HERBICIDE PHOSPHINOTHRICIN CAUSES DIRECT STIMULATION HORMESIS

Herbicide phosphinothricin (PPT) inhibits glutamine synthetase (GS), a key enzyme in nitrogen assimilation, thus causing ammonia accumulation, glutamine depletion and eventually plant death. However, the growth response of Lotus corniculatus L. plants immersed in solutions with a broad range of PPT concentrations is biphasic, with pronounced stimulating effect on biomass production at concentrations ≤ 50 μM and growth inhibition at higher concentrations. The growth stimulation at low PPT concentrations is a result of activation of chloroplastic isoform GS2, while the growth suppression is caused by inhibition of both cytosolic GS1 and GS2 at higher PPT concentrations. Since the results are obtained in cell-free system (e.g. protein extracts), to which the principles of homeostasis are not applicable, this PPT effect is an unambiguous example of direct stimulation hormesis. A detailed molecular mechanism of concentration-dependent interaction of both PPT and a related GS inhibitor, methionine sulfoximine, with GS holoen- zymes is proposed. The mechanism is in concurrence with all experimental and literature data

Fruit characteristics in walnut tree population in relation to growing season onset

The objective of walnut selection is to obtain promising genotypes characterized by later growing season onset, shorter period of vegetation, resistance to diseases, stable fruit productivity and high fruit quality. Aiming at obtaining genotypes with favorable properties, in five localities of Eastern Serbia, where walnut is widely grown, we studied the correlation among growing season onset on the one hand, and major pomological properties and fruit quality on the other. In the studied population, trees with early growing season onset and fruit mass up to 8.0 g (30.1%) were predominant, whereas those with late growing season onset were in minority, fruit mass ranging from 10.1 to 12 g (0.07%). Kernel ratio was highest in the former (20.69%), and the lowest in the latter (0.07%). Similar was observed in oil and raw proteins content in kernel which was highest in fruits of early trees (33.62%, 47,55%), while it was remarkably lower in late ones (0.72%, 0.49%). The obtained results suggest that the studied population was dominated by early trees and unfavorable or less favorable fruit properties. In spite of that, we evidenced some trees with favorable properties which can be used in breeding as donors of useful genes

Use of Chenopodium murale L. transgenic hairy root in vitro culture system as a new tool for allelopathic assays

We investigated Chenopodium murale transgenic hairy root in vitro culture system as a new tool for allelopathic assays. Transgenic hairy roots were induced by Agrobacterium rhizogenes A4M70GUS from roots, cotyledons, leaves, and internodes of C. murale seedlings. Roots were found to be the best target explants, providing transformation efficiency of up to 11.1%. Established hairy root clones differed in their morphology and growth potential. Molecular characterization of these clones was carried out by PCR, RT-PCR and histochemical GUS analyses. No differences in rol gene expression were observed. Liquid culture system of characterized hairy root clones was maintained for over 2 years. Six hairy root clones were selected for assaying the allelopathic effect of their growth medium against germination and seedling elongation of wheat and lettuce test plants. The inhibitory potential varied depending on the hairy root clone. Some transgenic clones showed significantly higher inhibition compared to wild-type roots. These results revealed that hairy roots as an independent system synthesize some bioactive substances with allelopathic activity and exude them into the growth medium. Concentrations of caffeic, ferulic and p-coumaric acids (0.07-2.85 mu mol/L) identified by HPLC analysis in the growth media were at least 1000 times lower than the inhibitory active concentration (5 mmol/L) of pure grade phenolic acids, suggesting that they have a limited role in the allelopathic phenomena of C murale. The presented hairy root system appears to be a suitable tool for further investigation of the potential and nature of root-mediated allelopathic interference of C. murale