IRKUTSK, RUSSIA
Institute of Plant Physiology and Biochemistry

Relationship between the levels of free l-phenylalanine and l-tyrosine and phenol compounds in the maize root cells at lowered temperatures

— Makarova, LE; Akimova, GP; Luzova, GB; Sobenin, AM; Sokolova, MG

Low temperature was found to affect the synthesis of phenolic compounds (PC), increasing or decreasing their content in root cells depending on the phase of their growth and on a variety’s resistance to low temperatures (MNL 78:18, 2004). The present work sums up more complete data on the phenolic compounds content in the root cells of ethyolized seedlings of two maize varieties differing in resistance: a highly resistant variety (Omskaya 2) and a non-resistant variety (Uzbekskaya tooth-like).

The present investigation attempts to establish a link between the degree of PC accumulation and the level of free amino-acids as direct predecessors of phenol-carbonic acids (PCA) in the cells subjected to the impact of different temperatures: optimal (27°C) and low (10°C).

Maize typically uses l-phenylalanine and l-tyrosine as PCA predecessors (Havir et al., 1971). That is why we determined the content of both amino-acids (in free form) in the cells.

Amino-acids were extracted by water from the plant homogenate 3–4 times. Water extracts were collected and centrifuged. Over-precipitate liquid was subjected to thermal treatment at 80°C for 30 minutes. The solutions were left overnight at 4°C and then, after centrifuging (8,000–10,000 rotations per minute) and separating from the sediment, were steamed at low pressure down to the volume of 2.0–2.5 ml. 4-volume-chloroform was added to the solutions, and the containers were shaken and left overnight in the dividing funnels. The water layer containing amino-acids was separated and steamed to dry at low pressure.

An amino-acid analysis was conducted on the automatic analyzer T-339 (Czechoslovakia). The amount of amino acids was calculated per average cell of the growth zone: meristem (M) and those starting and terminating the extension (BEx and EEx). Contents of PCA and PCA-ethers were investigated by chromatographic and spectroscopic methods.

Correlation ratios were calculated for comparison of the content parameters of the amino acids under study and PC in the root cells (Tables 1 and 2). For l-phenylalanine, the amounts were 0.982 and 0.942; for l-tyrosine, 0.991 and 0.979. The first value is for the Omskaya 2 variety, the second one for the Uzbekskaya tooth-like variety.

The presented values of the ratios point to the high degree of connection between PC accumulation and their immediate predecessors (l-phenylalanine and 1-tyrosine), despite the fact that meristematic cells at low temperature show a certain discrepancy between the trends of amino acids and PC accumulation (Tables 1 and 2).

The acquired data may be treated as a fact confirming a direct link between the content of free amino acids as immediate predecessors of PC, and PC content in the plant cells. The data prove the statement of U. Margna and his colleagues (1974, 1977) concerning regulation of PC accumulation in the plant cells by the level of substrates l-phenyl-ammonia-lyase (PAL).

Table 1. Content of free l-phenylalanine and l-tyrosine in the maize root cells at 27°C and 10°C (× 10-6 nM/cell)

* M: Meristem
 BEx: actively-extending cells
 EEx: the cells which terminated the extension

Table 2. Temperature impact on PC content in the maize root cells (× 10-6 μg/cell)

Total PC content includes data on the content of free and combined phenol-carbonic acids and complicated complexes, primarily consisting of aromatic compounds and lignin. The growth zones are marked in the same way as in Table 1.

Return to the MNL Volume 79 Index
Return to the index of Maize Newsletters
Return to the Maize Genome Database Page