Effects of continuous leaf wetness on photosynthesis: adverse aspects of rainfall

Above-ground parts of Phaseolus vulgaris L. plants were treated with artificial misty rain (‘rain’) in a growth chamber to investigate the effects of leaf wetness on photosynthetic performance. The following results were obtained. (1) Stomata closed completely within 2 min of the onset of continuous ‘rain’ application and gradually opened to half the original aperture by 60 min. The rate of CO₂ exchange measured on such wet leaves changed in parallel with the changes in stomatal aperture and attained 60 to 70% of the control level by 1h. (2) The dependence of the rate of leaf photosynthesis, A, on the intercellular CO₂ concentration, c_i [A(c_i) relationship], examined in thoroughly dried leaves which had been treated with ‘rain’ did not change until after 4 h of treatment. However, leaves treated for 6h showed discernible decreases in A at high c_i (c_i>500μmolmol ^?1). The photosynthetic rate of leaves treated with ‘rain’ for 24 h was reduced at all c_i, and A at the ambient CO₂ concentration of 350μmolmol^?1 was 60 to 70% of that of the control level. The rate of photosynthesis did not recover even after 3 d of treatment of the plants in a dry environment. These results clearly indicate that leaf wetness causes not only instantaneous suppression of photosynthesis but also chronic damage to the photosynthetic apparatus. Potential effects of leaf wetness on photosynthetic performance in nature are also discussed.     

Thigmomorphogenesis: Ethylene evolution and its role in the changes observed in mechanically perturbed bean plants

Mechanical perturbations, in the form of either rubbing or wounding, cause ethylene evolution from bean internodes ( Phaseolus vulgaris L. cv. Cherokee Wax). This evolution begins 45 to 60 min after perturbation or wounding and peaks about 2 h later. Maximal thigmomorphogenesis occurs if internodes are perturbed when they are 10 mm or less in length. Maximal ethylene evolution, however, occurs in longer internodes. When one internode is perturbed, ethylene evolution is not observed from other internodes even though they respond thigmomorphogenetically by exhibiting decreased elongation. Ethylene evolution is apparently a result of increased 1-amino-cyclopropane-1-carboxylic acid (ACC) production after perturbation. Inhibitors of ACC and ethylene synthesis block increased radial growth but not reduced elongation. Ethylene may therefore be only one of several factors causing thigmomorphogenesis.     

Evolution of ethylene by sulphur dust addition

Kidney-bean plants ( Phaseolus vulgaris L. cv. Contender) were dusted with sulphur 25 days after germination. The amount of ethylene evolution was measured in shoots (with attached leaves) and roots from plants in several stages of development. The growth of shoots and roots was also measured, and the flowering time observed. The ethylene evolution was associated with precise morphogenic stages. The amounts of ethylene produced from sulphur treated plants, compared with that evolved from control plants, showed two stages of stimulation in shoots, one preceding full bloom and one preceding fruit-set. Inhibition of ethylene evolution due to sulphur dust occurred in roots before initiation of floral primordia and before full bloom. The treatment with sulphur dust seemed to increase the number of leaves per plant, but only in the vegetative stage. Likewise, the earliness of flowering was enhanced. The effects of elemental sulphur dust treatments on ethylene evolution may be attributed to a slow oxidation of elemental sulphur in air producing SO²; this SO² greatly enhances ethylene evolution from leaf tissues.     

Effect of Cytokinin 4-PU-30 on the Lipid Composition of Water Stressed Bean Plants

Fourteen days-old bean plants, grown on sand with Knop's nutrient solution were subjected to water stress (three days without irrigation). The stress led to a decrease in almost all lipid classes except phospholipids in the primary leaves. The content of palmitic acid increased, and that of the linolenic acid decreased. An increase of hexadecenoic acid in phospholipids was also observed. Rewatering for 24 h led to the recovery of the stressed plants including that of the photosynthetic apparatus, but the changes in the lipid composition were insignificant. The spraying of the plants before and after the water stress with 5 × 10-6 M solution of the phenylurea cytokinin 4-PU-30 alleviated negative effect of water stress on the lipid membrane composition permitting the plants to resist the harmful environment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Alterations in Endogenous Levels of Gibberellin-like Substances during Germination of Phaseolus vulgaris Seeds

The endogenous gibberellin-like substances were determined in mature dry and germinating bean seeds, Phaseolus vulgaris L. cv. Alabaster. Methanol extracts were partitioned against ethyl acetate and butanol at neutral and acid pH. Each phase was individually chromatographed on a silica gel column. The gibberellin activity was measured with the Tan-ginbozu dwarf rice micro-drop bioassay. Each extract was tested in two dilutions. Extracts from dry seeds showed the highest gibberellin activity, largely attributable to ethyl acetate-soluble substances. The activity was considerably reduced in extracts from seeds imbibed for 1 day. Gibberellin-like substances soluble in butanol appeared in extracts from seeds soaked for 1 or more days.     

