The answer is nuanced: while mature, functional sieve tube elements (the main conducting cells of phloem) do not have chloroplasts, companion cells (which are closely associated with sieve tube elements and support their function) do contain chloroplasts.
Here's a more detailed breakdown:
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Sieve Tube Elements: These are the specialized cells primarily responsible for transporting sugars and other nutrients throughout the plant. To maximize space for transport, mature sieve tube elements lose many of their organelles, including the nucleus, ribosomes, vacuoles, and Golgi apparatus. They also generally lack chloroplasts. This loss of organelles allows for efficient translocation.
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Companion Cells: These are specialized parenchyma cells closely associated with sieve tube elements. They are connected to sieve tube elements through plasmodesmata (small channels). Companion cells are metabolically active and perform many functions to support sieve tube element function, including providing ATP and proteins. Companion cells do contain chloroplasts, although their primary function is not photosynthesis but rather to provide energy and metabolites to support the sieve tube element. The chloroplasts in companion cells are often less developed than those in mesophyll cells.
Why the confusion? The close proximity and functional interdependence of sieve tube elements and companion cells sometimes lead to a generalization that phloem cells have chloroplasts. It's more accurate to state that companion cells, a vital component of phloem tissue, contain chloroplasts.
In summary, while sieve tube elements, the key cells of phloem, typically lack chloroplasts, companion cells, which are essential for sieve tube element function, possess chloroplasts.
