Effects of boron foliar applications on vegetative and reproductive growth of sunflower

Foliar application may be used to supply boron (B) to a crop when B demands are higher than can be supplied via the soil. While B foliar sprays have been used to correct B deficiency in sunflower (Helianthus annuus L.) in the field, no studies have determined the amount of B taken up by sunflower plant parts via foliar application. A study was conducted in which sunflower plants were grown at constant B concentration in nutrient solution with adequate B (46 mum) or with limited B supply (0.24, 0.40 and 1.72 mum) using Amberlite IRA-743 resin to control B supply. At the late vegetative stage of growth (25 and 35 d after transplanting), two foliar sprays were applied of soluble sodium tetraborate (20.8 % B) each at 0, 28, 65, 120 and 1200 mm (each spray equivalent to 0, 0.03, 0.07, 0.13 and 1.3 kg B ha(-1) in 100 L water ha(-1)). The highest rate of B foliar fertilization resulted in leaf burn but had no other evident detrimental effect on plant growth. Under B-deficient conditions, B foliar application increased the vegetative and reproductive dry mass of plants. Foliar application of 28-1200 mm B increased the total dry mass of the most B-deficient plants by more than three-fold and that of plants grown initially with 1.72 mum B in solution by 37-49 %. In this latter treatment, the dry mass of the capitulum was similar to that achieved under control conditions, but in no instance was total plant dry mass similar to that of the control. All B foliar spray rates increased the B concentration in various parts of the plant tops, including those that developed after the sprays were applied, but the B concentration in the roots was not increased by B foliar application. The B concentration in the capitulum of the plants sprayed at the highest rate was between 37 and 93 % of that in the control plants. This study showed that B foliar application was of benefit to B-deficient sunflower plants, increasing the B status of plant tops, including that of the capitulum which developed after the B sprays were applied. (C) 2003 Annals of Botany Company.

Seed viability and dormancy mechanisms of Leucopogon melaleucoides Cunn. ex DC. (Epacridaceae)

Leucopogon melaleucoides, a flowering shrub, is desired by floricultural markets but is difficult to propagate. Seed viability was tested and dormancy mechanisms were studied to develop a commercial propagation system. Although around 56% of seed were viable, germination was completely inhibited unless the endocarp was removed. After-ripened seed (8 months after collection) germinated faster than fresh seed (2 days after collection), but germination occurred over a prolonged period (155 days). Germination of after-ripened seed was promoted with GA(3) or a commercial smoke product containing unknown plant growth regulators. All viable seed treated with GA(3) at 1000 mg L-1 had germinated after 24 days. The results suggest that both a physical and physiological dormancy mechanism occur for this species, with removal of the endocarp and pretreatment with 1000 mg L-1 GA(3) promoting complete germination of viable seed.

Adventitious root formation in cuttings of Backhousia citriodora F. Muell 2. Seasonal influences of temperature, rainfall, flowering and auxins on the stock plant

A 2-year study was carried out on established trees at two sites in southeastern Queensland, Australia, to identify environmental factors that influenced rooting of Backhousia citriodora from cuttings. Complex interactions of rainfall events above 20 mm from the preceding month and mean maximum temperature on stock plants resulted in a correlation with rooting success of r = 0.81 and 0.74 for sites at The University Of Queensland, Gatton Campus, and Cedar Glen, respectively. A more detailed investigation under controlled environmental conditions showed that maintaining stock plants at temperatures between 10 and 30degreesC had no direct effect on rooting capacity. However, temperature was correlated with growth, which may have an indirect effect on root formation. In spring floral initiation was found to only delay rooting and had no effect on the final rooting percentage. A series of seasonal experiments demonstrated that application of the auxins indole-3-acetic acid, indole-3-butyric acid and napthaleneacetic acid over a range of concentrations (1000-8000 mug/ml) did not significantly increase rooting compared to the control and there is no practical advantage in applying auxins. Seasonal results and the temperature experiment also suggest that under a glasshouse environment with higher temperatures in winter and an adequate supply of water, B. citriodora cuttings can be successfully rooted over the whole year. (C) 2004 Elsevier B.V. All rights reserved.

