosphofructokinase (PFK).
Growing cells of two maize varieties with contrasting cold resistance were used for the investigation. 48-hour-old seedlings of Omskaya 2 resistant variety and Uzbekskaya tooth-like non-resistant variety with zones marked 0-2 and 2-4 mm from the root tip were placed at temperatures of 270C and 100C (MNL 76:35-36, 2002). Cells of the 2-4 mm zone terminated extension at 270C in 6 and 8 hours, and at 100C in 48 and 96 hours in Omskaya 2 and Uzbekskaya tooth-like, respectively. There were also cells identified, which started extension within the time specified.
At 270C, extension of maize seedling root cells of both varieties was accompanied by an increase of activity of all glycolytic enzymes under study. Nevertheless, the proportion of key enzymes in these varieties differed (Table 1). In the cells of the Omskaya 2 variety PK was more active than HK, with PFK being the least active enzyme. In the cells of the Uzbekskaya tooth-like variety starting extension, the following proportion was observed: HK>PK>PFK; in the cells which have completed extension the propertion PK>HK>PFK was observed. Increase of glycolytic element activity in the extending cells is associated with new formation of enzyme proteins, which is faster than their disintegration.
Table 1. Activity of key glycolytic enzymes in root cells of maize
seedlings under low temperature, nmol of substrate/min per 106
cells.
|
Variety |
Root growth zones |
HK |
PK |
PFK |
|||
|
270C control |
100C test |
270C control |
100C test |
270C control |
100C test |
||
|
Omskaya
2 |
Extension start |
25.8�1.0 |
11.8�0.5 |
36.4�1.9 |
21.1�0.9 |
16.5�0.5 |
5.3�0.1 |
|
Extension termination |
31.0�2.2 |
33.4�2.3 |
44.0�2.8 |
46.4�2.8 |
30.0�1.9 |
30.2�2.2 |
|
|
Uzbekskaya
tooth-like |
Extension start |
27.8�2.3 |
48.6�3.2 |
16.4�0.7 |
47.6�3.1 |
12.2�0.6 |
18.8�0.9 |
|
Extension termination |
35.4�2.5 |
61.4�4.5 |
98.8�7.1 |
104.8�7.9 |
46.5�3.1 |
28.3�1.8 |
|
At 100C, in cells of the Omskaya 2 variety that had started extension, the level of potential activity of glycolytic enzymes decreased significantly. The cells that had finished extension demonstrated the same activity of enzymes in control and test.
The non-resistant Uzbekskaya tooth-like variety demonstrated a reverse regularity: cell transfer to extension at 100C was accompanied by the activity of the enzymes studied.
Thus, growth of maize root cells at low temperature is associated with differentiated effects in the activity of key glycolytic kinases depending on the cell growth stage and the resistance of the variety: root tip cells of the cold-resistant variety are characterized by the reduction of the speed of glucose destruction along the glycolytic pathway, with the traffic ability of the hexomonophosphate pathway increasing as shown before (Rodchenko, Maricheva, Akimova, 1988). This provides the cell with substrates for multiple syntheses and increases metabolism resistance to stress impact. Extending cells of the non-resistant variety demonstrate a high intensity of exchange, which apparently exhausts the energy resources of the cell. Further cooling kills the plant.
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