Concept explainers
To explain: The direction of growth of plant with respect to orientation of microtubules when grown in dark.
Introduction: The direction of cell growth in plants is an essential factor that determines the shape of the plants. Microtubules and the microfilaments are the structure in a cell that provides them strength and support. The regulation of direction of growth is supposed to be controlled by microtubules and they play an important role in cell morphogenesis. The direction of the plant will be transverse to the orientation of microtubules. The alignment of the microtubules in a cell will be always antiparallel to the direction of growth of plant.
Explanation of Solution
The direction of the plant growth will be vertical if their micro fibrils have horizontal orientation. Micro fibrils are the ones that actually regulate the direction of plant. The orientations of micro fibrils are connected with the orientation of the microtubules. The parallel orientation of the micro fibrils as well as the microtubules results in antiparallel expansion of the cells. That means, if the orientations of the microtubules are horizontal, then the cell expands in a vertical direction. The reason for the occurrence in opposite direction of cells and the microtubules is to provide enough space between the microtubules arranged across the cell walls without stretching them.
Here, actually the seedling is placed in a dark environment, that is, it is buried in the soil. So the germinating seed have the cells in their growing stem that would have horizontal orientation. For making space between the micro fibrils and the microtubules, the cells will expand in a vertical direction. Therefore, the stem of the seedling buried in the soil can actually speed up their expansion and can come out of soil.
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