Influence of the ion-balance in the growth medium on the yield and alkaloid content ofDatura stramonium L.

Plants ofDatura stramonium var.tatula L. Torr. were grown for 24 weeks on vermiculite and provided with mineral solutions where the relative proportions of the major anions (N, S, P) and cations (K, Ca, Mg) were varied within a constant total.With all treatments a cyclic transport of alkaloids (hyoscyamine) from the roots to the upper plant parts appeared. The fluctuations in alkaloid content in the leaves followed those in the roots with a delay of 4 weeks.The interionic ratios seemed to influence growth and alkaloid content rather than to affect the ontogenic variations. In general, the response to the different treatments could be divided into two types. The nitrogen treatments which gave at the same time a higher crop yield and an increased hyoscyamine content, and the other treatments where a much lower yield and content was obtained.The scopolamine content on the other hand seemed to be more affected by the developmental stage. Also, the time of maximal yield was not influenced by the ion-balance but rather the climatic conditions.     

Effects of boundary layer conductance on substomatal pressures of carbon dioxide

Abstract. Gas exchange measurements were made on single leaves of three C₃ and one C₄ species at air speeds of 0.4 and 4.0 m s⁻¹ to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m⁻² s⁻¹ at the lower air speed, and 1.2 to 1.5 mol m⁻² s⁻¹ at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C₃ species, and about 3 Pa lower in the C₄ species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C₃ species. The commonly reported values of substomatal carbon dioxide pressure for C₃ and C₄ species were found to occur only when measurements were made at the higher air speed.     

Host Status of Five Weed Species and Their Effects on Pratylenchus zeae Infestation of Maize

The host suitability of five of the most common weed species occurring in maize (Zea mays L.) fields in South Africa to Pratylenchus zeae was tested. Based on the number of nematodes per root unit, mealie crotalaria (Crotalaria sphaerocarpa) was a good host; goose grass (Eleusine indica), common pigweed (Amaranthus hybridus), and thorn apple (Datura stramonium) were moderate hosts; and khaki weed (Tagetes minuta) was a poor host. Only the root residues of khaki weed suppressed the P. zeae infestation of subsequently grown maize. When goose grass, khaki weed, and mealie crotalaria were grown in association with maize in soil infested with P. zeae, goose grass and khaki weed severely suppressed maize root development; this resulted in a low number of nematodes per maize root system and a high number of nematodes per maize root unit. Mealie crotalaria did not restrict maize root growth and did not affect nematode densities per maize root system or maize root unit. Special attention should be given to the control of mealie crotalaria, which is a good host for P. zeae, and goose grass, which, in addition to its ability to compete with maize, is also a suitable host for P. zeae.     

Effect of boundary layer conductance on the response of stomata to humidity

Abstract. Leaf conductance responses to leaf to air water vapour partial pressure difference (VPD) have been measured at air speeds of 0.5 and 3.0 ms⁻¹ in single attached leaves of three species in order to test the hypothesis that leaf conductance response to VPD is controlled by evaporation from the outer surface of the epidermis, rather than by evaporation through stomata. Total conductance decreased linearly with increassing VPD at both air speeds, but was decreased 1.6 3.0 times as much as by a given incrase in VPD at high than at low air speed. depending on species. In all species the relationship between leaf conductance and the gradient for evaporation from the epidermis was the same at both values of boundary layer conductance, supporting the hypothesis that direct epidermal evaporation controls stomatal guard cell behaviour in responses of stomata to VPD in these species.     

EVOLUTIONARY ECOLOGY OF DATURA STRAMONIUM L. IN CENTRAL MEXICO: NATURAL SELECTION FOR RESISTANCE TO HERBIVOROUS INSECTS

It has been assumed that herbivores constitute a selective agent for the evolution of plant resistance. However, few studies have tested this hypothesis. In this study, we look at the annual weed Datura stramonium for evidence of current natural selection for resistance to herbivorous insects. Paternal half-sib families obtained through controlled crosses were exposed to herbivores under natural conditions. The plants were damaged by two folivorous insects: the tobacco flea beetle Epitrix parvula and the grasshopper Sphenarium purpurascens. Selection was estimated using a multiple-regression analysis of plant size and of damage by the two herbivores on plant fitness measured as fruit production for both individual phenotypes and family breeding values (genetic analysis). Directional phenotypic selection was detected for both larger plant size and lower resistance to the flea beetles, whereas stabilizing phenotypic selection was revealed for resistance to S. purpurascens. However, performing the same analyses on the breeding values of the characters revealed directional and stabilizing selection only for plant size. Thus, no agreement existed between the results of the two types of analyses, nor was there any detectable potential for genetic change in the studied population because of selection on herbivore resistance. The narrow-sense heritability of every trait studied was small (all <0.1) and not different from zero. The potential for evolutionary response to natural selection for higher resistance to herbivores in the studied population of D. stramonium is probably limited by lack of genetic variation. Natural selection acts on phenotypes, and the detection of phenotypic selection on resistance to herbivores confirms their ecological importance in determining plant fitness. However, evolutionary inferences based solely on phenotypic selection analyses must be interpreted with caution.     

