The Effect of 2,3,6-Trichlorophenylacetic and 2,2-Dichloropropionic Acids on Nitrite Oxidation

The effects of two herbicides, 2,3,6-trichlorophenylacetic acid, sodium salt, and 2,2-dichloropropionic acid, sodium salt, on nitrite-oxidizing bacteria were studied by the soil perfusion technique. The time of application of 2,3,6-trichlorophenylacetic acid affected its toxicity to the nitrifier. When it was present in the environment as the nitrifier started growth, it was more toxic than if the organisms were allowed to nitrify actively before they were subjected to the herbicide.

The herbicide 2,2-dichloropropionic acid at rates up to 700 ppm had little effect on nitrite oxidation. The toxicity of 2,3,6-trichlorophenylacetic acid for Nitrobacter was reduced by 2,2-dichloropropionic acid irrespective of whether the cells came into contact with the agents before or during active oxidation. The mode of action for this phenomenon has not been determined.

     

Interactive effects of salinity, nitrogen and sulphur on the organic solutes in Spartina alterniflora leaf blades

Glycinebetaine, proline, asparagine, sucrose, glucose, and dimethylsulphoniopropionate(DMSP) were the major organic solutes in Spartina alternifloraleaf blades. To investigate the physiological role(s) of thesesolutes, the effects of salinity, nitrogen, and sulphur treatmentson leaf blade solute levels were examined. Glycinebetaine wasthe major organic solute accumulated in leaf blades grown at500 mol m^–3 NaCl, although asparagine and proline alsoaccumulated when the supply of nitrogen was sufficient. Thesesolutes may play a role in osmotic adjustment. In contrast,DMSP levels either did not change or were reduced in responseto the 500 mol m^–3 NaCl treatment. Furthermore, elevatednitrogen supply decreased leaf blade DMSP levels, which wasopposite to the response of glycinebetaine, proline, and asparagine.A 1000-fold increase in external sulphate concentration hadno effect on the leaf blade levels of DMSP, glycinebetaine,proline, or asparagine. These findings suggest that the majorphysiological role of DMSP in S. alterniflora leaf blades isnot for osmotic adjustment, even under conditions of nitrogendeficit and excess sulphur. Instead, DMSP which was presentat 45—130 µmol g^–1 dry weight, may play arole as a constitutive organic osmoticum. Key words: Spartina alterniflora, dimethylsulphoniopropionate, glycinebetaine, nitrogen, salinity     

Effects on Growth and Development of Individual Chromosomes from Slow-growing Lophopyrum elongatum Love when Incorporated into Bread Wheat (Triticum aestivum L.)

Aspects of growth and development were evaluated in the fast-developingannual Triticum aestivum L. ‘Chinese Spring’, theslow-developing perennial Lophopyrum elongatum Löve, theiramphiploid, and chromosome addition and substitution lines ofL. elongatum into ‘Chinese Spring’. Relative growthrates (RGR) of shoots of L. elongatum and the amphiploid werelower than those of ‘Chinese Spring’ (34 and 13%respectively) and main stem development was also slower. Therewas no difference in shoot RGR of any of the chromosome additionor substitution lines and that of ‘Chinese Spring’when assessed between Haun stages 2.0 and 5.0. In contrast,several aspects of plant development were observed to differin the chromosome addition and substitution lines. SubstitutingE genome chromosomes (with the exceptions of 3E and 4E) forD genome chromosomes, or adding E genome chromosomes, slowedthe rate of main stem development, at least up to Haun stage5.0. Despite these differences in the rate of main stem development,the appearance of adventitious roots commenced at approximatelyHaun stage 2.0 in all genotypes. However, the numbers of adventitiousroots and tillers at the 5.0 Haun stage differed between someof the lines when compared to ‘Chinese Spring’.Although incorporation of some L. elongatum chromosomes alteredaspects of plant development, all lines showed more similarityto bread wheat than to L. elongatum, reflecting, in part, thegreater genetic contribution made by bread wheat to these lines.Copyright 2001 Annals of Botany Company Adventitious roots, chromosome addition and substitution lines, Haun stage, Lophopyrum elongatum, relative growth rate (RGR), Triticum aestivum(wheat)     

Spatio-temporal relief from hypoxia and production of reactive oxygen species during bud burst in grapevine (Vitis vinifera)

Background and Aims Plants regulate cellular oxygen partial pressures (pO₂), together with reduction/oxidation (redox) state in order to manage rapid developmental transitions such as bud burst after a period of quiescence. However, our understanding of pO₂ regulation in complex meristematic organs such as buds is incomplete and, in particular, lacks spatial resolution.Methods The gradients in pO₂ from the outer scales to the primary meristem complex were measured in grapevine (Vitis vinifera) buds, together with respiratory CO₂ production rates and the accumulation of superoxide and hydrogen peroxide, from ecodormancy through the first 72 h preceding bud burst, triggered by the transition from low to ambient temperatures.Key Results Steep internal pO₂ gradients were measured in dormant buds with values as low as 2·5 kPa found in the core of the bud prior to bud burst. Respiratory CO₂ production rates increased soon after the transition from low to ambient temperatures and the bud tissues gradually became oxygenated in a patterned process. Within 3 h of the transition to ambient temperatures, superoxide accumulation was observed in the cambial meristem, co-localizing with lignified cellulose associated with pro-vascular tissues. Thereafter, superoxide accumulated in other areas subtending the apical meristem complex, in the absence of significant hydrogen peroxide accumulation, except in the cambial meristem. By 72 h, the internal pO₂ gradient showed a biphasic profile, where the minimum pO₂ was external to the core of the bud complex.Conclusions Spatial and temporal control of the tissue oxygen environment occurs within quiescent buds, and the transition from quiescence to bud burst is accompanied by a regulated relaxation of the hypoxic state and accumulation of reactive oxygen species within the developing cambium and vascular tissues of the heterotrophic grapevine buds.     

