Two common wheat (Triticum aestivum L.) cultivars were used: Saratovskaya 29 and Opal. They have contrasting degrees of resistance to drought. Saratovskaya 29 originates in the steppe ecotype of the Volga region and is very tolerant of drought. The cultivar Opal originates from Germany and is drought sensitive. Yet, these cultivars are comparable in their vegetation period: they are not essentially different in their phenophase periods or in leaf growth rate (Kumakov 1985). The synchronism of their development is particularly important in studying the stress-induced disruption of cellular proliferation and the subsequent repair.

Wheat seedlings were grown in glass tubes tied up in pairs and placed in containers filled with water. The seedlings were placed in a KTLK 1250 (Nema, Germany) controlled environment cabinet (temperature: 22°C, light intensity: 30,000 lux, irradiance: 17.2 W /m2, air humidity 60%). After being grown for 3 days in the dark and then 1 day in continuous light, the seedlings were subjected to osmotic stress.

Osmotic stress was given by placing the plant root system in Knoop's nutrient solution supplemented with 24% (w/v) polyethylene glycol (PEG) (Mr= 6000; Serva Feinbiochemica GmbH, Heidelberg, Germany), a concentration that corresponds to an osmotic pressure of 3.7-MPa (Nechiporenko and Rybalova 1980). The stressed plants were then returned to their original growth conditions (see above) in order to study the repair processes. The growth respplonse of the cultivate to osmotic stress was evaluated by the change in linear leaf size during post-stress repair.

To obtain the total meristem protein fraction containing PAI, we separated the seedling from the seed and excised a 2 to 3 mm piece of tissue with the stem apex and basal leaf meristems. The tissue was disrupted in liquid N₂ and was subjected to extraction for 1 h at 4°C in 50 mM Tris-HCI (pH 7.8) containing 0.02 M beta-mercaptoethanol (Ferns Laborat GmbH, Germany) and 0.001 M phenylmethylsulfonyl fluoride (Fluka Chemie AG, Buchs, Switzerland). The homogenate was centrifuged for 30 min at 20,000x g.
The supernatant liquid containing total water-soluble proteins was used to study post-stress repair.

The relative quantitative assay of PAI content was done with an immunochemical test-system using monospecific anti-PAT antibodies raised by us as described earlier (Evseeva et al. 2002). The PAl content in four-day-old seedlings of the control cultivar (Saratovskaya 29 grown under normal conditions, titer: 1:2) was taken as 100%.

The results of the PAI determination and growth evaluation were statistically processed. The arithmetic means (standard errors of the mean of four experiments, with three replicates per experiment) were calculated. Twenty-five seedlings were used in each replicate. The significance of differences in PAI content among the experiments was evaluated by a three-factorial analysis of variance (Maksimov 1980) at a significance level of 0.05.