Search

In this paper, a pH control system for an experimental recirculating hydroponic growth chamber for the NASA Mars exploration program has been modeled and implemented. The resulting model has a bilinear Weiner type structure. A novel approximation approach is presented to obtain a simplified plant model controller design. Perturbation analysis validates the applicability of the approximation for the specific pH control of a closed-loop hydroponic growth chamber. A modified PI controller that takes into account on-off nature of the solenoid valve actuator was designed to control the pH level. The closed-loop system is shown to be BIBO stable with respect to the original bilinear plant model. Experimental results for reference tracking and disturbance rejection in an operational hydroponic chamber with growing plants have demonstrated the effectiveness of the proposed approach.Copyright © 2006 by ASME

Plant roots are optimized to exploit resources from the soil and as each root explores this environment it will encounter a range of biotic and abiotic stimuli to which it must respond. Therefore, each root must possess a sensory array capable of monitoring and integrating these diverse stimuli to direct the appropriate growth response. Touch and gravity represent two of the biophysical stimuli that plants must integrate. As sensing both of these signals requires mechano-transduction of biophysical forces to biochemical signaling events, it is likely that they share signal transduction elements. These common signaling components may allow for cross-talk and so integration of thigmotropic and gravitropic responses. Indeed, signal transduction events in both plant touch and gravity sensing are thought to include Ca(2+)- and pH-dependent events. Additionally, it seems clear that the systems responsible for root touch and gravity response interact to generate an integrated growth response. Thus, primary and lateral roots of Arabidopsis respond to mechanical stimuli by eliciting tropic growth that is likely part of a growth strategy employed by the root to circumvent obstacles in the soil. Also, the mechano-signaling induced by encountering an obstacle apparently down-regulates the graviperception machinery to allow this kind of avoidance response. The challenge for future research will be to define how the cellular signaling events in the root cap facilitate this signal integration and growth regulation. In addition, whether other stimuli are likewise integrated with the graviresponse via signal transduction system cross-talk is an important question that remains to be answered.

Touch and gravity are two of the many stimuli that plants must integrate to generate an appropriate growth response. Due to the mechanical nature of both of these signals, shared signal transduction elements could well form the basis of the cross-talk between these two sensory systems. However, touch stimulation must elicit signaling events across the plasma membrane whereas gravity sensing is thought to represent transformation of an internal force, amyloplast sedimentation, to signal transduction events. In addition, factors such as turgor pressure and presence of the cell wall may also place unique constraints on these plant mechanosensory systems. Even so, the candidate signal transduction elements in both plant touch and gravity sensing, changes in Ca2+, pH and membrane potential, do mirror the known ionic basis of signaling in animal mechanosensory cells. Distinct spatial and temporal signatures of Ca2+ ions may encode information about the different mechanosignaling stimuli. Signals such as Ca2+ waves or action potentials may also rapidly transfer information perceived in one cell throughout a tissue or organ leading to the systemic reactions characteristic of plant touch and gravity responses. Longer-term growth responses are likely sustained via changes in gene expression and asymmetries in compounds such as inositol-1,4,5-triphosphate (IP3) and calmodulin. Thus, it seems likely that plant mechanoperception involves both spatial and temporal encoding of information at all levels, from the cell to the whole plant. Defining this patterning will be a critical step towards understanding how plants integrate information from multiple mechanical stimuli to an appropriate growth response.

The possibility of enhancing the intrinsic ex-situ bioremediation of a chronically polychlorinated biphenyl-contaminated soil by using cyclodextrins was studied in this work. The soil, contaminated with a large array of polychlorinated biphenyls and deriving from a dump site where it has been stored for about 10 years, was found to contain indigenous cultivable aerobic bacteria capable of utilising biphenyl and chlorobenzoic acids. The soil was amended with inorganic nutrients and biphenyl, saturated with water, and treated in aerobic batch slurry- and fixed-phase reactors. Hydroxypropyl-beta-cyclodextrin and gamma-cyclodextrin, added to both reactor systems at the concentration of 10 g/L at the 39th and 100th days of treatment, were found to generally enhance the depletion rate and extent of the soil polychlorobiphenyls. Despite some abiotic losses could have affected the depletion data, experimental evidence, such as the production of metabolites tentatively characterized as chlorobenzoic acids and chloride ion accumulation in the reactors, indicated that cyclodextrins significantly enhanced the biological degradation of the soil polychlorobiphenyls. This result has been ascribed to the capability of cyclodextrins of enhancing the availability of polychlorobiphenyls in the hydrophilic soil environment populated by immobilised and suspended indigenous soil microorganisms. Both cyclodextrins were metabolised by the indigenous soil microorganisms at the concentration at which they were used. Therefore, cyclodextrins, both for their capability of enhancing the biodegradation of soil polychlorobiphenyls and for their biodegradability, can have the potential of being successfully used in the bioremediation of chronically polychlorinated biphenyl-contaminated soils. Copyright 1998 John WileySons, Inc.

