Maize
Genetics Cooperation Newsletter 80. 2006.
Organic acids, their formation and transformation play an important role in plant life cycles. Organic acids grow in number in plant cells under stress factors, including low temperatures. Accumulation of organic acids appears in the course of cell transfer from division to extension and differentiation.
We made an attempt to reveal probable differences in the content of organic acids in low temperature resistant plant varieties and non-resistant ones, and to show a connection between these differences and a change in speed of seedling root cell growth under hypothermia.
Organic acids were identified in the growth zones (beginning and end of cell extension) of maize seedlings of the resistant variety Omskaya 2 and the non-resistant variety Uzbekskaya tooth-like. The samples were placed in liquid nitrogen, then extracted by ethanol. Alcohol was evaporated, water fraction was cleaned by chloroform and sequentially passed through the columns with Daueks 50 and Daueks 1. Elution was conducted by 16N formic acid. Eluate was dried in a lyophilic kiln and prepared for gas liquid chromatography (GLC).
GLC analysis demonstrated peaks of malonate, succinate, fumarate, citrate, and malate. Peaks on chromatograms from growth zones of seedling roots of the Uzbekskaya tooth-like variety grown at 100C were higher than those of seedlings grown at 270C. Omskaya 2 manifested no increase of organic acid content.
Content of dicarbonate acids (malic and oxaloacetic) was determined in the growth zones of maize seedling roots based on 1 average cell (Table 1).
Table 1. Impact of lower temperature on the content of malic and
oxaloacetic acids in the cells of maize seedling roots.
|
Root growth zones |
Variant |
Content, g х 10-12
per cell |
|
|
|
|
malate |
oxaloacetate |
|
Omskaya 2 |
|||
|
Extension start |
Control 270C, 6 h |
8.84�0.51 |
0.89�0.06 |
|
Test 100C, 48 h |
9.75�0.62 |
0.90�0.07 |
|
|
Extension termination |
Control 270C, 6 h |
8.38�0.49 |
1.16�0.08 |
|
Test 100C, 48 h |
8.65�0.50 |
1.48�0.09 |
|
|
Uzbekskaya tooth-like |
|||
|
Extension start |
Control 270C, 8 h |
18.63�0.09 |
4.99�0.02 |
|
Test 100C, 96 h |
30.80�1.91 |
5.97�0.03 |
|
|
Extension termination |
Control 270C, 8 h |
45.47�2.52 |
2.11�0.01 |
|
Test 100C, 96 h |
48.48�3.30 |
2.50�0.01 |
|
In cells of the non-resistant Uzbekskaya tooth-like variety that start extension at 100C, malate content is 1.7 times higher than the metabolite level in the cells extending at 270C. Content of oxaloacetate in the cells of cooled roots is insignificant. Temperature decrease did not considerably affect the number of these metabolites in the resistant variety.
Therefore, increase of organic acid content under hypothermia takes place only in cold-sensitive maize varieties, and is most pronounced in the cells that start visible growth at 100C. The latter presumably contributes to the growth of these cells� volume, which was described earlier (MNL 79:17, 2005), as well as to the decrease of cytoplasm pH, one of the plant responses to temperature change.
_________________________________________________
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