Salt tolerance in wild Hordeum species is associated with restricted entry of Na+ and Cl- into the shoots

Eight wild Hordeum species: H. bogdanii, H. intercedens, H. jubatum, H. lechleri, H. marinum, H. murinum, H. patagonicum, and H. secalinum, and cultivated barley (H. vulgare) were grown in nutrient solution containing 0.2 (control), 150, 300, or 450 mol m(-3) NaCl. In saline conditions, the wild Hordeum species (except H. murinum) had better Na+ and Cl- 'exclusion', and maintained higher leaf K+, compared with H. vulgare. For example, at 150 mol m(-3) NaCl, the K+:Na+ in the youngest, fully expanded leaf blades of the wild Hordeum species was, on average, 5.2 compared with 0.8 in H. vulgare. In H. marinum grown in 300 mol m(-3) NaCl, K+ contributed 35% to leaf psi(pi), whereas Na+ and Cl- accounted for only 6% and 10%, respectively. By comparison, in H. vulgare grown at 300 mol m(-3) NaCl, K+ accounted for 19% and Na+ and Cl- made up 21% and 25% of leaf psi(pi), respectively. At 300 mol m(-3) NaCl, glycinebetaine and proline together contributed almost 15% to psi(pi) in the expanding leaf blades of H. marinum, compared with 8% in H. vulgare. Decreased tissue water content under saline conditions made a substantial contribution to declines in leaf psi(pi) in the wild Hordeum species, but not in H. vulgare. A number of the wild Hordeum species were markedly more salt tolerant than H. vulgare. H. marinum and H. intercedens, as examples, had relative growth rates 30% higher than H. vulgare in 450 mol m(-3) NaCl. Hordeum vulgare also suffered up to 6-fold more dead leaf material (as a proportion of shoot dry mass) than the wild Hordeum species. Thus, several salt-tolerant wild Hordeum species were identified, and these showed an exceptional capacity to 'exclude' Na+ and Cl- from their shoots.     

Plant growth and physiology under heterogeneous salinity

Background

Soil salinity is heterogeneous, and within the root-zone of single plants the salinity of the soil solution can vary widely.

Scope

This review shows that water uptake by roots from the least saline part of the soil is the key factor driving shoot growth; plants with part of the root at low salinity (0–10?mM NaCl) had 3- to 10-fold higher shoot dry mass than plants with roots in uniformly saline (50–800?mM NaCl) media. Plants in heterogeneous salinity had shoot water potentials similar to those of plants growing in uniform low-salt media, and this was likely a result of uptake of low salinity water and reduced stomatal conductance. Under heterogeneous conditions, roots in saline media took up ions, resulting in higher shoot Na⁺ and Cl^- concentrations compared with plants growing in low-salt media.

Conclusions

Results from split-root experiments complement knowledge of plant responses to uniform salinities; the next challenge is to develop new protocols so that this understanding can be extrapolated to more complex soil- and field-based systems. More work is also required to understand the physiological mechanisms underlying changes in stomatal conductance and shoot ion regulation in plants under heterogeneous salinities and how these are linked to the saline parts of the root-zone.     

Photosynthesis in aquatic adventitious roots of the halophytic stem-succulent Tecticornia pergranulata (formerly Halosarcia pergranulata)

In flood-tolerant species, a common response to inundation is growth of adventitious roots into the water column. The capacity for these roots to become photosynthetically active has received scant attention. The experiments presented here show the aquatic adventitious roots of the flood-tolerant, halophytic stem-succulent, Tecticornia pergranulata (subfamily Salicornioideae, Chenopodiaceae) are photosynthetic and quantify for the first time the photosynthetic capacity of aquatic roots for a terrestrial species. Fluorescence microscopy was used to determine the presence of chloroplasts within cells of aquatic roots. Net O₂ production by excised aquatic roots, when underwater, was measured with varying light and CO₂ regimes; the apparent maximum capacity ( P _max) for underwater net photosynthesis in aquatic roots was 0.45  µ mol O₂ m⁻² s⁻¹. The photosynthetic potential of these roots was supported by the immunolocalization of PsbA, the major protein of photosystem II, and ribulose-1-5-bisphosphate carboxylase/oxygenase (Rubisco) in root protein extracts. Chlorophyllous aquatic roots of T. pergranulata are photosynthetically active, and such activity is a previously unrecognized source of O₂, and potentially carbohydrates, in flooded and submerged plants.