Jonathan N. Egilla

Mycorrhizal fungi enhance accumulation and tolerance of chromium in sunflower (Helianthus annuus)

Summary Chromium (Cr) is a heavy metal risk to human health, and a contaminant found in agricultural soils and industrial sites. Phytoremediation, which relies on phytoextraction of Cr with biological organisms, is an important alternative to costly physical and chemical methods of treating contaminated sites. The ability of the arbuscular mycorrhizal fungus (AM),Glomus intraradices, to enhance Cr uptake and plant tolerance was tested on the growth and gas exchange of sunflower (Helianthus annuus L.). Mycorrhizal-colonized (AM) and non-inoculated (Non-AM) sunflower plants were subjected to two Cr species [trivalent cation (Cr3+) {Cr(III)}, and divalent dichromate anion (Cr2O7−) {Cr(VI)}]. Both Cr species depressed plant growth, decreased net photosynthesis (A) and increased the vapor pressure difference; however, Cr(VI) was more toxic. Chromium accumulation was greatest in roots, intermediate in stems and leaves, and lowest in flowers. Greater Cr accumulation occurred with Cr(VI) than Cr(III). AM enhanced the ability of sunflower plants to tolerate and hyperaccumulate Cr. At higher Cr levels greater mycorrhizal dependency occurred, as indicated by proportionally greater growth, higherA and reduced visual symptoms of stress, compared to Non-AM plants. AM plants had greater Cr-accumulating ability than Non-AM plants at the highest concentrations of Cr(III) and Cr(VI), as indicated by the greater Cr phytoextraction coefficient. Mycorrhizal colonization (arbuscule, vesicle, and hyphae formation) was more adversely affected by Cr(VI) than Cr(III), however high levels of colonization still occurred at even the most toxic levels. Arbuscules, which play an important role in mineral ion exchange in root cortical cells, had the greatest sensitivity to Cr toxicity. Higher levels of both Cr species reduced leaf tissue phosphorus (P). While tissue P was higher in AM plants at the highest Cr(III) level, tissue P did not account for mycorrhizal benefits observed with Cr(VI) plants.

MYCORRHIZAL FUNGI INCREASE CHROMIUM UPTAKE BY SUNFLOWER PLANTS: INFLUENCE ON TISSUE MINERAL CONCENTRATION, GROWTH, AND GAS EXCHANGE

ABSTRACT As a potential phytoremediation system for phytoextraction of chromium (Cr), we evaluated the influence of the arbuscular mycorrhizal fungus Glomus intraradices on leaf tissue elemental composition, growth and gas exchange of sunflower (Helianthus annuus L.). Sunflower seedlings were either inoculated with mycorrhizal fungi (AM) or non-inoculated (Non-AM) and then exposed to two Cr species: {12 mmol of trivalent cation (Cr+3) [Cr(III)] or 0.1 mmol of divalent dichromate anion (Cr2O7 −) [Cr(VI)]}. Both Cr species depressed plant growth, decreased stomatal conductance (g s ) and net photosynthesis (A). However, Cr(VI) was more toxic than Cr(III) as indicated by early reduction in g s , and greater reduction in plant growth and arbuscule formation. Mycorrhizal fungi helped to partially alleviate Cr toxicity as indicated by greater growth in plants treated with either Cr species, and increased gas exchange of Cr(III) plants. With Cr(III), Cr concentrations were the same in tissue of AM and Non-AM plants, while Non-AM Cr(VI) treatments had higher Cr concentration than AM plants; however with both Cr species, the larger-sized AM plants had greater total Cr accumulation on a whole-plant basis. Chromium reduced leaf elemental nitrogen (N), phosphorus (P), and potassium (K), and increased aluminum (Al), iron (Fe), and zinc (Zn) uptake. Chromium-treated AM plants had higher K and decreased levels of Fe and Al than Non-AM plants. Except for the depression of arbuscular formation in Cr(VI) treated plants, high colonization occurred with either Cr species. While higher P may have contributed to mycorrhizal benefits with Cr(III) plants, it does not account for any AM benefits observed with Cr(VI) plants.

Effect of potassium on drought resistance of Hibiscus rosa-sinensis cv. Leprechaun : Plant growth, leaf macro- and micronutrient content and root longevity

As competition for the limited water supply available for irrigation of horticultural crops increases, research into crop management practices that enhance drought resistance, plant water-use efficiency and plant growth when water supply is limited has become increasingly essential. This experiment was conducted to determine the effect of potassium (K) nutritional status on the drought resistance of Hibiscus rosa-sinensis L. cv. Leprechaun (Hibiscus). All the treatments were fertilized with Hoaglands nutrient solution, modified to supply K as K2SO4, at 0 mM K (K0), 2.5 mM K (K2.5), and 10 mM K (K10), under two irrigation regimes (drought stressed [DS] and non-drought stressed [non-DS]). Regular irrigation and fertigation were adopted for 54 days, and drought stress treatment (initiated on day 55) lasted for 21 days; while non-DS control plants continued to receive regular irrigation and fertigation. Following the 21-day drought stress period, plants were labeled with 86Rb+ to determine the percentage of post-drought stress live roots. Both K deficiency (K0) and drought stress reduced shoot growth, but drought stress increased root growth and thus the root:shoot ratio. At K0, plants were K-deficient and had the lowest leaf K, Fe, Mn, Zn, Cu, B, Mo and Al, and highest Ca concentrations. Although the percentage of live roots was decreased by drought stress, K2.5 and K10 plants (with similar percent live roots) had greater root survival ratio after drought treatment than the K-deficient plants. These observations indicate that adequate K nutrition can improve drought resistance and root longevity in Hibiscus rosa-sinensis.

