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. Roots of many species grow downward (orthogravitropism) only when illuminated. Previous work suggests that this is a calcium-regulated response and that both calmodulin and calcium/calmodulin-dependent kinases participate in transducing gravity and light stimuli. A genomic sequence has been obtained for a calcium/calmodulin-dependent kinase homolog (MCK1) expressed in root caps, the site of perception...
. A number of features of the gravitropic response of roots are not readily accounted for by the classical Cholodny-Went theory. These include the observations that (i) in the later stages of the response the growth gradient is reversed with no evident reversal of the auxin gradient; (ii) a major component of the acceleration of growth along the upper side occurs in the distal elongation zone (DEZ),...
Abstract. The roles of the plasma-membrane (PM) NADPH oxidase in abscisic acid (ABA)- and water stress-induced antioxidant defense were investigated in leaves of maize (Zea mays L.) seedlings. Treatment by exogenous ABA (100M ABA) or osmotic stress (0.7MPa induced by polyethylene glycol) significantly increased the activity of the PM NADPH oxidase, the production of leaf O2, the activities of several...
Abstract. Root elongation occurs as individual cells along the growing zone increase in volume. This increase is caused by water entering the cell either by moving across the cell membrane from the apoplast via aquaporins, or entering through plasmodesmata that symplastically connect cells to each other or with the sieve element. In this investigation we used mercury, a known inhibitor of aquaporin...
Abstract. The plant hormone auxin affects cell elongation in both roots and shoots. In roots, the predominant action of auxin is to inhibit cell elongation while in shoots auxin, at normal physiological levels, stimulates elongation. The question of whether the primary receptor for auxin is the same in roots and shoots has not been resolved. In addition to its action on cell elongation in roots and...
Abstract. Modern corn (Zea mays L.) varieties have been selected for their ability to maintain productivity in dense plantings. We have tested the possibility that the physiological consequence of the selection of the modern hybrid, 3394, for increased crop yield includes changes in responsiveness to auxin and light. Etiolated seedlings in the modern line are shorter than in an older hybrid, 307,...
Abstract. Jasmonic acid (JA) has long been hypothesized to be an important regulator of insect-induced volatile emission; however, current models are based primarily on circumstantial evidence derived from pharmacological studies. Using beet armyworm caterpillars (BAW: Spodoptera exigua) and intact corn seedlings, we examine this hypothesis by measuring both the time-course of insect-induced JA levels...
The sulfur-amino-acid-rich -zeins of maize (Zea mays L.) are represented by 18-kDa and 10-kDa proteins. We have cloned a novel 11-kDa methionine-rich -zein from developing endosperm of the inbred line W23a1. The nucleotide sequence of this new -zein is identical to the published 10-kDa -zein, except for an insertion of 18 nucleotides between +316 and +333bp from the translation start site. Antibodies...
Cultured cells of maize (Zea mays L.) were pulse-labelled with l-[1-3H]arabinose (Ara) and then monitored for 7days. The 3H-hemicelluloses present in three compartments (protoplasm, cell wall and culture medium) were size-fractionated and the fractions assayed for [3H]xyloglucans and [3H]xylans. Protoplasmic [3H]xylans and [3H]xyloglucans initially (15min after [3H]Ara-feeding) had weight-average...
Adenosine diphosphate glucose pyrophosphorylase (AGPase; EC 2.7.7.27) synthesizes the starch precursor, ADP-glucose. It is a rate-limiting enzyme in starch biosynthesis and its activation by 3-phosphoglyceric acid (3PGA) and/or inhibition by inorganic phosphate (Pi) are believed to be physiologically important. Leaf, tuber and cereal embryo AGPases are highly sensitive to these effectors, whereas...
Young maize (Zea mays L., Poaceae) plants were grown in a complete, well-oxygenated nutrient solution and then deprived of their external source of sulphate. This treatment induced the formation of aerenchyma in roots. In addition to the effect of sulphate starvation on root anatomy, the presence and location of superoxide anions and hydrogen peroxide, and changes in calcium and pH were examined....
Hydroxyl radicals (OH), produced in the cell wall, are capable of cleaving wall polymers and can thus mediate cell wall loosening and extension growth. It has recently been proposed that the biochemical mechanism responsible for OH generation in the cell walls of growing plant organs represents an enzymatic reaction catalyzed by apoplastic peroxidase (POD). This hypothesis was investigated by supplying...
We measured fresh weight, dry weight, total protein, and the amounts of several individual proteins during endosperm development in three varieties of maize (Zea mays L.): W64A wild-type (WT) and opaque-2 (o2), and sweet corn (SW). By 28days after pollination (DAP), fresh weight was much higher in WT and SW than in o2, but o2 had a higher dry weight and thus a much lower water content. By 28DAP, protein...
The maize (Zea mays L.) glyceraldehyde-3-phosphate dehydrogenase gene4 (GapC4) promoter confers anaerobic gene expression in tobacco (Nicotiana tabacum L.), potato (Solanum tuberosum L.) and Arabidopsis thaliana (L.) Heynh. Here we have investigated its expression in hybrid poplar (Populus tremula P. alba). Our results show that the promoter is not expressed in leaves and stems under normoxic conditions...
To further understand post-translational modifications (PTMs) of plant -tubulin, post-translationally modified -tubulin isoforms from selected tissues of Zea mays L. were examined using two-dimensional electrophoresis and immunoblotting. Except for polyglycylated tubulin, tyrosinated, detyrosinated, acetylated and polyglutamylated -tubulin isoforms were all present in maize tissues. Tyrosinated -tubulin...
The maize (Zea mays L.) endosperm consists of an epidermal like layer of isodiametric aleurone cells surrounding a central body of starchy endosperm cells. In disorgal1 (dil1) and disorgal2 (dil2) mutants the control of the mitotic division plane is relaxed or missing, resulting in mature grains with disorganized aleurone layers. In addition to orientation of the division plane, both the shape and...
Volicitin (N-[17-hydroxylinolenoyl]-l glutamine) present in the regurgitant of beet armyworm (Spodoptera exigua) activates the emissions of volatile organic compounds (VOCs) when in contact with damaged corn (Zea mays L.) leaves. VOC emission in turn serves as a signaling defense for the plant by attracting female parasitic wasps that prey on herbivore larvae. Chemical tracking of volicitin within...
Cell-suspension cultures of maize (Zea mays L.) released soluble extracellular polysaccharides (SEPs) into their medium. Some or all of the SEPs had feruloyl ester groups. Pulse-labelling with [3H]arabinose was used to monitor changes in the SEPs Mr (estimated by gel-permeation chromatography) with time after synthesis. Newly released 3H-SEPs were 1.31.6MDa, but between 2days and 3days after radiolabelling...
Nitric oxide (NO) is a reactive gas involved in many biological processes of animals, plants and microbes. Previous work has demonstrated that NO is formed during hypoxia in alfalfa (Medicago sativa L.) root cultures and that the levels of NO detected are inversely related to the levels of expression of class-1 hemoglobin expressed in the tissue. The objectives of this study were: to examine whether...
The Casparian strip in the endodermis of vascular plant roots appears to play an important role in preventing the influx of salts into the stele through the apoplast under salt stress. The effects of salinity on the development and morphology of the Casparian strip in primary roots of maize (Zea mays L.) were studied. Compared to the controls, the strip matured closer to the root tip with increase...
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