We therefore speculate that Ev1.1 may have first gained the mutation in rsiX and was selected for owing to increased eps expression, whereas later on the increased matrix production was reverted by the mutations in gtaB, resulting in a non-functional protein and thereby reduced precursors for EPS production, which was selected for owing to the reduced cost. In accordance with the mutations observed in this study, a non-synonymous mutation in sinR in two isolates forming Snow-type colonies and increased in root colonization as well as several mutations in gtaB in two isolates with a Smooth colony morphology were observed in our recent study on diversification of B. subtilis during adaptation to A. thaliana roots.To get a more general insight into the mutations arising in B. subtilis during EE on A. thaliana roots, the seven endpoint populations were also sequenced. This revealed mutations within genes related to biofilm formation , flagellar motility , and cell wall metabolism across independent populations. Moreover, there is limited data available on the impact of Fe plaque formation on Cd accumulation by different rice varieties usually grown in Australia as significant genetic variations were reported among rice varieties in the accumulation of metals in rice grain . Thus, it is important to investigate the performance of Fe plaque formation by different rice varieties and subsequent Cd accumulation. Consequently, the objectives of this present study was to: explore the protective function of Fe plaque in reducing Cd accumulation and translocation in different varieties and comprehend the interaction effect of Fe and Cd in rice seedlings. Cadmium is a highly toxic heavy metal and it does not have any beneficial physiological functions in plants when it is accumulated, affects all aspects of growth and development .
Cd toxicity stress causes the reduction in the rice growth and biomass yield . Consistent with these observations, the dry biomass of rice cultivar’s roots and shoots were significantly reduced with increasing Cd . In the absence of Fe additions to the nutrient solution, chicken fodder system Cd0.5 and Cd1.0 significantly decreased the dry weight of roots and shoots compared with the control Cd0. Our findings are in good agreement with a recent hydroponic study conducted by Hussain et al. who demonstrated that roots and shoots biomass reduced with increasing Cd levels in solutions. Liu et al. also found that rice plants treated with Cd had smaller dry weights of roots and shoots compared with plants grown with no added Cd under hydroponic conditions. It has been shown that a reducing photosynthetic activity attributed with decremental rice biomass production under Cd stress . In this study, substantial increases in the biomass of roots and shoots were observed when Fe was added to the nutrient solutions with added Cd, and this is most likely due to the Fe plaque deposition, which alleviated the effects of Cd toxicity on the growth of rice plants. Our results differ from those obtained with other toxic trace elements. According to Liu et al. , Fe plaque or Fe supplement with As had no advantageous effects on the rice seedling’s growth raised in culture suspension. Ye et al. also demonstrated that the Fe addition or root plaque did not influence the yield of common cattail seedlings. However, our findings are consistent with those of others who observed that seedlings with high Fe plaque formation tended to greater root and shoot biomass production compared to those not having Fe plaque. The results also showed that CBD-Fe and Feroots and Feshoots of rice seedlings increased significantly when the Fe concentration of the nutrient solution increased, irrespective of Cd supply. Exogenous Fe application or Fe plaque have been shown to elevate the Fe content of plants , which is consistent with this study’s findings. Similar findings were reported by Sebastian and Prasad who found that greater Fe plaque deposition on the rice seedling’s root surface after FeSO4 application.
This also led to an increase in the Fe content of rice plants, which protected the rice plants from Cd-induced Fe deficiency and metal toxicity. The amount of Fe in Fe plaque are in agreement with numerous researchers who reported results for hydroponically grown rice seedlings with concentrations of Fe . Excessive Fe plaque coating on the root was reported when additional Fe was supplied to the growth medium . The presence of large quantities of Fe plaque on the root tends to extensive Cd adsorption and sequestration and this was evident by the elevated Cd concentration in CBD extractant solution of rice seedlings when subjected to exogenous Fe . Several reports showed a positive correlation between concentration of Fe and metals such as As, Cd etc. in root plaque . In this present investigation, the Cd concentration in Fe plaque increased with the iron supplementation which implied that Fe plaque demonstrated strong Cd sequestration capacity in terms of Cd immobilization and translocation by rice seedlings. Liu et al. also observed that higher CBD-Cd and root Cd concentration substantially reduced the Cd concentration in the shoots of rice seedlings. The root plaque deposition could alter and diminish the translocation and accumulation of heavy metals in the upper portions of rice plants but opposite results were reported . This inconsistency could possibly be ascribed to variations in the amounts of Fe plaque being formed, growth medium, pH, metal ion type, metal ion content, different plant types and cultivars. In this study, the use of Fe50 and Fe100 concentrations significantly decreased the concentration of Cdshoots of the rice seedlings compared with control Fe0 at both Cd supply concentrations . This observation is consistent with Liu et al. who found Cd concentrations in shoots were reduced by Fe plaque produced from 100 mg Fe L− 1 and with 0.1 mg L− 1 Cd in nutrient solutions. It was further confirmed in a recent hydroponic study conducted by Hussain et al. who observed that Cd concentration in rice seedling’s roots and shoots were reduced under sufficient Fe supplementation. Literature shows that the accumulation of Cd among various rice genotypes varied significantly . A study reported that the three key transport processes responsible for Cd accumulation such as root uptake, shoot transport through xylem and finally grain loading via the phloem .
