Iranian Journal of Plant Physiology
Volume:7 Issue: 3, Spring 2017

One of the important and necessary practices for improving nutrients availability in sustainable agriculture is using microorganisms. Beside the negative effects of chemical fertilizers on the soil and human health, plant growth promoting rhizobacteria are known as an alternative to supply the organic nutrients of plants during the past two decades. Enriching soil fertility by eco-friendly methods in medicinal plants could well-support plants growth and production. Most studies found that bio-fertilizers such as plant growth promoting rhizobacteria (PGPR) could promote physio-morphological characteristics and yield of medicinal plants. The mechanisms of plant growth promoting rhizobacteria could be summarized in symbiotic and associative nitrogen fixation, solubilization and mineralization of nutrients, production of phytohormones, vitamins, and antagonistic components against pathogens which enhance plant resistance to the stress and non-stress conditions. This paper also argued that beside the soil type, environmental variables, soil management practices, and microbial interactions, plant species could affect bacterial diversity and composition of the rhizosphere. Three major secondary metabolites of medicinal plants such as Terpenoids, phenolics and alkaloids were also increase due to the impact of microorganisms in metabolic pathway of plants such as Jasmonic acid signaling pathway. Thereby, significant increases in growth and yield of medicinal plants in response to inoculation with PGPR could be one of the promising approaches in sustainable agriculture.

In this study, the effect of vermicompost and mycorrhizal fungi was investigated on growth, yield, chlorophyll pigments, leaf antioxidant enzymes, and seed silibinin content of Silybum marianum, milk thistle. The seeds were inoculated by two species of mycorrhiza fungi, Glomus mosseae and G. intraradices, and plants were irrigated and treated with 0, 25, 50, and 75% vermicompost after culturing. The treated plants were then compared to control plants in a greenhouse experiment. The results showed that growth parameters including leaf area, and plant height and yield significantly increased in mycorrhiza fungi treated plants especially along with 75 % vermicompost treatment. The effects of symbiotic relationship between milk thistle and G. intraradices were more pronounced than G. mosseae. Moreover, combination of mycorrhiza and vermicompost increased the photosynthetic pigments chlorophyll (a), chlorophyll (b), total chlorophyll, and carotenoid. Also, a significant decrease was observed in activities of peroxidase, superoxide dismutase, and catalase after vermicompost and mycorrhiza treatment. The results showed that silibinin decreased significantly in vermicompost application.

Oxidative stress is commonly induced when plants are grown under drought stress conditions.To analyze how salicylic acid (SA) can partly alleviate drought-induced oxidative stress and negative impacts of drought on physiology and growth of Salvia nemorosa plants, we investigated the physiological responses of S. nemorosa to SA application under drought stress. The treatments were composed of Co (control, 100% field capacity), Dr (drought, 50% field capacity), SA (500 µM) and DSA (SA drought). Plant growth and relative water content (RWC) were negatively affected by drought stress; however, SA treatment significantly improved the growth rate and enhanced the drought tolerance of seedlings. This increased tolerance in SA-supplied plants was obtained by reduced damaging effect on performance index (PIabs) and maximal quantum yield of photosystem II (PSII) (Fv/Fm) through improvement of reaction centers (RC/CS) with associated changes in excitation energy trapping (TRo/CS) and electron transport (ET0/CS) per excited cross-section of leaf. Additionally, under drought condition, plants cultivated with SA exhibited better protection against oxidative damage because of higher catalase (CAT) and ascorbate peroxidase (APX) activities and lower levels of malondoialdehyde (MDA) and hydrogen peroxide (H2O2). The present study suggests that salicylic acid can play a protective role during drought stress by enhancing the photosynthetic capacity and the antioxidant defense system.

Organic vegetable production has specific research and innovation requirements which are not shared by other parts of the food and farming sector. A pot experiment was conducted to investigate the interactive effects of few permitted organic inputs such as arbuscular mycorrhizal fungi, biochar, and different ratios of peat:worm casting on tomato (Solanum lycopersicum L.) growth, mycorrhizal dependency, biomass production, fruit yield, and soil respiration. The experimental design was a factorial arrangement based on completely randomized design with three replicates. Factors included worm casting at three levels (0, 15 and, 30% of the media volume), organic peat-based potting soil at three levels (70, 85, and 100% of the media volume), two Glomus intraradices treatments (inoculated at sowing or un-inoculated), and two biochar levels (10% of total weight of the media or unlamented). Results indicated that worm casting × peat combination significantly affected all measured traits except for the number of fruits in plant and mycorrhizal dependency. Mycorrhizal symbiosis had a significant effect only on shoot dry weight and mycorrhizal dependency. Moreover, biochar application significantly affected shoot dry weight, stem diameter and carbon mineralization. Among the different ratios of worm casting and peat in the growing media, 15% worm casting × 85% peat formed the most suitable medium condition for plants and 100% peat without worm casting was the least suitable. The highest fruit fresh weight (228.7 g/plant) was achieved in 15% worm casting × 85% peat and the lowest fruit fresh weight (175.1 g/plant) was achieved in 100 peat treatment.

