Chlorophyll loss

During drought stress, ABA regulates stomatal closure, whereas increased ethylene production has an inhibitory influence on ABA action. An inhibition of ethylene synthesis delays drought-associated chlorophyll loss, supporting the role of ethylene in drought-induced senescence. °°... 

Schemske DW, Bradshaw HD (1999) Pollinator preference and the evolution of floral traits in monkeyflowers (Mimulus). Proc Natl Acad Sci USA 96 11910-11915 Wang HC, Huang XM, Hu GB, Yang Z, Huang HB (2005) A comparative study of chlorophyll loss and its related mechanism during fruit maturation in the pericarp of fast- and slow-degreening litchi pericarp. Sci Hortic 106 247-257...

Carbon dioxide and Ag+ ions clearly suppressed senescence, as determined by chlorophyll loss. Aminoethoxy vinylglycine (AVG), the inhibitor of ethylene biosynthesis, also significantly suppressed senescence, as determined by preservation of chlorophyll in the leaf disks aging in the dark.Combinations of C0-, Ag ions and AVG were especially effective on preserving chlorophyll, presumably by suppressing both ethylene biosynthesis and action at the two receptor sites. After 6 days aging at 25° in the dark, the controls contained only 7% of the chlorophyll present at the start, whereas 84% of the chlorophyll was retained by the leaf disks treated with a combination of CO-, Ag and AVG. 

Many of the effects that occur as a result of these fumigations can probably be attributed to a destruction of chlorophyll. Chlorophyll loss attributed to fumigation with ozone or ozonated hexenes has been described (37, 39, 40, 41) and can be used as a quantitative measure of injury to cultured plants by certain pollutants. However, in the case of N02, growth suppression of tomato and bean occur after exposure to 0.5 ppm N02 for 10-12 days with a concomitant greening of the leaves, indicating the possibility of nitrogen accumulation and no chlorophyll destruction by the pollutant. 

Yamauchi and Watada (1993) studied natural senescence of parsley leaves. When chlorophyll a decreased, chlorophyll a-l increased to about 3% of the content of chlorophyll a (Fig. 8.8). With storage, a small accumulation of chlorophyllide a was noted, but the accumulation did not continue nor was it retained and it did not increase to the extent of the amonnt of chlorophyll a lost. The pheophytin a content was in general low and no pheophorbides were detected leaving the formation of colomless by-prodncts as the only explanation of chlorophyll loss dnring post-harvest senescence (Heaton and Marangoni, 1996a). 

Chlorophyll loss, a desirable trait for many climacteric fruits, results in quality loss for many vegetables. Chlorophyll degradation during the senescence of green vegetables can be reduced by low O2 and elevated CO2 (Ku and Wills, 1999). 

The mesophyll cells of highly resistant plants defend themselves against the invading parasite by the very efficient hypersensitive reaction (8), i.e. the infected cells lignify and collapse within some hours after penetration. Thus, the fungus starves and just a few cells are affected by infection. The minor chlorophyll losses due to the hypersensitive reaction are compensated by a somewhat intensified photosynthesis and the integrity of the thylakoid membranes and electron transfer are by no means disturbed. 

At physiological pH in plants, polyamines exist as proton-ated forms. These protonated forms bind to the negatively charged phospholipid head groups and other anionic sites in membranes and alter the stability and permeability characteristics of such membranes. Polyamines also stabilize chloro-plast thylakoid membranes and retard chlorophyll loss in senescing barley leaf tissue. Polyamines also influence membrane fluidity, affect membrane localized proton pumps, and alter plant hormone responses, perhaps by competing for... 

Duckweed (Lemna pausicostata L.) has proved to be a sensitive bioassay for AAL-toxin, FBj and related compounds (75). Duckweed is a small aquatic plant that can be easily grown in the laboratory (75). Phytotoxic effects can be easily quantified by measuring chlorophyll loss and cellular leakage (74). AAL-toxin was about 10-fold more active than FBj in the duckweed bioassay, causing maximal effect at a 0.1 pM concentration. FBi, FB2 and FB3 caused effects identical to those of AAL-toxin in duckweed at 1 pM. The hydrolysis products, APi and AP2 were much less active, and FAi and FA2 were completely inactive in the duckweed bioassay (75). 

Phytosphingosine and sphingosine also have phytotoxic effects on duckweed at higher concentrations (50 pM) causing increased conductivity and chlorophyll loss (75). This suggests that the build-up of free sphingoid bases is toxic to cells (65, 75). The... 

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