It has been found that the acquisition of Cd in rice plant is mediated by the translocation from root to shoot through xylem, which is the main pathway of Cd entry in shoots and grain of rice plants . Another study revealed that application of Fe and Cd in nutrient solution increased relative expression of OsNRAMP1, OsNRAMP5, OsIRT1, CAL1and OsNAAT1 in the roots of rice plants and reduced the expression of OsHMA3, which lead to increase Cd content in rice plants nurtured in solution culture . Our results demonstrated that the concentration of Cdroots was higher than the CBD extracts and in shoots of rice seedlings. The percentage distribution of Cdroots in rice seedlings accounted for approximately 64.6–93% of the total Cd in the rice seedlings, which was greater than that in CBD extracts and in shoots . The higher proportional distribution of Cdroots indicated that root systems absorbed a lot of the Cd and serve as an effective barrier to hinder Cd delivery in rice plants. This is essentially in agreement with Ye et al. who indicated that root cells were exhibited the stronger barriers to suppress the accumulation and transportation of Cd and Pb in rice plants. In hydroponics experiments, Liu et al. revealed that Cd roots displayed approximately 65% of the total Cd concentration and in shoots and CBD extracts, the concentrations ranged from 9 to 40%. Exogenous Fe application can increase the Cd compartmentation and detoxification in the root cells which needs further investigations. The world population is expected to increase to 9.5 billion people in the next 40 years. This calls for an increase of over 60% in food production worldwide at least by 2050 to combat the crisis faced by the continuously increasing population . Unfortunately, natural resources such as: land meant to sustain food production and meet the demands of such an expected population increase are diminishing coupled with the high cost of the limited existing land . The high rates of urbanization and environmental degradation caused in the last decade have negatively impacted on the quality and quantity of food production . Besides the above challenges, there is a problem of nutrient depleted soils and water scarcity across the globe and these are expected to exacerbate in the face of the increasing population especially in urban areas .
We therefore speculate that Ev1.1 may have first gained the mutation in rsiX and was selected for owing to increased eps expression, whereas later on the increased matrix production was reverted by the mutations in gtaB, resulting in a non-functional protein and thereby reduced precursors for EPS production, which was selected for owing to the reduced cost. In accordance with the mutations observed in this study, a non-synonymous mutation in sinR in two isolates forming Snow-type colonies and increased in root colonization as well as several mutations in gtaB in two isolates with a Smooth colony morphology were observed in our recent study on diversification of B. subtilis during adaptation to A. thaliana roots . To get a more general insight into the mutations arising in B. subtilis during EE on A. thaliana roots, the seven endpoint populations were also sequenced. This revealed mutations within genes related to biofilm formation , flagellar motility , and cell wall metabolism across independent populations. Moreover, there is limited data available on the impact of Fe plaque formation on Cd accumulation by different rice varieties usually grown in Australia as significant genetic variations were reported among rice varieties in the accumulation of metals in rice grain . Thus, it is important to investigate the performance of Fe plaque formation by different rice varieties and subsequent Cd accumulation. Consequently, the objectives of this present study was to: explore the protective function of Fe plaque in reducing Cd accumulation and translocation in different varieties and comprehend the interaction effect of Fe and Cd in rice seedlings.Cadmium is a highly toxic heavy metal and it does not have any beneficial physiological functions in plants when it is accumulated, affects all aspects of growth and development.Consistent with these observations, the dry biomass of rice cultivar’s roots and shoots were significantly reduced with increasing Cd . In the absence of Fe additions to the nutrient solution, Cd0.5 and Cd1.0 significantly decreased the dry weight of roots and shoots compared with the control Cd0. Our findings are in good agreement with a recent hydroponic study conducted by Hussain et al. who demonstrated that roots and shoots biomass reduced with increasing Cd levels in solutions. Liu et al. also found that rice plants treated with Cd had smaller dry weights of roots and shoots compared with plants grown with no added Cd under hydroponic conditions.
