IRKUTSK, RUSSIA
Institute of Plant Physiology and Biochemistry

Low positive temperature impact on the growth of maize sprouts primary roots

— Akimova, GP; Sokolova, MG; Makarova, LE; Nechaeva, LV

Maize is a heat-loving plant, its optimal growth and development take place within the temperature range 25–27°C. Like other heat-loving cultivars, maize has much lower thermo-adaptive abilities than cold-resistant plants, which does not contradict the existence of variations between the degree of thermo-adaptation of different varieties.

One of the most important physiological processes to a certain extent reflecting resistance to cold and warmth, is growth of the whole plant or its individual organ. Growing root was selected as an organ whose growth may serve a parameter of the adaptation degree, and, consequently, characterize the variety’s resistance.

The present work was aimed at identification of regularities of the growth response of the sprouts primary roots of several maize varieties and hybrids under low positive temperature at early stages of ontogenesis and use of these responses for the characteristics of the variety.

We determined the growth speed of primary roots of 48 hour old maize sprouts at low temperature and growth restoration at normal temperature according to the scheme (MNL 71:93, 1997), which allows to compare the plants of the same age under different growth conditions (with the same root length), control — 6 and 8 hours of growth at 27°C, test — 48, 72 and 96 hours of growth at 10°C, depending on the maize variety. Test plants after termination of cold impact were transferred to the medium with 27°C for growth restoration.

The following maize hybrids and varieties were used for the tests: Zherebkovsky 86, Kollektivny 244, Dneprovsky 320, Odessky 80, VIR 42, Bekke LLO, Bukovinsky 3, Omskaya 2. Uzbekskaya tooth-like variety characterized by late ripening and sensitivity to low temperature impact was used as a classifying variety.

Exposure to heat (27°C) and to cold (10°C) equaled the time of extension growth termination in the root section marked (2–4 mm from the root tip). It was shown (Table 1) that the cells of the initial extension zone reached final dimensions in 6 (Omskaya 2 and Bukovinsky 3 hybrid, Zherebkovsky 86, Kollektivny 244, Bekke LLO) and (Uzbekskaya tooth-like and Dneprovsky 320, VIR 42, Odessky 80 hybrids) hours of growth at optimal temperature (control, 27°C). The temperature of 10°C considerably decreased the root growth speed: only after 48 (Omskaya 2, Zherebkovsky 86), 72 (Bukovinsky 3 hybrid, Kollektivny 244, Bekke LLO) and 96 (Uzbekskaya tooth-like and Dneprovsky 320, VIR 42, Odessky 80 hybrids) hours of growth at this temperature the cells of the initial extension zone reached final dimensions, and the root growth equaled that of control. As a result the root growth speed decreased by 10–13 times in Omskaya 2 and Bukovinsky 3, Zherebkovsky 86, Kollektivny 244, Bekke LLO hybrids and by 15–20 times in Uzbekskaya tooth-like and Dneprovsky 320, VIR 42, Odessky 80 hybrids.

Root growth speed restoration after the plants were returned to the warmth differed considerably in different varieties. Omskaya 2, Bukovinsky 3, Zherebkovsky 86, Kollektivny 244 at 27°C restored growth by 70–85% in 6 hours. Other varieties and hybrids restored growth only by 30–45% of control.

Therefore, the data acquired allowed to conclude that growth responses of maize sprouts primary roots — the degree of root growth speed deceleration in cold conditions, the time of cells extension termination, restoration of root growth in optimal conditions — to a certain extent characterize the variety’s resistance. The variety’s peculiarities in root response (as shown in MNL 76: 35–36, 2002) are conditioned by the degree of deceleration of the speed of division, transfer to extension, and cells extension proper. The revealed peculiarities of maize root growth under low temperature allows to state that adaptation mechanisms are formed in the cells starting their growth by extension in the hardening conditions (growth at 10°C). The time of cells extension termination determines this process.

Maize varieties Control, 27°C Test, C Growth restoration at 27°C, % of control
Extension time, hour Root growth speed, mm/hour Extension time, hour Root growth speed, mm/hour 2 hour 6 hour 24 hour
Uzbekskaya tooth-like 8 1.34 ± 0.08 96 0.09 ± 0.00 12 41 85
Omskaya 2 6 1.22 ± 0.06 48 0.12 ± 0.01 70 85 104
Maize hybrids
Zherebkovsky 86 6 1.23 ± 0.05 48 0.10 ± 0.00 68 82 100
Bukovinsky 3 6 1.28 ± 0.05 72 0.10 ± 0.00 60

 70 100
Kollektivny 244 6 1.20 ± 0.04 72 0.12 ± 0.01 65 85 105
Odessky 8 1.00 ± 0.03 96 0.05 ± 0.00 10 35 82
VIR 42 8 0.83 ± 0.03 96 0.05 ± 0.00 6 30 85
Dneprovsky 320 8 0.86 ± 0.02 96 0.05 ± 0.00 11 45 80
Bekke LLO 6 0.92 ± 0.04 72 0.07 ± 0.00 8 30 100

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