Antioxidant enzymes are an important part of the defence mechanisms against free radical damage. Little is known, however, about the relationship between sex steroid hormones and cellular antioxidant systems. We have investigated the effect of physiological sex steroid changes on the erythrocyte antioxidant glutathione peroxidase (GSH-Px) activity during the menstrual cycle in a population of healthy normomenorrhoic women.Prospective, controlled.Ten normally cycling women (age range: 19-28 years; mean: 23.3 years) were recruited for alternate-day blood sampling from the first day of one menstrual bleed until the first day of the subsequent menstrual phase.Plasma was analysed for LH, FSH, oestradiol (E2) and progesterone (P4) concentrations. Erythrocyte GSH-Px activity was evaluated on the same days in all subjects. Pyruvate-kinase (PK) activity, as an index of red blood cell population age, was also determined.All the women examined had a normal ovulatory cycle, as indicated by the hormone plasma pattern. Cycle length was standardized on the basis of the preovulatory E2 peak. Significant cycle phase-related changes in GSH-Px (P0.03) were observed, with higher GSH-Px activity levels being found from the later follicular to early luteal phase as compared to early follicular phase (chi 2 = 8.53, P0.001 and chi 2 = 5.54, P0.002, respectively). A significant positive correlation was observed between mean E2 and GSH-Px cycle-related changes (r = 0.78, P = 0.001). Conversely, no significant cycle phase-dependent variations were detected in PK.The findings support the hypothesis that physiological ovarian E2 production during the menstrual cycle may play an important role in regulating erythrocyte glutathione peroxidase activity.

Electrical cost, primarily for lighting, is one of the largest factors inhibiting the development of “warehouse-based” controlled environment agriculture (CEA). In a jointly sponsored collaboration, we have developed a reconfigurable LED lighting array aimed at reducing the electrical energy needed to grow crops in controlled environments. The lighting system uses LED “engines” that can operate at variable power and that emit radiation only at wavelengths with high photosynthetic activity. These light engines are mounted on supports that can be arranged either as individual intracanopy “lightsicles” or in an overhead plane of lights. Heat is removed from the light engines using air flow through the hollow LED strip mounts, allowing the strips to be placed in close proximity to leaves. Different lighting configurations depend on the growth habit of the crops of interest, with intracanopy lighting designed for planophile crops that close their canopy, and close overhead lighting intended for erectophile and rosette crops. Tests have been performed with cowpea, a planophile dry bean crop, growing with intracanopy LED lighting compared to overhead LED lighting. When crops are grown using intracanopy lighting, more biomass is produced, and a higher index of biomass per kW-h is obtained than when overhead LEDs are used. In addition, the oldest leaves on intracanopy-grown plants are retained throughout stand development, while plants lit from overhead drop inner-canopy leaves due to mutual shading after the leaf canopy closes. Research is underway to increase the energy efficiency and automation of this lighting system. This work was supported in part by NASA: NAG5-12686.

Plasma levels of 17 beta-estradiol (E2) and malondialdehyde and erythrocyte antioxidant enzyme [superoxide dismutase, catalase, and glutathione-peroxidase (GSH-Px)] activities were evaluated in 20 healthy eumenorrhoic women (EW) on day 7 of the menstrual cycle and in 48 secondary hypothalamic amenorrhea patients (AP) (time 0). The AP were randomly divided into four subgroups of 12 subjects and treated with transdermal E2 for 30 days (subgroup A), oral medroxyprogesterone-acetate for 30 days (subgroup B), and transdermal E2 plus medroxyprogesterone-acetate for 30 days (subgroup C). The fourth subgroup acted as control. E2 and malondialdehyde plasma levels and superoxide dismutase, catalase, and GSH-Px activities were evaluated in subgroups A, B, and C on day 30 of therapy and in the control subgroup. GSH-Px activity was significantly higher in EW than in AP at time 0. A statistically significant increase in E2 plasma levels and GSH-Px activity was observed in subgroups A and C on day 30 of treatment, and there was a significant positive correlation between E2 plasma levels and GSH-Px activity in both subgroups. After a month of treatment, erythrocyte GSH-Px activity in subgroups A and C was not significantly different from that observed in EW. After a month of treatment, no significant variation was found in subgroup B nor in the control group. These results strongly suggest that when plasma E2 is restored to physiological levels in AP, it stimulates erythrocyte GSH-Px activity. Progesterone therapy did not induce significant modifications.