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Fiber Physiology

Much of our current understanding about the role of phytohormones in fiber growth and development comes from studies of isolated ovules in culture [1, 2]. Fiber initiation in unfertilized ovules is promoted by the addition of auxin and gibberellic acid. Either hormone can promote fiber initiation in unfertilized ovules and the effect is additive when both hormones are present. Ovule epidermal cells are competent to respond to phytohormones about two days prior to anthesis [5]. In some cotton varieties, although not in TM1 or the isogenic mutants, fiber initials are evident prior to anthesis [4]. This condition seems to be a property of newer cotton varieties such as G. hirsutum DeltaPine 90 & Maxxa, with older varieties such as TM-1 & Acala SJ-2 delaying visible signs of fiber initiation until after anthesis [2, 4]. This observation suggests that efforts to increase fiber yield in modern commercial varieties may have inadvertently selected for ovules that are less influenced by physiological events occurring at anthesis. Regardless of whether fiber cells are visible pre-anthesis or not, exogenous application of IAA and GA3 to flower buds in planta and unfertilized ovules in vitro results in increased fiber numbers [4]. A recent study simultaneously improved the yield and quality of cotton fiber [6]. The key to their success in achieving this elusive goal lies in regulated overexpression of a gene responsible for the synthesis of the auxin indole-3-acetic acid (IAA) at the right time and place during ovule and fiber development [3]. The study, validated by field trials spanning four years, underscores the importance of precise temporal and spatial regulation in harnessing plant growth regulators for improvement of cotton fiber in particular and many other crops in general.

References

  1. Beasley CA: Hormonal regulation of growth in unfertilized cotton ovules. Science 179: 1003-1005 (1973).
  2. Beasley CA, Ting IP: The effects of plant growth substances on in vitro fiber development from unfertilized cotton ovules. Amer J Bot 61: 188-194 (1974).
  3. Chen ZJ, Guan X: Auxin boost for cotton. Nat Biotechnol 29: 407-9 (2011).
  4. Gialvalis S, Seagull RW: Plant hormones alter fiber initiation in unfertilized cultured ovules ofGossypium hirsutum. J Cotton Sci 5: 252-258 (2001).
  5. Graves DA, Stewart JM: Chronology of the differentiation of cotton (Gossypium hirsutum L.) fiber cells. Planta 175: 254-258 (1988).
  6. Zhang M, Zheng X, Song S, Zeng Q, Hou L, Li D, Zhao J, Wei Y, Li X, Luo M, et al.: Spatiotemporal manipulation of auxin biosynthesis in cotton ovule epidermal cells enhances fiber yield and quality. Nat Biotechnol 29: 453-8 (2011).