Extended Abstract
1-Introduction: Silicon (Si) is considered as a beneficial nutrient in most plants which can contribute to various positive physiological impacts. It is well documented that Si can alleviate a broad range of biotic and abiotic stresses, so this element is an effective inorganic antistress. As tomato is usually attacked by different pathogens like fungi, in addition it is vulnerable against a vast range of abiotic stresses including water stress, chilling, freezing and so forth, Si treatment can be a good strategy for strengthening the plant defense system. It is so obvious that Si treatment should be applied before stress; because of this, comprehension of this element behavior in normal conditions can be important. However, most experiments about Si have been conducted in stressful conditions, but evaluation of the Si effect in normal conditions, its behavior in plants, and its distribution in different organs need to be explored. Recently, the active gene of S1Lsi1 which is responsible for Si influx, was detected in tomato, but efflux gene named S1Lsi2 was inactive, therefor translocation of Si from root to above parts of plant might be seriously restricted. Evaluation of tomato potential for Si root absorption and after that transporting of the element to the aerial parts can shed light on the efficiency of Si fertilization. So, this research was outlined to monitor the Si uptake by root, its distribution in different plant organs, and its effects on biomass and yield in tomatoes treated by different concentrations of Si.
2-Material and methods: In this research, Si uptake and translocation in tomato plant was evaluated in completely randomized design experiment with 11 treatments (0, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 mg Si/l from K₂SiO₃), and four replications in an open field soil pot experiment. Potassium silicate treatments were applied every 10 days up to 8 times during the experiment conduction. Each pot was fertigated 200 ml of Si contained solution. Fresh and dry weight of fruits, fresh and dry weight of old leaves, fresh and dry weight of young leaves, fresh and dry weight of stem, fresh and dry weight of root, and Si content of different parts of plant were determined in this experiment. Analysis of variation was carried out by SAS 9.1 software and the Duncan test was used for mean comparison.
3-Results and discussions: PCR Based on obtained results, treatments of 300 and 600 mg/l caused an increase in fresh weight of old leaves and stem. A huge amount of Si settles down on the cell wall; as a result, the stronger stem of plants in these treatments can be expected. Also, Si in 600, 700, 800, and 900 mg/l led to more fruit dry biomass. Two treatments of 500 and 600 mg/l produced the highest yield per plant, but the highest fruit number was observed just in 600 mg/l treatment. According to regression analysis the highest fruit yield per plant will be obtained in 548mg/l of Si. Positive effect of Si on the yield of different crops was frequently reported which is in harmony with our results. Si fertigation in 600mg/l concentration significantly contributed to more Si content in old leaves and total plant. Recently, it was reported that Si accumulation in old leaves is more than young once which can be related to the immobility mode of this element in plants. Distribution model of Si in tomato plants showed 73.09% of absorbed Si accumulated in fruits and after that stem, leaves and root placed in lower levels with 11.49, 13.81 and 1.61% respectively. So, the hypothesis of low Si translocation from root to aerial parts in tomato was contradicted by the present results. Accumulation of Si in fruits is a promising indication, because positive influences of Si can be observed in fruits especially in postharvest phase.
4-Conclusion: It can be definitely said that Si applied through the fertigation was absorbed by tomato root and the large percentage of the element was transported to other organs especially fruits which received a large extent of absorbed Si. Overall, treatment of tomato plants with 600 mg/l of Si improved vegetative growth, stem strength, yield, and fruit number per plant, so this concentration can be recommended for growing tomato; in contrast, low or high concentrations were not efficient enough.