Allopathic effects of Nerium oleander L. on growth and anatomy structure of Hordeum vulgare (monocotyledon) and Vicia sativa (dicotyledon) seedlings.
Allelopathy involves plant chemical interactions in both natural and agro-ecosystems. These interactions are due to the release of secondary metabolites from producer plants to the environment. These 'allelochemicals' can then interfere with the metabolism of other plants. If the effect of these allelochemicals is harmful to plant growth and development, it becomes a biotic stress known as allelochemical stress, which can have an indirect or direct effect on the receiver plant. Thus, allelochemical stress can act as a mechanism of interference and can influence the pattern of vegetation, weed growth and crop productivity an allelochemical stress can have several molecular targets in the receiver plants and consequently can interfere with different cellular processes causing inhibition of growth .
Most of plants have allelopatic potential with releasing allelopatic compounds. These compounds are found in all part of plant root, steam, rhizomes, flowers and leaves . We can use allelopatic compounds to control weed but allelochemicals often are in low concentration and interaction with each other. Now just 3% of allelochemicais are recognized . Nerium oleander is a toxic plant that has been known for its compounds of glycosides and flavonoids. The most important glycoside of this plant is Oleandrine. For studying allelopatic effect of Nerium oleander, on the germination of seed and growth of seedling of selected monocotyledon (Hordeum vulgare) and dicotyledon (Vicia sativa) were examined.
Materials and Methods
Nerium oleander was used in allelopatic experiments where samples were prepared from plant's leaves and flowers in young and elder ages separately on May 2009 at Pardisan, an Iran-Tehran National Biodiversity park.
The plant samples were dried in laboratory conditions then they were ground into powder and sterilized. 1g and 3g of each sample were mixed with 100g distilled water. After 48 hours they were smoothed with filter papers (Slow).
Seeds were surface sterilized in dilution of commercial hypochlorite bleach 5% for 5 minutes and rinsed and several times with distilled water. 10 seeds of every plant were place on filter paper at Petri dishes. Extract solutions were added to each dish and distilled water was used as control. Treatment included [T.sub.1], [T.sub.2], [T.sub.3], [T.sub.4], [T.sub.5], [T.sub.6], [T.sub.7], [T.sub.8] and [T.sub.9] that mean control, young leaves 1%, young leaves 3%, elder leaves 1%, elder leaves 3%, buds 1%, buds 3%, flowers 1% and flowers 3%.Seedling root and shoot length and fresh weight were measured after 7 days for leave extracts and 10 days for flowers extracts. Seedlings were oven dried at 50[degrees]C for 48 hours.
The results were analyzed with software SPSS. The means of treatments were grouped with least significant difference (LSD) procedure at the 0.05 probability level.
For studying anatomy of plants, segments of roots tissue of barley (Hordeum vulgare) and Vicia sativa were fixed in Alcohol and glycerin in the ratio of 80 to 20 for 1 week. Sections were cut with blade and stained by bleu de metyle and carmin alune. Thin sections were viewed with Nikon light microscope and recorded by digital camera.
Result and Disscution
Coleoptile length of 7 and 10 days control of barley seedlings were 3.47 and 3.7 respectively. Barley seedlings that treated with flower extract at 3% concentration have been the lowest coleoptile.
Leaf length of barley seedling was shortened with Nerium oleander extracts significantly at P < 0.05 probability from 8.9cm (control) to 0.25 (floral 3% extract). Epicotyl and hypocotyl of Vicia sativa seedlings were lower with elder treatments more than younger one.
Also fresh weight of barley seedling are reduced with floral extract more than leaf extracts. On the other hand most of N. oleander extracts were significantly affected on fresh weight of V. sativa. All aqueous caused great decreasing of root length seedlings of barley and V. sativa at P<0.001 probability. Minimum root length was belonging to flowers extract.
For studying roots anatomy of barley, section from 1cm under basal (pass root to shoot) were made. On cross section of 10 days barley roots at control sample from outside to inside: root hairs, epidermis, cortex parenchyma, endodermis, pericycle, tissue conductors and medulla were observed. Samples treatments by young leaves 3% extracts had less root hair. Cortex was suberizes with elder leaves 1% and 3% aqueous also number of vascular bundles have been from 8 to 10. Lacking of root hairs, slightly suberization and mount of vascular bundles were caused of both buds extracts. Medulla was losing by high concentration buds and flowers of N. oleander.
