Imbibition period as the critical temperature sensitive stage in germination of lima bean seeds

Lima bean seeds (Phaseolus lunatus L.) and excised embryonic axes can be injured during imbibition at temperatures below 25°. The early imbibitional stage is critical; imbibition at 25° followed by low temperature exposure does not cause injury. Sensitivity to chilling injury is conditioned by the pre-harvest seed history. Low vigor (bleached) seeds are most sensitive to injury, the effects of which can be intensified by restricted oxygen supply during early axis growth. The seed coat, by preventing water uptake, can permit the seed to avoid injury. This protective mechanism is most effective at low temperature and high moisture stress. Immediately following low temperature imbibition, injured axes lose organic materials, probably nucleotides. This organic leachate is a potential influence on soil microorganisms and, together with the temperature sensitivity, vigor, and seed coat effect undoubtedly is important in controlling the potential variability in germination shown by a seed population.     

Sucrose metabolism in lima bean seeds

Developing and germinating lima bean (Phaseolus lunatus var Cangreen) seeds were used for testing the sucrose synthase pathway, to examine the competition for uridine diphosphate (UDP) and pyrophosphate (PPi), and to identify adaptive and maintenance-type enzymes in glycolysis and gluconeogenesis. In developing seeds, sucrose breakdown was dominated by the sucrose synthase pathway; but in the seedling embryos, both the sucrose synthase pathway and acid invertase were active. UDPase activity was low and seemingly insufficient to compete for UDP during sucrose metabolism in seed development or germination. In contrast, both an acid and alkaline pyrophosphatase were active in seed development and germination. The set of adaptive enzymes identified in developing seeds were sucrose synthase, PPi-dependent phosphofructokinase, plus acid and alkaline pyrophosphatase; and, the adaptive enzymes identified in germinating seeds included the same set of enzymes plus acid invertase. The set of maintenance enzymes identified during development, in the dry seed, and during germination were UDP-glucopyrophosphorylase, neutral invertase, ATP and UTP-dependent fructokinase, glucokinase, phosphoglucomutase, ATP and UTP-dependent phosphofructokinase and sucrose-P synthase.     

Contrasting consequences of plant domestication for the chemical defenses of leaves and seeds in lima bean plants

Plant domestication is assumed to result in reduced levels of defensive compounds in crops, because this makes the plants more suitable for consumption by humans and livestock. We argue that this should mainly be reflected in the concentrations of defense compounds in the plant parts that are used for consumption and not necessarily for other parts of crop plants. We tested this hypothesis for domesticated lima bean (Phaseolus lunatus), by comparing its chemical defenses against a leaf herbivore, the beet armyworm (Spodoptera exigua), and a seed predator, the beetle Zabrotes subfasciatus. For seeds and leaves we determined the concentrations of cyanogenic glycosides (CNGs) in cultivated varieties and wild populations and evaluated the preference and performance of the herbivores when exposed to leaves and seeds from wild and cultivated plants. Concentrations of CNGs were significantly different between wild and cultivated plants. In the leaves the concentration of CNGs in the cultivated varieties were more than double that of the wild leaves. In contrast, seeds from cultivated plants had up to 20 times lower CNG concentration compared to seeds from the wild populations. Insect preference and performance do not parallel the chemical data. Larvae of S. exigua preferred wild leaves but had higher survival on cultivated leaves. The beetles, however, strongly preferred seeds from cultivated plants and females developed more quickly on these seeds. We conclude that domestication of P. lunatus has altered the concentration of CNGs in both the seeds and the leaves in opposite directions. This results in differential effects on the herbivores that attack these two plant structures. The contrasting effect of domestication on different plant tissues can be explained by the fact that bean plants have been specifically selected for human consumption of the seeds. Tissue-specific effects of plant domestication on plant defenses can be expected for other crops as well.     

Association properties of trypsin inhibitors from lima bean

The molecular-weight properties of three purified proteinase inhibitors from lima bean were studied by using high speed sedimentation equilibrium. Two isoinhibitors [fraction I and II, nomenclature from Jones et al., (18)]do not self-associate at moderate pH and concentration (<4 g/liter). Fraction IV exists as a monomer at pH 2.0 and polymerizes at higher pH values. The molecular-weight data fit a monomer ? dimer equilibrium at pH 7.0, and a monomer ? dimer ? trimer equilibrium at pH 4.65.     

Crystallization and preliminary studies of lima bean trypsin inhibitor

Crystals of lima bean trypsin inhibitor (LBTI) were obtained by using the vapor phase equilibration technique with sodium/potassium tartrate as the precipitating agent. The space group was determined to be cubic, I2₁3 with a= 110.2 Å. These crystals diffract to about 1.9 Å resolution. Preliminary analysis of self-rotation maps (calculated from native x-ray intensity data) suggests the presence of two monomers in the asymmetric unit. LBTI is very thermostable and retains activity even after boiling for 10 minutes. This property is exploited as part of its purification procedure. © 1997 Wiley-Liss, Inc.     

Soil seed bank and seed dormancy in wild populations of lima bean (Fabaceae): considerations for in situ and ex situ conservation

Seed dormancy and its impact on the soil seed bank for wild Lima bean (Phaseolus lunatus) populations were studied in the Central Valley of Costa Rica. Five populations were selected in contrasted environments. In all cases, distribution of seeds in the soil was limited to 3 cm depth. No innate dormancy was observed but combination of hard seed coat and hilum opening controlled by environmental conditions were responsible for an induced dormancy and the constitution of a persistent seed bank. Breaking of this dormancy was obtained by a brief elevation of temperature from 25° to 45°C. Impacts of this phenomenon concern both genetic and demographic aspects of in situ conservation of the species. Consequences on ex situ conservation are mainly related with the regeneration of the seed collection.     

