The paper discusses the source-to-sink transport of sugar in plants and the regulatory effects of environmental factors. Sugar transport through the phloem is crucial for plant growth, involving the distribution of sucrose and other sugars across plant organs. Environmental factors such as water and salt stress, mineral deficiencies, CO2 levels, light, temperature, air, and soil pollutants can alter source-sink relationships and affect phloem transport. Abiotic constraints, such as mineral deficiencies, can alter the distribution of sugar among sinks, with roots being favored in cases of mineral deficiency. Biotic interactions, including mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants, also impact crop productivity. The paper reviews the mechanisms of phloem transport and the roles of various transporters in these processes. It highlights the importance of understanding the interplay between source supply and sink demand, and how environmental factors influence this balance. The effects of specific abiotic factors, such as water deficit, mineral deficiencies, salt stress, light, low temperatures, CO2, and pollutants like cadmium, are discussed in detail, emphasizing their impacts on sugar metabolism, phloem loading, and transport.The paper discusses the source-to-sink transport of sugar in plants and the regulatory effects of environmental factors. Sugar transport through the phloem is crucial for plant growth, involving the distribution of sucrose and other sugars across plant organs. Environmental factors such as water and salt stress, mineral deficiencies, CO2 levels, light, temperature, air, and soil pollutants can alter source-sink relationships and affect phloem transport. Abiotic constraints, such as mineral deficiencies, can alter the distribution of sugar among sinks, with roots being favored in cases of mineral deficiency. Biotic interactions, including mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants, also impact crop productivity. The paper reviews the mechanisms of phloem transport and the roles of various transporters in these processes. It highlights the importance of understanding the interplay between source supply and sink demand, and how environmental factors influence this balance. The effects of specific abiotic factors, such as water deficit, mineral deficiencies, salt stress, light, low temperatures, CO2, and pollutants like cadmium, are discussed in detail, emphasizing their impacts on sugar metabolism, phloem loading, and transport.