On the Relationship between the Activity of O-Methyltransferase and the Content of Lignin in Various Organs of Kidney Bean

The activity of O-methyltransferase (OMT) and the content of lignin in various organs of 12- to 14-day-old seedlings of kidney bean (Phaseolus vulgarisL., cv. Saksa) were determined. The epicotyl and hypocotyl were characterized by the highest OMT activity, and the leaves, by the lowest OMT activity. At the same time, the lignin content gradually increased in the following order: leaves < epicotyl < hypocotyl < roots. Thus, in kidney bean seedlings, there is no direct relationship between the OMT activity and the lignin content. It is suggested that lignin biosynthesis is limited by biosynthetic steps other than O-methylation of caffeic and 5-hydroxyferulic acids affected by OMT.     

A comparison of methods for inoculating bean plants with Elsinoë phaseoli and some factors affecting infection

Bean (Phaseolus vulgaris) leaves were inoculated with a conidial suspension of Elsinoe phaseoli by spraying, by applying a 10 μl drop, by a cotton wool technique or by using a camel hair brush. Spray application resulted in a uniform distribution of lesions over the leaf surface and gave consistent levels of infection between repetitions. Drop application allowed good control of the amount of inoculum applied. Although brush or cotton wool techniques gave high levels of infection it was not possible to control the amount of inoculum. Only immature tissues were susceptible to infection. Five cultivars were inoculated with two isolates and disease was scored on the basis of numbers of lesions and lesion type (scab severity). The small white cvs PAN 181 and Teebus were the most resistant; lesions were small and generally fewer than on the large-seeded red speckled sugar bean cvs Umlazi and Umvoti. The value of the different inoculation techniques in studies on bean scab is discussed.     

The importance of the ratio UV-B/photosynthetic active radiation (PAR) during leaf development as determining factor of plant sensitivity to increased UV-B irradiance: effects on growth, gas exchange and pigmentation of bean plants (Phaseolus vulgaris cv. Label)

To evaluate the effect of different naturally occurring irradiation conditions on the sensitivity of bean (Phaseolus vulgaris cv. Label) to increased UV-B levels, plants were grown under six different light treatments. In the control series (at ambient levels of UV-B), UV-B and visible light were decreased in parallel, resulting in three different total irradiation treatments with the same UV-B/PAR ratio. A second series with a 15% increase in UV-B irradiation at each PAR level was used to investigate the effect of UV-B under the varying total irradiance levels. The different total irradiance levels resulted in large differences in total dry weight, specific leaf weight, photosynthesis-light response and pigment concentrations. Nevertheless, the 15% increase in UV-B resulted in equal reductions in total dry weight (from 24.5 to 34.3%) and effective photosynthesis for all light levels. The accumulation of protective pigments in the primary bean leaves was strongly correlated to the total irradiance level (200% increase from the lowest to the highest light level), but was not influenced by increasing UV-B levels. As the UV-B/PAR ratio outside increases with decreasing total irradiance (when induced by cloud cover) this implies that low radiation levels are potentially dangerous to some plants, even though the UV-B levels may seem negligible.     

Influence of salinity and abscisic acid on the O2 uptake by N2-fixing nodules of common bean

The effects of NaCl and ABA on the respiration of N₂-fixing nodules were analysed in common bean (Phaseolus vulgaris) inoculated with Rhizobium tropici the reference strain CIAT899. Shoot and nodule growth was more inhibited by NaCl than root growth. The O₂ uptake by nodulated roots at 21 kPa O₂ was significantly inhibited by salinity. Raising pO₂ stimulated nodule respiration more under NaCl treatment than for the control, although it did not compensate totally for the inhibitory effect of NaCl. Short NaCl application was less destructive than long term application. Also, the external application of ABA inhibited nodule respiration, and this inhibition was partly compensated by raising pO₂.     

菜豆种质资源RAPD多样性的研究Ⅱ

本研究收集了我国43个栽培品种,国际热带农业中心13个半野生品种,波兰4个矮生品种共60个菜豆品种资源,将其分成三大类型,即蔓生种35个,矮生种12个,半野生种13个,从RAPD标记上进行了研究,探明种内及各种群间的遗传相似度、遗传距离,绘制聚类分析图。综合RAPD标记聚类图,表明:蔓生种群分为五大类;矮生种群分为二大类;半野生种群分为二大类。我国是菜豆的主要育种、栽培地区,收集国内外菜豆种质资源,开展DNA水平的分子标记将有助于了解菜豆种内、各种群间的遗传基础,确定各资源材料间的亲缘关系,为我国菜豆种质资源的保存及培育优良品种工作提供一定的理论依据。