Plant hormone homeostasis and the control of avocado fruit size
2001
Taylor, N. | Cowan, K.
Control of plant hormone homeostasis is crucial for normal organ development in plants. To elucidate the contribution of plant hormone homeostasis to fruit growth, tissue distribution and activity of xanthine dehydrogenase (XDH), abscisic aldehyde (AB-ald)- and indole acetaldehyde (IA-ald) oxidase, and cytokinin oxidase (CKOX) were determined in seed, seed coat and mesocarp of normal 'Hass' avocado and its small-fruit phenotype during the linear phase of growth. Activity of these enzymes was related to the tissue content of indole-3-acetic acid (IAA) and abscisic acid (ABA). IA-ald oxidase was present only in seed tissue whereas AB-ald oxidase and XDH activity was found in seed and mesocarp tissue. Seed of the small 'Hass' fruit had increased XDH and AB-ald oxidase activity and high endogenous ABA, but reduced IA-ald oxidase activity and adenine. There was no difference in seed, seed coat and mesocarp CKOX activity between normal and small fruit. Inhibition of XDH activity in whole fruit by treatment with allopurinol decreased IAA and increased ABA of seed tissue. In mesocarp of ripening fruit allopurinol increased ABA and IAA but had no effect on levels of iP. Results indicate that activity of IA-ald and AB-ald oxidases in avocado fruit contribute to maintenance of the IAA/ABA ratio in seed and mesocarp tissue and that increased AB-ald oxidase, or reduced IA-ald oxidase, may be part of the syndrome associated with the appearance of a small-fruit phenotype.
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