Mycorrhizal fungi enhancement of growth and gas exchange of micropropagated guava plantlets (Psidium guajava L.) during ex vitro acclimatization and plant establishment.

Psidium guajavaL.) plantlets was determined during acclimatization and plant establishment. Guava plantlets were asexually propagated through tissue culture and grown in a glasshouse for 18 weeks. Half of the plantlets were inoculated with a mixed endomycorrhiza isolate from Mexico, ZAC-19, containing Glomus diaphanum, G. albidum and G. claroides. Plantlets were fertilized with modified Long Ashton nutrient solution that supplied 11 μg P ml−1. Gas exchange measurements were taken at 2, 4, 8, and 18 weeks after inoculation using a portable photosynthesis system. All micropropagated guava plantlets survived transplant shock. After 6 weeks, mycorrhizal plantlets had greater shoot growth rates and leaf production than non-mycorrhizal plantlets. This also corresponded with increased photosynthetic rates and stomatal conductance of mycorrhizal plants. By 18 weeks, mycorrhizal plantlets had greater shoot length, leaf area, leaf, stem, and root dry mass. However, gas exchange was comparable among treatments, in part because the container size was restricting growth of the larger mycorrhizal plantlets. Non-mycorrhizal plantlets had greater leaf area ratios and specific leaf areas than mycorrhizal plantlets. Increased leaf tissue mineral levels of P, Mg, Cu, and Mo also occurred with mycorrhizal plantlets. Roots of inoculated guava plantlets were heavily colonized with arbuscules, vesicles and endospores. Guava plantlets were highly mycotrophic with a mycorrhizal dependency index of 103%.

Physiological changes and growth of micropropagated chile ancho pepper plantlets during acclimatization and post-acclimatization

Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during acclimatization. Plantlets were transferred to ex vitro conditions to study selected physiological changes and growth performance during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM). Chile pepper plantlets became acclimatized within 6 days after transplantation. During this period, physiological adjustments occurred, which were critical for plantlet survival. After initial ex vitro transplanting, plantlets experienced water deficit [leaf wilting and reduced relative water content (RWC)], which corresponded with reduced stomatal conductance (gs) and transpiration (E), and an increase in stomatal resistance (rs). Thus, leaf stomata that developed in vitro were functional ex vitro. Because of this stomatal control, plantlets minimized transplant shock, recovered and survived. Prior to transplanting, plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, gs, E, and A were significantly lower two days after transplanting. However, within 6 days after transplanting, plantlets recovered and became photoautotrophic – attaining high A, gs, and E. Water use efficiency was initially low during the first days after transplanting, but increased dramatically at the end of the acclimatization period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with increased plantlet growth.

Iron stress response of three peach rootstock cultivars: Ferric‐iron reduction capacity 1

Abstract Three peach rootstocks were evaluated for their capacity to reduce ferric‐iron (Fe3+) after iron‐stress treatment. Neither of the rootstocks with tolerance to iron (Fe) chlorosis [Titan1 x Nemaguard (Prunus dulcis (all.) D. A. Webb x Prunus persica (Batsch) L.] nor ‘Montclar’ (P. persica) showed consistently higher Fe‐stress induced Fe3+ reduction/g root fresh weight (RFW) compared to the less tolerant rootstock Nemaguard [(P. persica)]. However, non‐stressed ‘Titan’ x Nemaguard (TNG) showed higher leaf chlorophyll content than both ‘Montclar’ (MC) and Nemaguard (NG) and higher mean Fe3+ reduction by root released reductants than Nemaguard. The reduction rate by root released reductants was approximately 22–34% for NG, 15% for MC, and 29% by TNG. ‘Titan’ x Nemaguard and Montclar maintained better root growth (i.e., had less root necrosis) under Fe‐stress than NG which resulted in greater Fe3+ reduction per plant. This indicates that the maintenance of a greater root surface area during Fe‐stress ...

Micropropagation of Crinum 'Ellen Bosanquet' by tri-scales

Crinum lilies (Crinum spp. L.) are tropical and sub-tropical bulbous plants with excellent potential for southern US landscapes. Unfortunately, the more desirable crinum cultivars are slow and expensive to propagate by traditional offsets. The objective of this research was to develop reliable procedures for multiplying Crinum ‘Ellen Bosanquet’ by tissue culture. A sterilization procedure for cleaning explants was developed in which bulb chips containing a basal plate were submersed and agitated in 0.525% hypochlorite for 1 h. For shoot formation, tri-scales (three scales attached to a section of the basal plate) were used as the explant source and grown on MS-based media containing five levels of benzyladenine (BA) (0‐22.2 mM) and five levels of naphthaleneacetic acid (NAA) (0‐5.3 mM). The greatest shoot formation was obtained from the highest level of BA (22.2 mM) without NAA. In a subsequent experiment, explants were cultured for 4 months on media containing 35.5‐88.8 mM BA, and then transferred to hormone-free media for 3 months. BA at 35.5 mM stimulated optimal shoot (8.4) and bulblet (2.8) formation. Plantlets were successfully acclimatized and rooted ex vitro. # 1999 Elsevier Science B.V. All rights reserved.