Response of transgenic rape plants bearing the <Emphasis Type="Italic">Osmyb4</Emphasis> gene from rice encoding a trans-factor to low above-zero temperature

Accumulation of soluble sugars (sucrose, fructose, and glucose), proline, phenols (total phenols and flavonoids), and antocyanins during adaptation to low-temperature stress (4°C) of two lines of spring rape (Brassica napus L., cv. Westar) characterized by weak (Bn-1) and strong (Bn-3) expression of the Osmyb4 transgene was studied. Vegetatively propagated transgenic and wild-type plants were grown in the hydroponic culture at 24°C; at the stage of 5–6 leaves, plants were exposed to 4°C for 5 days and then returned to the optimum temperature of 24°C for recovery. Transgenic plants were established to manifest improved cold and frost tolerance, which was evident from more active biomass accumulation at 4°C as compared with wild-type plants and from sustaining their viability after 2-day-long exposure to −6°C. Determination of MDA content showed that one of the reasons of their improved cold tolerance was their capability of maintaining oxidative homeostasis under low-temperature stress. This suggestion is supported by intense accumulation of phenols and antocyanins, manifesting pronounced antioxidant effects, by transgenic plants during their cold adaptation. Thus, during 2–5 days of plant exposure to 4°C, in transgenic plants the total content of phenols increased by 2.6–3.7 times, flavonoids — by 3.7–4.7 times, and antocyanins — by 3.5–5.3 times as compared with control plants growing at 24°C. Transgenic Bn-3 plants with strong expression of the Osmyb4 gene accumulated phenols and antocyanins at 4°C more actively than Bn-1 plants characterized by weak expression of this gene. Transgenic rape plants subjected to cold stress accumulated more proline, manifesting stress-protection effects, and lesser accumulation of soluble sugars. Before the beginning of experiment, the content of soluble sugars was approximately similar in wild-type plants and transgenic lines; at 4°C their level in transgenic plants was substantially lower than in control plants. As distinct from the process of cold adaptation, during recovery, the content of all tested stress-protection compounds dropped sharply. The results obtained indicate that active expression of the Osmyb4 gene from rice in the rape plants was accompanied not only by accumulation of compatible osmolytes but also by biosynthesis of antioxidants of phenolic nature.