One‐Degree Increments in Soil Temperatures Affect Maize Seedling Behavior

One‐degree differences in soil temperatures, ranging from 12 to 35C, induced changes in the growth and nutritional behavior of maize seedlings (Zea mays L.) amounting to as much as 30 to 40% per degree. An improved system was developed to provide the precise environmental control required. The system provided for nearly isothermal control of soil temperatures even when soil and air temperatures differed by as much as 15C. The system also provided for uniform control of air temperature within ±0.7C and relative humidity within ±1% throughout the growing region in the 2 by 2.75 by 2 m growth chamber.

With each degree increase in soil temperature from 12 to 26C, total seedling dry weights were an average of 20% greater than weights at each previous soil temperature and an average of 12% smaller with each degree increase from 26 to 35C. Nutritional status, leaf lengths and numbers, stem lengths, and root numbers also were very dependent upon soil temperature. Of special interest, a soil‐temperature‐dependent disorder resembling Ca deficiency was observed in the maize shoot. Also, the uptake of B was uniquely different from that of other elements. Surprisingly, the same total uptake of B occurred regardless of the soil temperature below 21C.

The desirability of rigidly controlling soil temperature in pot experiments and the importance of minor changes in soil temperature on plant behavior have been clearly demonstrated. [1]

Photomorphogenic Responses in Maize Seedling Development

As an emerging maize (Zea mays) seedling senses light, there is a decrease in the rate of mesocotyl elongation, an induction of root growth, and an expansion of leaves. In leaf tissues, mesophyll and bundle sheath cell fate is determined, and the proplastids of each differentiate into the dimorphic chloroplasts typical of each cell type. Although it has been inferred from recent studies in several model plant species that multiple photoreceptor systems mediate this process, surprisingly little is known of light signal transduction in maize. Here, we examine two photomorphogenic responses in maize: inhibition of mesocotyl elongation and C4 photosynthetic differentiation. Through an extensive survey of white, red, far-red, and blue light responses among a diverse collection of germplasm, including a phytochrome-deficient mutant elm1, we show that light response is a highly variable trait in maize. Although all inbreds examined appear to have a functional phytochrome signal transduction pathway, several lines showed reduced sensitivity to blue light. A significant correlation was observed between light response and subpopulation, suggesting that light responsiveness may be a target of artificial selection. An examination of C4 gene expression patterns under various light regimes in the standard W22 inbred and elm1 indicate that cell-specific patterns of C4 gene expression are maintained in fully differentiated tissues independent of light quality. To our knowledge, these findings represent the first comprehensive survey of light response in maize and are discussed in relation to maize breeding strategies. [2]

Unveiling the mechanism of melatonin impacts on maize seedling growth: sugar metabolism as a case

Melatonin regulates growth in many plants; however, the mechanism remains unclear. In this study, exogenous melatonin feeding resulted in both promotional (≤10 μm) and inhibitory (≥100 μm) effects on maize seedling growth. Initial analyses suggested positive correlations between the amount of melatonin and sucrose synthesis and hydrolysis‐related gene expression, enzyme activities, and sucrose metabolites. However, assays of photosynthetic rate, hexokinase (HxK) activity, expression of photosynthetic marker genes, and HxK‐related genes showed opposite effects under 10 μm (positive) and 100 μm (negative) melatonin treatments. Similarly, 10 μm melatonin accelerated starch catabolism at night, whereas 100 μm melatonin significantly decreased this process and led to starch accumulation in photosynthetic tissues. Furthermore, expression analysis of genes related to sucrose phloem loading resulted in a slight upregulation of sucrose transporters (SUT1 and SUT2) when seedlings were induced with 10 μm melatonin, while treatment with 100 μm melatonin resulted in significant downregulation of these sucrose transporter genes (SUT1 and SUT2), as well as tie‐dyed2 (Tdy2) and sucrose export defective 1. Taken together, these results suggest that low doses of melatonin benefit maize seedling growth by promoting sugar metabolism, photosynthesis, and sucrose phloem loading. Conversely, high doses of melatonin inhibit seedling growth by inducing the excessive accumulation of sucrose, hexose and starch, suppressing photosynthesis and sucrose phloem loading. [3]

Effects of Petroleum Products in Soil on α-Amylase, Starch Phosphorylase and Peroxidase Activities in Cowpea and Maize Seedlings

Aims: To determine the effect of petroleum products (kerosene, diesel, engine oil and petrol) contaminated soil at various concentrations on the activities of α-amylase, starch phosphorylase in the cotyledons of cowpea and maize seedlings as well as peroxidase activity in the leaves of both seedlings.

