Postharvest Enhancement of Phenolic Phytochemicals in Apples for Preservation and Health Benefits - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 348

Endogenous sources
Mitochondria
Peroxisomes
Lipoxygenases
NADPH-Oxidase
Cytochrome P450

Antioxidant defenses
Catalase, SOD, glutahione
peroxidase, thioredoxin
reductase
Glutathione, Ascorbate,
tocopherol

Exogenous sources
Ultraviolet
Ionizing radiation
Environmental toxin
Chemotherapeutics
Inflammatory cytokines

Reactive oxygen species (ROS)
Reactive nitrogen species (RNS)
(Superoxide, peroxide, singlet oxygen, hydroxyl radical, NO, OONO)

Impaired physiological
function

Homeostasis Impaired physiological

function

Random
cellular
damage

Specific
signaling
pathways

Decreased proliferative response Normal growth

and metabolism

Defective host defenses

Aging Disease Cell death

Reactive oxygen species and cellular homeostasis.

Fig. 16.4

reduced reductant levels increased the rate of senescence in a number of herbaceous species
(Philosoph-Hadas et al., 1994; Meir et al., 1995).

16.5 Proline-linked pentose phosphate pathway for effective
antioxidant activity and phenolic synthesis enhancing
postharvest preservation

Another commonly seen stress response in plants is an increase in the synthesis of proline.
Studies have shown proline biosynthesis to be stimulated in cases of water stress and salinity
stress (Stewart and Larher, 1980; Thompson, 1980; Rhodes, 1987; Taylor, 1996; Hare and
Cress, 1997). Proline synthesis and accumulation is also seen during senescence, freezing
tolerance, water stress, salt stress, and dehydration in plant cells (Rhodes et al., 1986;
LaRosa et al., 1991; Reddy and Veeranjaneyulu, 1991; Kiyosue et al., 1996; Sudhakar
et al., 1993; Xin and Browse, 1998). It has been suggested that proline protects membranes
in times of stress like those mentioned earlier (Paleg et al., 1981; Santoro et al., 1992).