Rapid recovery of photosynthetic cell suspension cultures following heterotrophic bleaching

Summary Seven suspension-cultured lines of five different species (Amaranthus powellii Datura innoxia, Glycine max, Gossypium hirsutum, andNicotiana tabacum × Nicotiana glutinosa fusion hybrid), which had been grown under photomixotrophic conditions, were placed under heterotrophic conditions (darkness and media with 3% sucrose or starch) where the chlorophyll levels declined to near zero. After three transfers over a 70-d period, the cells were placed back into photomixotrophic or photoautotrophic conditions where regreening occurred rapidly and continued growth was observed. This rapid adaptation to photosynthetic conditions contrasts with the original initiation process for these cultures, which required many months and an apparent selection since many of the original cells died. Thus, these seven photosynthetic cell suspension cultures appear to be different from the original cultures due possible to genetic or adaptive changes.     

Establishment and characterization of photosynthetic hairy root cultures of Datura stramonium

Twelve different lines of Datura stramonium (normal and hairy) root cultures were subjected to conditions which induce photoautotrophy. Two of the hairy root lines responded to induction, showing clearly a diminished growth rate when compared to heterotrophic cultures, an increase in chlorophyll, a net O₂ evolution, CO₂ fixation, and de novo synthesis of the ribulose 1,5 biphosphate carboxylase enzyme. A time course of growth and tropane alkaloid levels in the tissue and medium, revealed a correlation between the development of the photosynthetic apparatus and the increase in scopolamine. Although normal cultures did not grow photosynthetically, they showed some greening response under the first step of the induction. The correlation between development of photosynthesis and increase in scopolamine synthesis were corroborated with normal root cultures. This experimental model is used for the basic study of the regulatory enzymes involved in the biosynthesis of tropane alkaloids, as well as for the study of their mechanisms of transport.     

A covert contaminant of cultured plant cells: elimination of a Hyphomicrobium sp. from cultures of Datura innoxia (Mill.)

We have discovered a bacterial contaminant in some cell cultures of Datura innoxia (Mill.). The bacterium was tentatively identified as a species of Hyphomicrobium on the basis of its morphology and life cycle, and was isolated and grown in pure culture on a defined medium. The contaminant was not macroscopically observable in plant cell cultures. It caused neither a reduction of plant cell growth nor a noticeable increase in culture turbidity. Furthermore, it was not readily detectable by many standard assays for culture contamination: it would not grow alone in plant culture medium or yeast extract potato dextrose medium, and grew only very slowly on nutrient agar or beef-peptone medium. Repeated treatments with a combination of streptomycin (100 g/ml) and carbenicillin (100 g/ml) eliminated the contaminant from D. innoxia cell cultures without harming the plant cells.     

Sodium chloride resistant cell line from haploidDatura innoxia mill

Summary A cell line resistant to sodium chloride was selected from callus cultures of haploidDatura innoxia by cloning under selective pressure. Cells of the resistant cell line retained their resistance even after subculture in absence of NaCl. Plantlets could be regenerated from resistant cells in the presence as well as absence of NaCl. In contrast, regeneration of plantlets was not possible from normal cells in the presence of NaCl, although regeneration readily occurred in the absence of NaCl.To examine the stability of the resistance in the long-term, callus cultures were initiated in presence of NaCl from stem expiants of the differentiated plantlets. All expiants of plantlets derived from resistant cells showed callus formation. This callus, derived from resistant explants, retained the trait of resistance upon subculture.     

Protein Kinase Activity of in vitro Cultured Plant Cells in Relation to Growth and Starch Metabolism

Taking tetcyclacis, a norbornenodiazentine derivative, as an example, the influence of a growth retardant on the shoot growth of sunflower, soybean, and maize seedlings grown and treated in hydroculture was investigated. In detail, the reduction in the length of various shoot sections {epicotyl, 1st internode, leaf blade) caused by the retardant was studied. At low concentrations of the retardant (\lt10^-6 M) the shortening effects are substantially attributable to an influence on cell elongation, whereas cell division is inhibited as the concentration increases (τ10^-6 M). A comparison of the effects of tetcyclacis in cell suspension cultures of appropriate plant species showed that also in this system concentrations τ 10^-6 M inhibited cell division growth, i. e. there is comparability of plant/ cell culture regarding the retardant effect on cell division. In contrast to the intact plants, however, cell elongation appears to be of only subordinate importance for the growth of cell cultures, as it has been shown using parsley cell suspension cultures.It is discussed to what extent influencing the gibberellin or sterol biosynthesis by means of tetcyclacis provides an explanation for the concentration-dependent effect on the cell division and cell elongation processes.