Direct observation of local xylem embolisms induced by soil drying in intact Zea mays leaves

The vulnerability of vascular plants to xylem embolism is closely related to their stable long-distance water transport, growth, and survival. Direct measurements of xylem embolism are required to understand what causes embolism and what strategies plants employ against it. In this study, synchrotron X-ray microscopy was used to non-destructively investigate both the anatomical structures of xylem vessels and embolism occurrence in the leaves of intact Zea mays (maize) plants. Xylem embolism was induced by water stress at various soil drying periods and soil water contents. X-ray images of dehydrated maize leaves showed that the ratio of gas-filled vessels to all xylem vessels increased with decreased soil water content and reached approximately 30% under severe water stress. Embolism occurred in some but not all vessels. Embolism in maize leaves was not strongly correlated with xylem diameter but was more likely to occur in the peripheral veins. The rate of embolism formation in metaxylem vessels was higher than in protoxylem vessels. This work has demonstrated that xylem embolism remains low in maize leaves under water stress and that there xylem has characteristic spatial traits of vulnerability to embolism.117Ysciescopu

Ancient DNA in Archaeologically Charred Zea Mays L: Prospects and Limitations

Plant remains are an integral part of any archaeological investigation given the large role they play in ancient subsistence economies, medicinal practices, technologies and folklore. However, despite new developments in ancient genetics, research in plant ancient DNA (aDNA) is a relatively young and untouched discipline accounting for less than 7% of all aDNA analyses published in academic literature. As a result, paleoethnobotanists, archaeologists and geneticists have not understood the feasibility and limitations of each other’s field. Few are aware that DNA extraction from charred plant remains is rare and without any kind of standard or working protocol. The possibilities of retrieving aDNA from charred Zea mays L. is considered in this study using modern maize for polymerase chain reaction (PCR) optimization and combining purification methods on ancient samples (1150-1250 AD), resolving the question of whether or not archaeologically charred plants are a viable source for genetic material. The confirmed positive results generate questions about the added-value of maize and how knowledge of genetic attributes can contribute to the growing field of archaeology and ethnobiology while demonstrating the value of these findings as they pertain to the treatment of charred floral remains by archaeologists and First Nation communities

Mapping of QTLs for lateral and axile root growth of tropical maize

Maize genotypes may adapt to dry environments by avoiding desiccation by means of a deeper root system or by maintaining growth and water extraction at low water potentials. The aim of this study was to determine the quantitative genetic control of root growth and root morphology in a population of 236 recombinant inbred lines (RILs) from the cross between CML444 (high-yielding)×SC-Malawi (low-yielding), which segregates for the response to drought stress at flowering. The RILs and the parental lines were grown on blotting paper in growth pouches until the two-leaf stage under non-stressed conditions; the parents were additionally exposed to desiccation stress induced by polyethylene glycol with a molecular weight of 8000 Dalton (PEG-8000). The lengths of axile and lateral roots were measured non-destructively at 2, 5, 7 and 9days after germination, by scanning with an A4 scanner followed by digital image analysis. CML444 had a lower rate constant of lateral root elongation (kLat) than SC-Malawi, but the two genotypes did not differ in their response to desiccation. QTLs affecting root vigor, as depicted by increments in kLat, the elongation rate of axile roots (ERAx) and the number of axile roots (NoAx) were identified in bins 2.04 and 2.05. QTLs for NoAx and ERAx collocated with QTLs for yield parameters in bins 1.03-1.04 and 7.03-04. The correspondence of QTLs for axile root traits in bins 1.02-1.03 and 1.08 and QTLs for lateral roots traits in bins 2.04-2.07 in several mapping populations suggests the presence of genes controlling root growth in a wide range of genetic background

High-resolution quantification of root dynamics in split-nutrient rhizoslides reveals rapid and strong proliferation of maize roots in response to local high nitrogen

Patches rich in nitrogen are rapidly colonized by selective root growth in maize, which was quantified at high time resolution with state-of-the-art non-invasive imaging techniques in a paper-based growth syste