Modulation of higher-plant NAD(H)-dependent glutamate dehydrogenase activity in transgenic tobacco via alteration of beta subunit levels

Glutamate dehydrogenase (GDH; EC 1.4.1.2-1.4.1.4) catalyses in vitro the reversible amination of 2-oxoglutarate to glutamate. In vascular plants the in vivo direction(s) of the GDH reaction and hence the physiological role(s) of this enzyme remain obscure. A phylogenetic analysis identified two clearly separated groups of higher-plant GDH genes encoding either the alpha- or beta-subunit of the GDH holoenzyme. To help clarify the physiological role(s) of GDH, tobacco (Nicotiana tabacum L.) was transformed with either an antisense or sense copy of a beta-subunit gene, and transgenic plants recovered with between 0.5- and 34-times normal leaf GDH activity. This large modulation of GDH activity (shown to be via alteration of beta-subunit levels) had little effect on leaf ammonium or the leaf free amino acid pool, except that a large increase in GDH activity was associated with a significant decrease in leaf Asp (similar to 51%, P=0.0045). Similarly, plant growth and development were not affected, suggesting that a large modulation of GDH beta-subunit titre does not affect plant viability under the ideal growing conditions employed. Reduction of GDH activity and protein levels in an antisense line was associated with a large increase in transcripts of a beta-subunit gene, suggesting that the reduction in beta-subunit levels might have been due to translational inhibition. In another experiment designed to detect post-translational up-regulation of GDH activity, GDH over-expressing plants were subjected to prolonged dark-stress. GDH activity increased, but this was found to be due more likely to resistance of the GDH protein to stress-induced proteolysis, rather than to post-translational up-regulation.

The effect of copper toxicity on the growth and root morphology of Rhodes grass (Chloris gayana Knuth.) in resin buffered solution culture

A solution culture experiment was conducted to examine the effect of Cu toxicity on Rhodes grass (Chloris gayana Knuth.), a pasture species used in mine-site rehabilitation. The experiment used dilute, solution culture to achieve external nutrient concentrations, which were representative of the soil solution, and an ion exchange resin to maintain stable concentrations of Cu in solution. Copper toxicity was damaging to plant roots, with symptoms ranging from disruption of the root cuticle and reduced root hair proliferation, to severe deformation of root structure. A reduction in root growth was observed at an external Cu concentration of < 1 mu M, with damage evident from an external concentration of 0.2 mu M. Critical to the success of this experiment, in quantitatively examining the relationship between external Cu concentration and plant response, was the use of ion exchange resin to buffer the concentration of Cu in solution. After some initial difficulty with pH control, stable concentrations of Cu in solution were maintained for the major period of plant growth. The development of this technique will facilitate future investigations of the effect of heavy metals on plants.

New insights into growth hormone action

It has been 75 years since Evans and Long identified a somatic growth-promoting substance in pituitary extracts, yet it is only in the last 20 years that the molecular basis for this action has been established. Three key elements in this elucidation were the cloning of the GH receptor, the identification of Janus kinase (JAK) 2 as the receptor-associated tyrosine kinase, and the delineation of signal transduction and activators of transcription (STAT) 5a/b as the key transcription factor(s) activated by JAK2. The interaction between these three elements results in enhanced postnatal growth and is the subject of this review. We describe a new model for GH receptor activation based on subunit rotation within a constitutive dimer, together with the phenotype and hepatic transcript profile of mice with targeted knockins to the receptor cytoplasmic domain. These support a central role for STAT5a/b in postnatal growth.

Effect of NaCl on emergence and growth of a range of provenances of Eucalyptus citriodora, Eucalyptus populnea, Eucalyptus camaldulensis and Acacia salicina

High salt levels in mine spoils have been identified as one of the major chemical limitations to plant establishment after coal mining in central Queensland. Soil solution extracts from spoils indicated that EC levels of up to 26 dS/m could be encountered. Glasshouse trials examined the emergence and growth of Eucalyptus citriodora, Eucalyptus camaldulensis and Eucalyptus populnea provenances and Acacia salicina subjected to such EC levels. Relatively low levels of salt (100 mM NaCl, or 11 dS/m) with respect to the levels encountered on mine spoils, were enough to substantially reduce the rate and percentage emergence of all eucalypt provenances. A. salicina was found to be superior to the eucalypts in its ability to emerge and survive under saline conditions. It was the only species to have seedlings emerge and survive at 200 mM NaCl (20 dS/m), and the effect of salt on decreasing seedling dry weight was less pronounced for A. salicina than for any of the eucalypts. Established plants survived the range of salt treatments far better than emerging seedlings, with survival of established plants being reduced only at 300 and 400 mM NaCl (28 and 36 dS/m, respectively). A. salicina performed significantly better at 300 and 400 mM NaCl than most of the eucalypts studied. (c) 2006 Elsevier B.V. All rights reserved.