Place and Duration of Study: This study was conducted in Delta State University, Abraka, Nigeria between April 2007 and August 2011.

Methodology: Improved varieties of maize (Zea mays L) and Vigna unguiculata (L) Walp were planted in soil contaminated at different concentrations comprising six groups. Each group was replicated five times. Groups 1 to 5 contained 0.1%, 0.25%, 0.5%, 1.0% and 2.0% (v/w) respectively of each of the petroleum products while group six served as control (0.0%). Three seeds were planted in each bag and watered daily. Four days after germination the activities of α-amylase, starch phosphorylase in the cotyledons of the cowpea and maize seedlings were analysed. This was followed by the determination of peroxidase activity in the leaves of cowpea and maize seedlings four, eight and twelve days after germination.

Results: The results showed that the petroleum products caused metabolic perturbations in the seedlings. This is indicated by the significant (P<0.05) decrease in the activities of starch degrading enzymes: α-amylase and phosphorylase as well as peroxidase activity compared to their respective control values.

Conclusion: Kerosene decreased the activities of the enzymes more than the other petroleum products. The effect of petroleum products contaminated soil was more severe in cowpea seedlings relative to maize seedlings. [4]

Effects of Climate Change Critical Factors on the Seedling Growth and Development of Maize (Zea mays L.)

Crop production is highly dependent on weather and change in climate has a major effect on crop yield, and thus on food supply. The effect of critical factors for climate change on growth and development of Zea mays was investigated. The treatments used were water, temperature, light intensity and soil (pH and nutrients). Growth factors such as height, leaf area, fresh and dry weights as well as dry and fresh weight ratio were determined. An average weight of 3kg of sandy, clay, loamy and laterite (red) soils in black planting bags of 21 by 25cm were used. Single (SN) and double (DN) netted cages were constructed to reduce the amount of light absorbed by plants. The control was without net (WN) while another set without net1 (WN1) was subjected to drought (watered only once). Three replicates for each soil treatment were used, and the experiment lasted for 8 Weeks. The results revealed that seeds sown in clay and laterite soils for WN1 germinated and died after three weeks because of the drought condition. Loamy soil for SN showed the highest mean height of 125cm±0.95. Also, loamy soil (WN) had the highest values of 214.49cm2±0.35 and 92.90g±3.21 for leaf area and dry weight, respectively. Soil pH values for sandy and loamy soils were within the acceptable pH range of 6.5 – 8.5. Plants sown in loamy soil for SN, DN and WN flowered within the period of the experiment. The highest value of 1.80g weight for inflorescence was recorded for WN with loamy soil. For loamy soil, there was significant difference between all soil treatments (nutrient, temperature and light intensity) at P<0.05. Since salts (ions) absorption is through solution in the soil, water may be considered as the most critical factor for the growth and development of plants. [5]

Reference

[1] Walker, J.M., 1969. One‐degree increments in soil temperatures affect maize seedling behavior. Soil Science Society of America Journal, 33(5), pp.729-736.

[2] Markelz, N.H., Costich, D.E. and Brutnell, T.P., 2003. Photomorphogenic responses in maize seedling development. Plant Physiology, 133(4), pp.1578-1591.

[3] Zhao, H., Su, T., Huo, L., Wei, H., Jiang, Y., Xu, L. and Ma, F., 2015. Unveiling the mechanism of melatonin impacts on maize seedling growth: sugar metabolism as a case. Journal of pineal research, 59(2), pp.255-266.

[4] Achuba, F. I. and Okoh, P. N. (2014) “Effects of Petroleum Products in Soil on α-Amylase, Starch Phosphorylase and Peroxidase Activities in Cowpea and Maize Seedlings”, Journal of Experimental Agriculture International, 6(2), pp. 112-120. doi: 10.9734/AJEA/2015/9750.

[5] Edema, N. E. (2014) “Effects of Climate Change Critical Factors on the Seedling Growth and Development of Maize (Zea mays L.)”, Journal of Experimental Agriculture International, 4(12), pp. 1649-1657. doi: 10.9734/ajea/2014/10802.