Distribution of podolactone-type plant growth inhibitors in the coniferae

Plant growth inhibitors of the podolactone-type have been detected by bioassay in ten further species of Podocarpus. The most active extracts in P. elatus were from root tips, root cortex and very young leaves. Fifty-seven other conifers were examined for this type of activity. It is present in Cephalotaxus harringtonia where it is probably due to the presence of harringtonolide, which, like momilactone B from rice husks, shows podolactone-type inhibition of the growth of etiolated dwarf pea hooks.     

Steroid hormone effects on growth and apical dominance of sunflower

External application of estradiol-17β increased shoot growth but decreased root growth of sunflower seedlings. It completely inhibited cotyledonary axillary bud development in decapitated plants at the concentration of 1 μg/plant. Concentrations lower than this promoted cotyledonary axillary bud formation. Testosterone on the other hand inhibited both shoot and root growth and promoted cotyledonary axillary bud formation at all the concentrations used. Progesterone at high (0.25,μg/plant) concentration promoted shoot growth but inhibited root growth. A low concentration (0.1 μg/plant) of progesterone produced the opposite effect.     

The manipulation of polar head group composition of phospholipids in the wheat Miranovskaja 808 affects frost tolerance

Caryopses of the frost-resistant cultivar of the wheat Triticum aestivum L., Miranovskaja 808, were germinated and grown in the presence of various concentrations of choline chloride. Changes in the composition of leaf total phospholipids and leaf total fatty acids at two extreme temperatures (25°C and 2°C) as well as changes in frost resistance were followed. A choline chloride concentration-dependent accumulation of phosphatidyl choline was observed in the leaves. Seedlings grown at 2°C accumulated more phosphatidyl choline at each choline chloride concentration than those grown at 25°C. There was an inverse relationship between the contents of phosphatidyl choline and phosphatidic acid in the leaves. Neither the temperature nor choline chloride seemed to affect fatty-acid composition. Modification of polar-head group composition of phospholipids affected frost tolerance: Seedlings grown in the presence of 15 mM choline chloride at 25°C exhibited a freezing resistance equal to that of hardened controls. The data indicate that the polar-head group composition of membrane phospholipids in plants can be easily manipulated and point to the importance of phosphatidyl choline in cold adaptation processes.     

Correlations between proton-efflux patterns and growth patterns during geotropism and phototropism in maize and sunflower

By placing seedlings of sunflower (Helianthus annuus L.) or maize (Zea mays L.) on agar plates containing a pH indicator dye it is possible to observe surface pH patterns along the growing seedling by observing color changes of the indicator dye. Using this method we find that in geotropically stimulated sunflower hypocotyls or maize coleoptiles there is enhanced proton efflux on the lower surface of the organ prior to the initiation of curvature. As curvature develops the pattern of differential acid efflux becomes more intense. A similar phenomenon is observed when these organs are exposed to unilateral illumination, i.e. enhanced acid efflux occurs on the dark side of the organ prior to the initiation of phototropic curvature and the pattern of differential acid efflux intensifies as phototropic curvature develops. These observations indicate that differential acid efflux occurs in response to tropistic stimuli and that the acid efflux pattern may mediate the development of tropistic curvatures.     

Relationships between xanthoxin,phototropism, and elongation growth in the sunflower seedling Helianthus annuus L.

For phototropic curvature of a green sunflower seedling, only the hypocotyl has to be illuminated; the tip and cotyledons are not involved in stimulus perception. The etiolated seedling is phototropically insensitive, illumination of only the hypocotyl renders it sensitive. It is concluded that the photoreceptor is located within the responding organ. In curving seedlings, the endogenous indoleacetic acid (IAA) remains evenly distributed. However, the inhibitor, xanthoxin (Xa), accumulates on the illuminated side. The degree of phototropic response is generally related to the concentration of Xa. The amount of phototropic curvature is independent of the rate of elongation growth, the former can be changed without affecting the latter, and vice versa. The data conflict with the Cholodny-Went theory, whereas they support the hypothesis of Blaauw that the phototropic reaction is caused by the local accumulation of a growth-inhibiting substance on the irradiated side.Abbreviations CCC chlormequat, (2-chloroethyl)trimethylammonium chloride - GA₃ gibberellic acid - IAA indole-3-acetic acid - Xa xanthoxin     

Control of light-induced bean leaf expansion: Role of osmotic potential,wall yield stress,and hydraulic conductivity