IDENTIFICATION OF ULTRASTRUCTURAL AND BIOCHEMICAL MARKERS OF FROST AVOIDANCE IN THE CUTICULAR LAYER OF CORN

Abiotic stresses are a critical factor in the reduction of yield. Corn has been identified as a highly economically important yet, frost sensitive crop. Climate change trends are show increased frost damage. The global need for food production is increasing and current production will not meet demand. Corn is killed at the moment of freezing and therefore, developing frost avoidance is essential. The primary obstacle limiting production of new more cold sensitive crops in the Canadian prairies is the cooler climate and early frost events in both spring and fall which are preventing widespread expansion. While many studies have examined corn chilling and frost sensitivity, the impact of simulated autumn temperatures (termed chilling pre-treatment) preceding a frost has not been reported. The effect of chilling pre-treatment, on subsequent freezing avoidance was studied in mature hybrid grain corn of four contrasting genotypes (256 and 675 [chilling sensitive]; 884 and 959 [chilling resistant]). Chilling pre-treatment (18°C/6°C, 10 days) induced physical and biochemical changes in the cuticular wax layer in all four genotypes. These changes were measured using a suite of complementary techniques including: thermal imaging, hydrophobicity, Confocal Laser Scanning Microscopy (CLSM), Attenuated Total internal Reflectance (ATR-FTIR), and Gas Chromatography Mass Spectrometry (GC-MS). In all corn genotypes studied, chilling pre-treatment induced a warmer freezing temperature than non-chilled. No significant genotypic differences were observed, however, genotypes 675 and 959 were least responsive to the stressor which resulted in the smallest change in freezing temperature induced by chilling pre-treatment. Hydrophobicity was reduced following chilling pre-treatment in all genotypes with the most significant effect observed in genotype 675. Cuticular thickness (μ=3.25 μm) remained unchanged over the ten-day chilling pre-treatment under controlled environment conditions. By contrast, over the five-week field conditions, cuticle thickness increased in all genotypes. Genotype 256 had a significantly thinner cuticle (-0.25 μm) than the other genotypes indicating genotypic variation is accentuated under field conditions and sensitive lines may have a thinner cuticle. In the growth chamber, chilling treatment induced increasing cutan, cutin, & cuticular wax only in Region 1 (CH3 functional group) according to ATR-FTIR within 2 μm of the adaxial surface layer. By contrast, field treatment induced a reduction in cutan, cutin, and cuticular wax in all regions (1, 2, & 3) (CH3, Asymmetrical CH2, Symmetrical CH2) to the same 2 μm depth of ATR sampling. A primary challenge of proofing cuticle based studies in the field is the extremely strong environmental influence (high light intensity, wind abrasion, insects, temperature fluctuations) which induce modifications on the cuticle. Using GC-MS analysis, 142 known compounds were identified in both controlled environment (chilling treatment) and field samples from the adaxial cuticular wax extraction of mature grain hybrid grain corn. Of those identified compounds, 28 were found to represent significant (P<0.05) variation between chilling treated and non-chilled treatments under both growth chamber and field conditions. This variation represented 5 Classes of key compounds (Alkane, Alcohol, Fatty Acid, Triterpenes and other). It is clear that chilling treatment modifies both physical and biochemical properties of the cuticular layer. The degree and rate of detectable chemical changes induced by chilling treatment indicate physical cuticular modifications likely are contingent on biochemical changes. This may be due to the great number of chemical modifications and signals needed to induce a physical modification. ATR applications are more reflective of the cuticular composition in cases where the entire cuticular thickness is within the depth of sampling (2 μm). The investigation of the dynamic process of cuticular wax modification following chilling treatment using complementary techniques in Zea mays appears to be a useful system with practical applications for evaluating the correlation between the cuticle as a barrier to abiotic stress and chilling treatment in a whole plant system

Investigating the impact of pre-harvesting sprouting on maize hardness using near infrared (NIR) hyperspectral imaging and X-ray micro-computed tomography (μCT)