It has been shown that a reducing photosynthetic activity attributed with decremental rice biomass production under Cd stress . In this study, substantial increases in the biomass of roots and shoots were observed when Fe was added to the nutrient solutions with added Cd, and this is most likely due to the Fe plaque deposition, which alleviated the effects of Cd toxicity on the growth of rice plants. Our results differ from those obtained with other toxic trace elements. According to Liu et al. , Fe plaque or Fe supplement with As had no advantageous effects on the rice seedling’s growth raised in culture suspension. Ye et al. also demonstrated that the Fe addition or root plaque did not influence the yield of common cattail seedlings. However, our findings are consistent with those of others who observed that seedlings with high Fe plaque formation tended to greater root and shoot biomass production compared to those not having Fe plaque. The results also showed that CBD-Fe and Feroots and Feshoots of rice seedlings increased significantly when the Fe concentration of the nutrient solution increased, irrespective of Cd supply. Exogenous Fe application or Fe plaque have been shown to elevate the Fe content of plants , which is consistent with this study’s findings. Similar findings were reported by Sebastian and Prasad who found that greater Fe plaque deposition on the rice seedling’s root surface after FeSO4 application. This also led to an increase in the Fe content of rice plants, which protected the rice plants from Cd-induced Fe deficiency and metal toxicity. The amount of Fe in Fe plaque are in agreement with numerous researchers who reported results for hydroponically grown rice seedlings with concentrations of Fe . Excessive Fe plaque coating on the root was reported when additional Fe was supplied to the growth medium . The presence of large quantities of Fe plaque on the root tends to extensive Cd adsorption and sequestration and this was evident by the elevated Cd concentration in CBD extractant solution of rice seedlings when subjected to exogenous Fe . Several reports showed a positive correlation between concentration of Fe and metals such as As, Cd etc. in root plaque . In this present investigation, the Cd concentration in Fe plaque increased with the iron supplementation which implied that Fe plaque demonstrated strong Cd sequestration capacity in terms of Cd immobilization and translocation by rice seedlings. Liu et al. also observed that higher CBD-Cd and root Cd concentration substantially reduced the Cd concentration in the shoots of rice seedlings.
The root plaque deposition could alter and diminish the translocation and accumulation of heavy metals in the upper portions of rice plants but opposite results were reported . This inconsistency could possibly be ascribed to variations in the amounts of Fe plaque being formed, growth medium, pH, fodder systems for cattle metal ion type, metal ion content, different plant types and cultivars. In this study, the use of Fe50 and Fe100 concentrations significantly decreased the concentration of Cdshoots of the rice seedlings compared with control Fe0 at both Cd supply concentrations . This observation is consistent with Liu et al. who found Cd concentrations in shoots were reduced by Fe plaque produced from 100 mg Fe L− 1 and with 0.1 mg L− 1 Cd in nutrient solutions. It was further confirmed in a recent hydroponic study conducted by Hussain et al. who observed that Cd concentration in rice seedling’s roots and shoots were reduced under sufficient Fe supplementation. Literature shows that the accumulation of Cd among various rice genotypes varied significantly . A study reported that the three key transport processes responsible for Cd accumulation such as root uptake, shoot transport through xylem and finally grain loading via the phloem . It has been found that the acquisition of Cd in rice plant is mediated by the translocation from root to shoot through xylem, which is the main pathway of Cd entry in shoots and grain of rice plants . Another study revealed that application of Fe and Cd in nutrient solution increased relative expression of OsNRAMP1, OsNRAMP5, OsIRT1, CAL1and OsNAAT1 in the roots of rice plants and reduced the expression of OsHMA3, which lead to increase Cd content in rice plants nurtured in solution culture . Our results demonstrated that the concentration of Cdroots was higher than the CBD extracts and in shoots of rice seedlings. The percentage distribution of Cdroots in rice seedlings accounted for approximately 64.6–93% of the total Cd in the rice seedlings, which was greater than that in CBD extracts and in shoots . The higher proportional distribution of Cdroots indicated that root systems absorbed a lot of the Cd and serve as an effective barrier to hinder Cd delivery in rice plants. This is essentially in agreement with Ye et al. who indicated that root cells were exhibited the stronger barriers to suppress the accumulation and transportation of Cd and Pb in rice plants. In hydroponics experiments, Liu et al. revealed that Cd roots displayed approximately 65% of the total Cd concentration and in shoots and CBD extracts, the concentrations ranged from 9 to 40%. Exogenous Fe application can increase the Cd compartmentation and detoxification in the root cells which needs further investigations. The world population is expected to increase to 9.5 billion people in the next 40 years. This calls for an increase of over 60% in food production worldwide at least by 2050 to combat the crisis faced by the continuously increasing population . Unfortunately, natural resources such as: land meant to sustain food production and meet the demands of such an expected population increase are diminishing coupled with the high cost of the limited existing land . The high rates of urbanization and environmental degradation caused in the last decade have negatively impacted on the quality and quantity of food production . Besides the above challenges, there is a problem of nutrient depleted soils and water scarcity across the globe and these are expected to exacerbate in the face of the increasing population especially in urban areas . Traditional farming is generally faced with problems of weather changes, water pollution, soil degradation and soil infertility . Africa alone continues to fight the problem of food insecurity where improved yield and sustainability in the agriculture sector can best be achieved through climate smart agriculture . CSA has been defined as an intervention vital for maintainace of global food security and nutrition through changing and readjusting agricultural practices within the new era of climate change . In order to conserve sustainable crop production systems, there is need to utilize spaces like: non-arable fields that do not support crop cultivation and develop alternative cultivation methods . This justifies the increasing use of various smart agricultural technologies to meet these rising levels of food insecurity.
