Effects of moisture stress and senescence on the synthesis of abscisic acid in the primary leaves of bean

Abstract

The capacity for ABA synthesis during moisture stress of primary leaves of bean (Phaseolus vulgaris cv. Kinghorn) was defined in terms of leaf age and associated changes in several physiological parameters. The leaves were fully expanded within 9 days after emergence. Fresh and dry weights per unit of leaf area fell during all 5 weeks of the study, from leaf expansion through advanced senescence. The most significant losses in weight occurred during the third and fourth weeks and coincided with a sharp drop in protein content that began immediately after full‐leaf. Chlorophyll concentrations declined rapidly during leaf expansion and then more slowly through the end of the fifth week when the leaves were ready to abscise. The ratio of chlorophyll a to b rose steeply over the first 4 weeks of the study. Although a rapid loss of protein provided the most definitive indication of the early stages of leaf senescence, a marked decline in the ability to synthesize ABA was more closely associated with the termination of rapid leaf growth. This relationship between leaf expansion and the capacity for ABA synthesis during moisture stress remained unchanged when ABA content was expressed on a per unit chlorophyll, protein or dry weight basis. A water deficit between 5 and 10% of fresh weight, representing a drop in water potential of less than 150 kPa, was sufficient to initiate accumulation of ABA in young leaves. Slightly more intensive levels of stress were required to stimulate ABA synthesis in senescent leaves, but total accumulation was less than one‐tenth of the amount recorded in the younger tissue.

Senescence in cut carnation flowers: Temporal and physiological relationships among water status, ethylene, abscisic acid and membrane permeability

“…7, however, show that ethylene applied to Stage 1 flowers induced large rises in ABA and endogenous ethylene, to levels tbat were essentially equivalent to those recorded during Stages IV and V of natural senescence. In work with primary leaves of bean, Eze et al (1981) also noted that the capacity to synthesize ABA was highest in young, expanding tissue and that a marked loss in synthetic potential was closely associated with the termination of rapid leaf growth. The sharp decline in water content that preceded the ABA and ethylene peaks during Stage IV of senescence (Figs 1 and 4) was not observed during ethylene treatment.…”

“…3) may be the earliest physiological signal that senescence is under way, and the moderate decrease in ip, that ensues (Fig. 2) may stimulate both the synthesis of ABA (Eze et al 1981) and of ACC (Borochov et al 1982), the direct precursor of ethylene in higher plants.…”

Endopeptidase activity and nitrogen mobilization in senescing leaves of Nicotiana rustica in light and dark

“…A similar result was found by Choudhury and Biswal (1979) and Friedrich and Huffaker (1980) with Zea mays and Hordeum vulgare, respectively. In leguminous plants, however, the reversed order of the above was found (Storey and Beevers 1977, Wittenbach et al 1980, Eze et al 1981, Ragsterand Chrispeeis 1981.…”

Regulation of ABA levels in senescing petals of rose flowers

“…Such a correlation has often been reported for leaves (Wright 1977, Zabadal 1974), but has not yet been demonstrated for isolated petals. In primary leaves of bean, Eze et al (1981) noted that the capacity to synthesize ABA was highest in the young expanding tissue. A similar conclusion was suggested by Eze et al (1986) in carnation flowers where an ethylene treatment induced the highest increase in ABA concentration in the youngest flowers.…”