Abstract
Cotton fruits (Gossypium hirsutum L., cv. 'Albar') and their constituent part exhibiting typical sigmoid growth patterns were assayed for levels of endogenous auxin during development. During the first phase of fruit growth (0 to 10 days after flowering) a negative correlation between auxin concentration and growth was conspicuous. The contents of auxin in the intact fruit, lint and seed, and pericarp reached a maximum in phase two (10 to 20 days after flowering), coinciding with high meristematic activity in the seed and growth rate. Within phase three of cotton fruit growth (20 to 50 days after flowering), a positive correlation between the levels of auxin in the pericarp and growth was accompanied by a negative effect for the lint and seed. Fruit considered to be retained by the cotton plant contained amounts of auxin several times greater than those about to abscise. This strong negative correlation between total auxin and cotton fruit drop is regarded to be a consequence of a reduction in cell wall formation in the pericarp and the degeneration of the seed endosperm and embryo. The results are discussed in relation to our current understanding of the role of auxin in the growth and abscission of fruitlets.
