## 1 Introduction  
Marine polysaccharides are the main constituents of cell walls in seaweeds, or exoskeletons in crustaceans [1]. They are characterized by their linkage to sulfate ester groups and this distinguishes them from polysaccharides derived from terrestrial plants. The structure of marine polysaccharides depends on the type of species, its geographic origin, growth stage, and extraction method [2]. A previous study on water-soluble sulfated polysaccharides (SPs) extracted from _Codium fragile_ revealed that they consisted of D-galactose, L-arabinose, and D-xylose in respective molar ratios of 2:2:1, along with traces of uronic acid and L-rhannose [3]. In a different study, SPs separated from _Ulva lactuca_ in aqueous medium constituted L-rhannose, D-xylose, and D-glucose in molar ratios of approximately 4.2:1.3:1.0, respectively, together with 24% of D-glucuronic acid, 19% of ester sulfate and some traces of D-mannose [4]. In addition, sargassan obtained from _Sargassum liniifolium_ contained D-glucuronic acid, D-galactose, D-mannose, D-xylose, L-fucose, in respective molar proportions of 4.57:8.40:1.00:2.48:2.50 [5]. Different conventional and modern techniques have been utilized for the extraction of marine polysaccharides from seaweeds. An ultrasound-assisted extraction was utilized to obtain 44.8 g/Kg of polysaccharides from the green algae _Chlorella pyrenoidosis_ at optimal conditions of 400 W of ultrasound power, with an incubation in water at 100 \({}^{\circ}\)C for 4 h followed by a precipitation of polysaccharides with 80% ethanol [6]. In another study, the optimal yield of polysaccharides was obtained from the green algae _Ulva lactuca_ using an ultrasound-assisted extraction at 60 \({}^{\circ}\)C for 4 h [7]. The growth of plants and their response to environmental impacts entail modifications in the processes of metabolism, photosynthesis, gene expression and regulation of plant hormone levels. Plant hormones control all aspects of growth and development as well as immune responses. For example, ethylene and abscisic acid (ABA) act as plant growth inhibitors while cytokins, auxin and gibberellins act as plant growth stimulators [8]. The role of these phytohormones was reported in previous work that applied different concentrations of glucose to _Arabidopsis_ seedlings. After 7 days from glucose application, the primary root growth declined due to interactions between glucose and ABA [9]. Intensive agriculture encompasses the use of increased labor and capital to maximize productivity. It usually involves the utilization of fertilizers and heavy machinery. On the other hand, extensive agriculture relies on the natural circumstances of soil, rain and sunlight with minimal inputs of labor and capital. To increase productivity, it is mainly practiced in large areas of land where demand is moderate. Intensive agriculture provides more products per unit of land while extensive agriculture provides natural and less toxic products. So, while more productive, intensive agriculture is more inclined to cause environmental damage due to the use of chemicals and machinery which reduces soil quality [10; 11]. Therefore, utilizing bio-based stimulants and inhibitors that originate from natural sources would be favored to mitigate the drawbacks of intensive agriculture. Metal nanoparticles have been investigated for their phytotoxic effect on plants where they have been reported to act as either herbicides that inhibit plant growth or stimulants that promote growth. The effect of nanoparticles on plant growth depends on the type of plant, the means of nanoparticle application and the conditions of exposure. With the growing need for environmentally-friendly synthesis processes, the chemical methods for nanoparticle synthesis have been replaced with greener alternatives.