Abstract
Pearl millet (Pennisetum spicatum (L.) Körn.) and maize (Zea mays L.) are C4 grass species grown for feeding humans and animals in Almadinah Almunawwarah, which is in the western part of Saudi Arabia. During the winter, the mean temperature, which drops to 14°C, represents a major problem for the growth of these species in this region. Therefore, the objectives of this research were to investigate the growth response and the photosynthetic performance of P. spicatum and Z. mays under a low temperature stress. The treatments involved daytime and nighttime temperatures of 14/12°C (low temperature) and 24/22°C (optimum temperature). The results indicated that low temperature significantly reduced all growth and physiological parameters, including seed germination, leaf expansion, leaf area, shoot length and root length of the two species compared to those of the control. Additionally, the low temperature significantly decreased the light-saturated assimilation rate (Asat), quantum yield (ϕ), saturated rate of carbon dioxide uptake (Amax) and efficiency of carboxylation on both species compared to those of the control. Moreover, the values of Fv/Fm and the chlorophyll contents of both species were significantly reduced by low temperature compared to those of the control. It can be concluded that both species had little tolerance to low temperatures.
Highlights
One of the most critical variables that restricts plant development, distribution and production is low temperature [1,2,3]
At 24°C, seed germination of P. spicatum started on the first day and was completed on the third day, while seed germination of Z. mays started on the second day and was completed on the fourth day of the germination trial
At 14°C, seed germination of P. spicatum started on the first day and was completed on the third day, while seed germination of Z. mays started on the second day and was completed on the fifth day of the germination trial
Summary
One of the most critical variables that restricts plant development, distribution and production is low temperature [1,2,3]. The majority of C4 plants are mainly restricted to regions with relatively warm temperatures because low temperatures adversely influence their physiological processes [2,4]. Sowinski et al [5] observed that the rates of both leaf cell division and elongation of C4 plants were lower at low than warm temperatures. All stages of plant growth, including germination and early seedling growth, and a wide range of physiological processes are considered to be influenced by low temperatures [3,6,7,8]. Exposure of Z. mays to low temperatures impairs leaf growth and photosynthesis and breaks down chlorophyll in developed leaves [11]. The leaf expansion rate was found to be the major factor determining the variations in leaf growth
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