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Abstract. Potato (Solanum tuberosum L. cv. Dsire) plants were transformed to express a single-chain variable-fragment antibody against abscisic acid (ABA), and present in the endoplasmic reticulum at to up to 0.24% of the soluble leaf protein. The resulting transgenic plants were only able to grow normally at 95% humidity and moderate light. Four-week-old plants accumulated ABA to high extent, were...
Abstract. Low CO2 concentrations open CO2-sensitive stomata whereas elevated CO2 levels close them. This CO2 response is maintained in the dark. To elucidate mechanisms underlying the dark CO2 response we introduced pH- and potential-sensitive dyes into the apoplast of leaves. After mounting excised leaves in a gas-exchange chamber, changes in extracellular proton concentration and transmembrane potential...
Abstract. Exogenous abscisic acid (ABA) applied to the roots and excised shoots of aspen (Populus tremuloides Michx.) inhibited stomatal conductance. However, the effect of ABA on stomatal conductance was more pronounced in the excised shoots compared with the intact seedlings. Approximately 10% of the ABA concentration applied to the roots was found in the xylem exudates of root systems exposed to...
Abstract. A mathematical model of the diffusive transport of abscisic acid (ABA) and gibberellins (GAs) through the aleurone layer of barley (Hordeum vulgare L.) grain is presented. The model consists of two partial differential equations describing the accumulation of phytohormone in the apoplastic and symplasmic compartments of the aleurone layer, both spatially and temporally. The mathematical...
Abstract. In C4 plants, the photosynthetic enzyme phosphoenolpyruvate carboxylase (PEPCase; EC4.1.1.31) is subjected to a phosphorylation process via the light-dependent up-regulation of a Ca2+-independent PEPCase-kinase. The present work aimed to study the effect of salt stress on PEPCase phosphorylation in Sorghum vulgare Pers. leaves. The growth of salt-treated plants was reduced compared with...
Abstract. ABI1 and ABI2 are two protein serine/threonine phosphatases of type2C (EC3.1.3.16) that act as key regulators in the responses of Arabidopsis thaliana (L.) Heynh. to abscisic acid (ABA). They are involved in the control of ABA-mediated seed dormancy, stomatal closure and vegetative growth inhibition. Analysis of the enzymatic properties of ABI2 revealed high sensitivities towards protons...
Abstract. Germination of wild-type (WT) tomato (Lycopersicon esculentum Mill.) seed is inhibited by mannitol (100140mM) in light, but not in darkness, suggesting that light amplifies the responsiveness of the seed to osmotic stress (M. Fellner, V.K. Sawhney (2001) Theor Appl Genet 102:215221). Here we report that white light (W) and especially blue light (B) strongly enhance the mannitol-induced inhibition...
Abstract. In the desiccation-tolerant resurrection plant Craterostigma plantagineum Hochst. the chloroplasts undergo major ultrastructural changes during dehydration, which are reversible upon rehydration. Such alterations argue the need for efficient protective/stabilising mechanisms to exist. Here we describe a novel gene family that is rapidly and transiently expressed in response to both dehydration...
Abstract. Abscisic acid (ABA) induces the expression of a gene encoding a protein kinase, PKABA1, in wheat (Triticum aestivum L.). Transient expression of the cDNA encoding this kinase suppresses the gibberellin (GA)-induced expression of -amylase genes in barley (Hordeum vulgare L.) aleurone layers. We have cloned the cDNA and genomic sequences for the barley PKABA1 (HvPKABA1) to further study its...
Abstract. Transgenic tobacco (Nicotiana tabacum L.) plants ubiquitously accumulating a single-chain variable-fragment (scFv) antibody against abscisic acid (ABA) to high concentrations in the endoplasmic reticulum (RA plants) show a wilty phenotype. High stomatal conductance and loss of CO2 and light dependence of stomatal conductance are typical features of these plants. ABA was applied to these...
Abstract. The possible regulation of senescence-initiated remobilization of carbon reserves in rice (Oryza sativa L.) by abscisic acid (ABA) and cytokinins was studied using two rice cultivars with high lodging resistance and slow remobilization. The plants were grown in pots and either well-watered (WW, soil water potential = 0MPa) or water-stressed (WS, soil water potential = 0.05MPa) from 9days...
Abstract. Jasmonates (JAs) regulate Arabidopsis thaliana (L.) Heynh. wound and defense responses, pollen development, and stress-related growth inhibition. Significantly, each of these responses requires COI1, an F-box protein. We fused firefly luciferase as a reporter to the JA-responsive promoter for the vegetative storage protein gene (VSP) and used this to screen for mutants that failed to express...
Abstract. The roles of the plasma-membrane (PM) NADPH oxidase in abscisic acid (ABA)- and water stress-induced antioxidant defense were investigated in leaves of maize (Zea mays L.) seedlings. Treatment by exogenous ABA (100M ABA) or osmotic stress (0.7MPa induced by polyethylene glycol) significantly increased the activity of the PM NADPH oxidase, the production of leaf O2, the activities of several...
Abstract. We have developed experimental systems to study hydrotropism in seedling roots of Arabidopsis thaliana (L.) Heynh. Arabidopsis roots showed a strong curvature in response to a moisture gradient, established by applying 1% agar and a saturated solution of KCl or K2CO3 in a closed chamber. In this system, the hydrotropic response overcame the gravitropic response. Hydrotropic curvature commenced...
Abstract. High concentrations of cytokinins block cell proliferation and induce programmed cell death (PCD) in both carrot (Daucus carota L.) and Arabidopsis thaliana (L.) Heynh. cell cultures [13 and 27M N6-benzylaminopurine (BAP), respectively]. In the present work, cell death was scored by Evan's blue staining and was also demonstrated to be programmed by various parameters, including chromatin...
Abstract. The objective of this study was to increase our understanding of the hormonal regulation of de-etiolation by investigating endogenous hormone levels and response in etiolated pea (Pisum sativum L.) seedlings after exposure to continuous white light. Recent reports suggest that de-etiolation may result from the down-regulation of an enzyme in the brassinosteroid (BR) biosynthesis pathway...
Abstract. The development of Agrobacterium tumefaciens-induced plant tumors primarily depends on the excessive production of auxin and cytokinin by enzymes encoded on T-DNA genes integrated into the plant genome. The aim of the present study was to investigate the involvement of additional phytohormone signals in the vascularization required for rapid tumor proliferation. In stem tumors of Ricinus...
We explored the functioning of the slowly activating anion conductance, S-type or SLAC, and of the quickly activating anion conductance, R-type or QUAC, in whole guard cells of Vicia faba L.; details of QUAC activity had not previously been demonstrated in guard cells possessing their walls. The discontinuous single-electrode voltage-clamp method was used to record current responses to voltage pulses...
In this study, we examined the effects of ethylene and abscisic acid (ABA) upon heterophyllous leaf formation of Ludwigia arcuata Walt. Treatment with ethylene gas resulted in the formation of submerged-type leaves on terrestrial shoots of L. arcuata, while treatments with ABA induced the formation of terrestrial-type leaves on submerged shoots. Measurement of the endogenous ethylene concentration...
The role of maternally derived abscisic acid (ABA) during seed development has been studied using ABA-deficient mutants of Nicotiana plumbaginifolia Viviani. ABA deficiency induced seed abortion, resulting in reduced seed yield, and delayed growth of the remaining embryos. Mutant grafting onto wild-type stocks and reciprocal crosses indicated that maternal ABA, synthesized in maternal vegetative tissues...
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