The coleoptiles of wheat (Triticum aestivum L.) seedlings of cultivar Trémie are desiccation tolerant when 3 days old, although the roots are not. Cutting some of the coleoptiles open prior to dehydration rapidly increased the drying rate. This rendered the coleoptiles sensitive to desiccation, providing a useful model with which to study desiccation tolerance. Both sensitive and tolerant seedlings were dehydrated to 0.3 g H(2)O g(-1) dry mass (g.g) and thereafter rehydrated. Sensitive tissues accr- ued the lipid peroxidation products H(2)O(2)and MDA, and substantial subcellular damage was evident in dry tissues. H(2)O(2) and MDA accumulated slightly only in dry tolerant coleoptiles and no subcellular damage was evident. The activity of antioxidant enzymes glutathione reductase (EC1.6.2.4), superoxide dismutase (EC 1.14.1.1) and catalase (EC 1.11.1.6) increased on drying in both tolerant and sensitive tissues, but were sustained on rehydration in only the tolerant tissues. It is proposed that free radical damage sustained during rapid drying exceeded the ameliorating capacity of antioxidant systems, allowed accrual of lethal subcellular damage. Slow drying enabled sufficient detoxification by antioxidants to minimize damage and allow tolerance to drying. Three LEA- (p11 and Asp 52) and dehydrin- (XV8) like proteins were detected by western blots in tolerant coleoptiles dried to 3.0 g.g and below. Only one (Asp 52) was induced at low water content in rapidly dried sensitive coleoptiles. None were present in root tissues. XV8 RNA (northern analyses) was induced on drying only in tolerant coleoptiles and correlated with protein expression. These stress-putative protein protectants (and XV8 transcripts) appear to be down-regulated during germination but wheat seedlings temporarily retain the ability to reproduce them if drying is slow. Sucrose accumulation during dehydration was similar for both sensitive and tolerant tissues, suggesting that this sugar has little role, or is not effective in isolation, in protecting against desiccation damage in wheat seedlings. In summary, the slower rate at which tolerant coleoptiles were dried allowed for the mobilization of protection mechanisms with which to survive desiccation. Rapid drying of tissues precluded induction of some putative stress protein protectants and caused damage in excess of the ameliorating capacity of the antioxidant protection systems.

The potentisation process by which homeopathic preparations are produced raises the concern that these medicines have placebo effects only, since they theoretically no longer contain active molecules of the diluted substance. Plant models offer a method of examining the efficacy of homeopathically prepared solutions. This study examined the effects of homeopathically prepared gibberellic acid (HGA3) on the germination performance of barley (Hordeum vulgare L.) seeds. The effect of HGA3 (4-200 cH) on seed germination rate and seedling development was compared to that of the most commonly used form of gibberellic acid (GA3), 0.5 g l(-1), and control (distilled water). The extent and type of response was dependent on the vigour level of the seedlot. Treating seeds from three vigour groups in HGA3 consistently resulted in larger seedlings. High-vigour seeds treated with HGA3 4, 30 and 200 cH germinated faster, and roots of medium-vigour seedlots treated in HGA3 15 cH were longer. Biphasic effects of HGA3 were also demonstrated. As a plant model, germinating barley seeds successfully demonstrated the ability of HGA3 to produce a biological response.

tests appears to be directly related to the condition of the seedbed environment (Egli and TeKrony, 1996). Emergence of soybean [Glycine max (L.) Merr.] seedlings in theKnowledge of the precise causes of emergence failure field is frequently less than predicted by standard germination, but the causes of this emergence failure are not well understood. This and their relative importance is lacking, and would idenstudy explored the influence of soil pathogens and seed vigor on tify those factors in the soil environment which need to soybean seedling preemergent growth and emergence. Seed from six be countered or modified if emergence is to be successseedlots, representing a range in seed vigor, were planted as pregermifully predicted and achieved. Such knowledge may also nated and as dry seed into sterile and pathogen-infested soil maincontribute to the development of improved vigor tests tained at a constant soil water potential (Ϫ0.005 MPa). Final emerwith which to identify seedlots most likely to be tolerant gence (FE) and emergence rates from two planting depths (25 and of adverse soil conditions. mm) were recorded under ambient greenhouse conditions. OnceEmergence responses to seedbed conditions have prethe FE stage had been reached, nonemerged seedlings were exhumed, viously been examined primarily in prevailing field conand classified as stunted, abnormal, or dead. The FE of the high-and ditions, as opposed to controlled conditions (Hegarty, medium-vigor seedlots was always higher than the low-vigor seedlots, and the advantage was greatest under stressful conditions (deep plant- 1979; Halmer and Bewley, 1984; Finch-Savage and Pill,ing, nonsterile soil). The FE was always lower in nonsterile than sterile 1990). Few attempts have been made to distinguish be- soil. Seedlings emerged more slowly from deep plantings and whentween the effects of the seedbed environment, seed qualpathogens were present, and FE decreased as emergence was delayed ity, or soilborne pathogens on germination sensu stricto, in nonsterile soil. This relationship became more pronounced with and on preemergent growth. In fact, the two terms are low vigor seed. Planting pregerminated seeds always resulted in higher often erroneously used interchangeably, yet the two are FE than dry seeds, but it did not eliminate emergence failure. Abnorbiochemically distinct phases of growth (Perino and mal seedlings accounted for most of the emergence failure in sterile Cô me, 1991), with potentially different responses to spesoil, but the lack of germination or of growth immediately after germicific environmental conditions. The purpose of this study, nation was also important in nonsterile soil. Lack of germination alone therefore, was to investigate the nature of the relationtherefore does not account for lack of emergence; postgerminative, preemergent growth may be more important.

