Desiccation tolerance of five tropical seedlings in panama. Relationship to a field assessment of drought performance. (41/1763)

Studies of the desiccation tolerance of the seedlings of five tropical trees were made on potted plants growing in a greenhouse. Pots were watered to field capacity and then dehydrated for 3 to 9 weeks to reach various visual wilting stages, from slightly wilted to dead. Saturated root hydraulic conductance was measured with a high-pressure flowmeter, and whole-stem hydraulic conductance was measured by a vacuum chamber method. Leaf punches (5.6-mm diameter) were harvested for measurement of leaf water potential by a thermocouple psychrometer method and for measurement of fresh and dry weight. In a parallel study, the same five species were studied in a field experiment in the understory of a tropical forest, where these species frequently germinate. Control seedlings were maintained in irrigated plots during a dry season, and experimental plants were grown in similar plots with rain exclusion shelters. Every 2 to 4 weeks, the seedlings were scored for wilt state and survivorship. After a 22-week drought, the dry plots were irrigated for several weeks to verify visual symptoms of death. The field trials were used to rank drought performance of species, and the greenhouse desiccation studies were used to determine the conditions of moribund plants. Our conclusion is that the desiccation tolerance of moribund plants correlated with field assessment of drought-performance for the five species (r(2) > 0.94).  (+info)

Second positive phototropism results from coordinated co-action of the phototropins and cryptochromes. (42/1763)

Phototropism and hypocotyl growth inhibition are modulated by the coaction of different blue-light photoreceptors and their signaling pathways. How seedlings integrate the activities of the different blue-light photoreceptors to coordinate these hypocotyl growth responses is still unclear. We have used time-lapse imaging and a nontraditional mathematical approach to conduct a detailed examination of phototropism in wild-type Arabidopsis and various blue-light photoreceptor mutants. Our results indicate that high fluence rates of blue light (100 micro mol m(-)(2) s(-)(1)) attenuate phototropism through the coaction of the phototropin and cryptochrome blue-light photoreceptors. In contrast, we also demonstrate that phototropins and cryptochromes function together to enhance phototropism under low fluence rates (<1.0 micro mol m(-)(2) s(-)(1)) of blue light. Based on our results, we hypothesize that phototropins and cryptochromes regulate phototropism by coordinating the balance between stimulation and inhibition of growth of the hypocotyl depending on the fluence rate of blue light.  (+info)

Synthesis and root growth-inhibitory activity of 2- and 3-(haloacetylamino)-3-(2-furyl)propanoic acids. (43/1763)

A convenient synthesis of 2- and 3-(chloroacetylamino)-3-(2-furyl)propanoic acids (6a, 7a) and their fluoro analogs were developed. Both 6a and 7a showed 51-55% root growth-inhibitory activity towards rape seedlings at the concentration of 1.0x10(-4) M.  (+info)

New plant growth promoters, repraesentins A, B and C, from Lactarius repraesentaneus. (44/1763)

Three new plant growth regulatory sesquiterpenoids were isolated from the Lactarius repraesentaneus fungus. Their structures were elucidated to be a protoilludene sesquiterpene, namely repraesentin A (1), and two related sesquiterpenes, namely repraesentins B (2) and C (3). Compounds 1-3 showed promotion activities toward the radicle elongation of lettuce seedlings by 136%, 118% and 184% at 67 ppm, respectively.  (+info)

Activation parameters of the blue shift (Shibata shift) subsequent to protochlorophyllide phototransformation. (45/1763)

