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Title: The Effect of Calcium on Early Fiber Elongation in Cotton Ovule Culture

item Taliercio, Earl
item HAIGLER, CANDACE - North Carolina State University

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2011
Publication Date: 8/15/2011
Citation: Taliercio, E.W., Haigler, C. 2011. The Effect of Calcium on Early Fiber Elongation in Cotton Ovule Culture. Journal of Cotton Science. 15:154-161.

Interpretive Summary: Cotton ovular trichomes undergo four distinct stages of development to produce spinnable fiber. The first two stages of fiber development are initiation of the trichome on the ovule epidermis and rapid elongation. The fiber initial has been shown to accumulate calcium and membranes in the form of increased endoplasmic reticulum. We demonstrate that calcium plays an important role in fiber elongation during the initiation phase of fiber development. Super-optimal calcium levels inhibit fiber elongation. The calcium sensor, calmodulin, plays a role in transmitting the “elongation” signal near optimal calcium levels. Disruption of the calcium gradient actually enhances elongation, tentatively suggesting ctyoplasmic levels of calcium play a role in early fiber elongation, but a calcium gradient may not be required. Practically ovule cultures optimized for calcium at each stage of development may produce fiber more similar to in-vivo grown fiber.

Technical Abstract: Cotton fibers are single-cell trichomes that initiate on the ovule epidermis. Fiber initials accumulate calcium and membranes, including ER. Multiple calcium sensors, and small GTPase proteins that may act in calcium signaling pathways and/or primary cell wall biosynthesis were present in fiber initials where they may play a role in early fiber development. This research expands the evidence that calcium is a key regulator of fiber morphogenesis. Culturing ovules in vitro showed that higher calcium levels in the culture medium inhibited early fiber elongation, with the most sensitivity occurring in the first two days after flowering. Treatment with TFP, an inhibitor of calcium-dependent calmodulin signaling, resulted in shorter fibers. Treatment with calcimycin, an ionophore that can disrupt a calcium gradient, resulted in longer fibers. Expansin transcript levels in the fiber were highest when ovules were cultured in the low calcium medium that also promoted fiber elongation. These data provide evidence that calcium and calcium signaling exert regulatory roles during fiber initiation.