Cellular Expansion at Low Temperature as a Cause of Membrane Lesions

Raven

Lea

2013

300

169

The literature on nitrogen (N) form effects on plants at different stages of their development has been critically reviewed, assessing the possible mechanisms of these effects. In particular, nitrate (NO 3 − ) was compared with the other forms of N utilised by plants. It is concluded that the form of N available to plants can affect their time and rate of seed germination, leaf expansion and function, dry matter partitioning between shoot and root, and root architecture. The magnitude of these effects is dependent on environmental factors outside the supply of N. The mechanism of these effects is variable. Assessment of the importance of root or shoot NO 3 − assimilation under different environmental conditions is an important area for further study.

Section: Environmental Stress/change and N Formmentioning

confidence: 99%

Do plants need nitrate? The mechanisms by which nitrogen form affects plants

Raven

Lea

2013

300

169

“…Specifically, if the rate of leaf expansion increases, then the demand for membrane synthesis is greater. Low temperature decreases the rate of incorporation of lipid material into membranes (Willing & Leopold, 1983) and if the increased demand for membrane synthesis is not met, cellular disruption will result. This hypothesis needs testing.…”

Section: Photon and Water Costsmentioning

confidence: 99%

Can genetic manipulation of plant nitrogen assimilation enzymes result in increased crop yield and greater N‐use efficiency? An assessment

Lea

Raven

et al. 2004

140

The literature on the relations between plant nitrogen (N) assimilation enzymes and plant/crop N assimilation, growth and yield is reviewed to assess if genetic manipulation of the activities of N assimilation enzymes can result in increased yield and/or increased N use efficiency. The available data indicate that (I) levels of N assimilation enzymes do not limit primary N assimilation and hence yield; (II) root or shoot nitrate assimilation can have advantages under specific environmental conditions; (III) for cereals, cytosolic glutamine synthetase (GS1) is a key enzyme in the mobilisation of N from senescing leaves and its activity in senescing leaves is positively related to yield; and (IV) for rice (Oryza sativa), NADH-glutamate synthase (NADH-GOGAT) is important in the utilisation of N in grain filling and its activity in developing grains is positively related to yield. In our opinion, selection of plants, from either a genetically manipulated population or genetic resources, with expression of nitrate reductase/nitrite reductase primarily in the root or shoot should increase plant/crop growth and hence yield under specific environmental conditions. In addition for cereals the selection of plants with high GS1 in senescing leaves and in some cases high NADH-GOGAT in developing grains could help maximise the retrieval of plant N in seeds.

“…The proposed explanation for this relationship is as follows. Low temperatures decrease the elasticity of membranes and/or decrease the rate of incorporation of lipid material into membranes thus making them more vulnerable to strain (Willing & Leopold, 1983). As external nitrate concentration increases, the rate of nitrate uptake and its subsequent transport to the shoot both increase.…”

Section: Introductionmentioning

confidence: 99%

The effects of different external nitrate concentrations on growth of Avena sativa cv. Amuri treated with diclofop‐methyl

Dickson

Foreman

et al. 1989

Avena sativa cv. Amuri fed either low or high nitrate was sprayed with diclofopmethyl ( 1 kg a.i. ha-I) at the three leaf stage. The short term effects of the herbicide on chlorophyll concentration of leaves (laminae) and short and long term effects on d.wt of the component plant parts were determined by comparison with unsprayed plants.For unsprayed and sprayed plants, total leaf d.wt approximately doubled during the first twelve days after commencing treatments. Growth was substantially greater at high nitrate than low nitrate. For unsprayed plants, the increase in total leaf d.wt was due primarily to growth of leaf 3 but for sprayed plants it was due to growth of leaves 1 and 2. Twelve days after commencing treatments, d.wt of leaves 1 and 2 was substantially greater for sprayed plants than for unsprayed plants given similar nitrate, while chlorophyll concentration was substantially less. Leaf 3 d.wt and chlorophyll concentration were substantially greater in unsprayed plants than in sprayed plants given similar nitrate. For unsprayed plants, values were greater at high nitrate than low nitrate, for sprayed plants the converse was the case.Forty nine days after commencing treatments, unsprayed plants had a greater total plant d.wt than sprayed plants given similar nitrate. Total plant d.wt for unsprayed plants was greater at high nitrate than low nitrate, the opposite was the case for sprayed plants. Unsprayed plants a t both nitrate levels and sprayed plants given low nitrate produced seed heads but sprayed plants given high nitrate did not. Diclofop-methyl at a rate of 0.3 kg a.i. ha-' stopped seed head production at high nitrate. Retention and uptake of diclofop-methyl were not significantly different at low and high nitrate. At 1 kg a.i. ha-l diclofop-methyl, plants switched from low to high nitrate at spraying showed damage similar to that shown by plants given high nitrate throughout. Addition of 200 vg GA into the leaf sheaths two days prior to spraying increased the efficacy of diclofop-methyl at low nitrate.It is proposed that increased efficiency of diclofop-methyl at high nitrate is due to increased leaf damage caused by a greater rate of leaf expansion.