Lacking Root Hairs Research Articles

Boletinellus merulioides Alters Root Morphology of Pinus densiflora without Mycorrhizal Formation

A stimulatory effect of Boletinellus merulioides on the roots of Pinns densiflora was evaluated using pure culture synthesis. Seedlings of P. densiflora were inoculated with cultures of B. merulioides at high and low glucose levels. After 180 days, shoot weight was not enhanced over controls by inoculation with the fungus, but root weight was significantly increased and roots were highly branched. Short roots were dichotomously branched, lacked root hairs, and had an internal morphology similar to that of ectomycorrhizal rootlets. A loose weft of fungal hyphae surrounded the short roots, but did not penetrate the epidermis. Higher glucose levels further increased root weight and branching. Filtrates from liquid-grown cultures of B. merulioides and Pisolithus tinctorius were compared using high performance liquid chromatography. Both fungi produced measurable quantities of indole-3-acetic acid, the in-vitro production of which was enhanced by higher glucose levels.

Hormone-Resistant Mutants of Arabidopsis Have an Attenuated Response to Agrobacterium Strains

We have examined the response of the hormone-resistant mutants axr1 and axr2 of Arabidopsis thaliana to inoculation by Agrobacterium tumefaciens and Agrobacterium rhizogenes. Our results indicate that recessive mutations in the axr1 gene affect the frequency of tumor formation after inoculation with either Agrobacterium strain. In addition, tumors produced on axr1 plants were smaller than those growing on wild-type plants. These results indicate that the product of the AXR1 gene is important for both crown gall and hairy root tumor formation. In contrast, the dominant axr2 mutation has a more severe effect on the development of crown gall tumors than on hairy root tumors. Crown gall tumors produced on axr2 plants had a different morphology than wild-type tumors and did not grow when they were removed from the explant. In contrast, a large number of hairy root tumors were produced on wild-type and axr2 plants, and both types of tumors grew when they were removed from the explant. Like the roots of axr2 plants, roots produced on axr2 explants lacked root hairs.

A dominant mutation inArabidopsis confers resistance to auxin, ethylene and abscisic acid

We have screened a large population of M2 seeds of Arabidopsis thaliana for plants which are resistant to exogenously applied indole-acetic acid (IAA). One of the resistant lines identified in this screen carries a dominant mutation which we have named axr2. Linkage analysis indicates that the axr2 gene lies on chromosome 3. Plants carrying the axr2 mutation are severe dwarfs and display defects in growth orientation of both the shoot and root suggesting that the mutation affects some aspect of gravitropic growth. In addition, the roots of axr2 plants lack root hairs. Growth inhibition experiments indicate that the roots of axr2 plants are resistant to ethylene and abscisic acid as well as auxin.

Inhibition of Legume Seedling Growth by Residues and Extracts of Quackgrass (Agropyron repens)

Aqueous extracts of quackgrass [Agropyron repens(L.) Beauv. # AGRRE] shoots and rhizomes inhibited seed germination and root growth of alfalfa (Medicago sativaL. ‘Vernal’), soybean (Glycine max(L.) Merr. ‘Corsoy 79’], navybean (Phaseolus vulgarisL. ‘Seafarer’), and curly cress (Lepidium sativumL.) at concentrations of less than 2.5 mg dried extract/ml. Extracts of quackgrass shoots were generally more inhibitory than extracts of rhizomes. Root and shoot dry weights of snapbeans (Phaseolus vulgarisL. ‘Bush Blue Lake’) grown under sterile conditions were reduced by aqueous extracts of shoots. Root systems were stunted and necrotic and lacked root hairs. The growth ofRhizobiumspecies was not influenced by the presence of 40 or 80 mg/ml concentrations of extracts of shoots or rhizomes. Quackgrass may inhibit indirectly the legume-Rhizobiumsymbiosis by inhibiting root hair formation rather than directly inhibitingRhizobiumgrowth. The presence of soil microorganisms was not necessary for the development of quackgrass toxicity in soil or agar. Soil microorganisms reduced toxicity of quackgrass residues in soil.

The occurrence of vesicular-arbuscular mycorrhiza in isoetid-type submerged aquatic macrophytes under naturally varying conditions

The percentage infection of vesicular-arbuscular (VA) mycorrhiza was investigated for Isoetid-type species. Not all species lacking root hairs were found to possess VA-mycorrhiza. A range of habitats including marl and acid lakes, terrestrial and submerged plants and variations with depth showed little variation of VA-infection.

Structure and Development of Cyclanthus bipartitus Poit. (Cyclanthaceae) with Reference to Other Cyclanthaceae. I. Rhizome, Inflorescence, Root, and Symmetry

Plants of Cyclanthus bipartitus produce entirely subterranean rhizome systems or grow as epiphytes up to 2 m above ground level. This species has a stem unit (rhizome) which, outwardly resembling a single monopodial axis, is actually sympodial with renewal shoots having clearly demarcated evicted and nonevicted portions. A developing spadix forms pistillate units and staminate units. Pistillate units produce perianths, staminodes, and carpels and vary greatly in shape. Carpels within a unit are connate basally, free distally. Staminate units generally produce two rows of stamens. Also, two staminate units or rows thereof develop between two vertically adjacent continuous pistillate cycles. Consequently, at maturity four rows of stamens normally intervene between such cycles. Rhizomes bear adventitious roots, which may produce persistent root hairs or lack root hairs. Phyllotaxis of adult leaves is spirodistichous. Cyclanthus bipartitus exhibits a considerable mirror-image symmetry.