Reexamination of the carbohydrate binding stoichiometry of lima bean lectin

The carbohydrate binding stoichiometry of lima bean lectin component III was reexamined using equilibrium dialysis and quantitative affinity chromatography following limited chemical modification. Equilibrium dialysis employing methyl[2-14C]benzamido-2-deoxy-alpha-D-galactopyranoside as ligand demonstrated that the lectin tetramer bound 4 mol of sugar with Kassoc = 1.44 +/- 0.13 X 10(3) M-1 (T = 5 degrees C, pH 7.0, ionic strength 0.1). The previous report of two sites/tetramer [Bessler, W. and Goldstein, I. J. (1974) Arch. Biochem. Biophys. 165, 444] appears to be the result of partial inactivation of the lectin due to oxidation of essential thiol groups. Following limited chemical modification of the thiol groups by methyl methanethiosulfonate, multiple intermediate forms with reduced affinity for Synsorb A were obtained. The number and hemagglutinating activities of these intermediates provided further support for the presence of four carbohydrate binding sites on lima bean lectin component III.     

Imbibition conditions and seed dormancy of Arabidopsis thaliana

The optimal combinations of temperature in the range of 0 to 20°C and duration (1 to 14 days) of imbibition for the induction of germination of Arabidopsis thaliana (L) Heynh., ecotype "Landsberg-erecta", by red light were investigated. At 2°C, 10 days of imbibition are needed tor loss of dormancy, whereas at higher temperatures, e.g 15°C, it is already lost after 1 or 2 days. It is proposed that the development of light-inducible germination is governed by two temperature-dependent processes-the loss of primary or innate dormancy and the simultaneous induction of secondary dormancy. Data are discussed in terms of the availability of phytochrome, the availability of an unknown factor X and changes in sensitivity of the process of germination induction by the far-red absorbing form of phytochrome (Pfr).     

Alteration of spermosphere ecosystems affecting oviposition by the bean seed fly and attack by soilborne fungi on germinating seeds

In laboratory studies, treating ‘Butternut’ squash (Cucurbita pepo) seeds with ascospores of Chaetomium globosum NRRL 6296 and 6297 reduced oviposition by the bean seed fly Hylemya platura (Meigen), and reduced seed rot caused by Pythium ultimum and P. aphanidermatum. Treatment of seeds with thiram or captan increased oviposition by the bean seed fly. In the field, treatment of snap bean seeds with C. globosum NRRL 6296, or a commercial seed treatment mixture containing captan, diazinon, and streptomycin sulphate, resulted in significantly less damage by bean seed fly larvae than a treatment with thiram.     

Polyethylene glycol embedment for histological studies of bean seed testa of low moisture content

Light microscopic examination of the structure of seed testa of snap and semihard bean seeds with 6% and 12% moisture contents in paraffin sections was unsuccessful because of poor paraffin infiltration and subsequent separation of subjacent and palisade cell layers. We devised an alternative method using polyethylene glycol (PEG) as the embedding material. Specimens were killed and fixed in the usual manner. They were then run up through a graded series (25, 50, 75, 100%) of PEG 1000 to PEG 1450, and finally embedded in a mixture of PEG 1450 and 4000 (19:1 by weight). Transverse and longitudinal sections retained excellent morphological detail and were suitable for histological study. Sections temporarily stained with 0.025% thionin allowed good quality photomicrographs.     

Cell binding and mitogenic properties of the lima bean lectins

Two lectins, a tetramer designated LBL₄ and an octamer LBL₈ designated have been purified from the lima beanPhaseolus lunatus. The tetramer appears to be nonmitogenic for human lymphocytes and is a weak mitogen for bovine cells. The octamer and a chemically cross-linked form of the tetramer are good mitogens. The lima bean lectin binds to only certain sub-populations of human lymphocytes. The primary class which does not bind appears to be a sub-population ofT-lymphocytes. Comparisons of cell binding with other lectins which bind to 2-acetamido-2-deoxy-D-galactose have been carried out. Quantitative analysis of the binding to human erythrocytes is co-operative but binding to lymphocytes is non-co-operative. These results show that there may not be a direct correlation between mitogenic stimulation and cooperative binding to membrane receptors.     

Effect of seed size and plant growth on nodulation and nodule development in lima bean (Phaseolus lunatus L.)

Lima bean (Phaseolus lunatus L.) cultivars vary widely in their growth habit and seed size. Preliminary experiments indicated that a large-seeded pole cultivar (King of the Garden) formed many more nodules than a small-seeded bush cultivar (Henderson). The relative importance of seed size and shoot mass in determining nodule number and mass was assessed in five lima bean cultivars differing in seed size and growth habit. Between cultivars, significant positive correlations between initial seed mass, plant weight and nodule number and mass were observed during the first four weeks after planting. Comparisons within cultivars indicated a strong correlation between nodule mass and shoot dry weight. The influence of plant morphology on nodule formation and mass was secondary to the effects of seed and shoot mass. As plants matured, the increase in nodule mass paralleled the increase in plant mass, while nodule number was relatively stable after day 18. These results suggest that the highly regulated process of nodule formation was under the influence of seed derived factors, while the continued accumulation of nodule tissue was related to shoot growth.     

Control of Echinothrips americanus on lima bean by Franklinothrips vespiformis crawford using supplemental food

BioControl - Supplemental food application to crops as a resource for generalist predators has shown utility for promoting their establishment and persistence leading to enhanced biological control...