Thesis (MSc (Food Sc))--Stellenbosch University, 2016.ENGLISH ABSTRACT: Maize forms an integral part of the human energy intake in South Africa and its quality should always be maintained. A quality attribute important to the dry milling industry is maize hardness. In the milling industry, hard maize hybrids are described as kernels with a higher ratio of vitreous endosperm in comparison to floury endosperm. Certain circumstances such as agricultural conditions (e.g. pre-harvest germination), post-harvest conditions and improper treatments (e.g. no irrigation during periods of insufficient rain or improper drying procedures) will have a negative impact on maize hardness. This study focused on the impact of pre-germination on maize hardness, subsequently observations on the rate of the pre-germination process on three hardness variants (hard, intermediate and soft) were noted. Six maize hybrids with varying hardness levels were pre-germinated (from 0 – 22 h) bi-hourly and three imaging techniques (Scanning electron microscopy (SEM), near-infrared (NIR) h y p e r s p e c t r a l imaging and X -ray m i c r o computed tomography (X-ray μCT)) used to investigate the impact of the process on hardness. From the NIR hyperspectral imaging technique, principal component analysis (PCA) score plots and score images were employed in the investigations due to the amount of data obtained. Three types of endosperm (vitreous, intermediate or floury) were observed in the first principal component (PC1) of the score images. PCA classification plots revealed the three types of endosperm present within a maize kernel. Classification plots (both score plots and images) allowed for the isolation of the vitreous endosperm by removing the two clusters representing the floury and intermediate endosperm. PCA score images depicted decreasing trend in the content of the vitreous endosperm as pre-germination took place. Another observation from the PCA score images was that, the soft maize hybrids showed traces of vitreous endosperm after 8 h of pregermination. The intermediate hybrids showed a decrease in the endosperm content at 12 h and the hard hybrid was noted to be at 18 h. Pixel count (obtained from the PCA score plots) indicated a decreasing trend in all hybrids investigated. The graphs plotted from pixel counts of hard hybrids (i.e. H2 and H3), intermediate (H7) and soft (H9) depicted decreasing curvilinear plots. The rest of the hybrids’ graphs (H6 and H5) depicted a decreasing linear trend. X-ray μCT indicated fissures and shrinkage stress cracks occurring as a results of either or both of the pre-germination and drying processes. Larger fissures were assumed to have developed due to pre-germination and shrinkage stress cracks from the drying process. These (i.e. fissures and shrinkage stress cracks) were observed in all the 10 h and 22 h images, on 2D slices and 3D volumes. The side orientation 2D image slices depicted the intermediate and soft maize hybrids’ endosperm integrity as having deteriorated more than the hard hybrid at 10 h and 22 h incubation time period. The top orientation of the 2D slice images indicated the hard and intermediate deteriorated more than the soft hybrids. It was noted that the fissures and shrinkage stress cracks developed throughout the maize kernel. SEM was used to validate results obtained from the X-ray μCT imaging system, fissures could also be observed on SEM images. Starch and protein matrix deterioration was also observed. iii Stellenbosch University https://scholar.sun.ac.za Starch granules and protein matrix developed numerous pores on the surfaces indicating the extent of deterioration. Single kernel analysis using 2D slices at T8 = 21 h, crevices started to develop and propagated until the end of the pre-germination process at T19 = 143 h. Fissure measurement indicated an increment in all measured areas of the maize kernels, i.e. from the left side of the maize kernel fissures propagated from 1.51 mm at 99 h to 4.22 mm at 143 h, on the right side from 1.86 mm at 99 h to 3.65 mm at 143 h. At T15 = 123 h, a horizontal fissure was observed and measured to be 1.62 mm long while at T19 = 143 h it had propagated to 4.30 mm. The fissures were noted to be pathways used to transport hydrolytic enzymes and monomers (obtained from starch and protein hydrolysis) to the germ where the growing embryo utilises them as a source of nutrition. Volumes of the vitreous endosperm were also determined and a decreasing trend was noticed. At T1 = 0 h the content of the vitreous endosperm was 64.7 mm3 and at T19 = 143 h the content had decreased to 50.5 mm3. Endosperm deterioration due to pre-germination should thus be of great concern to the milling industry as it influences the desired end product.AFRIKAANSE OPSOMMING: Nie beskikbaar nie

Influence of exogenous abscisic acid on morpho-physiological and yield of maize (Zea mays L.) under drought stress

Abscisic acid (ABA) is naturally occurring plant hormone, its also known stress hormone, that act the plant responses to abiotic stresses, especially drought. Maize production losses due to drought prominently affect economics and livelihoods of millions of peoples. The current investigation the role of ABA in drought stress tolerance of maize. The influence of drought stress and foliar spray of abscisic acid diffent concentration (25, 50 ,75 and 100 µM) were analysed on morphological, physiological, and biochemical parameters. The present results revealed a most effective to increased after drought stress imposed with 75 µM ABA treated plants. Exogenous abscisic acid acts as a scavenger of ROS for mitigating the injury on cell membranes under drought were observed in the opening of stomata. Histochemical detection of more accumulation ROS (H2O2 and O2• –) was detected in drought stress shoot compared to other ABA treated and respective control. Fourier Infrared Spectroscopic (IR) study, ABA treated leaves indicated the presence of different functional groups. This study shows that can provide vital insights into maize leaves drought responses and could be beneficial in identifying novel drought tolerance characters. Drought and exogenous abscisic acid treatment increased the endogenous abscisic acid level, specifically at 75 µM concentration. The exogenous abscisic acid application effectively ameliorates the adverse effect of drought stress to improve the drought resistance. In concluded, the level of 75 µM concentration ABA was better growth charaterstics, biochmeical alterations and yiled under drought stress