When one hears the words growth promoting substances, phytohormones and plant nutrients comes into mind. This is because in agriculture, phytohormones and nutrients have been used successfully to increase crop yield. However scientific research has discovered other plant growth promoting substances that have not been used in agriculture and the research show that these substances are able to regulate and enhance growth in plants. These substances are alkamides, sphingolipids, lumichrome, smoke and strigolactones.

Alkamides: These are secondary metabolites that are produced naturally in plants. Examples of these are affinin and its derivatives. Studies have shown that alkamides plays a significant role in root development with emphasis on root hair growth. Root hairs are responsible for the absorption of water and nutrients from the soil into the plant. Therefore improving and increasing their growth will lead to better survival of plants in water deficient or nutrient deficient soils, as more root hairs will mean more surface area for absorption and thus enhanced growth. As these substances are already present in plants, if the genes responsible for their production can be up-regulated, it might lead to the plants surviving under low water and nutrient soils.

Sphingolipids: Like alkamides, sphingolipids are found naturally in plants. Sphingosine-1-phosphate is a sphingolipid that has been isolated from plants. These substances have been found to be essential components of plant cells. Research has shown that when sphingolipid synthesis in plants is reduced, it leads to plants compensating this low sphingolipid levels by reducing growth. This is not ideal in agriculture as it will reduce crop yields. To increase production of sphingolipids, the genes responsible can be up-regulated via genetic engineering.

Lumichrome: This is a rhizobia signal metabolite produced by the bacterium Sinorhizobium meliloti. It is a photoproduct of Riboflavin (Vitamin B). It has been shown in research to enhance root respiration and shoot growth. Root respiration lead to more root performance and thus increased water and nutrient uptake into the plant by the roots into the plant. This lead to more shoot growth, giving high yields which is as desired in agriculture.

Smoke: It has been observed for years that smoke can break seed dormancy without understanding how. The molecule 3-methyl-2H-furo [2, 3-c] pyran-2-1 has now been to be behind this activity. This compound has been shown to not only stimulate seed germination but lead to plants being able to produce stress response genes. This puts plant in a better position to be stress tolerant and thus stable plant growth.

Strigolactones: These substances are produced in plant roots and the identified ones are sorgolactrones and strigol. Research has shown that these substances inhibit lateral bud growth in plants. They have also been shown to regulate rhizobial growth of beneficial fungi (symbiotic mycorrhizal fungi) in plant roots. However this substance also signals the germination of parasitic weeds seed which are detrimental to plants. This substance have now been accepted and classified as a phytohormone.

Direct application of the artificially synthesised compounds of these substances might be not healthy for the environment. A good example will be strigolactones as their application will also lead to the growth of parasitic weeds thus out competing the plants or crops. As much as people are skeptic about biotechnology and its different techniques, sometimes understandably so, genetic engineering thus can come in handy to increase production of these substances by simply over-expressing them in plants. This will lead to more crop yields in Agriculture.

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