Environmental factors in the physiology of abscission.

This paper reviews the physiological effects of the principal environmental factors which can influence the process of leaf abscission. The factors include temperature, light, water, gases, mineral elements, soil conditions, and parasitic organisms. These factors influence a variety of internal physiological conditions and processes which in turn may either accelerate or retard the process of abscission. The most important internal factors include A) sugar, pectin, cellulose, and other carbohydrates; B) energy-yielding respiration; C) enzymic reactions; D) amino acids, purines, and other nitrogenous substances; E) levels of plant hormones; and F) the molecular biological pathway. The current information is consistent with the hypothesis that the environmental factors act in leaf abscission via direct or indirect influences on the synthesis or reaction rate of enzymes.