Inhibited Chlorophyll Degradation Research Articles

Nondestructive analysis of senescence in mesophyll cells by spectral resolution of protein synthesis‐dependent pigment metabolism

* Over 6 d of dark-induced senescence, leaf segments of wild-type Lolium temulentum lost > 96% chlorophyll a + b; leaves from plants containing a staygreen mutation introgressed from Festuca pratensis, which has a lesion in the senescence-associated fragmentation of pigment-proteolipid complexes, retained over 43% of total chlorophyll over the same period. * Mutant segments preferentially retained thylakoid membrane proteins (exemplified by LHCP II) but lost other cellular proteins at the same rate as wild-type tissue. The protein synthesis inhibitor D-MDMP inhibited chlorophyll degradation and partially prevented protein loss in both genotypes, but tissues treated with the ineffective L-stereoisomer were indistinguishable from water controls. * Principal-components analysis of leaf reflectance spectra distinguished between genotypes, time points and D-MDMP treatments, showing the disruption of pigment metabolism during senescence brought about by the staygreen mutation, by inhibition of protein synthesis and by combinations of the two factors. * The build-up of oxidized, dephytylated and phaeo-derivatives of chl a during senescence of staygreen tissue was prevented by D-MDMP and associated with characteristic difference spectra when senescent mutant tissue was compared with wild-type or inhibitor-treated samples. The suitability of senescence as a subject for systems biology approaches is discussed.

Effects of ethylene and 1-MCP on ripening and senescence of European seedless cucumbers

The effects of exogenous and endogenous ethylene combined with or without the ethylene action inhibitor, 1-methylcyclopropene (1-MCP), on the shelf-life of European seedless cucumbers (Cucumis sativus L.) were studied. Exogenous ethylene (3–5 μl l−1) accelerated the breakdown of chlorophyll but the degradation pathway was not altered by ethylene treatment. Chlorophyll catabolism in cucumbers seems to follow the same pathway as in parsley with replacement of Mg2+ as the first step with a minor role for chlorophyllide, followed by oxidative ring cleavage of the pheophytin a formed. Degreening was accompanied by an increasing amount of citric acid in the endocarp with a concomitant fall of malic acid but with the onset delayed until 50% of the chlorophyll had disappeared. Fresh cucumbers, fumigated with 1-MCP before continuous exposure to ethylene, did not deviate from those untreated, with inhibited chlorophyll degradation for 14 days in one experiment, but for only 9 days in another experiment, after which 1-MCP + ethylene resulted in a patchy degreening of the peel. However, in pre-stored fruit either continuously exposed to propylene or air, fumigation with 1-MCP prior to exposure did not prevent degreening indicating that breakdown of chlorophyll in aged fruit may be triggered and regulated by developmental factors and not by the low level of endogenous ethylene produced. It is therefore concluded that cucumbers probably show little benefit from fumigation with 1-MCP unless exogenous ethylene is present. Although the cucumbers were harvested before one quarter of the final weight was reached, they were able to develop the same ripening characteristics, i.e. yellowing, accumulation of citrate and tissue softening as if left on the plant until growth has ceased. These results suggest that cucumber ripening and senescence are overlapping processes and internal factors activating senescence-associated genes probably determine the keeping quality of cucumbers.

Factors Controlling the Retardation of Chlorophyll Degradation during Senescence of Detached Statice (Limonium sinuatum) Flower Stalks

Summary Detachment of green, flowering Limonium sinuatum flower stalks stimulated chlorophyll degradation. The loss of chlorophyll, which is regarded as a marker process of senescence, was accelerated when flower stalks were kept in the dark. Exposure of sections of the stalk to continuous white light or to brief red irradiations inhibited chlorophyll degradation. The effectiveness of the brief red i rradiations was similar to that of continuous white light, and could be completely reversed if each red irradiation was followed by a brief far-red irradiation. It is concluded that phytochrome is present in the flower stalks and mediates the retardation of flower stem senescence by light. Treatment of excised flower stalks with cytokinin (BAP) or gibberellin (GA3) significantly retarded the destruction of chlorophyll which occurred in the dark.

Effect of phytohormones on chlorophyll degradation during aging of chloroplastsin vivo andin vitro

Phytohormones like IAA and kinetin inhibit chlorophyll loss during aging of wheat chloroplasts duringin vivo andin vitro. GA, on the other hand, stimulates the pigment degradation during aging of attached leaves in contrast to its senescence inhibiting action in detached leaves and isolated chloroplasts. A shift in optimum concentration of hormone in inhibiting chlorophyll degradation suggests a differential pool size of endogenous hormone regulating aging of chloroplastsin vivo andin vitro. The retardation of chlorophyll loss by kinetin, IAA and GA during aging of chloroplastsin vitro would indicate that the effect of hormones in preventing yellowing of senescing leaves may be mediated through their direct action on chloroplasts.

Effect of α‐Tocopherol, β‐Carotene, Monogalactosyldiglyceride and Phosphatidylcholine on Light‐Induced Degradation of Chlorophyll a in Acetone

AbstractThe effect of α‐tocopherol, β‐carotene, monogalactosyldi‐glyceride and phosphatidylcholine on red light induced degradation of chlorophyll a was studied in acetone at 4°C. Monogalaclosyldi‐glyceride was ineffective up to a molar ratio of monogalactosyldi glyceride to chlorophyll of 1:10. α‐Tocopherol, β‐carotene and phosphatidylcholine inhibited chlorophyll degradation. Maximal protection by α tocopherol and β‐carotene was similar (76%) but on a molar basis a tocopherol was less effective. Protection by phosphatidylcholine was less than by a tocopherol and α‐carotene but the lipid was effective at a lower ratio of chlorophyll to protectant. Inhibition by phosphatidylcholine was independent of the degree of unsaturation of the fatty acids. Effects of β‐carotene and α‐tocopherol were additive at suboptimal concentrations, but addition did not increase the maximal protection of 76% by these substances alone. Phosphatidylcholine increased the effectiveness of α‐tocopherol and β‐carotene independent of their concentrations. It is suggested that interactions between lipids participate in the mechanism protecting chlorophyll a against photooxidation in the chloroplast membrane.

Effect of (2-Chloroethyl)phosphonic Acid on CCC-Induced Delay of Fruit Ripening

Chloroethyl)phosphonio acid ( CEPA) which is known to release ethylene in plant tissue, and (2-ehloroethyl)trimethylammonium chloride (CCC) were applied to ripening tomato and red pepper fruits. CEPA enhanced and CCC inhibited chlorophyll degradation and carotenoid formation. The inhibitory effects of CCC on fruit ripening were counteracted by CEPA treat ment. These results and those of other authors on gibberellin action in fruit ripening suggested that both CCC and gibberellin may interfere with the action of ethylene in ripening fruit.