While elongation of V. sativa roots were inhibited strongly, transverse growth was maintained regularly and was from outside to inside: root hairs, epidermis, cortex parenchyma, endodermis, pericycle, tissue conductors and parenchyma medulla. Although lateral roots organized in all treatments, root hair behold only on control samples because of stress and early aging. Extension of cortex layer and vascular bundles were affected by couple young and 3% elder leaves extracts respectively. Treatments by floral aqueous have been bordered lignin. Probably because of falling root hair on maturing suberin appeared.
Analysis of mean showed that Neriun growth stage and extract concentration had significant effect on all morphologic, physiologic and anatomic traits. Shoots (coleoptile and leaf length of barley and epicotyl and hypocotyl of V. sativa) have been miniature by the N. oleander aqueous.
Kadiaglu at 2004 has reported that potassium carbaxy actratyloside and hypoglycaemic isolated from Xanthum strumarium inhibited wheat coleoptile. It is likely that similar compounds in N. oleander is reduced coleoptile length. Also Onen and Ozer  have shown that essential oils of mugwort dramatically reduced coleoptile and radicula growth of crops.
In addition, allelopaty stress inhibited significantly radical growth on both selected plant. The same effect has been reported previously. Koseli showed an allelopathic effect of garden radish on johnsongrass (Sorghum halepense) rhizomes in petri dish, pot and field experiments. He concluded that garden radish inhibited johnsongrass rhizome emergence and growth. Purple nutsedge is a common weed species that causes losses in many summer crops. Purple nutsedge tubers decreased germination rate and radicula length of tomato, eggplant and bean. Inhibition was higher in light soils than in heavy soils .
Fresh weight of dicot had been decreased more than monocot. Beans were more affected than wheat by N. oleander extracts . Dhima et al,  have shown that fresh weight of corn seedling with increasing concentration of aromatic plants extracts was decreased.
Although the both development stage of Nerium oleander showed allelopaty potential, in most of time elder extract from leaves or flowers were more effectiv. Ben-hammuoda et al., were represented that allelopaty is the most proportion in physiologic maturity.
Fergoson et al.,  prepared aqueous extracts of leaf, wood chips with bark and fresh wood of some trees among N. oleander. They have shown extracts of elder plants are more effective.
It looks that floral extracts are more effective than leaf. Karraltin et al.  reported that allelopathic effects of oleander (N. oleander) root, stem, leaf, and bud extracts and their mixtures were tested on germination and early seedling growth of bean and wheat in petri dish assays., and especially bud extracts had negative effects on beans.
Anatomy structure results showed that the number of vessel of bundles in barley and diameter of roots in monocot and dicot increased incomparition to the control sample. Chon et al.  reported that coumaric acid and aqueous leachates of alfalfa leaves caused an increase in alfalfa root diameter due to an expanding of the vascular cylinder and cortex cell layers. The authors explained that coumaric acid inhibited cell division, and consequently the thickness of seminal roots was enlarged abnormally due to inhibition of longitudinal root growth.
Flower and leaves of Nerium oleander has allopathic potential. Because of different structure, function and gene expression, they have dissimilar intensity and flowers frequently are more allopathic. Furthermore allelopatic effects are not same at different development stage. Older parts of most plants are more allelopathic properties.
Roots particularly were reduced more than shoots. Owing to root is the first organ exposure and absorb allelopatic factors so significant changes are clear. Also V. sativa seedlings were more sensitive than barley.
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(1) A. Kazemi Mojarad, (2) A. Majd and (1) H. Fahimi
(1) islamic Azad University, Science and Research Branch, Faculty of Sciences, Department of Biology, Tehran, Iran
(2) Islamic Azad University, North Tehran Branch, Faculty of Biological science, Department of Biology, Tehran, Iran
A. Kazemi Mojarad, Islamic Azad University, Science and Research Branch, Faculty of Sciences, Department of Biology, Tehran, Iran
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|Title Annotation:||Original Article|
|Author:||Mojarad, A. Kazemi; Majd, A.; Fahimi, H.|
|Publication:||Advances in Environmental Biology|
|Date:||Apr 1, 2013|
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