The molecular marker (SSR) has been used to investigate the markers associated with the agronomic traits including days to 50% flowering, tube ring time, days to maturity, plant height, the number of main stems per plant, the number of tubers per plant, dry matter content, main stem diameter, a single tuber weight, average single tuber weight, and the total yield in potato genotypes. Ten primers used in 16 potato genotypes were investigated and principal component analysis and cluster analysis were used to determine genetic distance and genotype classification. A significant difference was found between all cultivars, indicating high genetic diversity for the traits under study, except for the diameter of stem trait. Yield showed a significant positive correlation with the number of tubers per plant, weight of tubers per plant, single tuber weight, and the number of main stems per plant. Special values resulted from components of 1-5 were higher than 1 in principal component analysis and totally justifying 76.70% of all variables variances. Molecular diversity of cultivars was measured using parameters of polymorphic information, the number of effective alleles, and Shannon index and the average of 39.03 SSR bands was achieved among which 9.41 bands were polymorphic. The average number of polymorphic bands varied for each primer from 1.56 to 2.12. Maximum and minimum polymorphic bands belonged to the HVM70 primer with 2.12 and the Bmacoo40 primer with 1.56, respectively. Also, the mean maximum band (4.4) and minimum band (3.1) belonged to Agra and Deyta cultivars, respectively. The morphologic data did not conform to the molecular data indicating that SSR marker had no genetic relationship with positions controlling the measured morphologic traits. Since the SSR markers were located in non-coding area of genome, no relationship between classifications of molecular markers and morphologic data was unexpected.

In order to improve the shoot proliferation rate of ‘Dwarf Cavendish’ banana shoot tip cultures, polyethylene glycol (PEG6000) was employed at concentrations of 2, 4, and 6% (w/v). The medium without PEG was considered as negative control. An increasing of shoot proliferation was achieved in MS medium containing 2% PEG. Furthermore, application of 2% PEG significantly increased the shoot dry weight (DW) as well as root/shoot DW ratio of the regenerated explants. The root/shoot DW ratio, chlorophyll a and chlorophyll b contents of leaves were decreased by the increase in PEG percentage. Application of PEG at high concentrations increased the leaf tissue chlorosis and necrosis. The proline and potassium contents of leaf tissue were increased in regenerated shoots from the media containing 2 and 4% PEG. Application of 2% and 4% PEG increased ex vitro plantlets survival rate up to 34% and 40%, respectively compared to the control. In conclusion, the mild osmotic stress caused by the application of PEG 2% improved the in vitro shoot proliferation rate accompanied by an increase in the ex vitro survival rate of regenerated plantlets. Seemingly, the promising results using PEG6000 at the resultant level (2%) are in the main part due to the stress simulation effects and later plantlets’ acclimatization through physio-biochemical mechanisms.

Zinc is a necessary micronutrient in plants whose deficiency can alter essential functions in plant metabolism. High concentrations of Zn can be potentially toxic to plants causing phytotoxicity by the formation of reactive oxygen species. On the other hand, sodium nitroprusside (SNP), a donor of nitric oxide (NO) can protect cells from oxidative damage produce by reactive oxygen species. In this study, we examined the effect of different concentrations of Zn (0, 50, 100, 300, and 500 μM) on growth and physiological parameters of Plantago major L. under various concentrations of Sodium nitroprusside (0, 50, 100, and 200 μM). The results showed that Zn treatment decreased fresh and dry weight and increased the contents of malondealdehyde, antioxidant, and osmolyte. The starch content on the other hand decreased. Moreover, application of different concentrations of sodium nitroprusside (especially 100 μM) as a donor of nitric oxide, had a favorable effect as it improved the heavy metal stress through increasing the plant’s tolerance against zinc toxicity. However, high concentration of Sodium nitroprusside had a deterrence effect on morphology and physiology of Plantago. major L.

This paper reports a study on the role of antioxidant enzymes and physiological characteristics of clover cultivars in their resistance against water deficit stress in the field conditions. Four cultivars of clover (Trifolium spp) namely, T. resupinatum L., T. incarnatum L., Trifolium pretense L., and T. alexandrinum L. under three levels of irrigation including %35, %50, and %65 soil moisture discharge were studied in a split plot experiment with completely randomized blocks design with three repetitions. Analysis of variance showed a significant effect of irrigation level on dry forage weight, leaf relative water content, and proline, catalase, peroxidase, chlorophyll b, and carotenoid contents. The effects of cultivars on dry forage weight, leaf relative water content, and proline, chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents of the plants were also significant (P≤0.01). Generally, with an increase in the percentage of soil moisture, the dry forage yield showed a significant decrease. Also, water deficit resulted in increased proline content and also increased activities of catalase, peroxidase, and superoxide dismutase antioxidants. On the other hand, no significant differences were observed between cultivars with respect to the level of antioxidant activities. In addition, the effects of soil moisture discharge on the activities of all antioxidants except for those of superoxide dismutase were significant. Moreover, increasing the percentage of moisture discharge led to the reduction in the relative water content of the leaves and chlorophyll and carotenoid contents of all four cultivars of clover under study. Finally, the study concludes with recommending T. incarnatum L. as the most suitable clover cultivar for the climatic condition of the study region and under low input management (low irrigation, minimum fertilizer application, no herbicide application, and no weeding).