PLANT-GROWTH REGULATORS IN CITRICULTURE - FACTORS REGULATING ENDOGENOUS LEVELS IN CITRUS TISSUES

Since the review on endogenous growth substances of citrus tissues by Goldschmidt in 1976 (HortScience, 11: 95-99), much information regardi ng this topic has been published in a wide array of journals. The pres ent review provides a comprehensive overview of published information on endogenous levels of the five classes of plant growth substances (i .e., auxins, cytokinins, gibberellins, ethylene, and abscisic acid), p lus polyamines and other endogenous substances that appear to have a r ole in regulating citrus growth and development. It is the first in a three-part series that next examines hormonal regulation of physiologi cal processes in citrus followed by review of current uses and commerc ial applications of plant growth regulators in citrus production. In t his article, a brief history of the detection and characterization of each class of plant growth substances is given. Following this, variat ion in endogenous levels associated with different organs (and/or tiss ues), stages of development, species, cultivars, cultural practices, a nd environmental factors is reviewed. For each class, current knowledg e regarding biosynthesis, metabolism and transport in citrus tissues i s summarized. The concluding section deals with future research direct ions.