Other Significant Processes That Occur in Chloroplasts

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In addition to photosynthesis, there are two very important sets of biochemical reactions that take place in chloroplasts (and also in the proplastids of roots).

1. Sulfates are reduced to sulfide via several steps involving ATP and enzymes. The sulfide is rapidly converted into important sulfur-containing amino acids, such as methionine and cysteine, which are part of the building blocks for proteins, anthocyanin pigments, chlorophylls, and several other cellular components.

chlorenchyma cell chlorenchyma cell

Photosynthesis

Figure 10.13 Crassulacean acid metabolism (CAM) photosynthesis found in orchids, pineapples, and many desert plants. CAM is similar to C4 photosynthesis, but the plants have their stomata closed during daylight heat, thus conserving water. The organic acids accumulate at night and break down during the day, releasing carbon dioxide, which then enters the Calvin cycle and C3 metabolism while the stomata are closed.

Figure 10.13 Crassulacean acid metabolism (CAM) photosynthesis found in orchids, pineapples, and many desert plants. CAM is similar to C4 photosynthesis, but the plants have their stomata closed during daylight heat, thus conserving water. The organic acids accumulate at night and break down during the day, releasing carbon dioxide, which then enters the Calvin cycle and C3 metabolism while the stomata are closed.

Chapter 10

2. Nitrates are reduced to organic compounds. Initially, the nitrates are reduced to nitrites in the cytoplasm. The nitrites are then transported into chloroplasts (or root proplastids) where, through several enzyme-mediated steps, they are converted to ammonia. The ammonia is then converted to amino groups that are integral parts of several important amino acids such as glutamine and aspartic acid. Glutamine is an important form of nitrogen storage in roots or specialized stems such as those of carrots, beets, and potato tubers.

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