Emami et al. described smart agriculture as the use of technology that has the capability to increase food security if well streamlined to the domestic levels. On other hand, CSA synchronizes actions by researchers, policy maker, private institutions, societies and farmers to promote climate resilient systems, practices and technologies .Soilless culture is one of the growing smart agriculture technologies in East Africa which encompasses growing crops with or without a media or using a static/flowing nutrient solution . Media refers to an organic or inorganic solid material that is used in the place of soil either in single or mixed form to provide support to the plant, for example: perlite, vermiculite, rice hulls, saw dust, coco-peat . Soilless farming is largely used under controlled environment mainly for horticultural crops and gives the opportunity to cultivate in areas with un favorable agriculture conditions such as: poor soils and limited space among other benefits . Soilless farming has the capacity of solving some of prior challenges such as: limited water availability and soil degradation, reduced pests and diseases, while promoting sustainable agriculture . Soilless farming is divided into 3 main categories which are: hydroponics, aeroponics and aquaponics . Aquaponics is a soilless farming system where plants and fish are raised in an associated relationship as the water is recycled through the system and plants uptake nutrients acquired from recycled fish waste water . Aeroponics on the other hand is a technique where devices like foggers are used to supply plant roots with nutrients inform of a mist .Arshad Mahmood et al. described hydroponics as an agriculture system for growing crops in water composed of mineral nutrients supported by medium. This system which uses less water as compared to soil farming has successfully been used for cultivation of different vegetables like: lettuce, spinach, cucumbers, tomatoes among other crops as these respond well to hydroponics due to low nutrient demands and short growth period . New drifts in agriculture have shown hydroponics as one of the new innovative soilless farming systems to realize satisfactory outcomes and has the potential to produce more yields in minimal space and promote food security through production of food vertically thus should be considered as a better farming option for East Africa facing a quandary of challenges as earlier discussed. Hydroponic farming has different types which include: Nutrient Film Technique , Wick system, Drip system, Ebb and Flow and Deep water culture . Wick system is the simplest hydroponic method which uses wicks to draw nutrients from the reservoir without use of pumps or timer while NFT hydroponics is a method where shallow channels are used to supply the nutrient solution to the bare plant roots through re-circulation process . DWC is a method of hydroponics in which plant roots are suspended directly into the nutrient rich water solution while drip system uses micro emitters to drip the nutrient and water directly to the plant roots with the help of a pump .
Arshad Mahmood et al. described hydroponics as an agriculture system for growing crops in water composed of mineral nutrients supported by medium. This system which uses less water as compared to soil farming has successfully been used for cultivation of different vegetables like: lettuce, spinach, cucumbers, tomatoes among other crops as these respond well to hydroponics due to low nutrient demands and short growth period . New drifts in agriculture have shown hydroponics as one of the new innovative soilless farming systems to realize satisfactory outcomes and has the potential to produce more yields in minimal space and promote food security through production of food vertically thus should be considered as a better farming option for East Africa facing a quandary of challenges as earlier discussed. Hydroponic farming has different types which include: Nutrient Film Technique , Wick system, Drip system, Ebb and Flow and Deep water culture . Wick system is the simplest hydroponic method which uses wicks to draw nutrients from the reservoir without use of pumps or timer while NFT hydroponics is a method where shallow channels are used to supply the nutrient solution to the bare plant roots through re-circulation process . DWC is a method of hydroponics in which plant roots are suspended directly into the nutrient rich water solution while drip system uses micro emitters to drip the nutrient and water directly to the plant roots with the help of a pump.