No, phloem does not carry significant amounts of oxygen. In fact, research indicates that oxygen concentrations within the phloem are notably low.
Low Oxygen Levels in Phloem: Evidence from Research
Multiple studies have demonstrated that oxygen levels inside the phloem are considerably lower than those in the surrounding environment. For example, one study measured oxygen levels as low as 15% (v/v) in phloem sap, even when plants were exposed to 21% (v/v) external oxygen.1 This low oxygen concentration necessitates metabolic adaptations within the phloem to function effectively.2, 3 This low oxygen environment is not conducive to efficient oxygen transport within the phloem itself. While some oxygen may passively diffuse into the phloem, the low concentrations suggest it isn't a primary transport pathway for oxygen.
- Study 1: Oxygen concentrations down to 15% (v/v) were measured in phloem sap, despite 21% (v/v) external oxygen.1
- Study 2 & 3: Low internal oxygen concentrations in the phloem lead to adaptive changes in phloem metabolism.2, 3
The phloem's primary function is the transport of sugars and other organic compounds produced during photosynthesis from the leaves to other parts of the plant. Oxygen transport is primarily handled by diffusion through the plant tissues, and not through the phloem itself. The xylem, on the other hand, transports water and minerals, which may include dissolved oxygen, but this is not its primary function either. The low oxygen within the phloem further supports the notion that it does not actively carry oxygen.
Note: While some dissolved oxygen might exist within the phloem sap, it's not a significant or primary component of its transport function.
