No abstract

As a potential phytoremediation system for phytoextraction of chromium (Cr), we evaluated the influence of the arbuscular mycorrhizal fungus Glomus intraradices on leaf tissue elemental composition, growth and gas exchange of sunflower (Helianthus annuus L.). Sunflower seedlings were either inoculated with mycorrhizal fungi (AM) or non-inoculated (Non-AM) and then exposed to two Cr species: {12 mmol of trivalent cation (Cr þ3 ) [Cr(III)] or 0.1 mmol of divalent dichromate anion (Cr 2 O 7 À ) [Cr(VI)]}. Both Cr species depressed plant growth, decreased stomatal conductance (g s ) and net photosynthesis (A).

Caimey, J. 1996, Gene expression under water deficit in loblolly pine (Pinus taeda): Isolation and characterization of cDNA clones, -Physioi. Plant. 97: 139-148,Poly(A*) RNA was extracted from roots of loblolly pine (Pinus taeda L.) seedlings subjected to gradual and prolonged water deficit. This RNA was used to constmct a cDNA library, A number of cDNA clones were isolated whose expression was induced by water deficit. Four of these cDNA clones, designated pLP2, pLP3, pLP4 and pLP5, were characterized further. Each of these pine genes has unique characteristics either in sequence or pattem of expression. The protein encoded by pLP2 shows 91% identity to S-adenosylmethionine synthetase from a range of plants. The protein encoded by pLP3 is similar to a tomato protein induced by water deficit and during fruit ripening, but the pine protein possesses a unique 34-amino-acid region near the aniino terminal. The LP4 protein is similar to stellacyanin, a copper-binding protein in the Japanese lacquer tree, but possesses a proline/serine-rich caiboxy terminus not found in other plants. Clone pLP5 encodes a novel glycine-rich protein with similarity to both silk fibroin and the rat chondroitin core protein, but the putative pine protein is distinct from previously characterized glycine-rich proteins. Transcript levels of the four genes rose under moderate water deficit stress and then declined as stress became severe (1 month without water), with the exception of pLP5 mRNA, which remained at elevated levels even under severe stress. The possible roles of the encoded proteins in cell wall reinforcement are discussed.

An arabinogalactan-protein (AGP) was puri®ed from dierentiating xylem of loblolly pine (Pinus taeda L.) and the N-terminal sequence used to identify a cDNA clone. The protein, PtaAGP3, was not coded for by any previously identi®ed AGP-like genes. Moreover, PtaAGP3 was abundantly and preferentially expressed in dierentiating xylem. The encoded protein contains four domains, a signal peptide, a cleaved hydrophilic region, a region rich in serine, alanine, and proline/ hydroxyproline, and a hydrophobic C-terminus. It is postulated to contain a GPI (glycosylphosphatidylinositol) anchor site. If the protein is cleaved at the putative GPI anchor site, as has been observed in other classical AGPs, all but the Ser-Ala-Pro/Hyp-rich domain may be missing from the mature protein. Xylem-speci®c AGPs are hypothesized to be involved in xylem development.

No abstract

Eight cultivars Sorghum bicolor (L.) Moench were grown as callus cultures under induced, prolonged water stress (8 weeks), with polyethylene glycol in the medium. Concentrations of soluble carbohydrates and organic acids in callus were measured at the end of the growth period to determine differences in response to prolonged water stress. Sucrose, glucose, fructose, and malate were the predominant solutes detected in all callus at all water potentials. All cultivars had high levels of solutes in the absence of water stress and low levels in the presence of prolonged water stress. However, at low water potentials, low levels of solutes were observed in drought-tolerant cultivar callus and high solute levels were observed in drought-susceptible cultivar callus. Estimated sucrose concentrations were significantly higher in water-stressed, susceptible cultivar callus. Large solute concentrations in susceptible cultivar callus were attributed to osmotic adjustment and/or reduced growth during water stress.Recently, a correlation between responses to drought in the field and responses to drought in culture has been established in sorghum (11). Subsequently, we observed that in callus cultures proline levels were increased in response to prolonged, moderate to severe, water stress, especially in one cultivar whose growth was very susceptible to drought; conversely, low proline levels were associated with a cultivar which sustained growth during water stress (1).In the present investigation we analyzed soluble carbohydrate and organic acid levels by GC in sorghum callus cultures when water stress was induced by additions of PEG to the culture medium. As in our previous investigation (1), the objective was to determine if there are inherent differences at the cellular level between cultivars during prolonged, sustained water stress. This might indicate what metabolic changes occur and whether or not any ofthese changes confer a significant advantage to any cultivar in response to drought.One of the metabolic changes in response to water stress that confers an advantage through turgor maintenance and sustained growth is osmotic adjustment whereby solutes accumulate (2, 6).

The amino acid, proline (PRO), may have an important role in plant adaptation to drought stress. To study the effect of drought stress on PRO content of pine tissues, we measured free PRO by high pressure liquid chromatography in control ( -0.4 MPa) and drought-stressed ( -0.8, -1.0, -1.3, -1.6 MPa) callus tissue of Pinus taeda L. after eight weeks of growth. Drought stress was induced by adding polyethylene glycol (PEG) to the nutrient media. The relation between PRO accumulation and water potential was influenced by composition of the medium and temperature. Callus growing in media with water potentials of -0.8 MPa showed no increase in PRO compared to control callus in media at -0.4 MPa. When callus tissue was subjected to low water potentials (-1.6 MPa), endogenous PRO concentration increased 40-fold, while callus fresh weight decreased by more than 90%. When exogenous PRO was added to the nutrient media, endogenous PRO was directly proportional to the exogenous PRO concentration rather than reduction in callus growth. Thus low water potential in callus results in endogenous PRO accumulation and large reductions in callus fresh weight growth. Proline accumulation in pine cells appears to be related to mechanisms associated with tolerance to desiccation.

Poly(A+) RNA was extracted from roots of loblolly pine (Pinus taeda L.) seedlings subjected to gradual and prolonged water deficit. This RNA was used to construct a cDNA library. A number of cDNA clones were isolated whose expression was induced by water deficit. Four of these cDNA clones, designated pLP2, pLP3, pLP4 and pLP5* were characterized further. Each of these pine genes has unique characteristics either in sequence or pattern of expression. The protein encoded by pLP2 shows 91% identity to S‐adenosylmethionine synthetase from a range of plants. The protein encoded by pLP3 is similar to a tomato protein induced by water deficit and during fruit ripening, but the pine protein possesses a unique 34‐amino‐acid region near the amino terminal. The LP4 protein is similar to stellacyanin, a copper‐binding protein in the Japanese lacquer tree, but possesses a proline/serine‐rich carboxy terminus not found in other plants. Clone pLP5 encodes a novel glycine‐rich protein with similarity to both silk fibroin and the rat chondroitin core protein, but the putative pine protein is distinct from previously characterized glycine‐rich proteins. Transcript levels of the four genes rose under moderate water deficit stress and then declined as stress became severe (1 month without water), with the exception of pLP5 mRNA, which remained at elevated levels even under severe stress. The possible roles of the encoded proteins in Cell wall reinforcement are discussed.