IRKUTSK, RUSSIA
Institute of Plant Physiology and Biochemistry

Differentiation process of maize root cells at reduced temperature

--Akimova, GP, Sokolova, MG, Makarova LE, Nechaeva, LV

The present work was aimed at the investigation of cooling impact on the speed of maize root cell differentiation based on biochemical indices. We took into account differences between varieties, which play an important role in the plants’ response to reduced temperature (MNL 76:35–36, 2002).

The tests were conducted on 48-hour-old seedlings. Maize varieties under investigation were characterized by different growth reaction to temperature decrease (MNL 71:93,1997); in particular, the highly resistant variety (Omskaya 2) has demonstrated stationary growth at intense temperature decrease, that is, the processes of cell formation and the beginning of their extension were equally slowed down. The non-resistant variety (Uzbekskaya tooth-like) demonstrates deregulation of these processes.

A temperature of 10 °C was proven to slow down the accumulation of basic components of cell capsules (pectins, hemicelluloses, cellulose, lignin). At the same time the resistant variety (Omskaya 2) in the zone of cells, which completed extension (in 48 hours at 10 °C), showed that the speed of accumulation of the components mentioned dropped in direct proportion to the deceleration of root growth (Table 1). The cells, which started extension at a temperature of 10 °C, exhibited a significant decrease in the speed of pectin accumulation, but an increase in the content of hemicelluloses, cellulose and lignin. The latter, in our view, characterizes a higher degree of differentiation of these cells at 10 °C and apparently represents a peculiarity of the resistant variety.

In the non-resistant variety the content of pectin in the capsules of cells, which started extension at 10 °C, increased considerably in control plants, whereas lignin content in percentage to the cell dry substance content did not change. Such a proportion between the components evidently brings about higher plasticity of the capsules, which results in a significant increase of the cell volume. The proportion of the capsules' major components (Uzbekskaya tooth-like variety) in the cells that completed extension, changed towards larger lignin accumulation with simultaneous reduction of pectin content at a low positive temperature. The capsules of these cells acquired intensified rigidity, which increased with the root growth and at 10 °C resulted in the deceleration of cell growth; consequently, it took considerably longer for the cells to reach certain dimensions than it did in optimal conditions (96 hours of growth at 10 °C versus 8 hours of growth at 27 °C).

Accumulation of phenolic compounds (lignin predecessors) increased in the cells under extension in both varieties. Nevertheless, in the non-resistant variety metabolism of hydroxycinnamic acids is significantly shifted towards the increase of content of soluble ethers, in the resistant variety — towards that of lignin. In the cells that completed growth, the balance of consumption of oxycinnaroic acids is shifted towards lignin synthesis in both varieties (Table 1).

Thus, peculiarities of cell capsule formation (linked to the change of speed of the capsule's accumulation of major components) at temperature reduction represent one of the key factors of cell extension.