The Shibata shift was analyzed in flash irradiated wheat (Triticum aestivum, L., cult. MV17) leaf homogenates in the pressure range of 0.1 to 500 MPa, at temperatures of 20, 30 and 40 degrees C. The kinetics of the blue shift (called Shibata shift in case of intact leaves) was followed by repeated recording of fluorescence emission spectra after phototransformation. At 20 degrees C, above 100 MPa, the blue shift slowed down remarkably. Two components of the blue shift could be distinguished, one was pressure-dependent and the other was almost pressure-independent. The pressure-independent component can be associated with minor conformational changes of the NADPH:protochlorophyllide oxidoreductase (POR) enzyme, followed by molecular movements of the newly formed chlorophyllide molecules. The calculated activation volume of the pressure-dependent component was 43+/-11 cm(3) mol(-1) at 20 degrees C. This value reflects major molecular reorganizations in the lipid system of the membrane and in the chlorophyllide-protein complexes, and corresponds to changes of the tertiary structure of proteins which can proceed directly or indirectly via structural changes of the membrane lipids. The process was inhibited by 300 and 400 MPa at 30 and 40 degrees C, respectively. The activation volume reduced to 35+/-1.5 cm(3) mol(-1) at 40 degrees C. The decrease of the activation volume with increasing temperature indicates that the blue shift requires loosened lipid structures. The activation energy of the blue shift (measured between 10 and 40 degrees C at atmospheric pressure) was 100+/-20 kJ/mol, indicating that the structural change involves rearrangement of strong molecular interactions.  (+info)

Ospdr9, which encodes a PDR-type ABC transporter, is induced by heavy metals, hypoxic stress and redox perturbations in rice roots. (46/1763)

Little is known about the role of pleiotropic drug resistance (PDR)-type ATP-binding (ABC) proteins in plant responses to environmental stresses. We characterised ospdr9, which encodes a rice ABC protein with a reverse (ABC-TMS(6))(2) configuration. Polyethylene glycol and the heavy metals Cd (20 microM) and Zn (30 microM) rapidly and markedly induced ospdr9 in roots of rice seedlings. Hypoxic stress also induced ospdr9 in rice roots, salt stress induced ospdr9 at low levels but cold and heat shock had no effect. The plant growth regulator jasmonic acid, the auxin alpha-naphthalene acetic acid and the cytokinin 6-benzylaminopurine triggered ospdr9 expression. The antioxidants dithiothreitol and ascorbic acid rapidly and markedly induced ospdr9 in rice roots; the strong oxidant hydrogen peroxide also induced ospdr9 but at three times lower levels. The results suggested that redox changes may be involved in the abiotic stress response regulation of ospdr9 in rice roots.  (+info)

EIN3-dependent regulation of plant ethylene hormone signaling by two arabidopsis F box proteins: EBF1 and EBF2. (47/1763)

The plant hormone ethylene regulates a wide range of developmental processes and the response of plants to stress and pathogens. Genetic studies in Arabidopsis led to a partial elucidation of the mechanisms of ethylene action. Ethylene signal transduction initiates with ethylene binding at a family of ethylene receptors and terminates in a transcription cascade involving the EIN3/EIL and ERF families of plant-specific transcription factors. Here, we identify two Arabidopsis F box proteins called EBF1 and EBF2 that interact physically with EIN3/EIL transcription factors. EBF1 overexpression results in plants insensitive to ethylene. In contrast, plants carrying the ebf1 and ebf2 mutations display a constitutive ethylene response and accumulate the EIN3 protein in the absence of the hormone. Our work places EBF1 and EBF2 within the genetic framework of the ethylene-response pathway and supports a model in which ethylene action depends on EIN3 protein stabilization.  (+info)

Beta-glucosidase, exo-beta-glucanase and pyridoxine transglucosylase activities of rice BGlu1. (48/1763)

The bglu1 cDNA for a beta-glucosidase cloned from rice (Oryza sativa L.) seedlings was expressed as a soluble and active protein in Escherichia coli and designated BGlu1. This enzyme hydrolysed beta-1,4-linked oligosaccharides with increasing catalytic efficiency (kcat/Km) values as the DP (degree of polymerization) increased from 2 to 6. In contrast, hydrolysis of beta-1,3-linked oligosaccharides decreased from DP 2 to 3, and polymers with a DP greater than 3 were not hydrolysed. The enzyme also hydrolysed p -nitrophenyl beta-D-glycosides and some natural glucosides but with lower catalytic efficiency than beta-linked oligosaccharides. Pyridoxine 5'-O-beta-D-glucoside was the most efficiently hydrolysed natural glycoside tested. BGlu1 also had high transglucosylation activity towards pyridoxine, producing pyridoxine 5'-O-beta-D-glucopyranoside in the presence of the glucose donor p-nitrophenyl beta-D-glucoside.  (+info)