The effects of mechanically-induced stress and plant growth regulators on the growth of lettuce,cauliflower and bean (Phaseolus vulgaris L.) plants

The plant growth regulators, gibberellic acid (GA₃), ethephon and chlormequat chloride (CCC) were sprayed on young lettuce, cauliflower and bean (Phaseolus vulgaris) plants, which had either been given or not been given a mechanically-induced stress (MIS) treatment. MIS was applied by brushing the plants with paper for 1.5 minutes each day. GA₃ increased extension growth of bean and leaf length of lettuce in unbrushed plants as much as in brushed ones. CCC and ethephon were less effective at reducing the height of brushed bean plants compared to unbrushed ones. The effects of CCC on the growth of cauliflower and lettuce plants was not influenced by brushing, whereas unbrushed plants responded more readily to ethephon than did brushed ones. The effects of CCC on growth were generally similar to those of MIS whereas the effects of ethephon were in many ways different to MIS.The results are discussed in relation to the use of PGR and MIS treatments for modifying plant growth.     

Interaction of N-methyl phenazinium radical cation with single-stranded polyriboadenylic acid

N-Methyl phenazinium radical cation (MPH^+?) is known to interact with DNA in a manner analogous to an acridine dye (1). In the present communication, we have investigated the interaction of MPH^+? with single stranded polyriboadenylic acid (poly A) through the combined use of electron paramagnetic resonance (EPR) and Fourier-transform proton magnetic resonance (FT-PMR). Use of a paramagnetic dye enables us to obtain average distances between three protons of poly A nucleotide and the unpaired electron on the dye, giving direct evidence for the π-π complexation of the dye with the adenine base. In addition, kinetic parameters for the complexation reaction are evaluated.     

The prevention of dehydration injury in celery seeds by polyethylene glycol, abscisic acid, dark and high temperature

Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion.     

The cellular and molecular basis for divergent allergic responses to chemicals.

Chemicals vary with respect to the nature of allergic reactions which they will elicit preferentially. A wide variety of environmental and industrial chemicals are known to cause allergic contact dermatitis (contact sensitivity). Some of these are able also to induce respiratory allergy. This article reviews the characteristics of immune responses to different classes of chemical allergens and the role which functional subpopulations of T helper (TH) cells and their soluble cytokine products play in the induction of allergic sensitization. In addition, new opportunities to identify and classify chemical allergens based upon characterization of divergent allergic responses is discussed.     

The involvement of the root apex and cytokinins in the control of lateral root emergence in lettuce seedlings

Removal of the apical 3 mm of the primary root of hydroponically-grown lettuce seedlings 3 or 5 days after sowing, prevented further elongation of the root and increased both the number and total length of lateral roots. The length of the lateral zone, i.e. the distance from the base of the parent root to the lateral nearest the tip, except on one occasion, remained the same as the control in both 3 and 5 day treatments, until the length of the decapitated root (which had ceased elongating) became limiting.Zeatin applied via the roots, at a concentration range from 3 × 10^–10 M to 10^–8 M reduced tap root extension growth at all concentrations. Lateral root emergence was enhanced by low zeatin concentrations and retarded by higher ones. In general, the lateral zone length was the same in cytokinin-treated plants as in untreated controls.     

Cytokines and Langerhans cell mobilisation in mouse and man

A critical event during the development of cutaneous immune responses, including those provoked by contact allergens, is the mobilisation of epidermal Langerhans cells (LC). These cells act as sentinels of the immune system in the skin, responding to a variety of local insults with migration and delivery of potentially foreign signals to draining lymph nodes. Experimental studies have revealed that the regulation of mobilisation and migration of LC display striking similarities in man and mouse. In both species it has been found that the successful induction of migration requires that LC receive (at least) 2 independent cytokine signals; provided by tumour necrosis factor-alpha (TNF-alpha) and interleukin 1beta. In addition, a similar heterogeneity in man and mouse is apparent with regard to the fraction of LC responding rapidly to mobilisation signals, with the same proportion of cells (20%-30%) being stimulated to migrate in each case. Other similarities exist between mice and humans with respect to LC function, including an age-related decrement in both LC frequency and responsiveness to TNF-alpha. Collectively these studies demonstrate that the mouse provides a valuable experimental surrogate for the human skin immune system, particularly with respect to LC biology, and suggest that it is possible to perform extrapolations between species with some confidence.     

Lactoferrin: influences on Langerhans cells, epidermal cytokines, and cutaneous inflammation.

It has been suggested previously that, in addition to other biological roles, lactoferrin (LF) may display antiinflammatory properties secondary to the regulation of cytokine expression. To explore this concept further, we have here examined in human volunteers the influence of recombinant homologous LF on the migration of epidermal Langerhans cells (LC), a process that is known to be dependent upon the local availability of certain proinflammatory cytokines including tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). In common with previous studies in mice, it was found that topical administration of LF prior to exposure at the same site to the contact sensitizer diphenylcyclopropenone resulted in a significant reduction of allergen-induced LC migration from the epidermis (measured as a function of the frequency of CD1a+ or HLA-DR+ LC found in epidermal sheets prepared from punch biopsies of the treated skin sites). However, under the same conditions of exposure, LF was unable to influence migration of LC induced by the intradermal administration of TNF-alpha data consistent with the hypothesis that one action of LF in the skin is to regulate the local production of this cytokine. Further support for this hypothesis was derived from experiments conducted with IL-1beta. This cytokine is also able to induce the mobilization of LC following intradermal injection, although in this case, migration is known to be dependent upon the de novo production of TNF-alpha. We observed that prior exposure to LF resulted in a substantial inhibition of IL-1beta-induced LC migration, data again consistent with the regulation of TNF-alpha production by LF. Collectively, these results support the view that LF is able to influence cutaneous immune and inflammatory processes secondary to regulation of the production of TNF-alpha and possibly other cytokines.