Emergence of soybean [Glycine max (L.) Merr.] seedlings in the field is frequently less than predicted by standard germination, but the causes of this emergence failure are not well understood. This study explored the influence of soil pathogens and seed vigor on soybean seedling preemergent growth and emergence. Seed from six seedlots, representing a range in seed vigor, were planted as pregerminated and as dry seed into sterile and pathogen‐infested soil maintained at a constant soil water potential (−0.005 MPa). Final emergence (FE) and emergence rates from two planting depths (25 and 60 mm) were recorded under ambient greenhouse conditions. Once the FE stage had been reached, nonemerged seedlings were exhumed, and classified as stunted, abnormal, or dead. The FE of the high‐ and medium‐vigor seedlots was always higher than the low‐vigor seedlots, and the advantage was greatest under stressful conditions (deep planting, nonsterile soil). The FE was always lower in nonsterile than sterile soil. Seedlings emerged more slowly from deep plantings and when pathogens were present, and FE decreased as emergence was delayed in nonsterile soil. This relationship became more pronounced with low vigor seed. Planting pregerminated seeds always resulted in higher FE than dry seeds, but it did not eliminate emergence failure. Abnormal seedlings accounted for most of the emergence failure in sterile soil, but the lack of germination or of growth immediately after germination was also important in nonsterile soil. Lack of germination alone therefore does not account for lack of emergence; postgerminative, preemergent growth may be more important.

A survey of the germination performance of some South African soya bean [Glycine max (L.) Merrill.] cultivars, produced at different localities, was conducted. Seeds were harvested from two early-maturing (Columbus and Crawford), two intermediate-maturing (Prima and Highveld Top), and two late-maturing cultivars (Ibis and Impala), from seven sites. The standard germination test was performed on all 42 seed lots. Germination performance was not linked to any particular maturity type or cultivar, but locality had a distinct effect. Germination of seeds of some seed lots harvested at Groblersdal and Potchefstroom was reduced, primarily due to the effect of seed-borne pathogens, which resulted in relatively large numbers of dead seeds. At Piet Retief, poor germination performance was inversely related to the large number of abnormal seedlings in the standard germination test, which was due to damaged seed coats. There were highly significant correlations between the number of dead seeds and the incidence of fungal infection, and between the number of abnormal seedlings and seedcoat damage. The predominant seed-borne pathogen was identified as Fusarium equiseti, a fungus not previously reported as being present in South African soya bean seed.Saadontkieming van verskeie Suid-Afrikaanse sojaboon [Glycine max(L.) Merrill.]-kultivars, wat in verskillende lokaliteite geproduseer is, is ondersoek. Saad van twee kortseisoen-kultivars (Columbus en Crawford), twee langseisoen-kultivars (Ibis en Impala) en twee intermediere tipes (Prima en Highveld Top) is op sewe lokaliteite geoes. Die standaardontkiemingstoets is op al42 saadlotte uitgevoer. Ontkiemingsprestasie het nie met groeiperiodetipe of kultivar verband gehou nie, maar daar was 'n duidelike invloed van lokaliteit. Ontkieming van sommige van die saadlotte wat op Groblersdal en Potchefstroom geoes is, is verlaag, hoofsaaklik as gevolg van die invloed van saadgedraagde patogene wat tot relatiewe hoe getalle dooie sade gelei het. Swak prestasie van saad afkomstig van Piet Retief was te wyte aan 'n hoe persentasie abnormale saailinge in die ontkiemingstoets wat die gevolg van beskadigde saadhuide was. Hoogs betekenisvolle korrelasies is gevind tussen die aantal dooie sade en die voorkoms van swaminfeksie, asook tussen die aantal abnormale saailinge en saadhuidskade. Die algemeenste saadgedraagde patogeen was Fusarium equiseti. Hierdie fungus is nog nie voorheen as 'n patogeen van Suid-Afrikaanse sojaboonsaad gerapporteer nie.