The role of three-turgor-related cellular parameters, the osmotic potential ( _s), the wall yield stress (Y) and the apparent hydraulic conductivity (L'p), in the initiation of ligh-induced expansion of bean (Phaseolus vulgaris L.) leaves has been determined. Although light causes an increase in the total solute content of leaf cells, the water uptake accompanying growth results in a slight increase in _s. Y is about 4 bar; and is unaffected by light. L'p, as calculated from growth rates and isopiestic measurements of leaf water potential, is only slightly greater in rapidly-growing leaves. The turgor pressure of growing cells is lower than that of the controls by about 35%. We conclude that light does not induce cell enlargement in the leaf by altering any of the above parameters, but does so primarily by increasing wall extensibility.Abbreviations and symbols RL red light - WL white light - L'p apparent hydraulic conductivity - OC osmotic concentration - Y wall yield stress - _s osmotic potential     

Photomodulation of growth and specific changes in fatty acid amounts in internodes of green Vigna sinensis L.

First internode growth of green Vigna sinensis L. can be widely modified by light or dark treatments. In all the treatments used there is a good correlation between the internode growth and the rate of C_18-1 accumulation. None of the other fatty acids show such a correlation.Abbreviations C_16-0 palmitoic acid - C₁₇ heptadecanoic acid - C_18-0 stearic acid - C_18-1 octadecenoic acid - C_18-2 linoleic acid - C_18-3 linolenic acid - D darkness - DW dry weight - FR far-red light - FW fresh weight - P_FR phytochrome in the FR absorbing form - R red light - W white light     

Effects of gibberellin and colchicine on microfibril arrangement in epidermal cell walls of Vigna angularis Ohwi et Ohashi epicotyls

Gibberellic-acid (GA₃) treatment of azukibean epicotyls resulted in alterations of the direction of newly deposited microfibrils, on the cell walls. Cells having transverse microfibrils on the inner surface of the wall were observed more frequently in GA₃-treated epicotyls than in untreated or water-treated ones. This effect of GA₃ was negated by simultaneously supplied colchicine. A crossed polylamellate structure was observed in the inner portion of the walls of GA₃-treated cells, but not in the inner portion of the walls of colchicine-treated cells. The wall formed under the influence of colchicine consisted of microfibrils running in the same direction.Abbreviations GA gibberellin - GA₃ gibberellic acid (gibberellin A₃)     

Criteria for the identification of potential colonizers*

Man's interference with the environment encourages colonization by species that are often undesirable, hence a technique by which potential colonizers can be identified is urgently required. It can be developed when general prerequisites for successful colonization are identified. These prerequisites can then serve as criteria to distinguish potential colonizers from non-colonizers. The proposed relevant prerequisites are associated with two problems encountered by all colonists: small founding populations and a difference in the environmental conditions between the source area and the target, making the target rather unpredictable. Both these features increase the risk of random extinction, which can be overcome by possessing a potential for rapid population growth (high r) and for rapid adaptation to environmental conditions (high genetic variability). The parameters associated with meeting these prerequisites can serve for the identification of potential colonizers and for ranking species as to their colonization ability. The proposed technique may best be tested by comparing the intrinsic growth rate and the electrophoretic variability of species that have recently colonized with closely related species that have not done so under similar circumstances. The colonization of the eastern Mediterranean by Red Sea species immigrating via the Suez Canal created an appropriate system for such a test.     

Growth and curvature in seedlings of Pisum sativum and an ageotropic mutant

In an attempt to explain the influence of gravity on the behaviour of ageotropic plant organs, a pea mutant (Pisum sativum ageotropum) and normal pea (Pisum sativum cv. Sabel) were examined. The mutant has a significantly lower germination rate (large seeds: 25%, small seeds: 10%) than normal pea seeds (55%). Removal of testa increased germination dramatically, the values obtained were 63 and 89%, respectively. Immediately after imbibition the mutant from which the testa had been removed, developed more slowly than normal pea seeds; after 28 h the difference in elongation rate between the two types was reversed. When continuously stimulated geotropically in the horizontal position the elongation in the mutant is larger than in the normal pea roots kept in the same position. During a 24 h period starting 48 h after imbibition the mutant root elongated 45.0 mm while the value for the normal pea root was 11.5 mm. The course of the geotropic curvature in roots of the two types has been followed during a period of 24 h. Normal pea roots develop an asymmetry in the extreme root tip region after 30 min of horizontal stimulation. After prolonged stimulation (exceeding 2 h) the asymmetry has disappeared and the curvature distributed over the entire growth region. When roots of normal pea are stimulated continuously at various angles, the optimum angle of geotropic response is 90° with decreasing responses in the order 135° (i.e. the root tip is pointing obliquely upward) and 45°. The presumed ageotropic behaviour of the mutant has only to a certain extent been confirmed in the present study. When stimulated at 135° a slight positive curvature developed; stimulation at 90° and 45° gave a slight negative curvature.