Abstract
Transitory starch granules result from complex carbon turnover and display specific situations during starch synthesis and degradation. The fundamental mechanisms that specify starch granule characteristics, such as granule size, morphology, and the number per chloroplast, are largely unknown. However, transitory starch is found in the various cells of the leaves of Arabidopsis thaliana, but comparative analyses are lacking. Here, we adopted a fast method of laser confocal scanning microscopy to analyze the starch granules in a series of Arabidopsis mutants with altered starch metabolism. This allowed us to separately analyze the starch particles in the mesophyll and in guard cells. In all mutants, the guard cells were always found to contain more but smaller plastidial starch granules than mesophyll cells. The morphological properties of the starch granules, however, were indiscernible or identical in both types of leaf cells.
Highlights
Transitory starch is a major storer of carbon and energy, and it allows plants to overcome dark phases when photosynthesis is impossible
Arabidopsis mutants not expressing the starch synthase isoform 4 (SS4) revealed that most chloroplasts are devoid of any starch granules, but a small proportion of chloroplasts contain more roundly formed starch granules, whereas most chloroplasts of the mesophyll cells were found to be free of starch granules
We revealed a decrease in the starch granule number in mutants such as ss4, dpe2/ss4, phs1/ss4, dpe2/phs1/ss4, and dpe2phs1, and the morphology was similar for both mesophyll and guard cells; guard cells possessed slightly more starch granules than the corresponding mesophyll cells
Summary
Transitory starch is a major storer of carbon and energy, and it allows plants to overcome dark phases when photosynthesis is impossible. The initiation of starch granules has been a research focus in recent years, as it is considered the first step in starch synthesis, starting with a primer-like structure/initiation complex formation [4] It determines or affects the features of the entire starch granule, such as size, number, and morphology. Mutants defective in the initiation process were impaired in degradation, implying that the normal starch granule number is essential for proper starch remobilization during the night [5] Such comprehensive alterations in size, quantity, and morphology reflect substantial changes in the starch metabolic system, which, in turn, increase the complexity of separating various starch parameters and decoding their underling mechanisms
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