Showing papers on "Amaranthus hypochondriacus published in 2003"

Dramatic difference in the responses of phosphoenolpyruvate carboxylase to temperature in leaves of C3 and C4 plants

Abstract: Temperature caused phenomenal modulation of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in leaf discs of Amaranthus hypochondriacus (NAD-ME type C4 species), compared to the pattern in Pisum sativum (a C3 plant). The optimal incubation temperature for PEPC in A. hypochondriacus (C4) was 45 ∞C compared to 30 ∞ Ci nP. sativum (C3). A. hypochondriacus (C4) lost nearly 70% of PEPC activity on exposure to a low temperature of 15 ∞C, compared to only about a 35% loss in the case of P. sativum (C3). Thus, the C4 enzyme was less sensitive to supraoptimal temperature and more sensitive to suboptimal temperature than that of the C3 species. As the temperature was raised from 15 ∞ Ct o 50∞C, there was a sharp decrease in malate sensitivity of PEPC. The extent of such a decrease in C4 plants (45%) was more than that in C3 species (30%). The maintenance of high enzyme activity at warm temperatures, together with a sharp decrease in the malate sensitivity of PEPC was also noticed in other C4 plants. The temperature-induced changes in PEPC of both A. hypochondriacus (C4) and P. sativum (C3) were reversible to a large extent. There was no difference in the extent of phosphorylation of PEPC in leaves of A. hypochondriacus on exposure to varying temperatures, unlike the marked increase in the phosphorylation of enzyme on illumination of the leaves. These results demonstrate that (i) there are marked differences in the temperature sensitivity of PEPC in C3 and C4 plants, (ii) the temperature induced changes are reversible, and (iii) these changes are not related to the phosphorylation state of the enzyme. The inclusion of PEG-6000, during the assay, dampened the modulation by temperature of malate sensitivity of PEPC in A. hypochondriacus. It is suggested that the variation in temperature may cause significant conformational changes in C4-PEPC.

Arabinogalactan proteins may facilitate the movement of pollen tubes from the stigma to the ovules in Actinidia deliciosa and Amaranthus hypochondriacus

Abstract: Sexual plant reproduction is a complex process that involves a series of interactions between the male gametophyte and the different cell types of the pistil. These interactions are believed to direct the pollen tube growth until its final target, the embryo sac. Arabinogalactan proteins are complex proteoglycans that are believed to be involved in these processes. The pistil is enriched in these highly glycosylated proteins and we provide results that show the selective presence of different AGP epitopes at the surface of the cells or in the ECM of the tissues that correspond exactly to the pollen tube growth pathway in Amaranthus hypochondriacus and Actinidia deliciosa. We also show that in Actinidia deliciosa, which is a dioecious plant with the male flowers having rudimentary ovaries where fertilization does not occur, there is no presence at all of the epitopes recognised by the monoclonal antibodies utilized in this study.

Marked modulation by phosphate of phosphoenolpyruvate carboxylase in leaves of Amaranthus hypochondriacus, a NAD-ME type C4 plant: decrease in malate sensitivity but no change in the phosphorylation status.

Abstract: The effect of Pi on the properties of phosphoenolpyruvate carboxylase (PEPC) from Amaranthus hypochondriacus, a NAD-ME type C4 plant, was studied in leaf extracts as well as with purified protein. Efforts were also made to modulate the Pi status of the leaf by feeding leaves with either Pi or mannose. Inclusion of 30 mM Pi during the assay enhanced the enzyme activity in leaf extracts or of purified protein by >2-fold. The effect of Pi on the enzyme purified from dark-adapted leaves was more pronounced than that from light-adapted ones. The Ki for malate increased >2.3-fold and >1.9-fold by Pi in the enzyme purified from dark-adapted leaves and light-adapted leaves, respectively. Pi also induced an almost 50‐ 60% increase in Km for PEP or Ka for glucose-6-phosphate. Feeding the leaves with Pi also increased the activity of PEPC in leaf extracts, while decreasing the malate sensitivity of the enzyme. On the other hand, Pi sequestering by mannose marginally decreased the activity, while markedly suppressing the light activation, of PEPC. There was no change in phosphorylation of PEPC in leaves of A. hypochondriacus due to the feeding of 30 mM Pi. However, feeding with mannose decreased the light-enhanced phosphorylation of PEPC. The marked decrease in malate sensitivity of PEPC with no change in phosphorylation state indicates that the changes induced by Pi are independent of the phosphorylation of PEPC. It is suggested here that Pi is an important factor in regulating PEPC in vivo and could also be used as a tool to analyse the properties of PEPC.

Effects of Irradiance on Photosynthesis and Activity of Protease Inhibitors in Amaranthus hypochondriacus

Abstract: Amaranthus hypochondriacus plants were grown under three photosynthetic photon flux densities (PPFD). Mature plants grown at full sunlight (38.8 mol m−2 d−1) had higher maximum net photosynthetic rate (PN) and significantly higher leaf trypsin inhibitor activity than plants that developed under lower PPFD (19.4 and 12.8 mol m−2 d−1). In contrast, seeds collected from plants fully exposed to sunlight showed the lowest activity of trypsin inhibitor, higher rate of germination and susceptibility to infection by Aspergillus niger.

Disease-tolerance of transgenic tobacco plants expressing Ah-AMP gene of Amaranthus hypochondriacus

Abstract: An antimicrobial peptide gene from Amaranthus hypochondriacus, Ah-AMP, was amplified by PCR and cloned. Sequence analysis results revealed that this gene is 261 bp in length encoding a precursor polypeptide of 87 amino acid residues. Ah-AMP gene was inserted in the binary vector pBin438 to construct a plant expression vector pBinAH916. Leave explants of Nicotiana tabacum var. SRI were transformed with Agrobacterium tumefaciens LBA4404 harboring the above expression vector. Results from PCR, Southern and Northern blot analyses confirmed that the Ah-AMP gene had been integrated into the tobacco genome and was transcribed at mR-NA level. Two bacterial-resistant transgenic plants were selected by inoculating the plants with Pseudomonas solanacearum and statistic analysis of two T1 lines showed that the resistance increased by 2.24 and 1.62 grade and the disease index decreased by 49. 6 % and 37.3% respectively when compared with the non-transformed control plants SR1. The results from challenging the...

Effect of temperature on the germination of grain Amaranth

Abstract: Amaranthus cultivation in South Africa has potential commercial importance. To make optimal use of the growing season planting under cool soil conditions is often necessary. The effect of temperature on seed germination of A. hypochondriaeus (unknown landrace) and A. cruentus, was determined. Whereas overall germination was advanced by increasing the temperature, only A. hypochondriacus germinated abundantly at temperatures as low as 12°C. A. hypochondriacus had a germination percentage of 70% at 12°C while A. cruentus had a germination percentage of less than 1% at the same temperature.