MadSci Network: Botany |
Your question contains a good clue to the answer. If the plant tissue lacks chloroplasts, then it cannot conduct photosynthesis, which requires carbon dioxide gas. Plants in tissue culture are given sucrose as their energy source. Thus, they produce carbon dioxide gas via cellular respiration rather than consume carbon dioxide gas in photosynthesis. Production of carbon dioxide via cellular respiration can lower the pH of the tissue culture medium because of the formation of carbonic acid. When a plant cell absorbs more positive ions than negative ions, it excretes hydrogen ions (H+) to maintain charge balance. The hydrogen ions lower the pH of the medium. When a plant cell absorbs more negative ions than positive ions, it excretes hydroxyl ions (OH-) to maintain charge balance. The hydroxyl ions raise the pH of the medium. The most common tissue culture medium is Murashige and Skoog. It contains a substantial amount of its nitrogen as ammonium (NH4+) and as nitrate (NO3-). Therefore, the medium pH can go either way depending on whether the cells absorb mainly ammonium or mainly nitrate. References Re: How do plants alter the pH of a fish tank? Murashige and Skoog tissue culture medium recipe Bhatia, P. and Ashwath, N. 2005. Effect of Medium pH on Shoot Regeneration from the Cotyledonary Explants of Tomato. Biotechnology. 4(1):7-10.
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