Plants experience water stress either when the water supply to their roots becomes limiting or when the transpiration rate becomes intense. Water stress is primarily caused by the water deficit, i.e. drought or high soil salinity. In case of high soil salinity and also in other conditions like flooding and low soil temperature, water exists in soil solution but plants cannot uptake it-a situation commonly known as 'physiological drought'. Drought occurs in many parts of the world every year, frequently experienced in the field grown plants under arid and semi-arid climates. Regions with adequate but non-uniform precipitation also experience water limiting environments. Since the dawn of agriculture, mild to severe drought has been one of the major productionlimiting factors. Consequently, the ability of plants to withstand such stress is of immense economic importance. The general effects of drought on plant growth are fairly well known. However, the primary effect of water deficit at the biochemical and molecular levels are not considerably understood yet and such understanding is crucial. All plants have tolerance to water stress, but the extent varies from species to species. Knowledge of the biochemical and molecular responses to drought is essential for a holistic perception of plant resistance mechanisms to water limited conditions in higher plants. 3. Effects of water stress on plants Drought, as an abiotic stress, is multidimensional in nature, and it affects plants at various levels of their organization. In fact, under prolonged drought, many plants will dehydrate and die. Water stress in plants reduces the plant-cell's water potential and turgor, which elevate the solutes' concentrations in the cytosol and extracellular matrices. As a result, cell enlargement decreases leading to growth inhibition and reproductive failure. This is followed by accumulation of abscisic acid (ABA) and compatible osmolytes like proline, which cause wilting. At this stage, overproduction of reactive oxygen species (ROS) and formation of radical scavenging compounds such as ascorbate and glutathione further aggravate the adverse influence. Drought not only affects plant water relations through the reduction of water content, turgor and total water, it also affects stomatal closure, limits gaseous exchange, reduces transpiration and arrests carbon assimilation (photosynthesis) rates. Negative effects on mineral nutrition (uptake and transport of nutrients) and metabolism leads to a decrease in the leaf area and alteration in assimilate partitioning among the organs. Alteration in plant cell wall elasticity and disruption of homeostasis and ion distribution in the cell has also been reported. Synthesis of new protein and mRNAs associated with the drought response is another outcome of water stress on plants. Under the water stress cell expansion slows down or ceases, and plant growth is retarded. However, water stress influences cell enlargement more than cell division. Plant growth under drought is influenced by altered photo...

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Lallemantia iberica (Lamiaceae) has pharmaceutical and nutritional importance owing to production of oily seeds and synthesis of commercially secondary metabolites. In the present study, total phenol and flavonoids content and quantitative changes in the shoot and callus pigments of L. iberica were investigated. Moreover, some growth parameters and volatile content of in vitro grown shoots were analyzed. Nodal segments and epicotyldons were used as the explants for shoot and callus formation, respectively. In the multiplication stage of shoot culture, MS medium supplemented with six concentrations of TDZ was employed. For callus induction, 1 mg/l of TDZ, NAA and a combination of NAA and BA were used. Extracted volatile products were analyzed by GC-mass spectrometry. According to the results, the concentration range of TDZ from 0.22 to 0.66 mg/l improved the flavonoids production and the highest content was reported to be in 2 mg/l TDZ (157.5 ± 25.9 mg QE/ g); also, the highest amount of total phenol (3.86 ± 1.02 mg PYRO/g) was observed in 0.66 mg/l TDZ. For induced calli, among the three tested types of PGRs, TDZ treatment was efficient for total phenol and flavonoids. In general, the higher content of flavonoids was obtained from L. iberica shoots while the callus of this plant was efficient for total phenol production. 55 components were identified using GC-MS analysis indicating a low amount of mono and sesquiterpenes and high quantity of alkan hydrocarbons.

Allelopathy is one of the important interactions among plants. Weeds can reduce crops productions in farms by their allelopathic effects. Redroot pigweed (Amaranthus retroflexus L.) is the most common weed in Iran with well-known allelopathic potential. In the presented experiment, the allelopathic effects of redroot pigweed on germination and growth of four important crop species including cucumber (Cucumis sativus L.), alfalfa (Medicago sativa L.), common bean (Phaseulus vulgaris L.) and bread wheat (Triticum aestivum L.) was studied. The effect of different concentrations of redroot pigweed leachate on seed germination and seedlings growth parameters of tested plants was significant, but not same in all studied species. Bread wheat and cucumber were more resistance in seed germination stage in comparison to common bean and alfalfa. Except alfalfa, all plant species showed certain rate of resistance in the most measured parameters. According to the obtained results, bread wheat and common bean were the most resistant species, cucumber was resistant at low concentration but sensitive at high concentration, and alfalfa was the most sensitive species to the redroot pigweed leachate treatments. Therefore, the cultivation of resistant plant species (such as bread wheat and common bean plants) in the regions with redroot pigweed's invasion is appropriate way in management of the farms. Alelopatija je ena izmed najpomembnejših interakcij med rastlinami. Pleveli lahko zmanjšajo pridelek zaradi njihovih alelopatičnih učinkov. Navadni ščir (Amaranthus retroflexus L.) je v Iranu najpogostejši plevel z dobro znanim alelopatičnim učinkom. V tej raziskavi smo preučevali alelopatski učinek navadnega ščira na kalitev in rast štirih pomembnih kulturnih rastlin in sicer kumar (Cucumis sativus L.), lucerne (Medicago sativa L.), navadnega fižola (Phaseulus vulgaris L.) in krušne pšenice (Triticum aestivum L.). Učinek različnih koncentracij izvlečka navadnega ščira na kalitev in rastne parameter preiskuševanih rastlin je bil značilen toda ne enak pri vseh rastlinah. Krušna pšenica in kumare so bile bolj odporne na stopnji kalitve v primerjavi s fižolom in lucerno. Z izjemo lucerne so vse preiskušene vrste pokazale določeno odpornost pri vseh merjenih parametrih. Glede na rezultate te raziskave sta se krušna pšenica in navadni fižol izkaza kot najbolj odporna, kumare so bile pri manjših koncentracijah ekstrakta navadnega ščira odporne, a občutljive pri velikih koncentracijah. Lucerna je bila najbolj občutljiva na izločke navadnega ščira pri vseh obravnavanjih. Na osnovi dobljenih rezultatov priporočamo kmetovalcem na območjih z večjim pojavljanjem navadnega ščira gojenje nanj odpornih rastlin kot sta krušna pšenica in navadni fižol.Ključne besede: alelopatija, navadni ščir, odpornost, kmetijske rastlines, koncentracije izvlečkov

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