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While barley (Hordeum vulgare L.) is the most sensitive species to Al toxicity among small-grain crops, variation in Al resistance between cultivars does exist. We examined the mechanism responsible for differential Al resistance in 21 barley varieties. Citrate was secreted from the roots in response to Al stress. A positive correlation between citrate secretion and Al resistance [(root elongation...
This investigation shows diurnal variations in the xylem sap composition of poplar (Populus tremula P. alba). All major macronutrients reached a maximum concentration in the first half of the light period and decreased to the middle of the night. The relative abundance of the nutrients did not change during the day. The sap flow, which responded very fast to the environmental changes (2.2-fold increase...
In order to elucidate the discrete steps in phosphoenolpyruvate carboxylase (PEPC) evolution concerning Km-PEP and malate tolerance a comparison was made between C3, C3C4 and C4 species of the dicot genus Flaveria. The PEPCs of this genus are encoded by a gene family comprising three classes: ppcA, ppcB and ppcC [J. Hermans and P. Westhoff (1990) Mol Gen Genet 224:459468, (1992) Mol Gen Genet 234:275284]...
Glutathione S-transferase (GST; EC 2.5.1.18) gene expression was examined in the coleoptile and new leaf tissue of etiolated shoots of the diploid wheat species Triticum tauschii (Coss.) Schmal., which is considered to be a progenitor and the D-genome donor to cultivated, hexaploid bread wheat Triticum aestivum L. GST expression (mRNA, protein, and enzyme activity with a herbicide substrate) in these...
Many species within the genus Cuphea (Lythraceae) produce seed with high levels of medium-chain fatty acids. Seeds of some Cuphea species lose viability when placed into storage at 18C. These species tolerate significant drying to 0.05g/g and may, therefore, be intermediate in their storage characteristics. The thermal properties of seed lipids were observed using differential scanning calorimetry...
We report on a new cDNA clone (Qshsp10.4-CI) of a Quercus suber L. class-CI small heat-shock protein (sHsp) obtained from cork (phellem), a highly oxidatively stressed plant tissue. The deduced gene product lacks the C-terminal extension and the consensusI region of the -crystallin domain, being the most C-terminally truncated sHsp reported to date. In an attempt to prove that a protective function...
Four different ferritin genes have been identified in Arabidopsis thaliana, namely AtFer1, 2, 3 and 4. AtFer1, which strongly accumulates in leaves treated with excess iron, contains in its promoter an Iron-Dependent Regulatory Sequence (IDRS). The IDRS sequence is responsible for repression of AtFer1 transcription under conditions of low iron supply. Arabidopsis plants transformed with a 1,400-bp...
Wood formation is being increasingly studied at cellular and biochemical levels; however, gene expression and regulation during wood formation remain poorly understood. Up to six types of wood can be studied within the same tree (early wood, late wood, juvenile wood, mature wood, reaction wood and opposite wood). These six types are characterized by different chemical, physical and anatomical properties...
Reproductive isolation mechanisms (RIMs) often become obstacles in crossbreeding. Hybrid lethality is a subtype of RIM but its physiological mechanism remains poorly elucidated. Interspecific hybrids of Nicotiana suaveolens Lehm. N. tabacum L. cv. Hicks-2 expressed temperature-sensitive lethality. This lethality was induced by programmed cell death (PCD) that was accompanied by the characteristic...
Gramineous plants, including the major agricultural crops wheat (Triticum aestivum L.), rye (Secale cereale L.) and maize (Zea mays L.), accumulate benzoxazinones (Bxs) as defensive compounds. Previously, we isolated cDNAs of the Bx biosynthetic genes in wheat, TaBx2TaBx5, that encode the enzymes catalyzing the sequential hydroxylation of indole to Bxs. In this study we isolated a cDNA of TaBx1, which...
Pathogen-induced plant responses include changes in both volatile and non-volatile secondary metabolites. To characterize the role of bacterial pathogenesis in plant volatile emissions, tobacco plants, Nicotiana tabacum L. K326, were inoculated with virulent, avirulent, and mutant strains of Pseudomonas syringae. Volatile compounds released by pathogen-inoculated tobacco plants were collected, identified,...
Mechanisms of photo- and antioxidative protection, the extent of oxidative stress, and salicylic acid accumulation in leaves of Phillyrea angustifolia L. (Oleaceae) plants exposed to drought and recovery in Mediterranean field conditions were studied. The amounts of -tocopherol increased up to 4-fold and those of zeaxanthin increased up to 3-fold at relative leaf water contents (RWCs) of ca. 60%,...
The molecular signals for the development of the ovary into fruit following ovule fertilization are not clear. However, in many species, including tomato (Lycopersicon esculentum Mill.), auxins and auxin transport inhibitors can substitute for fertilization as activators of fruit set, suggesting that this plant hormone plays a key role in this process. In agreement, transgenes for auxin biosynthesis...
The substrate specificity of the enzyme violaxanthin de-epoxidase (VDE) of the primitive green alga Mantoniella squamata (Prasinophyceae) was tested in in vitro enzyme assays employing the following xanthophyll mono-epoxides: antheraxanthin (Ax), diadinoxanthin (Ddx), lutein-epoxide (LE), cryptoxanthin-epoxide (CxE), 9-cis neoxanthin (cNx), all-trans neoxanthin (Nx), and xanthophyll di-epoxides: 9-cis...
Tracheid and sclereid differentiation was induced in callus cultures of Pinus radiata D. Don by culturing on a basal medium containing activated charcoal but no phytohormones; sclereids differentiated in callus derived from xylem strips, but not in callus derived from hypocotyl segments. The tracheids differentiated in hypocotyl-derived callus had helical, scalariform, reticulated or pitted secondary...
Allene oxide synthase (AOS) catalyzes the entrance reaction in the biosynthesis of the octadecanoids 12-oxophytodienoic acid (OPDA) and jasmonic acid (JA). The enzyme is feedback-regulated by JA and thus a target of the JA-signalling pathway. A fusion genetic approach was used to isolate mutants in this signalling pathway. Seeds from transgenic Arabidopsis thaliana plants expressing the Escherichia...
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